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F Leporé

Publications and source records attributed to F Leporé.

18 recordsLinked to original sources
PubMed1997

Hemiretinal contribution to the timing of the full-field PVEP as determined with the motor reaction time.

With the use of the simple motor reaction time (RT), we examined the contribution of the hemiretinas to the timing of the pattern reversal visual evoked potential (PVEP). RTs were obtained to the reversal of a progressively dimmer check falling either on the central, nasal, temporal, superior or inferior retina. Results were correlated with the peak time of the P1 wave evoked to the reversal of the entire checkerboard stimulus to the same luminance conditions as that used to generate the RT measurements. Our results clearly indicate that the time taken to trigger a manual response depends not only on the luminance of the stimulus, but also on where it falls on the retina. Comparing the above data with the peak time of the PVEP obtained to the reversal of the entire screen indicates that at brighter luminance the peak time of the P1 wave correlates with that measured from the most central retina, while at dimmer intensities it correlates with the mathematical average of all the retinal locations tested.

Adult↗
PubMed1994

Human strabismus: evaluation of the interhemispheric transmission time and hemiretinal differences using a reaction time task.

Experimentally induced strabismus in visually immature cats leads to abnormal development of the posterior corpus callosum. This, in turn, should lead to abnormal interhemispheric integration of unilaterally presented visual information. To test whether strabismus produces deficits in the human commissural visual system, the interhemispheric transmission time (ITT) was compared in strabismic and normal subjects. Simple unimanual reaction times (RT) were tested in 30 subjects in response to a lateralized target presented monocularly at 4 degrees and 35 degrees nasally and temporally from the fovea along the horizontal meridian. This method was also used to examine the effect of strabismus on the central and peripheral portions of each hemiretina. The results showed that in strabismic subjects with or without amblyopia, the ITT did not differ significantly from normals at both eccentricities. In non-amblyopic strabismic patients, RTs in the central and peripheral portions of hemiretina were comparable to normals. However, a reduced speed of response was found in the central visual field (4 degrees) in the amblyopic eye. Our results suggest that the ITT is normal in strabismic subjects and that the longer RTs in the central portion of the nasal and temporal hemiretina of the amblyopic eye may be associated with the severe amblyopic condition.

Adolescent↗
PubMed1981

Inter-hemispheric competition during postnatal development.

Functional asymmetries between the two sides of the brain, a well documented phenomenon in species as different as frog and man, are thought to arise from genetically determined anatomical differences which, at least in humans, may be observed in utero. Functional asymmetries can, however, be reversed after damage to one side of the brain. Here we report that rearing of kittens with the optic chiasm sectioned and one eyelid sutured during postnatal development results in a functional asymmetry in the corpus callosum, a bidirectional pathway which inter-connects the visual cortices on the two sides of the brain. Visual input originating on the side of the brain ipsilateral to the sutured eye loses the ability to influence cells on the other side of the brain. Conversely, visual input originating on the side of the brain ipsilateral to the exposed eye markedly increases its influence in the other hemisphere.

Animals↗
PubMed1981

[Interhemispheric competition during postnatal development].

The corpus callosum is a bidirectional pathway interconnecting the visual cortices on the two sides of the brain. Rearing kittens with the optic chiasm sectioned and one eyelid sutured during early development results in a functional asymmetry in this pathway. Visual input originating on the side of the brain ipsilateral to the sutured eye looses the ability to influence cells on the other side of the brain. Conversely, visual input originating on the side of the brain ipsilateral to the exposed eye markedly increases its influence in the other hemisphere. These physiologic findings are paralleled by anatomic results indicating that the terminal field of the corpus callosum is markedly expanded in the cortical hemisphere ipsilateral to the deprived eye and reduced in the other hemisphere.

Aging↗
PubMed1981

[Role of the contralateral cortex on the receptive field properties in the visual cortex of cats].

The aim of this series of experiments was to evaluate the receptive field properties of visual cells receiving part of their input the corpus callosum. Normal (control) and chiasma sectioned cats were recorded using conventional methods. The recording sites were the 17-18 border and the lateral suprasylvian (LS) cortex. The results indicated (a) the ocular dominance distribution was shifted towards the ipsilateral eye in the split chiasma cats; (b) orientation tunning and/or directional specificity were identical for the two eyes; (c) R.F. positions of binocular cells were also similar for each eye and were clustered near the vertical meridian, which they sometimes straddled; (d) R.F. sizes were larger in L.S. than in primary visual cortex but generally of equal dimensions for each eye. The results are interpreted with respect to the various functions which have been postulated for the corpus callosum.

