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A Fiorentini

Publications and source records attributed to A Fiorentini.

At least 55 records · Page 3Linked to original sources
PubMed1973

Neural correlate of perceptual adaptation to gratings.

Exposure of simple cells of the cat striate cortex to high-contrast drifting gratings greatly reduces the subsequent response of the cells to low-contrast gratings. This adaptation effect has an average duration of 30 seconds and shows interocular transfer and selectivity for spatial frequency and orientation. This effect is strikingly similar to the perceptual adaptation to high-contrast gratings.

Action Potentials↗
PubMed1973

Contrast perception and electrophysiological correlates.

1. Previous findings show that the amplitude of the human visual potentials evoked by gratings alternating in phase at several c/s is linearly related to the logarithm of the grating contrast.2. Similar previous experiments on the cat have shown that both the amplitude of evoked potentials and the amplitude of the response of simple cortical cells to alternating gratings increase linearly with the logarithm of the contrast. No such relation is found for single neurones in the retina or in the lateral geniculate body.3. In this work the contrast of a grating is evaluated psychophysically by human subjects in a range of more than 10 times above threshold, using a binocular matching technique.4. The apparent contrast is found to increase linearly with the logarithm of the stimulus contrast.5. The conclusion is drawn that the linear relation between apparent contrast and the logarithm of the objective contrast might be the outcome of a process of elaboration that is carried out at the simple cell level.

Evoked Potentials↗
PubMed1972

A second neural mechanism of binocular depth discrimination.

1. Rotation of an object about its horizontal axis, towards or away from the viewer's eyes, usually causes the images of its contours to have slightly different orientations on the two retinae.2. We recorded action potentials from binocular neurones in the cat's visual cortex and measured their orientation-selectivity carefully in both eyes.3. The optimal orientation for a single cell is not necessarily identical on both retinae. For a large sample of cells there is a range of more than + 15 degrees (S.D. about 6-9 degrees ) in the difference of preferred orientation in the two eyes. These interocular differences in receptive field properties cannot be attributed to rotation of the eyes or to the errors of measurement.4. During simultaneous binocular stimulation the images must not only lie in the correct place on both retinae but also have exactly the right orientation for both receptive fields in order to elicit the maximum response from a neurone.5. Therefore certain binocular cells respond specifically to objects tilted in three-dimensional space towards the cat, or away from it.

Action Potentials↗
PubMed1972

Physiological correlates of adaptation to a rotated visual field.

1. Perceptual adaptation to a 30 or 45 degrees visual tilt was induced in human subjects by means of prismatic spectacles worn for 5-7 days. Relative contrast thresholds and the amplitudes of the occipital potentials to vertical and oblique gratings were studied.2. During continuous exposure to the tilted visual environment the normal differences between contrast thresholds for vertical and oblique targets decreased or were no longer significant. In all subjects the change from control threshold differences was significant at the 0.005 level.3. During the course of adaptation the difference in amplitude of the potentials evoked by vertical and oblique oscillating gratings also decreased. The changes with respect to control differences were significant at the 0.005 level in each subject.4. Intermittent exposure to tilt in one subject resulted only in minor adaptation of the apparent vertical, and the evoked potential differences did not change from control levels.5. The changes are interpreted as suggesting that plastic changes in the extraretinal mechanism responsive to target orientation occur during adaptation to prismatic tilt.

Adaptation, Ocular↗
PubMed1970

Electrophysiological evidence for binocular disparity detectors in human visual system.

Evoked potentials have been recorded from humans in response to two moving gratings presented stereoscopically to both eyes. The amplitude of the evoked potential is greater when the two gratings have slightly different spatial frequencies, which produces an apparent inclination of the binocularly fused image. The amplitude of the response is correlated with the degree of the perceived inclination.

Animals↗