Petrizzo, I., Grasso, P.A., Anobile, G. & Arrighi R.

Neurophysiological Investigation of NumerosityAdaptation

4rd Brainstorming Research Assembly for Young Neuroscientists (BraYn Conference), Pisa (2021)



Visual adaptation is a phenomenon that occurs whenever the prolonged presentation of a stimulus biases the perception of the subsequent ones. This property of the visual system has been known for a long time (since the report of the waterfall illusion), and it is often exploited in psychophysical research to investigate brain perceptual mechanisms. One of the latest visual features that has been reported to be susceptible to adaptation is stimulus numerosity. As a consequence of a sustained exposure to a highly numerous array of dots, a subsequent array is grossly underestimated (and vice versa). Despite the robustness of this perceptual illusion (changes in perceived numerosity up to 50%), the brain mechanisms responsible for numerosity adaptation are still far from being fully understood. In the present study, we attempted to fill in this gap by leveraging on an electrophysiological approach. Previous evidence has found that non-symbolic numerosity perception modulates both early (N1) and late (P2p) components of the EEG signal. Here, we applied EEG to a well-established numerosity adaption paradigm to investigate whether short-term numerosity plasticity relies on the early or late component of numerical processing. Subjects were required to perform an active numerosity estimation task both in neutral and high-numerosity adapting conditions. To prevent any possible effect induced by other factors, non-numerical characteristics of the stimuli were carefully controlled for. Our preliminary results revealed a modulation of P2p induced by highnumerosity adaptation, with this effect being more prominent for stimuli presented in the left hemifield. Overall, these results suggest that numerosity adaptation is a phenomenon occurring at the later processing stages of the visual hierarchy, likely involving visual areas beyond the primary visual cortex.