Search PubMed⌕ Search

Biomedical subjects

L Maffei

Publications and source records attributed to L Maffei.

At least 145 records · Page 8Linked to original sources
PubMed1974

Behavioural contrast sensitivity of the cat in various visual meridians.

1. The contrast sensitivity of the cat as a function of the spatial frequency of the visual stimulus was determined by using behavioural techniques.2. No statistically significant difference was found for the contrast sensitivity thresholds at various orientations of the stimulus.3. A comparison of the contrast sensitivity curve of the cat with that of the human shows that the two species have rather different characteristics of visual spatial resolution.

Animals↗
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

The contrast sensitivity of the cat.

1. The experiments were carried out on pretrigeminal cats.2. By recording potentials evoked from the visual cortex by a grating stimulus, it was established that there was a linear relation between the voltage generated and the logarithm of the contrast of the grating.3. The voltage evoked by the grating was independent of the orientation of the grating.4. It has previously been shown in man that, if the contrast is determined by an extrapolation to the point at which a zero voltage occurs, this value corresponds to the psychophysical threshold. On the assumption that the threshold of the cat also occurs at zero voltage, thresholds for a number of spatial frequencies and orientations were determined.5. When the threshold sensitivity function for the cat is compared with man it is found to be displaced to lower spatial frequencies by a factor of about ten. This means that while the cat cannot see such high spatial frequencies as man, it can see lower frequencies better than man.

Animals↗
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↗