MIND WANDERING AND ITS EFFECTS ON EYE BEHAVIOUR
Eye Behaviour as Indicator of Positive and Negative Mind Wandering
ALESSANDRO AUSENDA
ANR: 916156
MASTER THESIS
Communication and Information Sciences,
Master Track Human Aspect of Information Technology
Faculty of Humanities
Tilburg University
Supervisor: Dr. K.A de Rooij
Second Reader: Dr. M. Postma-Nilsenová
“ It is imperfection - not perfection - that is the end result of the program written into that formidably complex engine that is the human brain, and of the influences exerted upon us by the environment and whoever takes care of us during the long years of our physical, psychological
and intellectual development.’’
Rita Levi Montalcini i Acknowledgments
My enrolment in the master's programme marked the start of a new and very challenging chapter of my life. I knew it would be full of moments to cherish and obstacles to overcome.
What drove me towards accomplishing this goal was to a large extent my determination to succeed, I have also been extremely lucky to meet so many wonderful people who helped me in this endeavour. First and foremost, I would like to express my deepest gratitude to my supervisors, Dr. Alwin de Rooij and Dr. Marie Postma-Nilsenová, for giving me the opportunity to work on this stimulating topic, and for supporting and expertly guiding me along the way. With their constructive insights and patience I believe I have been able to develop as a scholar and broaden my intellectual horizons. I am truly grateful for your endless energy and believing in my project.
I am indebted to Dr. Rein Cozijn for the technical support in the initial phase of working with the Eyelink II. Dr. Jaqueline Dake's assistance with the practical questions regarding the
Proefpersonenpool and lab D413 has been invaluable.
Many thanks to Sbenson Vidotto and Lieke Gelderloos for being such brilliant and constant study companions. Without our engaging and deep conversations on all possible topics my personal growth would not have been so pleasant and rich. A special thank you to my fellow labmate Ruben Vromans for the opportunity to exchange suggestions and get acquainted with the lab setting together. My sincere thanks to André and Marjolein who became a great second family during my stay in Tilburg. I also wish to acknowledge all the students who generously agreed to take part in my study for the sake of knowledge.
Last but not least, I would like to express my profound gratitude to my family and friends, especially to my mother, my father and Anne. Thank you for your generous support, precious and wise advice and for encouraging me to always do my best. ii Abstract
Mind wandering which is a complex yet common mental experience has been shown to have different kinds of impact on human cognitive abilities. These differences can be explained by the variable of valence, the effects of the positive type versus negative can be consistently divergent. In the present study oculesics has been selected as an effective way of detecting mind wandering. The main analyses of eye behaviour such as pupil dilation, saccades, fixation rate and fixation duration have produced interesting results concerning the role of eye movements as indicators of different types of mind wandering. The main results obtained by analysing eye movements show that negative valence mind wandering differs from the neutral mind wandering state with a distinctive pattern of a significantly greater pupil dilation. Moreover, fixation duration during positive valence mind wandering exhibits a marginally significant decrease when compared to negative valence mind wandering. The results provide evidence that the type of mind wandering can be manifested with a specific eye behaviour variation concerning the pupil size and the fixation duration.
In the case of pupil size with a large dilation after exposure to negative mind wandering stimuli, while for fixation duration with a shorter persistence if exposed to positive mind wandering stimuli. Interestingly, the exploratory analyses with a longitudinal approach have revealed even more significant differences between positive and negative valence states, which strongly corroborate the hypotheses already supported by the findings obtained in the main analyses.
Keywords: eye behaviours, mind wandering, oculesics, valence, pupil size, rumination
iii Contents
Acknowledgments ...... i Abstract ...... ii Table of Contents ...... iii List of Figures ...... v List of Tables ...... vi Chapter I – 1.Introduction ...... 1 1.1 Scientific and social relevance ...... 4 Chapter II – 2.Theoretical background ...... 6 2.1 Daydreaming, mind wandering ...... 8 2.1.2 Daydreaming and mind wandering styles ...... 11 2.2 Mind wandering and oculesics ...... 11 2.3 Presentation of research hypotheses ...... 15 2.3.1 Pupil dilation ...... 16 2.3.2 Saccade movements rate ...... 18 2.3.3 Fixation rate and fixation duration ...... 19 Chapter III – 3.Method ...... 21 3.1 Participants ...... 21 3.2 Apparatus ...... 23 3.3 Measurements ...... 23 3.3.1 Big Five Personality Inventory ...... 23 3.3.2 Thought related questionnaire ...... 24 3.3.3 Open questions mind wandering ...... 24 3.4 Stimuli ...... 24 3.5 Procedure ...... 26 3.6 Data analysis ...... 26 Chapter IV – 4.Results ...... 30 Chapter VI – 5.Discussion ...... 47 5.1 Study limitations ...... 49
iv Contents
1.6 Future Research ...... 50 Chapter VII – 6.Conclusion ...... 52 Reference ...... 54 APPENDIX A ...... 64 APPENDIX B ...... 65 APPENDIX C ...... 66 APPENDIX D ...... 67 APPENDIX E ...... 68
v List of figures
3.1 Induction procedure ...... 25 4.1 Pupil size variation from the baseline 0 ...... 33 4.2 Distribution of standardized residuals ...... 35 4.3 Distribution outcome variables ...... 36 4.4 Pupil size trends ...... 40 4.5 Saccade rate trends ...... 42 4.6 Fixation rate trends ...... 44 4.7 Fixation duration trends ...... 46 A.1 Experimental workflow in Open Sesame ...... 64 E.1 Scatterplots pupil size and Big Five Factors ...... 68
vi List of tables
4.1 Descriptive Statistics Eye Movements ...... 30 4.2 Descriptive Statistics Big Five Factors ...... 31 4.3 Descriptive Statistics Self-Generated Thoughts ...... 32 4.4 Fixed effects for Model 1 predicting pupil size ...... 33 4.5 Fixed effects for Models predicting eye behaviour outcomes ...... 37 4.6 Fixed effects for Model predicting pupil size across time ...... 39 4.7 Fixed effects for Model predicting saccade rate across time ...... 41 4.8 Fixed effects for Model predicting fixation rate across time ...... 43 4.9 Fixed effects for Model predicting fixation duration across time ...... 45
To Adriana and our beautiful moments,
they will never vanish.
1 Chapter 1. Introduction
1. Introduction
“For the poet is a light and winged and holy thing, and there is no invention in him until he has been inspired and is out of his senses, and the mind is no longer in him,” wrote Plato in Ion. A great thinker and, founding fathers of Western culture, whom was fascinated by the complexity of the human mind, which he separated from the body in his concept of dualism. As the passage above hints, the irrational and the creative behaviours of the mind have intrigued Plato profoundly. Did Plato's mind wander off, interrupted abruptly by a string of unrelated thoughts, while he was composing Ion? Most certainly it did. Because this is what happens to all of us, either when busy with a task or simply relaxing. We all know this feeling of realization that suddenly, without a warning, our mind has drifted away with a flow of new ideas, in an uncontrolled manner, but in one way or another connected to the initial reasoning, interferes and transports our minds in a different direction. This process is known as mind wandering and it occurs frequently and routinely in our everyday lives. In fact, it is estimated that almost 50% of our time awake is spent mind wandering (Killingsworth & Gilbert, 2010).
Studies have been conducted to investigate the nature, role, behavioural implications, and the positive and the negative aspects of mind wandering. In terms of negative aspects deriving from mind wandering, numerous studies have highlighted a number of associated potential deficits. These range from the negative impact on the mood (Smallwood & O’ Connor,
2011; Deng, Li & Tang, 2014) to detrimental effects on memory and working memory (Riby,
Smallwood, & Gunn, 2008; Mrazek, Smallwood, Franklin, Chin, Bard & Schooler, 2012). At the same time, some beneficial effects with respect to creativity were found to be associated with significant levels of mind wandering, which appeared to ease creative problem solving
(Baird, Smallwood,
2 Chapter 1. Introduction
Mrazek, Kam, Franklin & Schooler, 2012). Interestingly, mind wandering was shown to play a key role in future planning and management of personal goals. This research presented the activity of mind wandering not as a mere attentional lapse ascribed to a task performance impairment but as internal information processing aimed at enhancing organizational efficiency (Stawarczyk, Majerus, Maj, Van der Linden & D'Argembeau, 2011).
Cues linked to mind wandering have started being investigated extensively in recent research. These studies aim to identify recurrent indicators of this mental process. Attempts have been made to classify specific human reactions, and subsequently trace these back to mind wandering behaviours. In order to do that a large set of cues was investigated applying different types of techniques, such as electroencephalography (EEG), functional magnetic resonance imagining (fMRI), and eye-trackers (Braboszcz & Delorme, 2011; Barron, Riby, Greer &
Smallwood, 2011; Christoff, Gordon, Smallwood, Smith & Schooler, 2009). The study of non- verbal cues involved in the mind wandering process has yielded promising results, which demonstrated how important these features are when it comes to discretizing a possible state of mind wandering. Among the different categories of non-verbal cues eye behaviours have been found to be highly associated with cases of mind wandering.
