DOUBLE ORIENTATION TUNING IN THE CAT VISUAL-CORTEX UNITS

Orientation tuning of 271 neurons of the cat visual cortex (area 17) w as studied with a light bar flashing in the receptive field. Under dif ferent conditions, 27-57% of units were found to have double-orientati on tuning: they demonstrated the main preferred orientation and an add itional preferred orientation. The statistical reliability and reprodu cibility of additional preferred orientation were shown. The quality o f orientation tuning in the second maximum did not differ statisticall y from the first oner The angle between preferred orientation and addi tional preferred orientation was either 90 degrees (29% of cases) or a n acute one (60.1 +/- 3.1 degrees, 71% of cases). The ratio of dischar ge frequency in responses to additional preferred orientation and pref erred orientation was equal to 0.74 +/- 0.05. Neurons with double-orie ntation tuning dearly preferred 67 degrees and 157 degrees, while mono modal units preferred 0 degrees and 90 degrees. Probability of the dou ble-tuning increased under bar lengths of near 3 degrees and near 10 d egrees and with increase of stimulus/background contrast. At the same time some neurons displayed double-orientation tuning only with relati vely low stimulus/background contrast. The proportion of units with do uble-orientation tuning was lowered by about 1.5-times under general N embutal narcotization as compared with local anesthesia of the animal, In about one-third of units simultaneous stimulation by two flashing lines crossing in the receptive field center under an angle specific f or the cell, evoked a response from 1.5 to four times larger than to t he preferred orientation. Dependence of double-orientation tuning on t he existence of inhibitory end-stop and side-zones of receptive field, as well as possible functional meaning of such cells for an angle or line-cross detection are discussed.