An analysis of orientation selectivity in the cat's visual cortex.

The responses of cells in the cat's visual cortex to a moving bar of light have been analysed quantitatively, using an integration of the post-stimulus time histogram, with particular reference to orientation selectivity. The method is assessed as to its reliability and usefulness; it is shown that much precise information about a cell can be derived from its orientational tuning curve. Complex cells were found on average to show more spontaneous activity, greater response amplitude, and slightly broader orientational tuning, than either simple or hypercomplex cell types. Correlations between spontaneous and evoked activity and orientational selectivity give information as to the possible mechanisms of excitation and inhibition of the cells. The question of meridional variations in perception has been especially examined: the unexpected finding that many simple cells detecting orientations close to horizontal or vertical are very narrowly tuned, which is not the case for complex or hypercomplex cells, is discussed in relation to human psychophysical variations in orientation discrimination and contrast sensitivity. [ABSTRACT FROM AUTHOR]