How the early visual system extract angles and junctions embedded within contour stimuli?

In order to study neuronal basis to extract Angles and junctions embedded within contours, we conducted extracellular recordings, while two macaque monkeys performed the fixation task. Angle stimuli were the combination of two straight half lines. Each line was drawn from the center to outside the classical receptive fields in one of 12 directions. In the superficial layer of area V2, 91 out of 114 neurons showed selective responses to these angle stimuli. Of these, 41 neurons (36%) showed selective responses to wide angles between 60° and 150°, which were distinct from responses to straight lines or sharp angles (30°). When we tested these neurons’ selectivity to the 12 individual half lines, the preferred directions were more or less consistent with one or two components of the optimal angle stimuli. These results suggest that the angle selectivity in area V2 was largely dependent on the representation of individual line components. We suggest that area V2 is the first step to extract information of angles embedded within contour stimuli.