Animals↗
PubMed1981

[The role of the corpus callosum and other commissures in the interhemispheric transfer of visual information].

In order to assess the contribution of the lateral suprasylvian area and subcortical pathways other than the corpus callosum in learning and interhemispheric transfer, a series of studies was undertaken in the cat. Groups of animals which received different types of cortical and subcortical lesions were tested for learning and interocular transfer of visual pattern discriminations. Results have shown that : 1. the lateral suprasylvian area is of equal importance in learning and transfer as areas 17, 18 and 19; 2. in the absence of the corpus callosum, other commissures could preserve interocular transfer of visual information. The results obtained on commissurotomized neonate kittens clearly support this assumption.

Animals↗
PubMed1980

Abolition of optokinetic nystagmus in the cat.

Combining a behavioral and a surgical manipulation, namely complete visual deprivation with surgical section of the optic chiasm, results in the abolition of optokinetic nystagmus in the cat. This basic optomotor reflex remains relatively unaffected by either of these manipulations performed singly.

Animals↗
PubMed1976

[Neurobehavioral study of colliculectomized monkeys].

A battery of neurological tests was administered to normal and colliculectomized monkeys to determine the effect of the lesion on visually guided behavior, acoustically guided behavior, general locomotor performance and affective behavior. The tests were given at one week and three months post-operatively. The behaviors of the animals were filmed and the results were derived from a careful analysis of the films. The operated monkeys showed important deficits on most tests. After three months a considerable improvement was noted in many functions. However, some behaviors were still totally or partially abnormal. An attempt is made to relate the completeness of the collicular resection and the duration of some of these symptoms.

Animals↗
PubMed1975

Rod and cone sensitivity in destriate monkeys.

Photopic and scotopic spectral sensitivity of rhesus monkeys was determined before and after complete removal of the striate cortex. The monkeys were required to choose between a white and a series of monochromatic stimuli distributed throughout the visible spectrum. A modified method of limits was used to determine the psychophysical point of subjective equality at which the colored and white lights were perceived as being equally bright. The preoperative results indicated that the method of testing was appropriate to determine spectral sensitivity since the curves obtained compared favorably to the theoretical sensitivity curves. Postoperatively, the scotopic sensitivity curve was normal whereas the photopic curve was completely displaced towards the scotopic curve. The results as indicating that cone information is processed by the geniculo-striate visual system whereas the extra-striate structures receive their input mainly from the rod receptors of the retina.

Adult↗
PubMed1975

Spectral sensitivity in a female Cebus Griseus.

The photopic spectral sensitivity of one female Cebus Griseus was determined to complement published results showing that this monkey did not demonstrate the red deficiency typical of most New World monkeys. A modified method of limits was used to determine S's perceived brightness of different monochromatic stimuli. The results suggest that this monkey might be a normal trichromat.

Animals↗
PubMedDate not supplied

Monocular contribution to the peak time of the binocular pattern visual evoked potential.

The contribution of each monocular pathway to the timing of the binocular pattern visual evoked potential was assessed in situations where a significant interocular timing discrepancy was observed. Monocular and binocular pattern visual evoked potentials to 0.5 degree checks were recorded from normal subjects, normal subjects in whom one eye was blurred, patients with monocular amblyopia, and patients with resolved unilateral optic neuritis. Normal subjects showed facilitation, while suppression was evidenced in subjects with monocular blurring. In patients with amblyopia, the affected pathway had no effect on binocular pattern visual evoked potential latency, suggesting that the amblyopic eye was suppressed. In contrast, all patients with optic neuritis showed binocular averaging. Our results show that different forms of binocular interaction are evidenced in normal subjects, in amblyopia and in optic neuritis, and suggest that a comparative analysis of monocular and binocular pattern visual evoked potential peak times brings valuable information to the clinical evaluation that could be used to distinguish disease processes further.

Adolescent↗