Plaid Detectors in Macaque V1 Revealed by Two-Photon Calcium Imaging

Neuronal responses to one-dimensional orientations are combined to represent two-dimensional composite patterns; this plays a key role in intermediate-level vision such as texture segmentation. However, where and how the visual cortex starts to represent composite patterns, such as a plaid consisting of two superimposing gratings of different orientations, remains neurophysiologically elusive. Psychophysical and modeling evidence has suggested the existence of early neural mechanisms specialized in plaid detection, but the responses of V1 neurons to an optimally orientated grating are actually suppressed by a superimposing grating of different orientation (i.e., cross-orientation inhibition). Would some other V1 neurons be plaid detectors? Here, we used two-photon calcium imaging to compare the responses of V1 superficial-layer neurons to gratings and plaids in awake macaques. We found that many non-orientation-tuned neurons responded weakly to gratings but strongly to plaids, often with plaid orientation selectivity and cross-angle selectivity. In comparison, most (∼94%) orientation-tuned neurons showed more or less cross-orientation inhibition, regardless of the relative stimulus contrasts. Only a small portion (∼8%) of them showed plaid facilitation at off-peak orientations. These results suggest separate subpopulations of plaid and grating responding neurons. Because most of these plaid neurons (∼95%) were insensitive to motion direction, they were plaid pattern detectors, not plaid motion detectors.