Interestingly, the role of pupil dilation was linked to mind wandering cases (Franklin,
Broadway, Mrazek, Smallwood & Schooler, 2013; Grandchamp, Braboszcz & Delorme, 2014).
Additionally, other types of eye behaviours such as saccade and gaze fixation yielded consistent results which corroborated the existence of a strong connection with the activity of mind wandering (Smilek, Carriere & Cheyene, 2010; Schad, Nuthmann & Engbert, 2012;
Uzzaman & Joordens, 2011). This phenomenon manifests itself with peculiar types of eye behaviours, which co-occur with other important non-verbal cues such as variations in the rate of heartbeat, electrical brain activity, and blood oxygenation levels.
3 Chapter 1. Introduction
The effect of mind wandering depends mainly on its valence. With a positive connotation it is expected to bring beneficial effects by enhancing creativity, helping to visualize future-oriented goals and consolidate learning (Baird et al., 2012; Baars, 2010; Gruberger, Simon, Levkovitz,
Zangen & Hendler, 2011). In contrast, mind wandering with a negative valence has been shown to be directly linked with depressive symptoms such as dysphoria, repetitive thinking like rumination, and negative mood (Smallwood, O'Connor, Sudbery & Obonsawin, 2007;
Smallwood, Obsonsawin, Baracaia, Reid, O'Connor & Heim, 2003; Watkins, 2008). As such, the effects of different types of mind wandering have a profound impact on our quality of life.
This makes the endeavor to decode the valence of mind wandering a priority for current research.
Up to this point in time no study has been able to establish if eye behaviours can be an effective method for decoding the valence of mind wandering with all its implications. Yet a number of papers investigating eye movements and emotions, mental disorders, and arousal have suggested that the informative value of such behaviours is essential to discriminating different mental states (Lanatà, Armato, Valenza & Scilingo, 2011; Ettinger, Kumari,
Crawford, Flak, Sharma, Davis & Corr, 2005; Munoz, Armstrong, Hampton & Moore, 2003;
Sweeney, Takarae, Macmillan, Luna & Minshew, 2004; Barrowcliff, Gray, Freeman &
MacCulloch, 2004). The aim of the present research is to fill in this gap by identifying the presence or the absence of indicators connected to mind wandering with a positive or negative valence. More precisely, it attempts to discretize if a specific type of eye behaviour is elicited during a specific type of mind wandering.
4 Chapter 1. Introduction
1.1 Scientific and social relevance
Preliminary diagnosis of neurodegenerative disorders in combination with clinical examination of eye movements indicated the adjunct value of the eye behaviour in the diagnostic assessment.
It is important to bear in mind that the eye behaviour is not the primary diagnostic method in itself, but it represents a corroborative aspect of the diagnosis. Moreover, eye movements analyses have been extensively employed in several studies to predict and detect depression, dyslexia, and rumination (Alghowinem, Goecke, Wagner, Parker & Breakspear, 2013;
Bellocchi, Muneaux , Bastien-Toniazzo & Ducrot, 2013; Owens & Gibb, 2016). Thus, the role of eye behaviours applied to investigations regarding a broad range of clinical conditions, as well as psychological and emotional states, appears to be a consolidated procedure in the fields of medicine and social sciences alike. Unsurprisingly, explorations of the nature and the functions of the phenomena of daydreaming and mind wandering, has generated a significant body of research in recent years. If we accept the claims that the impact of daydreaming on cognitive processes in human beings and their patterns of decision making is significant, and especially that its significance has a negative value according to the findings of the previous scholarship, then the question such as “why do we spend so much of our time daydreaming?”, posited by McMillan et al. (2013), inevitably arises again
Given the different implications of mind wandering based on the type of valence, a preliminary detection by means of eye movements could represent an additional approach to be used to identify ruminative and depressive symptoms at early stages or in the case of a diagnosed disorder (anxiety, rumination or depression). As such, the detection of the specific valence of mind wandering could potentially become one of the new methods in routine medical examinations.
5 Chapter 1. Introduction
Another important area of research on cognition focuses on human creativity with our capacity to make long-term future projections and to improve our problem-solving skills. These abilities are fundamental for both children and adults, further investigations needs to focus on the study of whether eye behaviour could shed light on the connection between the valence of mind wandering in the case of positive elicitation with individual creativity or future planning and problem solving. Ideally, recognizing indicators as manifested by eye movements during positive mind wandering could lead to developing new solutions for enhancing and developing these crucial skills.
Independently from the specific type of valence of mind wandering involved in the detection, what has to be emphasized is the potential that decoding of these subtle indicators has for a range of complex mental conditions. Thus, more research on mind wandering and its implications on human beings’ effects is needed with the ultimate goal of minimizing the strain and maximizing the individual well-being.
Given the aforementioned premises the main research question in the present study is as follows: Can non-verbal cues such as oculesics, that is to say, eye blink rate, fixation, and pupil dilation, be treated as indicators of positive and negative mind wandering?
6 Chapter 2. Theoretical Background
2. Theoretical background
Mind wandering is a basic, integral part of our everyday mental experiences. It is one of our brain's preferred routines. In fact, most people hardly ever stop to think about what is happening to them exactly when the mind drifts away. However, researchers have been exploring this phenomenon systematically since the beginning of the twentieth century. Among the many questions posited, it is the effect on our cognitive abilities that has drawn a lot of attention.
What kind of impact can mind wandering have on our mood? Or on creativity and imagination?
Is the impact always the same or does it have multifaceted effects?
Lastly, what kind of approaches can we use to improve our understanding of how mind wandering works and why it is so vital for our species? The next section presents a review of the main theories which will be used to develop the hypotheses and methodology proposed in this thesis.
2.1 Inward fluctuations of mind: mind wandering and daydreaming
Processes of self-generated mental activity, such as daydreaming or mind wandering, have been described as psychological states (Smallwood, 2013). The nature and the exact role of these states in our everyday routine experience has for a long time now intrigued scholars working in different scientific domains. Likewise, the study of naturally occurring self- generated thoughts (Gorgolewski, Lurie, Urchs, Kipping, Craddock, Milham & Smallwood,
2014), referred to also as stimulus-independent, unconstrained or task-unrelated thoughts aka simply SGTs (Smallwood, 2013), has produced a significant body of research. More specifically, scholars have shown interest in SGTs' capacity of allowing us to gain insights on
7 Chapter 2. Theoretical Background
how our minds drift away and shift between the moments of externally- and internally- stimulated cognitive activities.
To quote a few examples, recent papers by Marchetti, Van de Putte & Koster (2014)
(2014) or Perkins, Arnone, Smallwood & Mobbs (2015) all focus on the role of SGTs and their connection to different mental states. Daydreaming is the mental experience of the stimulus-independent and task-unrelated flux of imagination and fantasy that routinely occurs when we are awake and often when we are engaged in some kind of activity, as well as during moments when no others activities are taking place. While in many contexts the terms daydreaming and mind wandering are used interchangeably, sometimes a more fine-grained distinction is made between the two. Mind wandering may be preferred in cases when the stream of imagination takes place simultaneously, and thus interrupting a different task being performed at the same time. In fact, it has been observed that mind wandering can occur during the performance of undemanding or routine tasks and also during difficult tasks (Smallwood,
Nind & O’Connor, 2009).
As regards the phenomena of mind wandering and daydreaming two salient points are made clear and explicit by Smallwood (2013), the first one concerns the crucial importance that these mental activities play in our lives, which makes the questions of why and how the mind wanders a priority for the collaborative interdisciplinary effort of cognitive scientists, neuroscientists, psychologists and other specialists. With the second point Smallwood highlights the main challenge that the scientists face, namely “our current inability to characterize the onset of the mind wandering state” (2013: 521).
The most recent experimental studies (Dumontheil, Hassan, Gilbert & Blakemore, 2010;
Engert, Smallwood & Singer, 2014; Beaty, Benedek, Silvia & Schacter, 2016) have produced interesting results when it comes to observing the flow, the contents and the patterns of SGTs.
Such investigations have aimed to explore more generic brain dynamics, using, for example, a
8 Chapter 2. Theoretical Background
sophisticated methodological combination of user-feedback questionnaires with the analysis of fMRI data acquired during experiments (Gorgolewski et al., 2014). These studies have been able to establish the empirical validity of investigating the processes that allow and control the production of SGTs and ultimately enable us to catch a glimpse of otherwise inaccessible intrinsic cognitive phenomena.
Taking these considerations as its starting-point, the present study will delimit its scope by focusing on the mental experience of mind wandering. It will attempt to improve our understanding of the role and the nature of this phenomenon with respect to eye movement behavior, which will be analysed in its relationship to the generation of self-induced thoughts occurring during mind wandering In the next section daydreaming and mind wandering will be discussed in more detail, to be followed by the section containing general theoretical and methodological premises of the study.
