Journal of Neurophysiology, Vol 63, Issue 3 404-423, Copyright © 1990 by APS
Modulation by a moving texture of cat area 18 neuron responses to moving bars
B. Gulyas, W. Spileers and G. A. Orban
Laboratorium voor Neuro- en Psychofysiologie, Katholieke Universiteit te Leuven, Belgium.
1. The influence of a moving texture on neuronal responses to a moving bar
was tested in 103 area 18 neurons of anesthetized and paralyzed cats. The
texture was a two-dimensional noise pattern, the bar moved at optimal
speed, and its contrast was adjusted to yield 50% of the maximum response.
2. The moving texture exerted two different but related effects: it
suppressed the response of area 18 neurons to the moving bar, and it
modulated the direction selectivity of parastriate neurons. These effects
were strongest when the texture moved at the same speed or faster than the
bar. 3. Genuine suppressive effects of the moving texture were
distinguished from lack of summation between bar and texture responses.
Suppressive effects of either type were observed in 75% of the area 18
cells and occurred more frequently among C family cells, velocity tuned
cells, and in layer 5 than in other groups of cells. 4. The modulation of
direction selectivity was distinguished from pseudomodulation because of
lack of summation of bar and texture responses. The direction selectivity
of 35% of the area 18 cells was modulated by the moving texture. Six
different relative direction selectivity (RDS) types were observed in area
18. 5. The neurons of which direction selectivity was modulated by the
moving texture occurred predominantly in layers 2-3 and 6, suggesting that
they represent a further stage of processing within area 18. 6. Many (75%)
area 18 cells responded to the texture moving on its own. Most of these
cells respond to isolated features ("grains") in the patterns rather than
to the movement of the whole pattern. Cells responding to the movement of
the whole pattern were generally C family cells, and their direction
selectivity was not modulated by the moving texture. 7. These results are
compared with those obtained under identical experimental conditions in
area 17. Although suppressive effects are similar in both areas, RDS types
are differently distributed in the two areas. 8. The possible origins of
the interactions and their functional significance are discussed.
