Abstract
Several investigations have shown enhanced sensitivity for stimuli presented in the lower visual field (LVF) as compared to identical stimuli presented in the upper visual field (UVF). However, conflicting reports have emerged regarding differences in UVF/LVF sensitivity, as enhanced sensitivity for some stimuli has been reported in the UVF. At VSS 2004, we showed that stimuli that differed in color produced better performance in the LVF than in the UVF, while stimuli differing in apparent depth due to interocular disparity were better discriminated in the UVF. We now extend these results to a more explicit investigation of the spatial frequency characteristics contributing to these differences. Our stimuli were suprathreshold Gabor patches (sinusoidal gratings multiplied by circular Gaussian windows). The subject was asked to determine which of three simultaneously presented patches had an orientation that differed from 45°. The trio of patches appeared at random either above or below fixation for 280 ms. By manipulating the spatial spread of the Gaussian and the spatial frequency of the grating (which could be in either cosine or sine phase relative to the center of the Gaussian), we found that performance is generally better in the LVF unless the spatial frequency spectrum includes significant low frequency and DC components. LVF performance improves with narrower bandwidth, while UVF performance is relatively insensitive to these parameters. This is consistent with our previous tentative conclusion that magnocellular processing is more influential in the UVF, while parvocellular processing is more influential in the LVF.