2.1.2 Daydreaming and mind wandering styles
When it comes to the scientific approaches to the styles of daydreaming, three specific styles of daydreaming have been identified (Singer, 1975). These include positive constructive daydreaming, dysphoric daydreaming and poor attentional control (Singer, 1975). Positive daydreaming is associated with the tendency to experience vivid imagery or fantasy life absorption with no internal conflict. Positive daydreaming also refers to the inner imagery which enables the pursuit of personal goals (Starker, 1974; Langens and Schmalt, 2002). The second style, dysphoric or negative daydreaming, is predominantly characterized by obsessive and anguished fantasies (McMillan et al., 2013). With the last style, known as poor attentional
9 Chapter 2. Theoretical Background
control, the focus shifts to the instances of anxiety and distraction, as well as absorption of two kinds, both bizarre and frightening (Starker, 1974).
While the positive style of daydreaming tends to have creative and overall positive associations, when it comes to mind wandering the general consensus is on its negative and counterproductive impact, especially at the expense of cognitive performance. These negative associations are stressed, for example, in the study by Mooneyham and Scholer (2013). In this investigation of mind wandering a review of the previous research highlights how in the last two decades the main focus has been on the observation of a range of different negative aspects that the phenomenon in question may produce. In other words, the exploration of the additional functions and potential benefits of mind wandering has been largely neglected, while its limitations with respect to memory, reading comprehension and sustained attention, to give just a few examples, have been discussed extensively in a number of studies (Risko et. al, 2012;
McVay and Kane, 2012a; McVay and Kane, 2012b).
In fact, depending on which one specifically of the three styles manifests itself, the nature and the quality of the subsequent creative output could vary significantly. This would mean that, in the long run, daydreaming practices may reveal themselves productive, as indicated by a handful of original earlier studies. For example, partial evidence which pointed at a possible connection between frequent daydreaming and higher creativity has been obtained in the investigation of storytelling and thematic creativity (Singer and Schonbar, 1961; Singer and McCraven, 1961). Elsewhere, the potentialities of daydreaming have also been praised for their crucial supporting role in enhancing and improving the communication between humans and computers, in an attempt to implement a computational theory of daydreaming (Mueller and Dyer, 1985).
10 Chapter 2. Theoretical Background
Positive daydreaming is associated with positive feelings and is future-oriented in that it may facilitate a projection of future goals. Schooler et al. (2011) elaborate on this aspect in their paper, pointing out that a consistent amount of mind wandering has been indeed found to be oriented to future thinking. To this extent, the evidence that mind wandering is involved in future planning and may, as a result, bring advantages in terms of executive processing skills, has been revealed in the study by Baird et. Al (2011). In fact, the study claims that during off- task thought two important contents are often associated, namely, the self-relevant content and the goal-directed one. Self-reflection appears to be a crucial element which is always part of the process of mind wandering in relation to future plans. This conclusion was further corroborated by the findings of the study conducted by Smallwood et al. (2011), who established a significant connection between the process of mind wandering and future thoughts. The participants in this study showed a stronger aptitude towards prospection during off-task thought, with similar findings regarding self-reflection and long-term goals, which were shown to be consistent (Smallwood et al. 2013). As the finding of these different studies indicate, the strong inclination of mind wandering towards future orientation seems to be a pivotal trait to be taken into account when devising new mind wandering induction tasks.
Another process regarding self-reflection in subjects prone to anxiety and depression, namely rumination, is an aspect to take into account with respect to mind wandering.
Rumination has been defined by Nolen-Hoeksema et al.(2008) as a perseverative process of thinking about a person’s feelings and problems instead of a defined content of thoughts, and it has been shown to play a very important part in its relation to depression, negative thinking and levels of anxiety. Consistent evidence about the presence of shared recurrent traits for the three phenomena of rumination, dysphoria and depression, specifically with respect to mind wandering, has been uncovered.
11 Chapter 2. Theoretical Background
In one study it was suggested that mind wandering might serve as a marker for depressive and negative thinking (Smallwood, O'Connor, Sudbery & Obonsawin, 2007). Despite the fact that the presence of self-reflection based on negative thinking has never been demonstrated to be directly represented by the negative dysphoric daydreaming, the two phenomena share the same constituents. For instance, dysphoric ruminative thought combined with negative mood is characterized by a pronounced focus on personal problems, more general negativity, and a critical aptitude towards the self (Lyubomirsky, Tucker, Caldwell & Berg, 1999). The evidence that different mind wandering styles exist have been confirmed and corroborated in the last two decades, the distinctive nature of such a phenomenon mainly depends on the type of valence which characterizes it. To a certain extent it can be noticed that two styles, respectively, positive and negative mind wandering have seized the attention of researchers.
2.2 Mind wandering and oculesics
With oculesics we can refer to the study of eye behaviours in terms of non-verbal communication (Tiwari 2016), which can help us collect information on the different cognitive statuses involved. Oculesics includes pupil dilation, saccades, eye blink rate and fixations, which will be investigated in the upcoming paragraphs as the main non-verbal cues enable us to detect mind wandering processes. The goal here is to demonstrate how effective this approach can be for the study of different mental experiences.
Fixations in natural behaviours have been shown to represent a valuable manifestation of eye behaviour, with previous investigations indicating that shifts in observer attentions are indeed manifested through fixations (Hayhoe & Ballard, 2005). Finally, the importance of pupil dilation, alternatively referred to also as pupillometry, is discussed in detail in the review
12 Chapter 2. Theoretical Background
of Laeng et. al (2012). In this review, the contribution that the study of this kind of non-verbal cues has made in the fields of psychology, neuroscience, and cognitive studies is highlighted.
Once again, pupil dilation as indicator of cognitive activity has been shown to be a consistent factor in the study conducted by Piquado et al. (2010), which confirms that this non-verbal cue plays a crucial role in the mental processes.
In their highly influential study on daydreaming and oculometer activity Antrobus et al. (1964) investigated the relationship between eye movements and internal cognitive processes. As its most important result, the study was able to establish a direct link between the high rate of eye movements and a rapid cognitive change. The relationship between eye movements and cognitive processes thus seemed to represent a key indicator for discretizing mind wandering states. More recent scholarship has given special attention also to fixation- duration, which appeared to be longer during mindless reading tasks with respect to normal reading tasks (Reichle, Reineberg & Schooler, 2010). Similar results were obtained in the study conducted by Foulsham et. al (2013) in which, for instance, average fixation duration was found to be longer during mind wandering reading tasks. These promising findings allowed for the assumption that focus engagement could be inferred directly from eye movements. Eye blinking represents a relevant non-verbal cue that has the potential to offer important insights on the ways in which the process of mind wandering unfolds. For example, to the shifts which take place once internal cognitive processing is interrupted by the perception of external stimuli.
Even if the causal relation between eye blink rate and mind wandering has not been established,
Smilek, Carriere, and Cheyne (2010) suggested that the change of rate in eye blinks, associated with these shifts from external task-related periods to internal thoughts, might represent the trade-offs between them. It appears clear that in the process of mind wandering external information is blocked to leave more room for inner reflection and this occurs almost at the same time as a considerable increase in eye blink rate is observed.
13 Chapter 2. Theoretical Background
The transition between external attention to internal focus with respect to eye movement reactions by means of task solving was investigated by Salvi et al. (2015), with somewhat unexpected and exciting results. In fact, the study demonstrated that external attention was associated with higher focus, lower level of blinking, and higher level of fixations, while the internal focus was linked to an increased level of blinking and a decreased frequency of eye movements.
Regarding pupil dilation and mind wandering, only a limited number of studies have so far attempted to investigate the role of this non-verbal cue. In addition to the previous studies which dealt with external and internal focus with respect to eye movements, the study conducted by Smallwood et al. (2011) showed promising results to support the predictions that, pupil dilation would increase considerably during online cognition and no significant pupil dilation would occur during periods of offline thought. Conversely, higher pupil dilation prior to off-task reading was found in the study conducted by Franklin et al. (2013). In this study the explanation suggested was that such findings shed light on the processes of mind wandering and could be used to keep track of attentional state, as well as for the development of mind wandering prediction algorithms. The external information obtained by observing pupil dilation, in addition to information collected by analysing the eye blink rate or eye movements represents a consistent methodological approach to investigate how SGTs can be multifaceted.
More precisely, Einhauser et al. (2008) report that pupil dilation increased before the perceptual switch and that the present phenomenon was indeed a predictor of perceptual stability. They also posited that pupil dilation, which reflects the production of norepinephrine, could have a crucial role in perceptual selection mirroring the way that it is realized in behavioural decision making.
14 Chapter 2. Theoretical Background
Finally, as concerns the informative value of saccade, the study conducted by Bixler and
D’Mello (2014) showed that such feature manifests a distinctive behavior in the process of mind wandering. The promising findings indicated that a percentage of 72 and 59 mind wandering states were predicted under two different experimental conditions. The two predictive models applied in the study included saccade length measures among their top features, which led the researchers to conclude that saccade length was an important indicator of mind wandering. This particular feature has been investigated extensively in a number of studies which focused on cognitive workload and task performance under stress conditions, as well as neurodevelopmental disorders, producing consistent findings about the reliable role of saccadic movements in relation to these phenomena (Cardona & Quevedo, 2014; Debue & Van
De Leemput, 2014; Matthews, Reinerman-Jones, Barber & Abich, 2015; Nakashima, Kim,
Flutura, Seiderer & André, 2015; Di Stasi, McCamy, Catena, Macknik, Canas, Martinez-Conde,
2013; Anderson & MacAskill, 2013; Otero- Millan, Schneider, Leigh, Macknik & Martinez-
Conde, 2013).
