Exploring the impact of apparent motion in V1 retinotopic representations and behavioral correlates in primates

It is still poorly understood how the visual system processes a simple stimulus moving along a trajectory. Any local, static, stimulus generates waves propagating in V1 retinotopic maps (Muller et al 2014, 2018). As a consequence, when these local stimuli are presented in sequence, in different positions in space and/or time, they trigger a complex cascade of embedded intra-cortical propagation waves that can shape the representation of the individual stimulus (Reynaud 2012, Chemla 2019). In this study, we employed a spatio-temporal sequence of three strokes eliciting long-range apparent motion (AM) and we measured the dynamic response of the V1 neural population in behaving macaques using voltage-sensitive dye imaging (VSDI). Expanding upon the findings of Chemla (2019), our results demonstrate that, after the first two dots appear, the spatial profile of the response to the third dot is significantly modified compared to the single-stroke control. This modification involves the facilitatory activation of the cortex ahead of motion direction and suppression leading to the displacement of the peak of activity in the opposite direction. Complex non-linear dynamical interactions are therefore changing the representation of the individual strokes suggesting at the same time motion extrapolation and motion repulsion in the retinotopic maps of V1. To explore this paradoxical phenomenon more comprehensively, we complemented our observation with (i) computational modeling approach, to investigate whether intra-cortical propagation of excitatory and inhibitory activity can explain this dual effect, and with (ii) psychophysics in humans, to test how such stimulus affect the perceived position of the last stroke of the same apparent motion stimulus.