Cognitive Brown Bag, 2/14/18, 12:00-1:15, Tobin 521B
Michele Fornaciai & Joonkoo Park (PBS)
Serial dependence in numerosity perception
Attractive serial dependence represents an adaptive change in the representation of sensory information, whereby current stimuli appear more similar to previous ones. Here, we characterize the behavioral and neural signatures of serial dependence in numerosity perception, demonstrating that the perceived numerosity of dot-array stimuli in different numerical ranges is biased by a preceding irrelevant stimulus (“inducer”) in an attractive way. Using electroencephalogram and a passive-viewing paradigm, we show that a neural signature of attractive serial dependence emerges even in the absence of an explicit task early in the visual stream, suggesting that serial dependence has a clear perceptual origin independently from a decision process. With a series of follow-up experiments, we further characterize serial dependence in visual number perception. First, we show that this effect has a weak spatial specificity and a relatively broad tuning for numerosity, and that it has a clear cortical origin (rather than subcortical). Second, we show that the attractive effect is strongly modulated by attention, suggesting the involvement of higher level modulatory influences. Our results collectively suggest that serial dependence results from a cortical neural computation starting from an early level of perceptual processing, possibly subserving perceptual stability and influencing downstream cognitive stages. However, these findings also suggest that the integration of past and present stimuli is in turn modulated by higher-level processes, and potentially amplified at later processing stages.