The interconnection between mind wandering and eye behavior has been investigated by several researchers in the last decades, these recent and seminal studies suggest that these features show informative patterns when it comes to discretize if a mind wandering process is occurring. These promising results represent a starting point from which delve deeper into connection between specific types of eye behaviour with respect to different styles of mind wandering.
15 Chapter 2. Theoretical Background
2.3 Presentation of the research hypotheses
Independently of the evidence that mind wandering may be associated with positive or negative effects with respect to creativity, problem solving, and cognitive skills, and given that this phenomenon still remains a grey area between two different schools of thought, the analysis of eye movements occurring during mind wandering constitutes a promising, albeit challenging research effort which deserves to be undertaken. The role of eye movements has so far been largely neglected and can be presented as an under-researched topic, with no prior studies up to date attempting to investigate what specific type of eye behaviour may be involved in the process of positive constructive daydreaming. In addition, despite the existence of an extensive body of scholarship dedicated to the phenomenon of rumination and its implications on several different levels, very little attention has been paid to the relation between rumination and eye movement patterns, such as, for pupil dilation, which occurs during this self-reflection process.
In this study positive mind wandering and negative mind wandering will be induced to unveil what kind of eye movement behaviour represent a valid and consistent indicator of such states. The novel approach to the investigation of the effects of mind wandering of different valence in terms of non-verbal cues, such as oculesics, that this study intends to pursue, draws on much earlier preliminary studies (as the seminal research conducted by Singer in 1975) on daydreaming styles and their implications. Given that no recent research has investigated this connection further, the present study aims to fill in an important scientific gap by studying non- verbal cues which can be associated with a specific type of mind wandering. It is important to stress that even if the approach adopted in the present study can be described as exploratory, important aspects of positive constructive daydreaming have been found to be pivotal in mind wandering studies with respect to eye movements. Moreover, consistent occurrence of the same
16 Chapter 2. Theoretical Background
eye behaviour both in positive constructive daydreaming (Singer, 1975) and mind wandering
(Smilek et al., 2010) suggests that both constructs are intertwined at least to some extent.
2.3.1 Pupil dilation
As the evidence collected in a number of studies suggests, the important role of pupil size, both as the indicator of specific states of minds and different types of emotional workload, represents a reliable feature to be analysed, making it a valuable and promising aspect to be explored more extensively. Recently, the research on pupil size dilation has concentrated more and more on the investigation of the relationship between the changes in size in response to stimuli of different valence.
Earlier studies, such as, for example, Partala and Surakka (2003), demonstrated a significant increase in pupil size dilation in response to positive, negative and neutral auditory stimuli, but with only marginal differences in the case pupil's response to either negative or positive stimuli. However, these findings were subsequently overturned in more recent papers, all of which focused on showing how the differences in emotional load of an experience can influence the reaction of the pupil. The study conducted by Banks, Welhaf, Hood, Boals, and
Tartar (2015) on the emotional valence of mind wandering was able to bring to light promising differences between positive and negative task unrelated thoughts with respect to task performance. When used to detect both online and off-line stress when compared to relaxation, the changes in pupil dilation were found to be consistent, indicating thus that the responses of the pupil subject to anxious states could be directly connected to the stress stimuli (Ren, Barreto,
Huang, Gao, Ortega & Adjouadi, 2014). This is due to the strong interaction between rumination and stress where the former was found to be a predictor of the latter (Morrison &
O’Connor, 2005).
17 Chapter 2. Theoretical Background
Similarly, the pupil dilation response investigated during mind wandering yielded consistent findings regarding a greater variability in the pupil diameter (Bixler & D’Mello, 2016), which was in line with previous studies (Smallwood et al., 2011; Franklin et al., 2013). In addition to the aforementioned consistent findings, pupil dilation was found to be significantly greater for participants who were subjected to high levels of anxiety compared to participants who experienced no anxiety (Tichon, Mavin, Wallis, Visser, & Riek, 2014). Studies regarding the relation between rumination and anxiety indicated that when a mind is ruminating, that it to say mind wandering negatively, a high level of anxiety is generated (McLaughlin, Borkovec
& Sibrava, 2007; Starr & Davila, 2012). Previous studies have also examined the reaction of the pupil under different conditions ranging from physiological reactions to task performance and mind wandering.
The different studies mentioned above all point to the possibility of establishing a direct link between the valence of a given stimulus and the fluctuations in pupil size dilation. This connection has already been observed in a number of cases which involved experiences with negative emotional load (Banks et al., 2015; Ren et al., 2015; Bixler & D'Mello, 2016; Tichon et. al, 2014), yet when it comes to pupil dilation and its relationship with mind wandering, no prior studies have attempted to discretize consistent differences produced by the changes in valence of the self-generated thought process, from positive to negative. By focusing on this under-researched aspect, the present study aims to identify and differentiate the responses as indicated by the changes in pupil size occurring during the process of mind wandering under different conditions based on the valence, which in this case will be positive, negative or neutral.
The first two hypotheses posited using the findings of the existing scholarship are as follows:
18 Chapter 2. Theoretical Background
H1a: Negative mind wandering is characterized by a greater pupil dilation with respect to neutral mind wandering.
H1b: Negative mind wandering is characterized by a greater pupil dilation with respect to positive mind wandering.
2.3.2 Saccade movements rate
The saccade represents yet another important type of eye behaviour which may be studied to gain interesting insights into the nature of mind wandering. The relation between eye behaviours and mind wandering during tasks was investigated by Foulsham et al. (2013).
However, this study was not able to demonstrate any differences in saccade length between the two conditions. Yet an earlier study conducted by Uzzaman and Joordens (2011) attempted to demonstrate that eye movements can be an objective measure of mind wandering. This study reported a lower level of saccade count together with a decrease in total number of saccades during mind wandering.
Also in the case of this specific type of eye behaviour, the valence of the stimuli has been established as an important variable. In fact, several studies have demonstrated that states of anxiety and preoccupation can be linked to rumination and that this connection is confirmed by a consistent increase in saccade movements. For example, the relevance of saccade with regards to valence was investigated by Schmidt, Belopolsky and Theeuwes (2015), who compared saccades during fear-conditioned and neutral stimulus conditions in two different experiments. In both cases faster initiation of saccades was found to be consistent in the fear- conditioned stimulus when compared to the neutral one. These findings thus indicated the existing significant changes in the manner of the activation of saccadic movements precisely in response to the exposure to threat and negative stimuli. Another study, conducted by Tichon et al. (2014), can be cited in support of these findings. Here the investigation showed that the saccadic rate increased in anxious participants when compared to those who did not experience
19 Chapter 2. Theoretical Background
anxiety. Conversely, the study of Wadlinger and Isaacowitz (2006) demonstrated that in their experiment, participants who were induced into positive mood were subsequently found to produce a greater number of saccades given specific types of stimuli. This suggests that the valence of a specific condition might in turn affect the saccade rate in a specific manner.This overview of the relevant studies shows that saccadic movements appear to be strongly affected by the type of mood induced or the valence of the stimuli, independently from the relation with mind wandering. However, lack of solid data that could be used to explain how the valence of mind wandering can affect the eye behaviour, in this specified case, saccadic movements, calls for a new tentative approach to be proposed and tested. In order to elicit supportive evidence the following hypothesis is postulated:
H2 Saccade rate during negative mind wandering is expected to be greater than during positive mind wandering
2.3.3 Fixation rate and fixation duration
In addition to the eye movements discussed above, fixations appear to represent another important eye pattern to be taken into account in the investigation of the relation between mind wandering and eye behaviour. Several studies have investigated the present feature with respect to rumination, personality traits, and mood, suggesting that fixations play a crucial role in providing information on specific behaviours (Duque, Sanchez & Vazquez, 2014; Eisma, Schut,
Stroebe, van den Bout & Boelen 2014; Rauthmann, Seubert, Sachse & Furtner, 2012;
Isaacowitz, Derek, Toner & Neupert, 2009). Fixations and mind wandering were investigated by Smileket al. (2010), although no significant difference on fixations durations were found in this study. Instead Uzzaman and Steve (2011) achieved a very different result, demonstrating that fixation durations were longer in the mind wandering condition. The study of Foulsham et
20 Chapter 2. Theoretical Background
al. (2013) on fixation rate provided consistent results supporting the hypothesis that during the process of mind wandering the number of fixations would increase significantly. Interestingly, when fixation rate was investigated in dysphoric and non-dysphoric conditions with participants subjected to positive, neutral and negative visual stimuli, the group with the dysphoric condition showed consistently lower fixation rate in response to all three kinds of stimuli, showing that specifically in dysphoric conditions the fixation rate exhibits a consistent decrease (Sears, Thomas, LeHuquet & Johbsob, 2010). The present findings seem to corroborate the previously mentioned studies which indicate that the negative valence of mental states affect directly eye behaviours. In a different study conducted by Muris, Roelofs,
Rassin, Franken, & Mayer (2005) a decrease in fixation rate was found in neurotic subjects, pointing to the fact that rumination may be responsible for the oscillation in the frequency of this type of eye behaviour. It would be hence plausible to postulate that the change in the valence of the stimulus from negative to positive would lead to an increase in fixation rate during positive mind wandering. The authors of the study discussed (Muris et al., 2005) also suggest that in neurotic subjects fixation duration may increase considerably. Although no data is given to support the statement, in the present study one of the working hypothesis will draw on this suggestion. Given the aforementioned premises it can be hypothesized that while for the fixation duration significant difference may manifest itself across the positive and negative conditions, the fixation rate might show interesting changes in valence conditions. The following hypotheses are therefore proposed:
H3a Fixation rate during positive valence mind wandering is expected to be greater than during negative valence mind wandering
H3b Fixation durations during the positive valence mind wandering is expected to be lower during negative valence mind wandering
21 Chapter 3. Method
3. Method
In the present study a between subject design was applied. Participants were randomly assigned to three different conditions: positive, negative, and neutral, which represented the independent variables. In the positive condition participants were exposed to positive valence stimuli while in the negative condition negative valence stimuli were used. The neutral valence condition in which neutral items were introduced served as control group. Pupil dilation, saccades, fixations as outcome variables were measured in order to discretize possible differences between the different conditions.
