Population responses in V1 encodes stimulus visibility in backward masking

The visibility of a briefly presented stimulus is diminished when followed by a mask, a phenomenon known as backward masking (BM). As the interval between the stimulus and the mask (stimulus-to-mask onset asynchrony [SOA]) becomes shorter, the stimulus visibility decreases. Yet, the neural mechanism underlying BM remains poorly understood. To investigate this, monkeys were trained to discriminate oriented targets in a pattern BM paradigm. Using voltage-sensitive dye imaging, we measured the population responses in the primary visual cortex (V1). The behavioral performance in short SOAs was lower, and reaction times were slower. Population response in V1 showed a figure-ground modulation (FGm) with lower values for short SOAs. A classification analysis revealed the differences in temporal dynamics of the model accuracy in relation to stimulus visibility and spatial rearrangements of the informative neural patterns. These results suggest that the mask interferes with FGm in V1, possibly leading to diminished stimulus visibility.