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J C Armington

Publications and source records attributed to J C Armington.

At least 19 recordsLinked to original sources
PubMed1992

Electroretinograms (ERGs) and visual-evoked potentials (VEPs) elicited by pattern displacement.

The relation between the amplitude of visual responses to a checkerboard stimulus and the degree of lateral displacement of the checks was examined across different check sizes with simultaneously recorded electroretinograms (ERGs) and visual-evoked potentials (VEPs). The amplitudes of both the b-wave and the after-potential of the ERG increase linearly with pattern displacement. However, the major components of the VEP (N70 and P100) were smaller than expected from linearity for both small checks with small displacements (thresholding) and for large checks with large displacements (saturation). These results suggest that the ERG is proportional to the number of receptors stimulated, but the VEP reflects neural processes influenced by the spatial structure of the stimulus.

Adult↗
PubMed1991

Spatial properties of ganglion cell activity in the turtle retina.

Ganglion cell activity in response to drifting or alternating stimulus patterns was recorded in an eyecup preparation of the turtle. The stimuli were sinusoidal gratings with various spatial frequencies and spatial phases. Spike histograms of the activity were Fourier-analyzed. The results indicated that the retinal circuitry always functioned in a nonlinear manner. The average, first, and second harmonics of the activity were all a function of stimulus conditions, including spatial phase. Similar outcomes were obtained with full-field (retina-wide) and a small-field (1 mm diameter) stimulation. In the middle of the spatial-frequency range, the ratio of second to first harmonic activity was higher in response to static, contrast-reversing gratings than for drifting, constant-contrast ones. The findings suggest that, as distinct from the usual X, Y, and W segregation of ganglion cell properties in other retinas, there is a single class of cells whose responses seem to have attributes of one or another of the usual categories depending on stimulus characteristics. This may be the result of a degree of stimulus-dependent functional modification in the retinal input circuitry to the turtle ganglion cells.

Animals↗
PubMed1990

Local pattern electroretinograms and ganglion cell activity in the turtle eye.

1. Local electroretinograms and spike activity from ganglion cells were recorded from an eye cup preparation of the turtle retina. The responses were elicited with striped and plaid stimulus patterns. 2. The results obtained with the two forms of recording were highly similar. Both depended on the spatial phase of the pattern with respect to the recording electrode. Both had maximal response at the same stimulus spatial frequency. 3. The optimum spatial frequency (both for maximum electroretinogram amplitudes and spike discharge rates) shifted to lower values with the administration of the GABA antagonist, picrotoxin. 4. The low frequency falloff associated with this spatial tuning may point to a mechanism of lateral interactions common to the local electroretinogram and spike responses.

Animals↗
PubMed1989

Isolation of scotopic human electroretinograms using color adaptation and pattern reversal stimuli.

The human electroretinogram was recorded in response to alternations of a 500 nm checkerboard stimulus pattern presented against adaptation backgrounds of different wavelengths. A modification of Stiles' color adaptation paradigm was adapted to electroretinography. The results provided electrophysiological t.v.i. curves (threshold versus intensity curves) and permitted a determination of spectral sensitivity. The t.v.i. curves matched those seen in psychophysics. The spectral curve showed a close agreement with the scotopic CIE function.

Color Perception↗
PubMed1989

Temporal spacing of pattern alternation and human visual response.

The electroretinogram and the visual evoked potential were recorded in response to checkerboard stimuli presented in phase alternation. The times in which the pattern was in its two positions were changed within a fixed total cycle time of two seconds. Both the amplitude of the electroretinogram and the evoked potential were affected by the length of the time interval between alternations, but in opposite directions. An electroretinogram that closely followed a preceding response was reduced in size while an evoked potential was larger. The results indicate that there is an interaction between adjacent pattern areas at the retinal level.

Electroretinography↗
PubMed1987

Adaptation, stimulus color, and the human electroretinogram.

(1) The human electroretinogram was recorded using two procedures that were designed to change the ratio of photopic to scotopic activity. (2) With the first procedure, responses were recorded with patterns that alternated with an asymmetrical time period to produce two average responses, one of which was more adapted than the other. (3) The second employed symmetrical alternation, but red and blue stimulation were used. (4) The electroretinogram was larger in responses to patterns of low spatial frequency for all conditions. The evoked potential, which was recorded simultaneously, was larger at intermediate frequencies. (5) The electroretinogram must be mediated before the antagonistic receptive field organization. (6) Sensitivity of electroretinogram with blue stimuli was higher than those with red at low spatial frequency. The possible scotopic contribution was discussed.

Adaptation, Ocular↗
PubMed1984

Temperature effects on the electroretinogram of the isolated carp retina.

The electroretinogram was recorded from the isolated retina of the carp while the temperature was varied systematically and while the preparation was under the influence of various pharmacological agents. In addition to the a-wave and the b-wave, the electroretinogram gave evidence of early and late oscillatory potentials. The procedures selectively modified the prominence of these and other less conspicuous components. A particularly significant finding was that some oscillatory potentials are largest at intermediate temperatures, but that they persist to very low ones. It is suggested that temperature control, variation of stimulus intensity, and the application of pharmacological agents may be combined to provide a useful method of separating retinal response components.

Animals↗
PubMed1984

Blinks, negative flashes, and visual responses.

Evoked visual responses that were triggered by spontaneous blinking were recorded from the human subject. Although their waveform resembled that of conventionally recorded responses, two differences were noted: there was an early potential that was seen only with blink responses, and the late negative potential was smaller than that seen with conventional recording. Off- and on-components were seen in the blink responses, and these were compared with those produced by switching the stimulus off and on. The amplitudes of all of the components increased with stimulus intensity. The results suggest that blinking may play a role in vision, per se, as well as acting to protect the cornea.

Blinking↗
PubMed1981

Effects of stimulus location and pattern upon the visually evoked cortical potential and the electroretinogram.

The pattern properties of the visually evoked potential and the electroretinogram have been investigated for phase alternated patterns of checks presented to the near periphery of the retina. When the eye was light-adapted, coarse patterns became relatively more effective for eliciting the evoked potential as the stimulus was moved away from the fovea. Fine patterns were most effective in the center of the field. The electroretinogram responded best to coarse spatial frequencies at all retinal locations. At a lower level of light adaptation the sensitivity of the evoked potential shifted to coarse spatial frequencies in the center of the field, but did not change appreciably in the periphery. The results may reflect some of the dynamic properties of visual fields.

Adaptation, Physiological↗
PubMed1981

Visually evoked cortical potentials accompanying blinks.

Visual activity is initiated whenever there is a change in the light falling on the retinal receptors. In the present experiment, visually evoked cortical potentials, elicited by the light transients that accompany blinking, were recorded with an electrode array that minimized artifact pickup. Although these evoked potentials were roughly similar to those obtained by more conventional recording procedures, specific waveform features were observed.

Blinking↗
PubMed1977

Psychophysical applications of human electroretinography.

Rapid developments in human electroretinography during recent decades have greatly increased its value for investigating psychophysical problems. This review of the current status of electroretinography considers the response waveform, recording techniques, and data analysis. Several examples of electroretinal data that have psychophysical significance are presented.

Electroretinography↗