eye movement recording and analysis in visual stimulus experiments

Investigating Oculomotor Responses in Visual Duration Perception Tasks

Time perception abilities have attracted increasing research attention over the last years, in part due to accumulating evidence that these may be linked to reading skills or pathological conditions1,2,3,4,5. Visual duration perception-the ability to estimate, discriminate, or compare time intervals defined by visual events-is one subfield of interest6,7in which eye-tracking methods could make a contribution. However, results remain focused on poststimulus behavioral decisions like pressing a button to indicate how much time has passed (estimate), whether time intervals are the same or different (discrimination), or which of a series of time intervals is the longest or shortest. A few studies have attempted to correlate behavioral results with eye-tracking data8,9 but they failed to find correlations between the two, suggesting that a direct relation is absent.
In the current paper, we present a protocol for registering and analyzing oculomotor responses during stimulus presentation in a visual duration perception task. Specifically, the description refers to an interval comparison task where participants saw sequences of three events that defined two time intervals and were asked to judge whether they speeded up (first interval longer than second) or slowed down (first shorter than second). The time intervals used in the study spanned from 133&#160;to 733&#160;ms, adhering to the principles of the Temporal Sampling Framework (TSF)10. TSF suggests that the brain&#39;s oscillatory activity, particularly in frequency bands such as delta oscillations (1-4 Hz), synchronizes with incoming speech units such as sequences of stress accents. This synchronization enhances the encoding of speech, improves attention to speech units, and helps extract sequential regularities that may be relevant in understanding conditions like dyslexia, which exhibit atypical low-frequency oscillations. The goal of the study in which we developed the method presented here was to determine whether dyslexics&#39; difficulties in visual duration perception (group effects on the interval comparison task) reflect problems in processing the visual object itself, namely movement and luminance contrasts11. If this was the case, we expected that dyslexics&#39; disadvantage towards controls would be larger for stimuli with movement and low luminance contrasts (interaction between group and stimulus type).
The main result of the original study was driven by poststimulus behavioral judgments. Eye-tracking data - pupil size and number of fixations - recorded during stimulus presentation were used to explore processes preceding the behavioral decisions. We believe, however, that the current protocol may be used independently from behavioral data collection, provided that the goals are set accordingly. It may also be possible to adjust it for interval discrimination tasks. Using it in time estimation tasks is not so immediate, but we would not rule out that possibility. We used pupil size because it reflects cognitive load12,13,14, among other states, and may thus provide information on participants&#39; skills (higher load meaning fewer skills). Regarding the number of fixations, more fixations may reflect the participants&#39; stronger engagement with the task15,16. The original study used five stimulus types. For simplification, we only used two in the current protocol (Ball vs. Flash, representing a movement-related contrast).
The main challenge we tried to address was disentangling responses to the visual stimulus itself from those related to interval comparison since it is known that oculomotor responses change according to characteristics such as movement or luminance contrasts17. Based on the premise that the visual stimulus is processed as soon as it appears on screen (first interval), and interval comparison is only made possible once the second time interval begins, we defined three time windows: prestimulus window, first interval, second interval (behavioral response not included). By analyzing changes from the prestimulus window over the first interval, we would get indices of participants&#39; responses to the stimulus itself. Comparing the first to the second interval would tap into possible oculomotor signatures of interval comparison-the task participants were asked to perform.

Author Spotlight: Exploring the Link Between Time Perception of Visual Stimuli and Reading Skills

Eye Movements in Visual Duration Perception: Disentangling Stimulus from Time in Predecisional Processes

Eye Movement Recording and Analysis in Visual Stimulus Experiments

eye-movement-recording-and-analysis-in-visual-stimulus-experiments

Research

JoVE Journal

Behavior

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