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G Sandini

Publications and source records attributed to G Sandini.

6 recordsLinked to original sources
PubMed1979

A perceptual phenomenon and its neurophysiological correlate.

A square-wave grating from which the fundamental harmonic has been subtracted (missing fundamental grating) when viewed from a suitable distance appears similar to another grating of periodicity three times higher. The neurons of the visual cortex of the cat, in a given range of spatial frequencies characteristic of each cell, give similar responses to the two gratings.

Animals↗
PubMed1979

Responses of visual cortical cells to periodic and non-periodic stimuli.

1. The activity of neurones of the visual cortex (area 17) has been recorded in anaesthetized cats in response to gratings of different profile and to single light and dark bars. 2. At very low spatial frequencies, outside the frequency response range to sinusoidal gratings, the response to square-wave drifting gratings is obtainable from a combination of the response to the single bars of the grating presented in isolation. At higher spatial frequencies this is no longer true. 3. At very low spatial frequencies the responses to square-wave gratings and to missing-fundamental gratings (obtained by subtraction from the square-wave grating of its fundamental gratings (obtained by subtraction from the square-wave grating of its fundamental harmonic) are very similar. 4. At spatial frequencies near the peak of the spatial frequency tuning curve of the cell, the responses to square-wave grating and to sinusoidal gratings are very similar. At these spatial frequencies the response to the missing-fundamental grating is practically zero. 5. At spatial frequencies lower than that of best sensitivity for the cell, the response to square-wave gratings is correlated with the 1st and 3rd harmonic of the stimulus. 6. We conclude that at very low spatial frequencies of the grating the response of cortical cells is correlated with the light or dark edges (or light or dark bars) of the stimulus, because the edges contain high frequencies within the range of sensitivity of the cells. At higher spatial frequencies the results are interpreted best by assuming that cortical cells respond to the harmonics of the visual periodic stimulus. 7. When a background of dynamic visual noise is added to increase the spontaneous discharge of simple cells, their response to visual stimuli becomes linear or quasi-linear. The stimuli could be either single bars or gratings.

Action Potentials↗
PubMedDate not supplied

Regional cerebral blood flow in essential hypertension: data evaluation by a mapping system.

Regional cerebral blood flow was studied by means of the 133Xe inhalation method in 26 untreated and 10 treated patients with essential hypertension. The untreated subjects were divided into newly and previously diagnosed groups to assess the relation between regional cerebral blood flow and the duration of hypertension. The overall flow reduction was more marked in the frontal and temporal regions in the previously diagnosed group, and this was attributed to pathological changes in the district served by the middle cerebral artery. Regional temporal lobe impairment was also noted in the newly diagnosed and treated subjects. A significant correlation was found between regional cerebral blood flow and mean arterial blood pressure.

Aged↗