3.1 Participants
A total number of seventy-three student participants (26 male, 47 female, Mage = 24.45, age range: 18-33) enrolled in undergraduate (mainly bachelor) and postgraduate (pre-master, master and PhD level) programmes were collected by means of convenience sampling and human subject pool. Participants recruited through the human subject pool received one
Proefpersonenpool credit for taking part in the experiment. The rest participated on a voluntary basis without any type of compensation.
The participants were asked in advance not to use any type of eye makeup or wear glasses on the day of the experiment since this would interfere with the data collection made by means of Eyelink II. However, four participants disregarded the instructions given and used eye makeup. Due to technical reasons they were asked to remove their makeup before the experiment could start. They were provided with all necessary material to remove it safely.
However, it is necessary to note that in a few cases slight residue of the makeup could still be
22 Chapter 3. Method
seen on the participant's eyelashes, making it therefore a matter of concern in terms of potential confounding effect. Another participant arrived on the day of the study wearing sight glasses, contrary to the researcher's specific request not to use glasses. After being asked to take them off, he started the experiment, but the sight deficiencies in this case interfered so strongly that the stimuli could not be read from the standard distance of 50 cm. As a result, this particular participant had to be excluded. With five participants technical problems which occurred during the calibration and recording process resulted in data inconsistency, therefore these five had to be discarded as well. Lastly, two more participants, whose particular subjective physical traits such as very dark hair, appeared to represent a problem for the quality of the data collected, had to be excluded. In their case the dark pigmentation of the eyelashes was perceived as the pupil pigmentation resulting in multiple pupils detected for each eye.
The final samples size was hence composed of 60 participants, 39 female and 21 male aged between 18 and 33 (Mage= 24.5). Before the start of the experiment, it was explained to each participants that there were no possible risks attendant on the study. After, they were asked to read carefully and then sign a detailed consent form. Before presenting the participants with the consent form, the researcher asked a several questions about mood habits in order to establish the likelihood of any depressive issues. This was done to make sure that the participants would not be exposed to any type of threat or distress to their mental condition.
Two participants mentioned depressive tendency and personal issues, thus they could only be allowed to complete the part of the study with the neutral stimuli, after which they were removed from the data.
23 Chapter 3. Method
3.2 Apparatus
Eye movement behaviours were assessed with the eye tracking headset EyeLink II by SR
Research, which is equipped with two eye cameras with built-in infrared illuminators. This eye tracking device has a resolution which is noise-limited at < 0,01° and a data rate recording speed of 500 samples per second. Due to the large size of the headset the connecting cables were attached to the ceiling of the booth in order to minimize the discomfort given by the weight. The experiment was developed and built in Open Sesame, an open source software built to create experiments of this kind (Mathôt, Schreij & Theeuwes, 2012). After implementing the workflow of the experiment (Appendix A) with the different types of stimuli several pilots were carried out in order to test the efficiency of the design and at the same time to identify possible problems or limitations. The experiment, which was automatically paced, was conducted in a sound-proof booth. A total number of 8 stimuli were presented on a 22’’
DELL P2210 monitor with a resolution of 1680 x 1050 pixels.
3.3 Measurements
3.3.1 Big Five Personality Inventory
Before the mind wandering induction participants were asked to complete a ten item short version of the Big Five Personality Inventory which was adapted by Rammstedt and John
(2007). Personality was measured on a 5-point Likert scale (Appendix B) in order to identify the typology of participants who would take part in the experiment. It was decided that a pre- questionnaire would allow to collect the necessary information about the individual personality traits of the participants, which would then enable the researcher to link a specific kind of personality to each specific participant.
24 Chapter 3. Method
3.3.2 Thought related questionnaire
After concluding the experiment all participants were asked to fill in a second questionnaire.
The second survey was an adapted version of the questionnaire used by Ruby, Smallwood,
Engen, and Singer (2013) to report on participants' thoughts and mood. Participants were asked to rate 7 different statements on a 7-point Likert scale (Appendix C). The first 5 items were used to measure the engagement during the thinking process, while the last two items were needed to check the polarity of the mood, respectively, positive or negative, in line with the experimental design.
3.3.3 Open questions mind wandering
To collect more information, the second questionnaire contained three open questions which were added after the main part on the Thought related survey. These additional questions were related to the participants' mind wandering habits, perception and experience. The answers provided in this part were used to double check and to evaluate from a qualitative perspective the experiences of the individual participants, as well as to make sure that the mind wandering experience had been correctly induced. Interestingly, 90% of the participants reported that they experienced the process of mind wandering during experiment, while the remaining 10% were uncertain about it or simply focused on the stimulus itself.
3.4 Stimuli
According to the experimental design of the study, three different conditions with specific valence stimuli were created (Appendix D). The negative stimuli induction procedure made use of 8 items used by Lyubomirsky et al. (2003) to induce dysphoric and ruminative state of
25 Chapter 3. Method
mind. Neutral stimuli were induced using 8 items previously employed in a study conducted by Belleau, Taubitz and Larson (2014). Finally the positive stimuli induction employed 8 items which were self-developed and based on specific constructs used to elicit positive states of mind. Participants were shown a dot in the middle of the screen for 3 seconds, needed to be used as a baseline to measure eye behaviours before the actual stimuli were provided.
Subsequently, the dot disappeared automatically and the stimulus represented by a sentence was displayed on the screen for the duration of five seconds, which was deemed sufficient to allow the participant to read it. After the sentence was removed from the screen leaving it blank, the participant was given 30 seconds to generate thoughts while looking at the screen without stimuli. A recorded sound at this point would indicate to the participant that the time to mind wander was almost over. The aforementioned workflow was repeated 8 times with different stimuli eliciting the same valence until the experiment was concluded. Figure 1 shows the entire workflow of the experiment for the induction procedure.
Figure 3.1: Induction procedure
26 Chapter 3. Method
3.5 Procedure
The subjects participated in the study one by one. Upon arriving in the lab they were informed about the experiment’s procedure, and asked to sign the informed consent form. Once the pre- experiment phase was concluded, the participant was asked to enter the sound-proof booth to get acquainted with the setting and to allow the eyes to get used to the continuous exposure of light. As the first step the participant was asked to complete the first online questionnaire, Big
Five Personality one. Afterwards detailed instructions regarding the type of experiment were given in order to prepare the participant for the start of the study. At this stage, a relaxation video of 2 minutes was shown on the screen, as a way of helping the participant to settle in and feel comfortable and relaxed. The next step was to show them a total number of 8 stimuli on the screen. The duration of the stimulation part did not exceed 25 minutes in order to minimize the discomfort created by the invasive head-set placed on the participant’s head. As soon as the session was over, the participant was asked to fill in the thought related online questionnaire.
Following the completion of the second online questionnaire, each participant was debriefed, offered a hot drink and rewarded with Human Subject Pool credit if eligible or offered a chocolate donut/chocolate bar if not.
3.6 Data analysis
Physiological measurements such as pupil dilation and other eye movements are subject to high level variability due to individual differences, such as morphological and psychological ones.
Given the aforementioned aspects and the presence of multiple measurements for each participant, linear mixed-effects modelling was used to test the hypotheses. The present statistical analysis allows to account for the variance within subjects as well as to analyse the between subject differences. Thus, the hierarchy of the model consists of I=8 intra-subject
27 Chapter 3. Method
observations at level 1 nested within all the n=60 participants to the experiment, which represents the level 2 of the hierarchy. As a consequence, the outcomes of interest have been treated as level 1 variables, while the type of condition positive, negative or neutral (coded with two dummy variables) was treated as level 2 predictor.
The starting model of the analyses was therefore
NT NT P P 2 Level-1 model: Yji = αj+β *X j +β *X j + εji , with εji ~N(0,σ )
2 Level-2 model: αj = α0 +uj , with uj ~N(0,τ )
NT with j=1,…,n, i=1,…,I. The dummy variable X j is equal to 1 whenever a subject j is in the
P Neutral Task group, and 0 otherwise, while the dummy variable X j was set equal to 1 whenever
a subject j was in the Positive Task group, and 0 otherwise. In this way, the fixed effect α0 represents the mean of Y for all the subjects who belonged to the Negative Task group, and the
NT P fixed effects β and β represents the average deviation of the corresponding group from α0.
