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Biomedical subjects

A Fiorentini

Publications and source records attributed to A Fiorentini.

At least 55 records · Page 3Linked to original sources
PubMed1986

Impairment of stereoacuity in cats with oculomotor proprioceptive deafferentation.

Stereoacuity was measured with an operant conditioning technique in adult cats with unilateral deafferentation of oculomotor proprioception (section of the ophthalmic branch of the fifth cranial nerve). Binocular stereoacuity was found not to exceed monocular depth sensitivity, in contrast to what is obtained in normal cats. The results confirm previous findings and indicate a role of oculomotor proprioception in binocular depth perception of the cat.

Animals↗
PubMed1985

Deafferentation of oculomotor proprioception affects depth discrimination in adult cats.

Depth discrimination was tested behaviourally in adult cats prior to and after chronic section of the ophthalmic branch of the Vth cranial nerve, that contains the majority of oculomotor proprioceptive fibers. Binocular depth discrimination was considerably impaired following either unilateral or bilateral oculomotor proprioceptive deafferentation.

Afferent Pathways↗
PubMed1985

Pattern ERG in the monkey after section of the optic nerve.

Electroretinographic responses (ERG) to homogeneous light flashes and to alternating gratings were recorded from either eye of monkeys in which one optic nerve had been previously sectioned. Three weeks after optic nerve section the ERG response of the operated eye to alternating gratings was drastically reduced in amplitude and 5 weeks after surgery it was reduced to noise level. The uniform field ERG was unaffected. Histological examination of whole-mounted retinas of monkeys sacrificed 6 and 8 weeks after optic nerve section showed a loss of ganglion cells in the operated eye. It is concluded that the integrity of ganglion cells is essential for the generation of a normal ERG response to gratings.

Animals↗
PubMed1985

Dopaminergic drugs improve human visual contrast sensitivity.

Effects of dopaminergic drugs (L-dopa plus benserazide, or nomifensine) on human visual function have been tested in healthy volunteers by measuring the psychophysical contrast sensitivity for sinusoidal gratings of various spatial frequencies. After drug administration the contrast sensitivity improved in all subjects over a limited range of medium to high spatial frequencies.

Adult↗
PubMed1984

Right-hemisphere superiority in the discrimination of spatial phase.

Visual field differences have been investigated in various detection and discrimination tasks for simple sinusoidal gratings or for complex gratings composed of two sinusoids of spatial frequencies f and 3f. Sinusoidal gratings were employed to evaluate contrast sensitivity, subthreshold summation effects, aftereffects of adaptation to a high-contrast grating, and spatial-frequency discrimination. The tasks with complex gratings were detection of the 3f component in the presence of a high-contrast f component and spatial-phase discrimination. The stimuli were presented either in the left or in the right visual hemifield. The results indicate a lack of lateralization for detection and spatial-frequency discrimination of sinusoidal gratings, and for the bandwidth of subthreshold summation effects and adaptation aftereffects, whereas the detection of the 3f component in the presence of a high-contrast f component, as well as spatial-phase discrimination of f +3f gratings, show a left-field advantage. This suggests a right-hemisphere superiority in the processing of spatial phase.

Cerebral Cortex↗
PubMed1984

Pattern reversal evoked potentials in infantile spasms.

Visual evoked potentials in response to sinusoidal gratings of various spatial frequencies, alternating in contrast at 8 Hz were recorded from infants affected by an idiopathic form of infantile spasms (West syndrome). In two infants in whom the spasms began at 3 and 5 months of age, respectively, the VEP's were found to be depressed in amplitude at and around a spatial frequency of 3 and 5 c/deg, respectively. This midfrequency depression, which has never been reported in the literature for normal infants, suggests that infantile spasms in idiopathic patients may interfere at least temporarily with the development of visual function.

Evoked Potentials, Visual↗
PubMed1984

Development of retinal acuity in infants evaluated with pattern electroretinogram.

The electroretinographic (ERG) response to patterns of constant mean luminance (sinusoidal gratings reversed in contrast at 12 rev/s) has been recorded in infants 7 weeks to 6 months old. At each age the amplitude of the ERG for relatively fine gratings decreases with increasing spatial frequency and vanishes for a spatial frequency that can be defined as ERG acuity. It has been found that ERG acuity increases progressively with age. The acuity evaluated from cortical evoked potentials (VEP) recorded simultaneously with the ERG increases with age in parallel with ERG acuity. These findings are in agreement with data reported in the literature for the cat, indicating a parallel postnatal development of acuity at a retinal and cortical level.

Electroretinography↗
PubMed1983

Development of retinal and cortical responses to pattern reversal in infants: a selective review.

