The Effect of Cognitive Load and Meaning on Selective Attention

Rebecca A. Weast ([email protected]) Department of Psychology, Franklin & Marshall College Lancaster, PA 17604 USA

Nicole G. Neiman ([email protected]) Department of Psychology, Franklin & Marshall College Lancaster, PA 17604 USA

Abstract memory (or other task) contains fewer items, there is more cognitive capacity available to focus on Nillie Lavie’s Load Theory of selective attention suggests that the size of the cognitive load affects selective relevant information, while effectively weeding our attention ability: the larger the cognitive load, the poorer perceived distractors. This cognitive system only the selective attention performance. Other authors have comes into play in conditions of low perceptual found that the relationship between distracting and load, when distractors have been perceived and need relevant information can influence how well distractors to be actively suppressed (Lavie, Hirst, de Fockert are ignored. Our study hypothesized that a) larger & Viding 2004; Lavie & Cox, 1997; Lavie, 1995). cognitive load would (as previously shown) hinder Many studies have addressed the intricacies of reaction time on a selective attention task, b) that this model, usually using simple, single letter or distractors (words) semantically related to the words being digit stimuli. Past studies used stimuli that are held in memory (as part of the cognitive load manipulation) would be more distracting than unrelated unrelated to each other and that carry as little and neutral distracters. The findings instead showed that semantic information as possible. Presumably, they unrelated distractors were more distracting. do this to get at the attention issue in its purest form, with the simplest stimuli possible. Stimulus material Lavie’s Load Theory of selective attention suggests used in past studies includes letters, numbers, that the quantity of stimuli presented to a person colors, and simple black and white symbols. Few determines how their selective attention system will have examined the model in relation to the semantic, function – whether they will be more or less content of the stimuli. This raises the obvious distractible (Lavie, Hirst, de Fockert, & Viding, questions: are distractors more distracting when they 2004). The Load Theory suggests that selective are meaningfully related to task-relevant attention consists of two mechanisms: a passive, information? Is this effect modulated by cognitive perceptual system, and an active mechanism of load? cognitive control. The perceptual system functions Most of the work done to test Load Theory has in line with the early selection model, where the focused on the perceptual mechanism of selective number of stimuli modulates the effectiveness of attention. Lavie and colleagues have investigated the attentional selection. When there is a low load on effect of cross-modal distractor presentation in a the perceptual system – as in a visual search task decision task, and the possible relationship between with few (1-3) items to search through – there is the cognitive load resulting from task-switching extra, unused perceptual capacity that involuntarily between and within sensory modalities (Rees, Frith picks up other (irrelevant, distracting) & Lavie, 2001; Brand-D’abrescia & Lavie 2008). environmental information, and the person is more Only Lavie’s 2004 study has really addressed the likely to perceive distractors. In a high perceptual effect of cognitive load on selective attention tasks. load condition, the opposite is true: the task uses up This makes sense; the question of involuntary all attentional capacity, and extra environmental attention grabbing by stimuli is a more direct way to elements can’t interfere. In this model, the second study selective attention, and according to the Lavie stage of selective attention is an active, cognitive model, the cognitive system plays only a supporting process. In conditions of high cognitive load, where role in attention control. However, we wanted to most of the person’s cognitive capacity is consumed investigate the effect of cognitive load further. The with a difficult working memory task, for example, current study investigated the impact of the the person has few cognitive resources available to cognitive load on selective attention. More resist distraction by irrelevant information. The specifically, we examined what effect, if any, the person can better disregard distractors in a low- semantic content of the information being held in cognitive load condition. When the working working memory has on distractibility when