The outcome, Y, will vary according to the analysis performed (model on the pupil size, model
on the saccades rate, and so on). The error term εji captures the deviations of each level-1 observation from the subject-specific mean, while the term uj represents the subject-specific random effect, that is, the subject-specific random deviation from the fixed part of the model.
In order to quantify the level-1 and level-2 random deviations, the terms εji and uj are assumed
2 2 normally distributed, with mean 0 and variances respectively equal to σ and τ , which are parameters to be estimated. Observations with missing values were removed from the dataset before the analyses.
The model has been estimated through the NLME package in R, which offers maximum likelihood estimates of the parameters. Since the multilevel structure considered in this study consists of longitudinal data (i.e., data that are observed across time), there is the
28 Chapter 3. Method
possibility that error terms are not independent one from another, as standard multilevel modeling assumes. In this standard case, variance of the errors is assumed to be equal across the 8 different stimuli, and the covariances between a single stimulus and the other 7 are constant across time. In particular, the covariance between the errors of two stimuli T and T+k is assumed to be equal to cov(εt, εt+k) = τ2, and their variance equal to var(εt) = σ2+τ2. However, it is possible that the residual term of a stimulus given at a specific time T affects the reaction to a stimulus at time T+k in its own way, for each T, k, and that the error of each stimulus has its own variance.
In this case, an unstructured covariance matrix of the errors is obtained, where each of the entries is free to vary. Another option is that the error term of a specific stimulus at time T affects the reaction to the subsequent stimulus, at time T+1. While the variance of the errors is assumed to be constant across time, the covariance structure in this latter case will follow an
AR(1) model, an auto-regressive model of order 1. With the function “lme” from the nlme package it is possible to fit the model with these different covariance structures for the error term and evaluate (for instance, through AIC indices comparison) which one fits the data better.
When using pupil size as outcome, the best fitting covariance structure for the residuals of the model used turned out to be the AR(1) model.
Therefore, in the following the results for the structural part of the model will be presented assuming an AR(1) process underlying the error terms. This implies that the reaction to a stimulus at time T does not depend only on the structural part of the model, but also on the reaction to the stimulus given at time T-1. Concerning the covariance structure for the other outcome variables, the same comparison procedure was followed as used when the pupil size was the outcome.
In particular, for each new outcome variable the comparison of AIC indices of the models was done that assumes standard, unstructured and AR(1) correlation structures for the error
29 Chapter 3. Method
term. It turned out that for some of the outcomes (namely saccades mean duration and saccades rate) the unstructured structure was the best fitting one, while when the outcome was fixation rate the best covariance structure was the AR(1) model for the error term. Finally, with fixation mean duration as outcome the best fitting covariance structure was the standard one, which assumes constant covariances and error terms across time.
30 Chapter 4. Results
4. Results
Descriptive statistics for Eye Movements are summarized in table 4.1.
Table 4.1 Descriptive statistics for Eye Movements for Negative, Neutral and Positive condition (N= 60).
Variables Negative Neutral Positive
Mdn M SD Mdn M SD Mdn M SD
Pupil size (u/px) 518.16 581.64 202.23 490.20 541.09 172.99 507.63 513.92 151.72
Saccade rate (sac/sec) 71.90 71.24 32.54 74.39 73.95 35.49 76.36 92.68 57.22
Fixation rate (fix/sec) 43.11 45.52 33.32 41.89 47.94 33.66 52.19 63.60 44.67
Fixation duration (fix/ms) 285.53 283.02 30.48 271.19 277.23 53.86 269.32 256.01 53.75
Eye-blink rate (blink/sec) 7.21 14.49 12.39 10.01 14.95 12.19 12.47 14.05 9.15
A summary of scores per condition for the Big Five Factors short version used to control
participants personality at the beginning of the study is represented in table 4.2, personality
was measured by means of a 5 points Likert scale ranging where 1 corresponded to strongly
disagree and 5 to strongly agree. Additionally, scatter plots for the 480 observed scores for
pupil size and the Big Five Factors can be found in the appendix E.
31 Chapter 4. Results
Table 4.2.
Descriptive statistic for Big Five Factor scores (N=60) Variables Negative Neutral Positive
Mdn M SD Mdn M SD Mdn M SD
Big Five Factors
Extraversion 3.00 3.02 .71 3.00 3.07 .43 3.00 3.17 .56
Agreeableness 4.00 3.85 .77 4.00 3.75 .63 3.5 3.40 .98
Conscientiousness 3.00 3.27 .88 3.25 3.25 .89 3.5 3.37 .75
Neuroticism 2.75 2.82 1.11 3.00 3.12 1.14 2.25 2.50 .91
Openness 3.50 3.55 .82 3.00 3.22 .99 3.75 3.67 .92
Prior to performing the main test analyses a manipulation check was conducted to ensure that each specific type of mind wandering was correctly elicited. A MANOVA was used to compare the difference among the three different conditions. The multivariate result was significant for the type of condition, F(14,102)= 3.571, p < .001 , Wilks' Λ = .450 indicating a significant difference among positive, negative and neutral condition. Descriptive statistics for Self –
Generated thought scores are displayed in table 4.3 Table 4.3
32 Chapter 4. Results
Table 4.3
Descriptive statistics for Self-Generated Thoughts for Negative, Neutral and Positive condition (N= 60). Variables Negative Neutral Positive
Mdn M SD Mdn M SD Mdn M SD
On task 6.00 5.85 .87 6.00 5.75 1.11 6.00 5.85 1.30
Past oriented 4.50 3.95 2.01 6.00 5.35 1.63 5.00 4.40 1.78
Future oriented 6.00 5.65 1.59 2.00 2.90 1.68 6.00 5.65 1.49
Self-oriented 6.00 5.65 1.84 5.00 4.05 1.79 6.00 6.00 .72
Other oriented 5.00 4.60 2.08 4.50 3.70 2.12 5.00 4.10 2.04
Positive trait 6.00 5.55 1.09 6.00 5.55 1.50 6.00 5.55 1.19
Negative trait 3.00 3.35 1.49 2.00 2.20 1.54 3.00 3.25 1.80
Pupil size
Before running the analysis, a correction was applied to the original pupil size variable, which
was performed by subtracting the individual pupil size baseline measurement 0 from each pupil
size measurement under stimuli. This correction was applied in order to set the average pupil
size in absence of stimuli to be equal to each other for all conditions. By doing this, the
deviation of the pupil size under stimuli from the pupil size in a relaxed condition becomes the
new outcome Yji. Figure 2 shows the boxplots of the distributions of the 160 level-1
observations for each condition.
33 Chapter 4. Results
Figure 4.1: Pupil size variation from the baseline 0
Table 4.4
Fixed effects for Model 1 predicting pupil size (N=480)
Estimates SE
Intercept 4.07 18.09
Neutral -62.16* 25.58
Positive -24.82 25.58
Notenter-subject and intra-subject variability * p < 0.05
34 Chapter 4. Results
Hypotheses 1a and 1b were tested by specifying a model, Model 1, with the type of condition
(negative, positive and neutral) as predictor for the pupil size. Table 4.4 reports estimates and standard errors for the parameters of the fixed part of the model, along with estimates for the random component.
Results showed a main effect for the neutral condition NT= -62.16 (SE=25.58), t(57)= - 2.42, p= 0.01, indicating that on average the pupil size expressed in unit-pixel became smaller with respect to the negative condition under stimuli. No significant differences between negative and positive conditions were found P= -24.82 (SD=25.58), t(57)= - 0.97, p= 0.33, suggesting that the observed differences between the two groups were due to chance. In the present model
71% of the pupil size variance was due to inter-subject differences and the remaining 28% was due to intra-subject differences across the different stimuli.
In order to assess the normality of the residuals, one of the model assumptions, we inspected the standardized residuals of the model. Figure 3 shows the QQ-plot for the standardized residuals of Model 1. These showed a good fit with the theoretical quantiles of the standard normal distribution, thus satisfying one of the assumptions of the model.
35 Chapter 4. Results
Figure 4.2: Distribution of standardized residuals
Other variables
In order to test if saccade rate was greater during negative mind wandering with respect to positive mind wandering and fixation duration/rate were different when comparing negative mind wandering with positive one, the outcome variables were modelled maintaining the explanatory fixed and random parts used in Model 1. Figure 4 displays the boxplots of the distributions of the other outcome under consideration, for each condition. From the figure, it is possible to notice the absence of systematic differences in the medians of the three groups, independently from the outcome obtained.
