Characteristics of the responses of visual cortex neurons with sensitivity to bars or cross-shaped figures in cats

The magnitudes and latent periods of spike responses were recorded from 280 individual neurons tuned to the orientation of light bars or cross-shaped figures in the primary visual cortex (field 17) of the cat. In control experimental conditions, half of 195 cells preferred the bar (first group), the remainder preferring crosses (second group); the responses of neurons of the first group to bars and crosses were of similar magnitude, while in the second group, responses to crosses were significantly larger than responses to bars. The latent periods of responses to optimal bars in the first group of neurons were shorter than those in the second group, and became longer on exposure to crosses, while latent periods in the second group were shorter on exposure to crosses. In conditions of local bicuculline blockade of intracortical inhibition, about a quarter of 85 neurons were sensitive only to the bar, regardless of the presence or absence of inhibition. The remaining neurons were sensitive to crosses in at least one of the states and continued to have responses which were smaller in terms of absolute magnitude than the responses of group 1 neurons. The significance of these data for understanding the mechanisms of tuning of striate neurons to signal features and the temporal sequence of their operation is discussed.