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C M Cicerone

Publications and source records attributed to C M Cicerone.

31 records · Page 2Linked to original sources
PubMed1984

Spectral efficiency of blackness induction.

The spectral efficiency of blackness induction was measured in three normal trichromatic observers and in one deuteranomalous observer. The psychophysical task was to adjust the radiance of a monochromatic 60-120' annulus until a 45' central broadband field just turned black and its contour became indiscriminable from a dark surrounding gap that separated it from the annulus. The reciprocal of the radiance required to induce blackness with annulus wavelengths between 420 and 680 nm was used to define a spectral-efficiency function for the blackness component of the achromatic process. For each observer, the shape of this blackness-sensitivity function agreed with the spectral-efficiency function based on heterochromatic flicker photometry when measured with the same 60-120' annulus. Both of these functions matched the Commission Internationale de l'Eclairage V lambda function except at short wavelengths. Ancillary measurements showed that the latter difference in sensitivity can be ascribed to nonuniformities of preretinal absorption, since the annular field excluded the central 60' of the fovea. Thus our evidence indicates that, at least to a good first approximation, induced blackness is inversely related to the spectral-luminosity function. These findings are consistent with a model that separates the achromatic and the chromatic pathways.

Adult↗
PubMed1982

Retinal sensitivity measured by the pupillary light reflex in RCS and albino rats.

The effects of retinal degeneration on the sensitivity of the retina were studied in the Royal College of Surgeons (RCS) rat by measuring the light reflex of the pupil in response to ganzfeld (full field) flashes. Light reflex thresholds were measured for animals from 32 to 683 days of age, and an age-related decrease in sensitivity of 5.2 log units (maximum) was measured. In contrast, thresholds for non-dystrophic albino controls increased only slightly during a comparable period. RCS rat thresholds increased more for short wavelength light than for long wavelength light. The end result was an altered action spectrum of the light reflex which largely, but not exclusively, reflected cone function. Even in cases of advanced degeneration the light reflex thresholds we measured showed significant input from rods. Pupiliary dark adaptation measured following ganzfeld bleaches (10%) with test stimuli of two different wavelengths revealed two mechanisms; a photopic mechanism (gamma max = 520) determined thresholds early in dark adaptation, but later a scotopic mechanism (gamma max = 500) participated in the light reflex.

Aging↗
PubMed1981

Signal transmission from rods to ganglion cells in rat retina after bleaching a portion of the receptive field.

1. Recordings from single axons of retinal ganglion cells in the rat's optic tract in response to small flashing test lights were used to follow the course of dark adaptation after exposing half of the receptive field to a bleaching light. 2. The recovery of log sensitivity followed an exponential time course in the exposed and unexposed half-fields. The curves had different time constants, with the exposed side taking longer to recover. 3. The time constants of recovery were increasing functions of exposure, but the rate of increase was different in the exposed and the unexposed half-fields. Direct exposure increased the time constant at a greater rate than did indirect exposure. 4. Comparison of the time constants of recovery in the exposed half-fields with those for pigment regeneration suggests that sensitivity recovers with the time course of rhodopsin regeneration. 5. Increment thresholds were determined using steady backgrounds which illuminated half of the receptive field. A greater threshold elevation was produced in the directly illuminated half-field compared with the half-field illuminated only by scattered light. Comparisons of the threshold-raising capacity of direct and indirect illumination were used to establish an 'upper bound' on the magnitude of light scatter. The time courses of the recovery of sensitivity after two different bleaches were compared. First, thresholds were measured in the unexposed half-field after a half-field bleach. Secondly the recovery of sensitivity after direct bleaching-exposure to the predetermined scatter upper bound' was measured. Recovery was more rapid in the latter case than the former, thus indicating that adaptation spreads laterally via some process other than light scattering.

Animals↗
PubMed1980

Light adaptation within the receptive field centre of rat retinal ganglion cells.

