Effects Of Lateral Inhibition Research Articles

Detection of light and flicker at low luminance levels in the human peripheral visual system. I. Psychophysical experiments.

The interaction between summation and adaptation mechanisms near the absolute threshold of vision is studied. In this paper, results are presented of measurements of both light detection and flicker detection for circular flashes with a diameter of 5.7-480 min of arc, a flash duration of 5-1000 msec, a period of 0-8000 msec, and at eccentricities of 7 and 40 deg in the temporal retina. It is confirmed that the estimates of the summation times obtained from the light-detection-threshold energy as a function of the period and from the light-detection threshold as a function of the flash duration are similar; these estimates depend on the stimulus size and eccentricity. It is suggested that two summation mechanisms can be distinguished, one for the preprocessing and one for the detection mechanism. The summation time of the first mechanism is estimated to be about 100 msec; that of the latter, about 500 msec. At 40-deg eccentricity, decreasing the period of presentation leads initially to a rise in the light-detection threshold, pointing to adaptational phenomena. The flicker threshold is determined by the energy per flash (for brief flashes); when the flash duration exceeds 100 msec, the intensity of the flash is the important parameter. The flicker threshold depends strongly and in an irregular way on the stimulus size because of lateral inhibition effects.

A model of visual threshold detection

A model of visual incremental threshold detection is presented, having the following features. 1. (1) From Crozier's Law we deduce that all thresholds, for conventional as well as for noisy images, are ultimately determined by noise. Other evidence, which is described, supports this conclusion. 2. (2) It is proposed that signal and noise are sampled by apertures at a hypothetical “decision site” in the visual cortex. These apertures, which may consist of cortical receptive fields, “match” the signal as projected on the cortex. 3. (3) For circular signals < 10 mrad, the diameter of the relevant sampling aperture is equal to that of the signal as modified by the point spread-function of the optical and neural components. The signal intensity and the noise power are therefore integrated over the modified signal diameter. The model accurately predicts the contrast threshold function over a wide range of conditions for signals <10 mrad. 4. (4) For circular signals > 10 mrad, one of three qualitative mechanisms is tentatively proposed: first, a limit to the size of receptive fields, second, a limit to the active area of receptive fields and third, the effect of lateral inhibition on the large-area signal-to-noise ratio.

Effect of removal of corticofugal influences on receptive fields of lateral geniculate neurons in the cat

Unilateral division of corticogeniculate connections increases the number of spikes in unit responses of the ipsilateral lateral geniculate body to receptive field stimulation and potentiates the effects of lateral inhibition. The area of the zone of complete summation of all lateral geniculate neurons recorded on the side of operation depends on contrast of the local photic stimulus. It is concluded that cortical fibers descending to the lateral geniculate body are inhibitory in nature and that the existence of receptive fields with a variable zone of spatial summation is due to intrageniculate mechanisms.

Associative recall of images.

Orthogonal projection operations in a linear vector space are shown to have a close relation to the processes by which optimal associative recall of patterned information can be implemented. Two association schemes, the autoassociative mapping and the associative encoding, are introduced. The latter has a bearing on pattern recognition, especially in the recognition of an optical image from a small fragment of it. Analytical expressions for the quality of the recollections are derived, and computerized demonstrations of associative recall with 3024-element optical images are presented. Some preprocessing principles of the images are studied, whereby the two-dimensional Laplacian is found very effective. This finding may have some connection to lateral inhibition effects occurring in biological visual systems.

