Poster D123, Monday, March 27, 8:00 – 10:00 am, Pacific Concourse
Temporal evolution of visual representation: From physical to perceived numerosity
Michele Fornaciai1, Joonkoo Park1; 1University of Massachusetts Amherst
The physical properties of a visual scene become percepts through complex neural machinery in the visual stream. However, little is known about the processes that make a given percept available in the content of subjective visual awareness, and when such percepts arise in the visual stream. In this study, we investigated the temporal evolution of visual representation by exploiting a simple yet very powerful visual illusion, whereby the perceived numerosity of dot arrays containing pairs of connected dots is strongly underestimated compared to isolated dots. We recorded brain activity by means of electroencephalogram while participants passively viewed a stream of arrays containing 16 or 32 dots, either isolated or pair-wise connected by straight lines. The results showed that the early latency visual evoked potentials (~ 100 ms) reflect physical, rather than perceived, numerosity, while the later latency potentials (~ 150 ms) reflect perceived, rather than physical, numerosity. A multivariate pattern analysis in the time domain confirmed such a pattern and further demonstrated that both the effects of physical and perceived numerosity persist until later latency (~ 400 ms). These results demonstrate that the physical information of a visual scene undergoes a series of manipulations along the visual stream that could radically change its content before being available in the subjective visual experience.
Topic Area: PERCEPTION & ACTION: Vision