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Nicola Binetti, Charlotte Harrison, Isabelle Mareschal, Alan Johnston; Cortical arousal signals are actively read out by a face processing system to evaluate the duration of gaze . Journal of Vision 2016;16(12):724. doi: 10.1167/16.12.724.
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© ARVO (1962-2015); The Authors (2016-present)
Gaze plays a fundamental role in regulating interpersonal interactions. Although many studies have investigated the brain mechanisms responsible for estimating gaze direction, gaze duration is equally important. In this study participants (N=10) were asked to compare the duration of direct and averted gaze shifts performed sequentially by two avatar face stimuli. While performing this task we recorded changes in pupil diameter during both duration encoding and decisional/response selection phases. Previous studies have shown that arousing stimuli lead to longer estimates of elapsed time (e.g. by comparing frightening Vs neutral stimuli). These studies however confound sensory differences in the stimuli, with differences in their arousing effects. We compared pupil responses within a standard binary choice duration discrimination psychophysical paradigm. Pupil size measurements, known to reflect variations in cortical arousal, were grouped on trials in which the standard and comparison stimuli were identical, on the basis of which interval was judged "longer" vs "shorter". This approach enabled us to directly evaluate how differences in cortical arousal (within identical stimuli) are linked to different perceptual outcomes. We observed, during the time encoding phase, that "longer" responses were associated with greater increases in pupil dilation/arousal (direct gaze "longer" Vs "shorter": p=.003; averted gaze "longer" Vs "shorter"=p.02). This time encoding dissociation was only observed in the subsecond range of durations. This pattern of results were not replicated when timing equivalent phase shifts of Gabor stimuli, indicating the difference is face processing dependent. In both datasets however we observed a positive relationship between task difficulty and rate of pupil increase during the decisional/response selection phase (harder Vs easier trials: p=.04). These results demonstrate that endogenous arousal signals are actively exploited by a face processing system (opposed to passively affecting a generic timing system) to encode the duration of gaze shift information.
Meeting abstract presented at VSS 2016
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