Journal of Neuroscience, Vol 8, 1131-1143, Copyright © 1988 by Society for Neuroscience
Analysis of discontinuity in visual contours in area 19 of the cat
H Saito, K Tanaka, Y Fukada and H Oyamada
NHK Science and Technical Research Laboratories, Tokyo, Japan.
Previous ablation studies have suggested that area 19 of the cat plays an
important role in pattern discrimination. To clarify the functional roles
unique to area 19, we studied the receptive-field properties of cells in
area 19 and compared them with those of cells in area 17. Recordings were
made of anesthetized and immobilized animals. The majority (72%) of the
cells in area 17 responded maximally to an elongated bar at a particular
orientation, while they responded only weakly or not at all to a small spot
(elongation-requiring cells). In contrast, more than half (63%) of the
cells in area 19 showed a good response to a nonoriented small stimulus
moving in any direction (dot- responsive cells). Two-thirds of the
dot-responsive cells in area 19 failed to respond when the moving slit was
elongated to more than some length in any orientation. These dot-responsive
cells of the "inhibited- by-length" type responded strongly to the end of a
long bar, and many of them also responded strongly to a break point in the
middle of a long bar. We suggest that these dot-responsive cells of the
"inhibited- by-length" type detect discontinuities in contours. Though they
are in the minority, elongation-requiring cells constitute a considerable
population (37%) in area 19, and dot-responsive and elongation- requiring
cells from columnar patches in the same area. We conclude that, in contrast
to area 17, whose main role is the decomposition of patterns into oriented
contours, area 19 analyzes both orientation and discontinuities, with a
strong bias towards the latter.