A study of sine-wave contrast sensitivity by two psychophysical methods

In the literature on visual contrast thresholds for sine wave gratings, little attention has been paid to the psychophysical methods used to obtain these spatial-frequency response curves. Here we report a comparison of such data obtained by two quite different psychophysical methods, but otherwise under identical conditions, using five Ss. Both experiments were run by computer: (1) In the method of adjustments, the computer program merely controls the order of the stimuli and records S’s contrast settings. (2) In the forced-choice staircase (FCS) technique, the program determines how often S can discriminate the sinusoidal grating from a uniform field, informs S of his accuracy, controls the stimulus contrast on the basis of S’s preceding responses, and brackets his threshold by a series of successive approximations. Method 2 eliminates criterion effects that occur in Method 1, and hence tends to minimize individual differences. However, the FCS technique requires an order of magnitude more observing time to obtain equally smooth contrast sensitivity curves. FCS also increases the/overall sensitivity of some Ss by as much as five times, but it does not significantly change theshape of the contrast sensitivity curve; both methods show strong effects of lateral inhibition at low spatial frequencies.

Regulation of middle ear sound transmission in the nonanesthetized rabbit.

AbstractThe regulation of sound transmission through the middle ear of nonanesthetized rabbits was quantitatively investigated by comparing the excitation of the cochlea before and after surgical inactivation of m. stapedius and/or m. tensor tympani in the stimulated ear. The crossed middle ear reflex was used as a measure of the excitation of the cochlea to stimulation with pure tones in the range from 0.5 to 8.0 kHz at intensities up to 125 dB SPL. Sounds through this frequency range were attenuated above a level of 90 to 100 dB SPL. Low frequency tones (0.5 kHz) were attenuated by all levels of activity in the m. stapedius and m. tensor tympani. High frequencies were attenuated only by m. stapedius activity at high intensity levels above reflex threshold (20–30 dB). The m. tensor tympani had no influence on high frequencies, above 2.0 kHz. Improved sound transmission due to reflex activity was not regularly found. The efficiency of the regulation was regarded as high: a 1.0 dB increase in sound level in the ear canal gave only a 0.3 dB increase in the excitation of the cochlea (i.e. the regulating efficiency of the closed‐loop system was 0.7 dB attenuation per 1.0 dB increase in stimulus sound intensity). The regulating efficiency of the open‐loop system was about 2 dB/dB. The open‐loop gain was estimated to 4 during steady‐state. The oscillations in the middle ear reflex response were found to be generated in the m. stapedius feed‐back loop regulating the sound transmission through the middle ear. It was concluded that the function of the acoustic middle ear reflexes can be described as extending the dynamic range of the cochlea and adaptation and it may also be compared with the effect of lateral inhibition.

Psychophysical evidence for lateral inhibition in hearing.

Although there are some indications of the possible role of lateral inhibition in hearing, there has been no clear demonstration of it in psychophysical experiments. Either the phenomenon plays only a minor role, or it has escaped psychophysical verification. Accepting for a moment the second possibility, is argued in this paper that the threshold of a test tone presented simultaneously with a masker does not reflect clear lateral-inhibition effects since the inhibition affects both the test tone and the masker. Two different methods, in which the test tone and the masker were presented succsesively, give clear psychophysical evidence of lateral inhibition in hearing. Firstly, the threshold curve of short test-tone bursts presented in the gaps between repeated masker bursts (noise with a steep negative or positive gradient at a particular frequency) shows marked edge effects. Secondly, the results of psychophysical measurements on two-tone suppression indicate that the nervous activity due to one frequency component may be suppressed by another component. The effect at the edges of the frequency spectrum are comparable with visual Mach bands, and the interaction of two tones is suggestive of the two-tone inhibition found in auditory-nerve fibers.

Effects of lateral inhibition on fluctuations of the impulse rate.

Inhibition from neighboring eccentric cells has an effect on the variability of firing of a given eccentric cell. The reduction in the average impulse rate which is caused by inhibition decreases the variance of the impulse rate. However, this reduction of the average rate increases the coefficient of variation of the impulse rate. Inhibitory synaptic noise should add to the low frequency portion of the variance spectrum of the impulse rate. This occurs because of the slow time course of inhibitory synaptic potentials. As a consequence, inhibition decreases the signal-to-noise ratio for low frequency modulated stimuli.