The visual system tends to assign contrast borders to one of the adjacent regions, as if the borders were occluding contours of objects in 3D space. Orientation selective neurons of V2 and V4 of the monkey visual cortex are often border ownership selective, responding more strongly to a contrast border when it belongs to a figure on one side of the receptive field than when it belongs to a figure on the other side (Zhou et al., J. Neuroscience 20, 6594-6611, 2000). Thus, each piece of border seems to be represented by two pools of neurons, one for each side of ownership. Here we demonstrate a tilt aftereffect that depends on the ownership of the adapting line. The same retinal location (0.5° beside fixation) was adapted alternatingly with a right-tilted line that was the left side of a trapezoid, and a left-tilted line that was the right side of another trapezoid. The result was that a vertical test line appeared tilted to the left when it belonged to a square on the right, but appeared tilted to the right when it belonged to a square on the left. The size of the aftereffect was comparable to the classical tilt aftereffect. The small size of the "minimum response fields" of V2/V4 neurons predicts that the aftereffect should be localized. The relative size invariance of neural border ownership selectivity predicts that adaptation figures larger than the test figures should be similarly effective in producing ownership contingent aftereffects as adaptation figures of the same size. The results confirmed these predictions. Testing locations 1° left or right of the adapted position reduced the aftereffect by 60-80%. Same size and larger adaptation figures produced similar aftereffects. These results shed new light on the neural basis of the tilt aftereffect and show that border ownership is coded at early stages of human visual cortex.
ASJC Scopus subject areas
- Sensory Systems