The sensitivity of X- and Y-cells in the dorsal lateral geniculate nucleus of the cat to small, temporally modulated displacements of grating stimuli was measured at 0.175, 0.25, 0.50, 1.00, and 2.00 ...c/deg. For every cell, two threshold measures were determined: first, a contrast threshold with a counterphase grating and then a displacement threshold with a grating matched in spatial frequency, but whose contrast was 2.5 times the threshold value. The results showed that displacement thresholds of both X- and Y-cells decreased with increasing spatial frequency. At low spatial frequencies, mean displacement thresholds of X- and Y-cells were similar, but at intermediate spatial frequencies, Y-cell thresholds were lower than X. X-cell displacement thresholds were lower than Y only at the highest spatial frequency tested. Consistent with previous reports, contrast thresholds also varied with spatial frequency for both X- and Y-cells. The local luminance differences produced by the contrast threshold and displacement threshold stimuli for the two classes of cells were compared. Across all spatial frequencies, the change in position of the gratings at displacement threshold produced smaller luminance differences than the counterphase gratings at contrast threshold. This enhanced sensitivity of X- and Y-cells to a local luminance changes produced by grating displacement was related to the high spatial contrast of the grating and not to the displacement per se.
Contrast thresholds for sinewave gratings were measured as a function of the number of cycles in the grating for two different orientations and three spatial frequencies. At high spatial frequencies, ...where an oblique effect of contrast sensitivity was demonstrated, there was a greater increase in contrast sensitivity as a function of the number of cycles for the vertical gratings than for oblique gratings. At a lower spatial frequency, where the contrast sensitivity anisotropy was greatly diminished, both orientations displayed a similar increase in contrast sensitivity when the number of cycles in the gratings was increased.
The inferior contrast sensitivity for oblique gratings has been previously demonstrated at high spatial frequencies with an absolute criterion. In this study contrast sensitivity at oblique and main ...axis orientations was obtained under separate pattern and flicker threshold criteria across a range of both spatial and temporal frequencies. The anisotropy of contrast sensitivity was not observed at low spatial frequencies under any stimulus or criterion conditions. At high spatial frequencies the anisotropy was observed for both pattern and flicker thresholds, although the flicker anisotropy was less pronounced. If, as previously suggested, this anisotropy is mediated by X cells, then these psychophysical findings suggest a mixed model in which both pattern and flicker systems receive input from both X and Y-cell pathways.
Spatial contrast sensitivity functions (CSFs) have been obtained for at least 9 species, including man. In the present paper, the shapes and octave band widths of these functions are compared. For ...most species, the shape of the CSF was an inverted-U, and the full width at half amplitude of the CSFs varied less than one octave. These similarities suggest that there is a close correspondence of the CSFs of these diverse animals; the major difference is the location of each CSF in the spatial frequency domain.
Stereopsis in the Falcon Fox, Robert; Lehmkuhle, Stephen W.; Bush, Robert C.
Science (American Association for the Advancement of Science),
1977-Jul-01, Volume:
197, Issue:
4298
Journal Article
Peer reviewed
Stereoscopic depth perception is demonstrated in the falcon, a non-mammalian with binocular vision. This result complements recent physiological evidence for binocular interaction in the bird visual ...system, and suggests that stereopsis may be a general attribute of vertebrate vision and not an exclusive product of mammalian evolution.
Falcon Visual Acuity Fox, Robert; Lehmkuhle, Stephen W.; Westendorf, David H.
Science (American Association for the Advancement of Science),
1976-Apr-16, Volume:
192, Issue:
4236
Journal Article
Peer reviewed
Grating acuity, the ability to resolve high-contrast square-wave gratings, was measured in a falcon and in humans under comparable conditions. This behavioral test of falcon acuity supports the ...common belief that Falconiformes have superb vision-the falcon's threshold was 160 cycles per degree, while the human thresholds were 60 cycles per degree. Falcon acuity, however, was much more dependent on luminance, declining sharply with decreases in luminance.
The responses of X- and Y-cells to a small flashing test probe modulated at 2 Hz were measured as a function of the diameter of a concentric circular background. The background was either a static ...homogeneous disk, a flickered homogeneous disk, a static radially-vaned disk, or a rotating vaned disk, all of equivalent space- and time-averaged luminance. Variation of background diameter produced systematic changes in response that reflected general X- and Y-cell receptive field differences. Initial increases in background diameter decrease the response to the test probe ("desensitization") of both X- and Y-cells to a minimum level at a diameter that approximates the size of the receptive field center. Further increases in the background diameter result in an increase of the response to the test probe ("sensitization") that is very large for X-cells and much less for Y-cells. Temporal modulation of the background does not alter the desensitization of X- or Y-cells, but strongly reduces the sensitization of X-cells. Temporal modulation of the background by flicker and by motion produced equivalent effects. These results are compared to similar human psychophysical tests used clinically. Implications concerning the mediation of psychophysical sensitization are also considered.
Spatial contrast sensitivity was behaviorally determined for two monocularly lid-sutured cats. The spatial contrast sensitivity function for the non-deprived eyes matched previously reported ...functions obtained from normally reared cats. In comparison, sensitivity was significantly lower at all spatial frequencies for the deprived eye of both cats. In one cat, subsequent removal of the non-deprived eye resulted in a two to threefold increase in sensitivity at all spatial frequencies. However, no improvement in sensitivity was observed for the second animal. Single-unit electrophysiological recording in the striate cortex of these two animals revealed a postenucleation difference in the percent of visually influenced cells. In the cat for which no behavioral improvement occurred, only 13% of striate cortex cells could be driven by visual stimulation of the previously deprived eye. In contrast 38% of striate cortex cells were similarly influenced in the cat for which visual improvement was observed. These data suggest a correlation between the physiological effectiveness of the postcritical period enucleation procedure and the visual capacity of monocularly lid-sutured cats.
