[Orientational tuning of visual cortex neurons to different stimulus intensities in the cat]

The orientation tuning of field 17 neurons of the visual cortex was studied in immobilized and unanesthetized cats under different intensities of test light slits and constant light background. Orientation tuning of five neurons was invariant to stimulus intensity: their preferential orientation did not change. Thirteen cells were variable as during the change of the contrast they showed a statistically significant displacement of orientation tuning from 22 degrees to 90 degrees. Changes in other neurons were not significant. Invariant neurons differed from variable ones in several characteristics. The mechanisms of orientation tuning changes during contrast variations are discussed.