36 Chapter 4. Results
Figure 4.3: Distribution outcome variables
37 Chapter 4. Results
Table 4.5 Fixed effects for Models predicting eye behaviour outcome variables (N=480) Estimates
Saccade rate Fixation rate Fixation duration Eye blink rate
Intercept 71.59* (8.92) 49.16* (8.18) 282.60* (10.24) 14.01* (2.19)
Neutral 0.37 (12.64) - 1.17 (11.59) -5.39 (14.51) 0.14 (3.08)
Positive 21.93 (12.62) 14.92 (11.58) -27.04* (14.49) 0.65 (3.08)
Intra-subject variability 39.12 34.32 42.42 9.00
Inter-subject variability 29.84 26.47 46.09 8.01
Notenter-subject = and intra-subject variability =
The results shown in table 4.5 confirmed that there was no significant effect for the saccadic
rate under the neutral condition NT= 0.37 (SE=12.64), t(57)= 0.02, p= 0.97 and for the positive
condition P= 21.93 (SE=12.62), t(57)= 1.73, p= 0.08 with respect to the negative one.
Similarly, there was no main effect when controlling fixation rate both in the neutral condition
NT= -1.17 (SE=11.59), t(57)= -0.10, p= 0.91 and in the positive condition P= 14.92
(SE=11.58), t(57)= 1.28, p= 0.20. As regards fixation duration a marginal main effect was
found for the positive condition P= -27.04 (SE=14.49), t(57)= -1.86, p= 0.06 while there was
no significant effect for neutral condition NT= -5.39 (SE=14.51), t(57)= -0.37, p= 0.71.
Finally, the results for the eye-blink rate did not show any significant main effect both for the
neutral condition NT= 0.14 (SE=3.08), t(56)=0.04,p=0.96 and for the positive condition P=
0.65(SE=3.07), t(56)= 0.21, p=0.83 with respect to the negative condition.
38 Chapter 4. Results
Further exploratory analyses
In addition to the statistical hypotheses testing, further exploratory analyses were performed to understand better the phenomena of valence mind wandering with respect to eye behaviours from a longitudinal perspective. In order to investigate variation across time, a mixed effect model for repeated measures analyses was performed, one for each eye feature treating the stimulus as a continuous variable. As a matter of fact all stimuli for each condition are assumed to elicit the same type of mind wandering. The variable time, denoted by T, was coded from
T=0 to T=7 where each number represents a stimulus. In this way, T was entered as an explanatory variable in the fixed part of the model, along with the dummy variables representing the condition whose effect will be denoted by βT.
Since interactions between times and conditions were also entered in the model, the effects of these interactions will also be reported. In this way, βT represents the main effect of time for the reference group, i.e. the negative group, while βT:NT and β T:P represent the deviations from
βT of the time effect for the corresponding group. With this specification, the intercept and the main effects of the condition dummy variables referred to a possible group effect at time T=0, that is, during the first stimulus, when the time effect (due to repetition of the stimulus) was clearly not present yet. In all the models described in this section the type of covariance structure assumed constant covariance for the error terms (equal to t2 in a linear mixed model) across the time.
39 Chapter 4. Results
Table 4.6
Fixed effects for the model predicting pupil size across time (N=480)
Estimates SE
Intercept 30.29 18.99
Neutral -59.76* 26.86
Positive -41.73 26.86
Time -7.39* 1.46
Neutral*Time -0.9 2.07
Positive*Time 4.60* 2.07
Notenter-subject and intra-subject variability * p < 0.05
The results shown in table 4.6 summarize the effect of mind wandering types through time.
When the longitudinal model described above used the pupil size as outcome, a significant main effect (at time T=0) was found for the neutral condition, βNT= -59.16 (SE=26.86), t(57)=
- 2.22, p= 0.03 with respect to the negative condition, a main effect for time across the task was found βT = -7.39 (SE=1.46), t(57,417)= - 5.03, p < 0.01. Moreover, results showed an interaction between the positive condition and the time when compared to the negative condition βT:P = 4.60 (SE=2.07), t(57,417)= - 5.03, p = 0.02. Graph 4.4 shows how the pupil size changes through the time in each condition.
40 Chapter 4. Results
Figure 4.4: Pupil size trends
For the pupil size variable a negative trend can be noticed for all conditions through the time.
As regards the positive condition, the decrement appears to be less pronounced. Interestingly, as time goes by, pupil sizes for both negative and positive conditions seem to converge until the point when the two appear to reach almost the same size. Pupil size in the neutral condition maintains a constantly lower dilation through time.
41 Chapter 4. Results
Table 4.7
Fixed effects for the model predicting saccade rate across time (N=480)
Estimates SE
Intercept 59.99* 10.04
Neutral 11.99 14.20
Positive 35.70* 14.20
Time 3.21* 0.95
Neutral*Time -2.63** 1.35
Positive*Time -4.07* 1.35
Notenter-subject and intra-subject variability * p < 0.05, ** p = 0.05
Table 4.7 reports estimates and standard errors for the saccade rate for different mind wandering over time.
Using saccade rate as outcome, the results indicate that there was a main effect in the positive condition βP= 35.70 (SE=14.20), t(57)= 2.51, p= 0.01 when compared to the negative one, a main effect for time across the conditions was found βT = 3.21 (SE=0.95), t(57,415)= 3.35, p
< 0.01. Moreover an interaction between positive condition and time was found βT:P = -4.07
(SE=1.35), t(57,415)= - 3.00, p < 0.01. Figure 4.5 displays the trend of saccade rate during time.
42 Chapter 4. Results
Figure 4.5: Saccade rate trends
When analysing the saccade rate across time it can be observed that the rate in the negative condition appears to be the lowest when compared to the other two conditions. Despite the presence of this initial difference, the saccade rate level in the negative condition gradually increases, outdoing the saccade rate in the neutral condition. Overall, the trend for the neutral condition shows a constant tendency towards the positive which in its turn is characterized by a decrease through time.
43 Chapter 4. Results
Table 4.8
Fixed effects for the model predicting fixation rate (N=480)
Estimates SE
Intercept 37.55* 8.75
Neutral 6.37 12.40
Positive 25.59* 12.36
Time 3.17* 0.87
Neutral*Time -1.89 1.26
Positive*Time -2.95* 1.23
Notenter-subject and intra-subject variability * p < 0.05
Results shown in table 4.8 represent estimates and standard errors for fixation rate among the different style of mind wandering during the pass of time. Fixation rate showed a main effect between condition and time βT= 3.17 (SE=0.87), t(57,388)= 3.64, p < 0.01. Furthermore an interaction effect was found between positive condition and time βT:P= -2.95 (SE=1.23), t(57,388)= -2.39, p = 0.01. The fixation rate changes across time per condition are shown in graph 4.6.
44 Chapter 4. Results
Figure 4.6: Fixation rate trends
In the case of the fixation rate the general trend displayed resembles that of the saccade rate.
However, in this case the fixation rate for the positive condition remains constant, while both neutral and negative conditions increase in a different manner: slower for the neutral and faster for the negative.
45 Chapter 4. Results
Table 4.9
Fixed effects for the model predicting fixation duration (N=480)
Estimates SE
Intercept 303.89* 11.69
Neutral -26.60 16.59
Positive -47.00 16.50
Time -6.07* 1.60
Neutral*Time 6.05* 2.31
Positive*Time 5.68* 2.27
Notenter-subject and intra-subject variability * p < 0.05
Results for fixation duration for each mind wandering condition across time are reported in table 4.9. It can be noticed that, when controlling for fixation duration variations across time results indicated a significant main effect for time βT = -6.07 (SE=1.60), t(57,388)= -3.78, p
< 0.01, a significant interaction between positive condition and time was found βT:P = 5.68
(SE=2.27), t(57,388)= 2.49, p = 0.01 and also a significant interaction between neutral condition and time βT:NT = 6.05 (SE=2.31), t(57,388)= 2.60, p < 0.01 was observed. Fixation duration variations are represented in figure 4.7.
46 Chapter 4. Results
Figure 4.7: Fixation duration trends
47 Chapter 5. Discussion
5. Discussion
The main purpose of the present study was to investigate whether eye behaviour could be an indicator of positive and negative mind wandering. In order to analyse specific patterns of eye behaviours eye tracking technology was used. Four different features, namely pupil dilation size, saccade movements rate, fixation rate and fixation duration were scrutinized in the experiment, which allowed us to gather data necessary to distinguish possible differences across the three different conditions.
In line with previous research which suggested that the valence of a stimulus could explain the nature of fluctuations in pupil size dilation (Bixler et al 2016; Smallwood et al.,
2011; Franklin et al., 2013) this feature was expected to manifest a greater dilation for negative valence mind wandering when compared to a condition where the process of mind wandering would be positive and neutral. Secondly, drawing on literature which discussed the impact of the valence of a stimulus on the mood induced, it was hypothesized that the saccadic rate would be consistently greater in the negative valence daydreaming condition with respect to the positive one. Finally, with respect to fixation rate and fixation duration the former was expected to be greater for positive condition with respect to negative, following earlier studies which pointed in this direction (Seubert et al., 2012; Duque et al.,2014). Specifically for the fixation duration it was hypothesized that this feature would be significantly lower for positive valence one when compared to the negative valence mind wandering.
The findings in this study suggest that for some of the eye behaviour features, such as pupil size and fixation duration, there are differences according to a specific type of valence, namely, positive, negative, and neutral which are manifested in the process of mind wandering.