1477 distractors are related to the information in working white letters, numbers, symbols, etc.). Therefore, the memory. Lavie et al.’s 2004 study used digits to experimenters focused on the effects of truly-task compose their memory sets, the current study used irrelevant distractors, distractors that were words. By using words instead of digits, the completely unrelated to the target stimuli. Such memory set words could be related to each other, studies are valuable because they aim to more and could allow for distractors to also be related (or closely simulate real-world distraction and selective not) to the words in the memory set. By attention in a controlled clinical setting. During a manipulating the meaningful relationships between visual search task, participants had to identify memory set and distractor we hoped to have an whether an X or an N was present. During the task effect on distractor interference. standard distractors (X or N) were presented in 80% One study has examined the effects of distractors of trials, related distractors (similar to target items) with semantic meaning (words) when that meaning were presented in 10% of trials, and unrelated is either task congruent or non-congruent. Fabrice distractors (images of cartoon characters) were Parmentier (2008) found that task-relevant and task- presented in the remaining 10%. They found that irrelevant novel distractor words modulated these novel distractors could create more disruption performance of a decision task in a way that of performance than standard distractors, but only suggested that the words were semantically when participants had a longer period of time to analyzed immediately following presentation. identify the target. When a time pressure was added Specifically, when an auditory distractor word to the search task—they were given 500 ms to (either ‘left’ or ‘right’), presented simultaneously respond rather than no time limit—the extra with a target arrow, was incongruent with the interference of irrelevant distractors was eliminated direction of a target arrow, it took longer than with a in high perceptual load conditions, in agreement congruent distractor word for participants to identify with the Load Theory’s prediction. the direction of the arrow. This suggests that task Belke, et al. (2008) also investigated the effects of relevant information can be more distracting than target-similar distractor items in a visual search task. task irrelevant information. It should be noted, Their experimental tasks presented participants with however, that this interference did not occur when a target, presented as a single word, followed by an the congruent and incongruent distractors were array of images. In some trials the array would standard distractors (presented on every trial). The contain the target, and some trials would contain an authors conducted two different manipulations of item semantically related to the target (target: the neutral:word distractor ratio, and observed “shirt,” related item: an image of a pair of pants). interference only when a neutral distractor was used Using an eye-tracker, they found that when the (a sinusoidal tone) on 80% of trials, and congruent target was present, even in trials where the related and incongruent distractors each appeared in 10% of item was also present the participant’s first fixation trials. This indicates that interference occurred only would fall on that target significantly more when the meaningful distractors were novel as well. frequently than non-target items. When the target (The current study also examined the interference was absent, however, the first fixation would fall on caused by semantically relevant and irrelevant the related item significantly more than the other distractors, but in a uni-modal design. Parmentier items in the array (Belke et al., 2008). These results (2008) used a bimodal design, with auditory suggest that, when primed with a target item, the distractor words and a visual decision task.) participant is more likely to look at an item related Lavie and colleagues have also manipulated the to that prime than an item unrelated to that prime. similarity of the distractor and the target in a visual Finally, Belke et al. (2008) found that items search task. For example, in sections of her study semantically related to a target are more attention- outlining the two-part attention model, half of the grabbing than unrelated items. This, along with the distractors would be the same as the target (X and broad finding that task-congruent distractors are X), and half of them would be different (X target more distracting than neutral distractors (Lavie et. with N distractor) (Lavie et al., 2004). These studies Al. 2004; Parmentier, 2008; Lavie & Forester 2008), have shown that task non-congruent distractors and Parmentier’s findings that semantic information cause greater interference with attention control than can be obtained from novel distracters, lead us to congruent distractors. Still, these studies used only four hypotheses. First, we hypothesized that stimuli and distractors without semantic meaning. distractors with semantic content related to the Lavie and Forester (2008) noted that most semantic content of the memory set would cause selective attention studies (including most of more interference (more distraction, slower RTs) Lavie’s own) utilize the same or similar stimuli as than either distractors unrelated to the memory set, the distractor item and target item (i.e. black and or neutral distractors (which should have caused the

