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On the Control of Visual Fixation Durations in Free Viewing of Complex Images Atten Percept Psychophys DOI 10.3758/s13414-011-0090-1 On the control of visual fixation durations in free viewing of complex images Sebastian Pannasch & Johannes Schulz & Boris M. Velichkovsky # Psychonomic Society, Inc. 2011 Abstract The mechanisms for the substantial variation in Keywords Eye movements . Fixation duration . Modes of the durations of visual fixations in scene perception are not attention . Distractor effect . Scene perception . Two visual yet well understood. During free viewing of paintings, pathways gaze-contingent irrelevant distractors (Exp. 1) and non- gaze-related time-locked display changes (Exp. 2) were It is known that visual fixation durations in continuous visual presented. We demonstrated that any visual change—its tasks such as reading and scene perception vary from less than onset and offset—prolongs the ongoing fixation (i.e., delays 100 ms to several seconds, thereby resulting in a positively the following saccade), strongly suggesting that fixation skewed distribution, with modal values between 200 and durations are under the direct control of the stimulus 350 ms (Rayner, 1998; Unema, Pannasch, Joos, & information. The strongest influence of distraction was Velichkovsky, 2005). Durations vary a great deal from one observed for fixations preceded by saccades within the fixation to the next (Buswell, 1935;Stratton,1906; Yarbus, parafoveal range (<5° of visual angle). We assume that 1967). It has been suggested that fixation durations are these fixations contribute to the focal in contrast to the determined by information processing (Groner & Groner, ambient mode of attention (Pannasch & Velichkovsky, Visual 1989;Just&Carpenter,1980), cognitive processes Cognition, 17, 1109–1131, 2009; Velichkovsky, Memory, 10, (Shebilske, 1975), and eye-movement preprogramming 405–419, 2002). Recent findings about two distinct (Buswell, 1935;Zingale&Kowler,1987). “subpopulations of fixations,” one under the direct and Visual attention is among these factors, as has been another under the indirect control of stimulation (e.g., shown in a number of studies (e.g., Brockmole & Boot, Henderson & Smith, Visual Cognition, 17, 1055–1082, 2009; Pannasch & Velichkovsky, 2009). In particular, we 2009), are reconsidered in view of these results. found that a combination of relatively long (>180-ms) fixations surrounded by small-amplitude saccades (i.e., saccades within the parafoveal range of 5°) significantly improves both recognition of foveated picture fragments S. Pannasch (*) (van der Linde, Rajashekar, Bovik, & Cormack, 2009; Brain Research Unit, Low Temperature Laboratory, Velichkovsky, Joos, Helmert, & Pannasch, 2005)and Aalto University School of Science, P.O. Box 15100, FI-00076 AALTO, reaction to sudden hazardous events in a simulated dynamic Espoo, Finland environment (Velichkovsky, Rothert, Kopf, Dornhoefer, & e-mail: [email protected] Joos, 2002). We attributed this difference in performance to : : the different modes of visual attention—focal versus S. Pannasch J. Schulz B. M. Velichkovsky — Applied Cognitive Research/Psychology III, ambient and supposed that the underlying brain mecha- Technische Universität Dresden, nisms are localized in ventral and dorsal parts of posterior Dresden, Germany cortex (Corbetta, Patel, & Shulman, 2008;Milner& Goodale, 2008). Since good visual acuity is limited to the B. M. Velichkovsky Kurchatov Research Center, Institute of Cognitive Studies, parafoveal region (i.e., 5° of visual angle; see, e.g., Moscow, Russian Federation Wyszecki & Stiles, 1982), it can be assumed that Atten Percept Psychophys subsequent fixations remaining within this region are rather distractor presentation experiments, especially in their gaze- related to the processing of details and identification of contingent version (Pannasch, Dornhoefer, Unema, & objects (Velichkovsky et al., 2005). In contrast, visual Velichkovsky, 2001; Reingold & Stampe, 2000). The fixations subsequent to large-amplitude saccades (>5°) are distractor presentation experiments usually introduce sudden likely to be involved in processing of information about the changes in the visual environment (Lévy-Schoen, 1969; spatial arrangement of rather undifferentiated visual “blobs” Walker, Deubel, Schneider, & Findlay, 1997). Various (cf. Trevarthen, 1968). This allows for classifying fixations studies in reading and scene perception have shown a on the basis of the prior saccadic amplitude: If the reduction of the saccade probability from 90 to 120 ms preceding amplitude is larger than 5°, this fixation is following the change (Reingold & Stampe, 2000, 2002). This presumably in the service of the ambient attention mode, probability reduction can be viewed as a prolongation of