As concerns pupil size, the analysis of data produced results which supported the hypothesis
48 Chapter 5. Discussion
that negative mind wandering would generate a larger pupil size dilation. In fact, a greater pupil dilation was observed in participants exposed to negative stimuli. Such findings are in line with the study conducted by Tichon et al. (2014) indicating that during processes of mind wandering negative mind wandering have a greater variation activity which leads to an increase in the pupil area. This greater dilation is due to the higher level of stress generated during the process of rumination. The present findings are supported by the results of the study conducted by
Pedrotti, Mirzaei, Tedesco, Chardonnet, Merienne, Benedetto and Baccino (2014) which demonstrated that pupil size dilations have discriminating power with respect to stress detection. Conversely, when exposed to neutral valence mind wandering the pupil size shows a significant decrement. However, it has to be added that no significant differences in terms of pupil size dilation were found between the positive and negative mind wandering condition which indicates the rejection of the first hypothesis B.
With the second hypothesis, it was expected that saccade rate would be significantly greater for negative valence mind wandering when compared to positive valence mind wandering.
Against this expectation, no significant increase for saccade rate was found in the comparison between negative and positive conditions. Although overall the saccade rate for the participants exposed to the negative mind wandering process was greater than the positive, the difference was not significant enough to reject the null hypothesis, which leads to the conclusion that the second hypothesis cannot be supported by the findings of this study. Interestingly, the results are in contrast with previous research where divergent results based on the type of condition were found (Wadlinger et al., 2006, Tichon et al., 2014).
49 Chapter 5. Discussion
The third hypothesis A posited that fixation rate would be greater in participants which underwent the positive induction procedure when compared to the negative one. Contrary to the expectations, the analysis indicated that no significant differences could be observed between the fixation rate in the positive and negative mind wandering procedure. The present results are not in line with previous which indicated significant differences across different conditions, for instance a lower fixation rate during rumination (Rassin, Franken and Mayer,
2005). Therefore, these results do not support the third hypothesis A.
Finally, the third hypothesis B suggested that a decrease of fixation duration would occur when participants were given positive mind wandering stimuli. The findings demonstrated that a consistently shorter fixation duration was indeed the distinctive eye behaviour for positive valence participants. The present finding are therefore in line with a previous study conducted by Muris et al. (2015), as it shows the opposite behaviour when compared to negative mind wandering, which has been characterized by ruminative and neurotic traits.
5.1 Study limitations
The rejection of the second hypothesis regarding saccade rate and the third hypothesis A concerning the fixation rate, a number of potential practical and methodological deficiencies have to be discussed. The two hypotheses were tested without applying the same normalization process used to test the pupil size data, which was obtained subtracting the baseline 0 (no stimuli moment) to the stimuli measurements. It is important to mention that baseline 0 represents the least biased comparative measure available in the present research. However, as explained above, the design of the experiment was composed of 8 different baselines of 3 seconds each and 8 different stimuli of 30 seconds each. In terms of eye behaviour data
50 Chapter 5. Discussion
collection 3 seconds are sufficient to gather pupil size information to serve the purpose of baseline measure. In fact, even if the variations of the pupil size are micro, this is still a highly informative feature given the consistency and stability of these variations which can be detected by the eye-tracker in a very short timespan. This was not the case for the other features such as saccade and fixation, since the other eye behaviour movements require a broader time lapse to be recorded in a reliable fashion
Additionally, the relatively small size of the sample used for the present study could represent another limitation to be taken into account. The results produced by 20 participants for each condition might not yield significant differences across the conditions due to the great individual variability, meaning that the main expected behaviour is concealed by these large variations. Finally, low ecological validity represents another relevant aspect given the nature of the experiment which took place in a sound-proof booth with a control level of light brightness, using a considerable invasive head set placed on the participant’s head.
5.2 Future research
The important role of eye movements during cognitive processes has been investigated extensively over the last two decades in different fields. However, even if the existing literature covers a substantial number of features analysed, only in a handful of studies so far an attempt has been made to establish a set of eye movements as standardized parameters to discern mental processes of various nature. In order to work towards the possibility of automated recognition of specific eye behaviours as reliable indicators of different states of mind, cognitive processes or thought generation, what needs to be done is to determine which eye behaviours are the most interesting and informative.
51 Chapter 5. Discussion
Mind wandering processes, which we routinely engage in when we are awake, undoubtedly represent mental experiences vital in our day-to-day activities. In fact, previous research has demonstrated that these processes can be beneficial in terms of creativity, problem solving and future oriented planning. At the same time, the counterpart of these positive process has been indicated in the frequent occurrences of negative mind wandering, which occurs during cases of rumination, neuroticism and also early stages of depression, making this process highly detrimental for the well-being of the individual. Moreover, it would greatly improve our understanding of the nature of the different mental experiences, if more efforts were undertaken to detect the external, non-verbal indicators connected to the different mind wandering processes. The step that would follow would lead to the possibility to recognize the specific type of the mind wandering process which is especially important in cases where the individual needs to be treated in cases of rumination, anxiety and depression. Likewise, also in the case of positive mind wandering, such research would lead to gaining new knowledge of the positive aspects that this process can generate.
52 Chapter 6. Conclusion
6. Conclusion
The present study produced promising findings which have partially confirmed the presence of specific eye movement behaviours during the process of mind wandering. The elicitation of a positive or negative valence wind wandering in the case of pupil size and fixation duration produced distinctive reactions in terms of eye behaviours. The current research attempted to improve our understanding of two macro valence categories which encompass several important constructs both for positive and negative conditions. The present finding indicated that for pupil size dilation the valence of the stimuli does play a crucial role, although the reaction for a positive stimulus is manifested in a manner which cannot be distinguished from a negative one. On the other hand, the present research findings indicated that when it comes to the duration fixation eye movement feature the valence generates a distinctive change between positive, which is manifested with shorter duration, and negative, which appears to be longer.
In addition, when using a longitudinal approach, the differences between the positive and the negative conditions with respect to eye behaviour are more clearly marked suggesting that the time of exposure to mind wandering stimuli has a crucial role in the process of classification.
While the results obtained are in line with the few hypotheses formulated initially, no definitive conclusions can be drawn at this stage of the exploratory analyses conducted. Finally, the present research supports previous studies which indicated that eye behaviours can be used as indicators of specific type of mental activity.
53
54 Reference
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64 Appendix
Appendix A
Figure A.1: Experimental workflow in Open Sesame
65 Appendix
Appendix B
Big Five Personality Inventory
INSTRUCTION : for each of the following statements select an option which describes the best your personality.
Disagree Disagree Neither agreee Agree Agree Strongly a little nor disagree a little strongly
I see myself as someone who...
1. is reserved
2. is generally trusting
3. tends to be lazy
4. is relaxed, handles stress well
5. has few artistic interests
6. is outgoing, sociable
7. tends to find fault with others
8. does a thorough job
9. gets nervous easily
10. has an active imagination
66 Appendix
Appendix C
Thought related questionnaire
INSTRUCTION : for each of the following statements select an option which describes the best your experience.
Disagree Disagree Neither agreee Agree Agree Strongly a little nor disagree a little strongly
During the experiment...
1. I was thinking about the items I was provided
2. I was thinking about other people
3. I was thinking about the past
4. I was thinking about myself
5. I was thinking about the future
6. I had positive thoughts
7. I had negative thoughts
67 Appendix
Appendix D
INSTRUCTION : For the next few minutes, try your best to focus your attention on each of the ideas on the following pages. Read each item slowly and silently to yourself. As you read the items ,use your imagination and concentration to focus your mind on each of the items. Spend a few moments visualizing and concentrating on each item. Please continue until the session is over and the experimenter returns
POSITIVE INDUCTION :
1. THINK ABOUT : How it will feel when you have completed a project you are working on 2. THINK ABOUT : Your future plans and how you are working to reach your personal goals 3. THINK ABOUT : What would you like to eat now and how it smells 4. THINK ABOUT : How you are constantly learning about new things 5. THINK ABOUT : How it will feel when you have time to be outdoors 6. THINK ABOUT : The moment of connection you share with your friends 7. THINK ABOUT : How you feel when you manage to find creative solutions to future problems
RUMINATION INDUCTION:
1. THINK ABOUT : The physical sensations you feel in your body 2. THINK ABOUT : Your character and who you strive to be 3. THINK ABOUT : The degree of clarity in your thinking now 4. THINK ABOUT : Why you react the way you do 5. THINK ABOUT : The way you feel inside 6. THINK ABOUT : The possible consequences of your current mental state 7. THINK ABOUT : How similar/different you are relative to people 8. THINK ABOUT : What would be if your present feelings lasted
NEUTRAL INDUCTION:
1. THINK ABOUT : A boat slowly crossing the Atlantic 2. THINK ABOUT : The layout of a typical classroom 3. THINK ABOUT : The shape of a large black umbrella 4. THINK ABOUT : The movement of an electric fan on a warm day 5. THINK ABOUT : Raindrops sliding down on a windscreen 6. THINK ABOUT : A double decker bus driving down a street 7. THINK ABOUT : A full moon on a clear night 8. THINK ABOUT : Clouds forming in the sky
68 Appendix
Appendix E
Figure E.1: Scatterplot pupil size and Big Five Factors
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