1478 least interference). Second, we also expected to see key if the X was present. Finally, participants were an effect of load on distractibility compatible with shown a word, and asked if it was present in the the Load Theory: we expected to see greater original set. distractibility (slower RTs) in the high cognitive This study had a 2x3 within subjects design: load condition. Third, based on the Load Theory we cognitive load x semantic content of distractors. hypothesized that there would be no interaction Cognitive load was defined here (as in Lavie et. al. between cognitive load and distractor type; past 2004) as the number of items presented in the studies produced no results that would suggest an memory set. The two conditions, high and low, were interaction either way. Finally, we expected to see a defined as memory sets containing 5 and 2 items higher rate of false positive identifications in the respectively. In the low load condition, the memory memory probe in the high load condition, as there set was presented for 2s and in the high load should have been less cognitive capacity available to condition it appeared for 4s. These presentation actively ignore distractor words. times were meant to eliminate extra search/reading time from the low load condition, while still Methods allowing enough time in the high load condition for Thirty-four Introduction to Psychology students the participant to read and process all memory set from Franklin and Marshall College participated, in words. A similar method was used in Lavie (2004) exchange for course credit. Participants volunteered when manipulating cognitive load. The two levels of for participation via sign up sheet. No demographic cognitive load, as manipulated by memory set size, factors were recorded or controlled for. were presented in separate experimental blocks. Stimulus images were generated using Graphic Participants were assigned one of two groups at the Converter software, and sets of stimuli (trials) were start of the study, and group assignments alternated constructed and ordered manually (although a every-other participant. Presentation order was random order was generated by computer to guide counterbalanced between groups. the organization of the trials). Stimulus sets were In order to allow distractors to be semantically presented using Generic Psychology Lab software. related (or not) to the words in the memory set, all All software was run on Mac OS9. Accuracy and memory sets consisted of either 2 or 5 words mean reaction times for each participant were meaningfully related to each other. Our study’s 3 recorded by the software and analyzed using SPSS distractor conditions were 1) a “neutral” distractor: a statistical software. single symbol (#) without semantic meaning; 2) Each trial consisted of three phases that were “related” distracters: words that are in the same presented serially at fixed time intervals: part 1, the semantic category as the words in the memory set; memory set presentation, part 2, the selective and 3) “unrelated” distracters: words that carry attention task, and part 3, the memory probe. The semantic meaning but are unrelated to the words in memory set consisted of a small set of words the its trial’s memory set. Words were semantically participants were asked to remember. The selective related based on broad categorization by meaning, attention task was a simple decision task. Each or words were grouped under one broad category. attention task presentation consisted of a target letter For example, a high load memory set could consist (N or X) and a non-target (an O), one above the of the words “apple, pear, grape, orange, cherry.” A fixation point and one below. The target appeared related distractor word would be “plum,” and an randomly and equally in each location. The trials unrelated distractor could be “truck.” were also split evenly between the two target letters, The memory probe could have either been one of each target letter appeared equally. One and only the words from the memory set (apple), or a word one of the two targets were present on every trial. still related to the set, but not present (peach). While Participants were asked to identify which of two words were recycled between the two trial blocks, target letters were present (X or N). During this no words were presented more than once in the time, a distractor presented simultaneously with the same trial block. Words were only used if they selective attention task, in the periphery of the contained less than three syllables, and were easily screen aligned horizontally with the fixation point. recognizable. The target and non-target stimuli (the N or X, and In order to preserve the novelty of the meaningful O) appeared, along with a flanker distractor, for distractors (which, according to Parmentier, 2008, 250ms. This display was followed immediately by a was essential to the recognition of the distractors), a blank screen. Participants had from the offset of the longer string of meaningless symbols (ex. #$%!?) selective attention screen (the onset of the blank was not used as the neutral distractor. Within each screen) onward to make their response, either block of trials, 50% of distractors were neutral pressing the N key if the N was present, or the X

1479 distractors (#), 25% were related, and 25% were distractors, t (31)=3.123 and p=.004. There was not unrelated. a significant difference between mean reaction times Reaction times on the decision task and accuracy of low related distractors and low neutral distractors, rates in the memory probe were collected. A 2 x 3 t(31)=.371 and p=.713. within subjects ANOVA (cognitive load x relatedness of distractor) was run to analyze the 10 possible effects of our variables as they pertain to 8 High Load e (% the first three hypotheses, and appropriate post-hoc Low Load tests were run as necessary. Error rates were also ) 6 or Rat calculated, and a 2x2 within subjects ANOVA ong