1. Responses from axons of single retinal ganglion cells in the rat's optic tract were used to measure the pooling of adaptive signals within the cells' receptive field. Computer-aided analyses of response measurements were used to evaluate sensitivity at a number of field locations. 2. A small adapting spot caused a localized decrease in sensitivity within the receptive field centre of ON- and OFF-centre ganglion cells. 2. The functions describing response versus test luminance were similar in shape for all test and adaptation configurations. This assured that, using a fixed criterion response, sensitivity determinations could be made just as well in any receptive field location and under any of the experimental conditions. 4. A concentric surround, antagonistic to the receptive field centre, was readily apparent only under conditions of light adaptation. Experiments on the local effects of small adapting spots, conducted with selective surround adaptation, showed that the non-uniform spread of adaptation within the receptive field centre was not linked to surround intrusion. 5. The possibility that the photopic mechanism intruded to contaminate these results was considered and rejected. 6. When a suprathreshold spot was alternated between two equally sensitive positions, the ganglion cell gave an approximately balanced response. An upset of this balance was produced by placing a small adapting spot at either position, thus demonstrating, in another way, the non-uniform spread of adaptation within the receptive field centre. 7. It is concluded that significant pooling of adaptation effects occurs prior to the combination of influences which contribute to the centre response of a ganglion cell.

Action Potentials↗
PubMed1980

Dark adaptation within the receptive field centre of rat retinal ganglion cells.

1. Recordings from single axons of retinal ganglion cells in the rat's optic tract were used to determine whether bleaching a small area of the receptive field reduced sensitivity globally or locally, near the bleached photoreceptors. 2. When a suprathreshold test spot was alternated between two equally sensitive positions, the ganglion cell gave an approximately balanced response. The balance was upset if a small-spot bleach was selectively applied to one position. Recovery of the balanced condition was rapid. 3. Varying the duration of a constant illuminance bleach varied the duration of the imbalance following the bleach. 4. The recovery of sensitivity after small-spot bleaches was measured both at the location of the bleach and also at another location, initially equally sensitive. The recovery at the bleached location lagged recovery at the unbleached location; but even in the bleached location, the return of sensitivity was rapid. 5. Recovery of sensitivity after half-field bleaches was measured in the bleached and unbleached halves of the receptive field. Recovery in the bleached half lagged that in the unbleached half. 6. A comparison between the effects of a small-spot bleach and a half-field bleach of the same strength show that the duration of dark adaptation depends on the area of the bleach.

Action Potentials↗
PubMed1979

Cone inputs to ganglion cells in hereditary retinal degeneration.

The photoreceptor layer degenerated, but cone nuclei apparently devoid of outer segments were retained in retinas of aged rats of the Royal College of Surgeons strain from which optic tract activity was recorded. Measures of sensitivity showed these single axons of retinal ganglion cells to have photopic spectral responses. Cone remnants containing a cone pigment may be the photoreceptive elements in these retinas.

Action Potentials↗
PubMed1978

Expansion of the half retinal projection to the tectum in goldfish: an electrophysiological and anatomical study.

The topographical retino-tectal projection of goldfish was electrophysiologically mapped at various intervals after surgical removal of the nasal half of the retina and pigment epithelium. The remaining projection was initially restricted to the appropriate rostral half of the tectum, even if the nerve was crushed and allowed to regenerate. But later, after 137 days or more, it showed a progressive expansion onto the foreign caudal half of the tectum. The magnification factor, the number of micrometers of tectum per degree in the visual field, doubled in the rostro-caudal but not in the medio-lateral direction. Analysis of the sequence of the expansion showed that a few fibers originally projecting nearest the denervated area were the first to spread over it. Then, progressively more fibers moved caudally until a nearly uniform representation of the half retina was established on the tectum. Radioautography also demonstrated that retinal fiber terminals had invaded the caudal tectum. The retinae of these fish were also examined histologically. The density of ganglion cells had not increased, but they consistently showed the axonal reaction. This was not found to be associated with any initial surgical trauma, but rather with the movement of their fiber terminals within the tectum. Frozen sections through half retinal and normal eyes, were cut and photographed for comparison of ocular geometry. Operated eyes were normal except for a slight but consistent loss of ocular volume. Analysis of the optical geometry showed that recording with fish in air produced two effects: Myopia (10 degrees blur circle, or less) and enlargement of the visual field by 15 percent to 20 percent.

Animals↗
PubMed1976

Cones survive rods in the light-damaged eye of the albino rat.

Exposure to constant light causes extensive rod photoreceptor damage but spares the photopic system in albino rats. The rod branch of the dark-adaptation curve shows considerable elevation in threshold; the cone branch is hardly affected. Longer exposure and chromatic adaptation suggest that there are three cone mechanisms with peaks near wavelengths of 450,520, and 560 nanometers.

Animals↗