Infant contrast sensitivity and visual acuity evaluated by recording steady-state visual evoked potentials (VEP) in response to sinusoidal gratings improve considerably during the first 6 months of life. Qualitatively similar findings are obtained in kittens 3-12 weeks old. In infants, the improvement in VEP acuity with age parallels the increase in retinal acuity estimated from electroretinographic (ERG) steady-state responses to sinusoidal gratings. Spatial frequency selective mechanisms with bandwidth substantially narrower than the overall contrast sensitivity function seem to be present in the visual system of very young infants. These findings are compared with data reported in the literature about the development of the cat and monkey visual system.

Animals↗
PubMed1983

The role of high spatial frequencies in face perception.

The relevance of low and high spatial-frequency information for the recognition of photographs of faces has been investigated by testing recognition of faces that have been either low-pass (LP) or high-pass (HP) filtered in the spatial-frequency domain. The highest resolvable spatial frequency was set at 15 cycles per face width (cycles fw-1). Recognition was much less accurate for images that contained only the low spatial frequencies (up to 5 cycles fw-1) than for images that contained only spatial frequencies higher than 5 cycles fw-1. For faces HP filtered above 8 cycles fw-1, recognition was almost as accurate as for faces LP filtered below 8 cycles fw-1, although the energy content of the latter greatly exceeded that of the former. These findings show that information conveyed by the higher spatial frequencies is not redundant. Rather, it is sufficient by itself to ensure recognition.

Discrimination, Psychological↗
PubMed1982

Electroretinographic responses to alternating gratings in the cat.

Electroretinographic (ERG) responses to alternating sinusoidal gratings were investigated in the anaesthetized cat. The alternating grating ERG, but not the flash ERG, is reduced in amplitude during electrical stimulation of the optic nerve. Temporary retinal ischaemia caused either by clamping of the retinal artery or by increased intraocular pressure differentially affects the ERG responses to gratings or flashes. It has also been confirmed that following retrograde degeneration of ganglion cells caused by unilateral section of the optic nerve the alternating grating ERG disappears while the ERG in response to flashes is unaffected. All these findings indicate that the various electrical retinal sources contribute in a different way to the pattern ERG and flash ERG and suggest that the main source of the pattern ERG is at the ganglion cell level.

Animals↗
PubMed1982

Role of extraocular proprioception in the orienting behaviour of cats.

We investigated the effects of unilateral deafferentation of extraocular proprioception on the orienting behaviour of cats. The ophthalmic branch of the Vth cranial nerve, in which most of the extraocular proprioceptive fibers are known to run, was cut unilaterally in adult cats. The animals had been previously trained to jump from a start box to a luminous target at various possible locations in the right or left visual hemifield. The postsurgical orienting performance of the animals, evaluated from the difference between landing position and position of the target, differed from the presurgical performance. The postsurgical errors were typically: (1) ipsiversive to the side of the section, (2) usually of a larger magnitude in the hemifield contralateral to the section, (3) present in binocular as well as in monocular viewing conditions and approximately of the same magnitude for jumps guided by either eye. These findings indicate that extraocular proprioception plays a role in the orienting behaviour of cats.

Afferent Pathways↗
PubMed1982

Correlation between the preferred orientation and spatial frequency of neurones in visual areas 17 and 18 of the cat.

1. In seventy-six penetrations through areas 17 and 18 of the cat, neurones were regularly sampled at intervals of 100 micrometers and preferred orientation, optimal spatial frequency and resolving power were determined for each neurone in response to drifting sinusoidal gratings. 2. As already shown for area 17, in tangential penetrations through area 18, whenever the preferred orientation rotates progressively from cell to cell, the optimal spatial frequency tends to remain constant. 3. A statistical analysis on 1574 cells in areas 17 and 18 showed that for pairs of cells separated 200-300 micrometers along a track the difference in preferred orientation delta alpha and the difference in optimal spatial frequency delta f are not randomly distributed: cell pairs with small delta alpha are most likely to have large delta f and vice versa. 4. These findings indicate that in areas 17 and 18 neurones with the same optimal frequency are aligned along a direction orthogonal to the orientation columns. 5. The optimal spatial frequency, resolving power and the velocity cut-off were averaged for cells from different penetrations located in the same cortical layer or sublayer of area 18: mean optimal spatial frequency and acuity are highest in layer IV and lowest in layers II and V, while the velocity cut-off is highest in layers II and V and lowest in layer IV. 6. Our data suggest that the layering of cells according to optimal spatial frequency is a more subtle subdivision than the six histological layers.

Action Potentials↗
PubMed1981

Electroretinographic responses to alternating gratings before and after section of the optic nerve.

Electroretinographic (ERG) responses to sinusoidal gratings reversed in contrast (pattern-reversal ERG) were recorded from both eyes of cats before and after unilateral section of the optic nerve. In the eye ipsilateral to the section, the pattern-reversal ERG remained unaltered for a few days after the section, the progressively decreased in amplitude, first at low and then at high spatial frequencies, to disappear completely about 4 months after the section, when ganglion cell degeneration was practically complete. The flash ERG remained unaltered. No alteration was observed in the contralateral eye.

Animals↗