Spatial frequency tuning and contrast threshold of striate neurons in Siamese cats.

The spatial frequency tuning and the contrast-response function of striate neurons in Siamese cats were investigated with drifting sinusoidal gratings of high contrast, and the results were compared to the data obtained in normally pigmented cats. The optimal spatial frequency of the tuning curves obtained from Siamese cats was shifted toward lower values, and the mean optimal spatial frequency was significantly lower as compared to that measured in normal controls. Furthermore, the spatial resolution was severely reduced in Siamese cats, and many tuning curves in these animals showed unusually broad band width. The contrast response functions are characterized by higher contrast thresholds and shallower slopes in experimental animals. The units in Siamese cats had much larger receptive fields. Finally, these abnormalities were found in both simple and complex striate neurons. The present findings are discussed in terms of anomalies in pre-cortical visual neurons and their possible relation to the visual behavior of Siamese cats.