Table 1.

Sample of cells in the test of unidirectionality

Stimulus set	Both	Density– size	Gradient– direction	Total
Significant modulation	92	51	8	151
Position invariance tested	71/92	33/51	5/8	109/151
Unidirectional	21/71	0/33	0/5	21/109

Sensitivities to the density–size and gradient-direction stimulus sets were tested in 170 V4 cells: 151 exhibited statistically significant modulation in response to at least one of the stimulus sets; the invariance of the directional tuning with respect to the position of the elements was tested in 109 cells; 21 were classified as unidirectional.