wr 4 (presence of the memory probe x cognitive load) was run to examine any patterns regarding false 2 positives or false negatives (as discussed in our Mean Err 0 fourth hypothesis). Present Absent Memory Probe Type Results Figure 2: Mean error rate (%) as a function of cognitive The 2 x 3 ANOVA (cognitive load x relatedness of load and memory probe condition. distractor) results indicated a significant main effect of relatedness, F(2,62)=16.008, p<.001, partial Discussion 2 η =.341. However, there was no main effect of The first hypothesis was not supported. While a cognitive load, F(1,31)=.018, p=.894, and partial significant main effect of distractor type was found, η2=.001. The interaction between cognitive load and the unrelated distractors caused more interference relatedness was statistically significant, than related distractors. Neutral distractors caused F(2,62)=.028, p=.028, and partial η2=.109. Fisher’s the least interference, in line with the hypothesis. LSD post hoc test was conducted to determine The background literature leading to this hypothesis which groups of relatedness were significantly was not cohesive, and at the time the hypotheses different in reaction times. Results revealed that all were written, the literature suggesting the greater three groups differed significantly. interference capacity of related, rather than 0.95 unrelated, distractor items was more compelling High than the other findings available. Given the current 0.9 Load findings, a second examination of the background Low 0.85 Load information highlights several studies that do 0.8 support the present results. As noted, Lavie et al. (2004) found that task non-congruent distractors eaction Time (s) 0.75 were more distracting than task congruent 0.7 distractors, Lavie & Forester (2008) found that Mean R 0.65 novel, task irrelevant image distractors were more distracting than familiar or relevant distractors, and Related Unrelated Neutral Parmentier (2008) found that task relevant items Distractor Type presented simultaneously with a task facilitated Figure 1: Mean reaction time as a function of cognitive performance, while irrelevant items interfered. load and distractor type. These results might suggest a sort of priming A 2 x 2 ANOVA (presence of memory probe x effect. Perhaps the memory set primes some larger cognitive load) indicated significant main effect of category or group meaning, and as a result the cognitive load, F(1,31)=6.779, p=.014, and partial participant is not surprised by the presence of a 2 related distractor; an unrelated distractor, then, is η =.179, as well as a significant main effect of presence, F(1,31)=30.998, p<.001, and partial unexpected and more attention-grabbing. This is not 2 completely satisfactory, however, because it might η =..500. There was no interaction between imply that related distractors would produce faster cognitive load and presence, F(1,31)=.005, p=.943, RTs than even neutral distractors would. This is and partial 2<.001. η only partially supported by our results. While in the Post-hoc t-tests were conducted to look at high load condition, the neutral distractor caused differences among related and neutral distractors in significantly less interference than the related different cognitive loads. The results revealed a distractor, in the low load condition the two significant difference between mean reaction times distractor categories produced mean RTs that were of high related distractors and high neutral

1480 virtually the same. If priming were involved, we characteristic that can mitigate the effects of would have expected to see related distractors cognitive load in both directions. In high load produce significantly faster RTs than both unrelated conditions, it appears that semantic grouping and neutral distractors, or very similar RTs to reduces the load that would otherwise be placed on a neutral distractors. While these results have cognitive system by trying to retain five unrelated or interesting implications in the broader discussion of meaningless items. Relating memory set provides a priming effects and working memory, further crutch, a strategy for the participant to make discussion of the topic is beyond the scope of this remembering easier. By relating the high load study. memory set items to each other, we may have Although our results are not consistent with our created a pseudo-high cognitive load, not high original predictions, they still build on the previous enough to mimic previous results. The current literature in valuable ways. All previous work cited manipulation of low load does differ from past here related their distractors only to the items in studies’. In Lavie et al. (2004), the low cognitive their selective attention or perceptual load tasks; the load condition contained one item: a single letter. In related (or unrelated) information appeared all on Belke et al.’s (2008) manipulation of cognitive load the same screen. The current study sought to a single number was used in the low load memory examine relatedness between the attention task and sets. To compare, the current study used two one- or the cognitive load, to manipulate relatedness across two - syllable words. Setting aside the extra item in tasks and attention mechanisms. Because of this the our low load condition, words have meaning, single results were slightly unpredictable, but valuable letters do not. It is possible that the combination of nonetheless. these two factors brought the low load condition’s The second hypothesis was also not supported: no difficulty closer to that of the high load condition. main effect of cognitive load was observed. This Adding the factor of meaningfully related memory result was unexpected, as the effect of cognitive sets, seems to have knocked the significance out of load has been observed in past work. A trend the effect of cognitive load. towards significance was observed—high load RTs Our third hypothesis was, again, not supported. A were slower than low load RTs—but only in the significant interaction occurred between cognitive ‘related’ and ‘unrelated’ condition. This suggests load and distractor relatedness. The relationship that, possibly, the cognitive load manipulations were between the two variables was very similar between not adequate representations of ‘high’ and ‘low’ the two conditions with meaningful distractors (the cognitive load. One possible explanation of this ‘related’ and ‘unrelated’ conditions). The interaction involves the related nature of the stimuli. Perhaps appears between these conditions and the neutral the fact that all memory set items fell under one distractor condition: neutral distractors were more broad category or meaning provided a strategy for distracting in the low load condition than in the remembering them: maybe participants remembered high. This is not consistent with load theory, which the group rather than each individual word would predict faster RTs in the low cognitive load (consciously or not) in an effort to reduce the load condition all around. Most of the background on the cognitive system. The results regarding our studies cited here disregard their neutral data, there fourth hypothesis provide more evidence to this isn’t much in the literature to compare our results to. effect. The degree of the difference between RTs of Our fourth hypothesis was supported. We contentful and non-contentful distracters—the fact observed significantly more false positives in the that the trend is reversed in the neutral condition— high load condition than in the low load condition: may indicate a different mechanism is at work when participants were failing to accurately remember the the distractor and the memory set information are words in the larger memory sets. After considering presented in the same form (all words, as opposed to the related nature of the memory set words, this words and symbols). This interpretation is not fully result suggests that participants noted the category compatible with the past findings, however. Lavie of the words presented along with individual words. and Forester (2008) found that when target stimuli As all memory set words, present and absent, were were letters and distractors were images of cartoon related to their memory set (it would have been too characters, the images were still significantly obvious had the probe words been unrelated) false distracting (when compared to letter distractors). positives indicate that participants recognized the This study, though, did not manipulate cognitive category membership/ semantic meaning of the load; the novel distractors were not novel to probe word and responded accordingly. cognitive load content, as in the current study, they The results concerning the second and fourth were novel to perceptual load items. Perhaps, as the hypotheses point to semantic grouping as a current results suggest, the interaction between