whereas for preceding saccadic amplitudes smaller than 5°, fixation durations (Pannasch et al., 2001) but can also be the fixation is assumed to belong to the focal attention interpreted as a delay of subsequent saccades (Reingold & mode (cf. Pannasch & Velichkovsky, 2009). Stampe, 2000) or a general inhibition of behavior found Various models can be developed to predict the spatial during the orienting response (cf. Sokolov, 1963). The latter and temporal aspects of eye-movement control. In contrast view is supported by the fact that gaze-contingent distractors to reading research, where considerable effort has been of different modalities have revealed habituation-like processes invested to predict when the eyes will move (Rayner, in eye movements and in cortical event-related potentials 2009), the focus of the work in scene perception has until (ERPs; Graupner, Velichkovsky, Pannasch, & Marx, 2007; very recently been on the question of where the eyes will Pannasch et al., 2001; Velichkovsky & Pannasch, 2001). move next (e.g., Itti & Koch, 2001; Tatler, Baddeley, & We performed two distractor paradigm experiments to Vincent, 2006; Torralba, Oliva, Castelhano, & Henderson, distinguish between direct and indirect control of fixation 2006; Underwood, Foulsham, & Humphrey, 2009). durations. In Experiment 1, gaze-contingent distractors For fixation duration, direct and indirect control mecha- appeared either early or late within selected fixations. The nismshavebeenproposed(Rayner,1998). While direct distractors were presented for different durations in order to control theories suppose that decisions about fixation allow for an experimental manipulation similar to the termination are made during the ongoing fixation, indirect manipulation of scene onset delay. In the second experiment, control theories suppose that the current fixation is deter- two different types of holistic display changes occurred time- mined by other factors. Direct control theories are supported locked within the presentation, independently of the actual by the fact that the available visual information influences gaze behavior. Our experiments address two as-yet- the duration of fixations (Loftus, 1985; Mannan, Ruddock, & unanswered questions. First, is it possible to determine which Wooding, 1995; Parkhurst, Culurciello, & Niebur, 2000). For mechanism (direct vs. indirect) controls fixation duration? example, Mannan et al. reported longer fixations for low- Second, can fixation control be modulated by two different pass-filtered than for unfiltered scenes. A prolongation of attentional mechanisms? fixations has also been found when the amount of either We anticipated that both distractor paradigm experiments foveal or peripheral information was limited by a gaze- would replicate the findings obtained with the scene onset contingent mask (van Diepen & d’Ydewalle, 2003). Results delay paradigm, demonstrating similar fixation behavior for from recent studies of scene perception led Henderson and changes of different qualities and quantities. Additionally, colleagues to suggest a mixed control model for fixation we predicted differential influences of visual changes, durations (Henderson & Pierce, 2008;Henderson&Smith, depending on the mode (focal vs. ambient) of attention. 2009; Nuthmann, Smith, Engbert, & Henderson, 2010). In Recent neuroanatomical research has made a distinction these experiments, the scene onset delay paradigm was between two frontoparietal networks of visual attention, a applied—that is, the scene was replaced by a pattern mask ventral one that interrupts and resets ongoing activity, and a during a saccade and reappeared in a subsequent fixation dorsal attention network specialized for spatial selection of after various delays. The authors reported a prolongation for stimuli and responses (Corbetta et al., 2008). In order to a certain proportion of fixations until the scene’s reappear- reconcile this distinction with our view of the modes of ance, but other fixations remained unaffected by the scene visual attention, the focal attention mode should require onset manipulation. The existence of the first group ventral network activity, whereas ambient processing would (“population” or “subpopulation”) of fixations was inter- be related to activity of the dorsal network. Regarding the preted as evidence for direct control by the scene informa- present study, this implies that an interruption by the tion, whereas the second group was considered as being appearance of a distractor should have a stronger influence under some form of indirect control. when the focal-processing mode is active, a claim that has The scene onset delay paradigm is similar to another been partly supported by previous experimental data well-known paradigm of eye tracking research, namely
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