Surviving Continuous Flash Suppression: A Two-Photon Calcium Imaging Study in Macaque V1

Continuous flash suppression (CFS) has been widely used to study visual consciousness or awareness. Although the flashing Mondrian noise presented to one eye can suppress the perception of a stimulus presented to the other eye, some low-level visual information can survive the suppression and participate in downstream visual processing subconsciously. However, it remains elusive how the responses of V1 neurons, which receive stimulus inputs from two eyes, are affected by CFS. To address this issue, we used two-photon calcium imaging to record responses of superficial-layer V1 neurons to a target under CFS in two FOVs of an awake, fixating macaque. The target was a circular-windowed square-wave grating (d=1°, SF=3/6 cpd, contrast=0.45, drifting speed=4°/s). The flashing stimulus was a circular Mondrian noise pattern (d=1.89°, contrast=0.50, TF=10 Hz). The stimuli were presented for 1000-ms with 1500-ms intervals. The square grating at various orientations was first presented alone to either eye to identify oriented-tuned V1 neurons (~700 per FOV) and calculate each neuron’s ocular dominance index (ODI). Then the grating target was presented to one eye and the flashing noise to the other eye to measure neuronal responses under CFS. With the presence of flashing noise, orientation responses of neurons preferring the noise eye (ODI>0.2), in the form of population orientation tuning function, were completely suppressed (by 96.5%) without measurable bandwidth, and those preferring both eyes (-0.2<ODI<0.2) were also severely suppressed (by 89.5%) with unmeasurable or very wide bandwidth. However, although the responses of neurons preferred the grating eye were also significantly suppressed (by 75.5%), the tuning bandwidth was still measurable, which increased from 11-13° to 19° (half-height half-width). These results indicate that only a small portion of the orientation responses in V1 neurons preferring the target eye can survive continuous flash suppression, while orientation responses of other neurons are mostly wiped out.