THE ABUTTING GRATING ILLUSION

Two line gratings abutting each other with a phase shift of half a cyc le elicit the perception of an illusory line running orthogonally betw een the two sets of grating lines. We found that rating strength incre ases with increasing number of lines, line length, and phase angle. In contrast, rating strength decreases with increasing spacing of lines, lateral misalignment, rotation of one grating relative to the other, and Line width. There is a pronounced oblique effect at 45 deg when th e orientation of the abutting gratings is changed from horizontal thro ugh diagonal to vertical. Findings are interpreted in terms of a neuro physiological model We conclude that the end-stopped receptive fields activated by the grating lines are about 6 deg long and 2 deg wide. On the other hand, the ''response fields'' of the cells, integrating ort hogonally across line ends, are assumed to be 5 deg long and less than 1 deg wide. The psychophysical data compare favorably with available neurophysiological data in Area V2 of the macaque suggesting that the perception of illusory contours in human observers may be based on cor tical cell properties similar to those found in the monkey.