Vernier and grating acuity in adult hooded rats: the influence of sex.

Although morphological sex differences are pervasive in the primary visual cortex of hooded rats, it is not known whether sex differences occur in vision in these rats. In this study, grating acuity was measured in a forced-choice Y maze and a jumping stand in adult hooded rats, and vernier acuity thresholds were established in the jumping stand. With a criterion of 34 correct/50 trials, the number of correct choices for both sexes was high (1.0-1.6 cycles per degree [c/deg]) for spatial gratings. Female rats made more correct identifications of the coarse gratings (0.125 and 0.25 c/deg) than male rats, but no sex differences were found for higher spatial frequencies. In contrast, male rats were better at detecting smaller vernier offsets in both the individual criterion and group averages than female rats, and all of the rats detected vernier misalignments at 34.1 min (equivalent to 1.75 c/deg), which is above their grating acuity. Vernier acuity may mirror some sex differences in visual cortex anatomy.