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R P Schuurmans

Publications and source records attributed to R P Schuurmans.

7 recordsLinked to original sources
PubMed1989

Responses to sinusoidal gratings of two types of very nonlinear retinal ganglion cells of cat.

Perhaps 35% of all of the ganglion cells of the cat do not have classical center-surround organized receptive fields. This paper describes, quantitatively, the responses of two such cell types to stimulation with sinusoidal luminance gratings, whose spatial frequency, mean luminance, contrast, and temporal frequency were varied independently. The patterns were well-focused on the retina of the anesthetized and paralyzed cat. In one type of cell, the maintained discharge was depressed or completely suppressed when a contrast pattern was imaged onto the receptive field (suppressed-by-contrast cell). In the other type of cell, the introduction of a pattern elicited a burst of spikes (impressed-by-contrast cell). When stimulated with drifting gratings, the cell's mean rate of discharge was reduced (suppressed-by-contrast cell) or elevated (impressed-by-contrast cell) over a limited band of spatial frequencies. There was no significant modulated component of response. The reduction in mean rate of suppressed-by-contrast cells caused by drifting gratings had a monotonic dependence on contrast, a relatively low-pass temporal-frequency characteristic and was greater under photopic than mesopic illuminance. If grating of spatial frequency, that when drifted evoked a response from these cells, were instead held stationary and contrast-reversed, the mean rate of a suppressed-by-contrast cell was also reduced and that of an impressed-by-contrast cell increased. But, for contrast-reversed gratings, the discharge contained substantial modulation at even harmonic frequencies, the largest being the second harmonic. The amplitude of this second harmonic did not depend on the spatial phase of the grating, and its dependence on spatial frequency, at least for suppressed-by-contrast cells, was similar to that of the reduction in mean rate of discharge. Our results suggest that the receptive fields of suppressed-by-contrast and impressed-by-contrast cells can be modeled with the general form of the nonlinear subunit components of Hochstein and Shapley's (1976) Y cell model.

Action Potentials↗
PubMed1985

Spatial tuning of the pattern ERG across temporal frequency.

The spatial response function of the electroretinogram (ERG) to contrast checkerboard pattern reversal at several check sizes was determined at a fixed contrast. The influence of the rate of modulation on the spatial response function was assessed. Reversing square wave patterns were presented at eight temporal frequencies ranging from 1 to 25 reversals per sec. The waveform consisted of an initial positive and a subsequent negative deflection. Irrespective of the temporal frequency, the spatial response function of the positive component did not show a spatial tuning. The amplitude of the negative component exhibited a pronounced attenuation of the response at check sizes larger than optimal. Mean maximal amplitude was found at an optimal check size between 25 and 50 min of arc. A distinction between a positive or negative component was not made for temporal frequencies higher than 10 reversals per sec, since the waveform at these modulation rates consisted merely of a sinusoidal steady-state response. The spatial response function obtained at 14 reversals per sec, resembling that of the negative component, exhibited a prominent spatial tuning. The results demonstrate that the pattern ERG has at least two components: a positive component which is not specific to changes in retinal distribution of contrast, followed by a negative wave showing spatial tuning across temporal frequency.

Electroretinography↗
PubMed1985

Luminance and contrast responses recorded in man and cat.

The major goal of this investigation was to describe and characterize response components of graded retinal responses in man and cat as a function of check size of the spatial stimulus. The arterially perfused cat eye enabled us to record the pattern reversal electroretinogram (PERG) and simultaneously summed activity of retinal ganglion cells by recording a compound action potential of the optic nerve (ONR). Checkerboard pattern reversal stimuli were presented at a low temporal frequency (recording 2 reversals in each trace), while a number of parameters such as check size, modulation depth and field size have been varied in order to elucidate similarities in response characteristics between the PERG and ONR. The striking similarity area dependence of the PERG and ONR points to ganglion cell activity as well as summation within the latter's receptive field center, reflected in the PERG. A fractionation was obtained of the PERG into two separate components generated by specific changes in spatial contrast and by luminance, respectively. The spatial response component of the PERG recorded in man from the enucleated cat eye closely resembled and consisted of a negative deflection. This component is preceded by a positive deflection sensitive to luminance changes and prominent upon peripheral retinal stimulation. It is anticipated that mild to moderate abnormalities of the ganglion cell activity will be first reflected in the negative contrast component upon central retinal stimulation.

Action Potentials↗
PubMed1984

Pattern reversal responses in man and cat: a comparison.

In 42 enucleated and arterially perfused cat eyes, graded potentials were recorded from the retina (ERG) and from the optic nerve ( ONR ) in response to checker-board stimuli, reversing at a low temporal frequency in a square wave mode. The ERG and ONR responses show an almost perfect duplication of the response to each reversal of the pattern and exhibit, in contrast to luminance responses, striking similarities in response characteristics such as amplitude, wave shape and time course. Furthermore, the amplitude versus check size plots coincide in both responses. In cat, pattern reversal responses can be recorded from 74 to 9 min of arc, correlating to the cat's visual resolution. In man, almost identical responses can be recorded for the pattern ERG. However, in accordance with the difference in visual resolution in man and cat, a parallel shift for the human pattern reversal ERG response to higher spatial frequencies is observed.

Animals↗
PubMed1980

[Intraocular pressure and coagulation of the vidian nerve (author's transl)].

A parasympathetic innervation of the choroidal blood vessels of facial nerve origin with a relay in the pterygopalatine ganglion has been described anatomically by Ruskell (1970). In three patients, we recorded the intraocular pressure before, during and up to 1 month after coagulation of the nerve of the pterygoid canal.

Adult↗