1481 attention mechanisms is qualitatively different than but not without a cost. While it is possible that that within mechanisms. This qualitative difference relating stimuli to one another reduces the cognitive is interesting and warrants further study. capacity required to retain it, retention and recall The size of the sample may have limited the suffer when such strategies are used. Knowing how study. Using additional participants was not attention and working memory are disrupted and feasible, however, and because of the within- aided could be particularly applicable in the field of subjects design was not essential. The software used education, and could be used to teach strategies for to present stimuli, and record reaction times, better retention and more effective methods of responses and error rates also limited our ability to teaching and information presentation. fully explore the data. A more sophisticated program like E-Prime could alleviate these References technological issues. Belke, E., Humphreys, G., Watson, D., Meyer, A. The current study is incomplete in that it does not and Telling, A. (2008). Top-down effects of compare related memory sets to unrelated memory semantic knowledge in visual search are sets. Further exploration is necessary to determine modulated by cognitive but not perceptual load. whether the results seen here are truly attributable to Perception & Psychophysics, 70 (8), 1444 – 1458. the semantic relatedness of the memory set and the Brand-D’abrescia, M. and Lavie, N. (2008). Task distractor, or if they are simply a product of using coordination between and within sensory whole words as stimuli. Adding a third independent modalities: effects on distraction. Perception and variable, that of memory set relatedness, would Psychophysics, 70 (3), 508-515. enhance the literature in this area. Forster, S. & Lavie, N. (2008). Failures to ignore More detailed data regarding error rates and the entirely irrelevant distractors: The role of load. type of distractor task would shed further light on Journal of Experimental Psychology: Applied, 14, the issue of false memories: it is possible that the 73-83. greater the interference of the distractor in the Lavie, N. (1995). Perceptual load as a necessary selective attention task, the higher the error rates condition for selective attention. Journal of would climb. If unrelated distractors are more Experimental Psychology: Human Perception & distracting, it follows that error rates in the unrelated Performance, 21, 451-468. distractor condition would be significantly higher Lavie, N., and Cox, S. (1997). On the efficiency of than those in the related or neutral conditions. visual selective attention: Efficient visual search Because of technological limitations, it could be leads to inefficient distractor rejection. valuable to re-examine the interaction between Psychological Science, 8, 395 – 398. distractor type and cognitive load. Validating the Lavie, N., Hirst, A., de Fockert, J., and Viding, E. current results regarding neutral distractors could (2004). Load theory of selective attention and point to different mechanisms used in ignoring cognitive control. Journal of Experimental extraneous information. Psychology: General, 133(3), 339-354. Parmentier, F. (2008). Towards a cognitive model of Conclusion distraction by auditory novelty: The role of A desire to better understand what interrupts or involuntary attention capture and semantic facilitates selective attention continues to drive processing. Cognition, 109, 345-362. research in cognitive psychology. While Lavie’s Rees, G., Frith, C., and Lavie, N. (2001). Processing Load Theory provides a valuable theoretical of irrelevant visual motion during performance of explanation of the phenomena, it is also vital that an auditory attention task. Neuropsychologia, studies explore selective attention in real-world 39(9), 937-949. settings using real-world stimuli. The present results Wilson, D., MacLeod, C., & Muroi, M. (2008). indicate that while the Load Theory provides a Practice in visual search produces decreased strong theoretical base, there are stimulus capacity demands but increased distraction. characteristics, like meaning and relationships Perception and Psychophysics, 70(6), 1130-113. between stimuli, that can alter the general pattern,

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