The lateral effect of oscillation of peripheral luminance gratings on the foveal increment threshold

Effects of remote stimulation on the modulated activity of cat retinal ganglion cells

The output of retinal ganglion cells depends on local and global aspects of the visual scene. The local receptive field is well studied and classically consists of a linear excitatory center and a linear antagonistic surround. The global receptive field contains pools of nonlinear subunits that are distributed widely across the retina. The subunit pools mediate in uncertain ways various nonlinear behaviors of ganglion cells, like temporal-frequency doubling, saccadic suppression, and contrast adaptation. To clarify mechanisms of subunit function, we systematically examined the effect of remote grating patterns on the spike activity of cat X- and Y-type ganglion cells in vivo. We present evidence for two distinct subunit types based on spatiotemporal relationships between response nonlinearities elicited by remote drifting and contrast-reversing gratings. One subunit type is excitatory and activated by gratings of approximately 0.1 cycles per degree, while the other is inhibitory and activated by gratings of approximately 1 cycle per degree. The two subunit pools contribute to a global gain control mechanism that differentially modulates ganglion cell response dynamics, particularly for ON-center cells, where excitatory and inhibitory subunit stimulation respectively makes responses to antipreferred and preferred contrast steps more transient. We show that the excitatory subunits also have a profound influence on spatial tuning, turning cells from lowpass into bandpass filters. Based on difference-of-Gaussians model fits to tuning curves, we attribute the increased bandpass selectivity to changes in center-surround strength and relative phase and not center-surround size. A conceptual model of the extraclassical receptive field that could explain many observed phenomena is discussed.

The effect of peripheral visual motion on focal contrast sensitivity in positive- and negative-symptom schizophrenia

The aim of the present research was to investigate the effect of peripheral (ambient) stimulation on focal visual processing using the far-out jerk effect in normal observers and subgroups with positive- and negative-symptoms in schizophrenia. The far-out jerk effect refers to a reduction in sensitivity of a briefly presented stimulus in central vision in the presence of a sudden movement or oscillation of a stimulus in peripheral vision. In order to measure the far-out jerk effect the focal contrast sensitivity of 5.0Hz modulated sinusoidal target gratings (0.5, 1.0, 2.0, 4.0, and 8.0 number of cycles per degree (c/degrees )) was measured in the presence of three kinds of peripheral surround: a blank field, a stationary 0.75 c/degrees grating, and a 5.0Hz drifting 0.75 c/degrees grating (far-out jerk effect). The findings showed that there were no significant differences in focal contrast sensitivity between the control and positive-symptom group with a blank field and stationary grating surround. However, a 5.0Hz drifting grating surround resulted in a significant reduction in contrast sensitivity at 0.5, 1.0 and 2.0 c/degrees in the positive-symptom group. In comparison with the control group the negative-symptom group showed a generalised reduction in focal contrast sensitivity, a significantly smaller far-out jerk effect, and a significant reduction in contrast sensitivity at 0.5 c/degrees with a stationary grating surround. The finding that both stationary and moving peripheral surrounds have an inhibitory effect on focal contrast sensitivity suggests that there is a dispersion in the visual demarcation between stationary and temporal events in the perception of visual motion in the negative-symptom group.

The contrast-response of the periphery effect

This report examines the effect of varying the contrast of a flickering remote surround on thresholds for flicker detection, and color detection in rapidly flickering red and green foveal test targets, presented on a steady white background. Flicker in the surround reduced flicker sensitivity for the foveal test stimuli and yielded a periphery effect (PE), whereas it had no effect on color sensitivity (no PE). The magnitude of the PE increased non-linearly as a function of increasing surround flicker contrast. Much of the increase took place at low contrasts (< 0.20) and half-saturation of the PE occurred at 0.16 and 0.29 contrast for the red and green targets, respectively.

The peripheral flicker effect: desensitization of the luminance pathway by static and modulated light

Previous studies have shown that luminance flicker, presented peripheral to a foveal test target, increases thresholds for target detection: the peripheral flicker (PF) effect. These studies have also shown that thresholds are elevated more for luminance targets, relative to chromatic targets. In the present study we examined the specificity of the PF effect on the luminance mechanism and assessed the contribution of modulated stray-light to the test field, as well as longer range spatial interactions. We found that the presence of a foveal luminance pedestal, as well as PF, caused a notch to appear in the spectral sensitivity function around 570 nm. This result confirms the hypothesis that the PF effect decreases the sensitivity of the luminance pathway. To assess the contribution of stray-light to the PF effect, we modulated a luminance pedestal without the presence of PF in order to simulate the stray-light effect in isolation. A decrease in sensitivity for wavelengths around 570 nm occurred with modulated stray-light, suggesting that modulated stray-light contributes substantially to this effect. We then minimized the modulated stray-light by phase-reversing a checkerboard pattern in the periphery. A significant, though smaller, threshold elevation to mid-spectrum stimuli was obtained, suggesting that long range spatial effects are also active in the PF effect. We conclude that the PF effect causes a desensitization of foveal luminance pathways via local and more long range spatial interactions. Our results are consistent with previous data which suggest that the PF effect is due to selective adaptation of cells in the magnocellular pathway (M-cells). Our data imply that local network adaptation may be a property of the magnocellular pathway.

Location vs feature: reaction time reveals dissociation between two visual functions

Reaction time in a detection or a location discrimination task was longer when a target appeared at the same location as in the previous trial (inhibition of return; IOR). However, it became shorter when the task was color or orientation discrimination (facilitation of return: FOR). This dichotomy was observed in the single target as well as in the popout displays. In additional experiments, vernier, size, and luminance discriminations all led to FOR, whereas eye-movement and arm-reaching tasks led to IOR. Moreover, identical stimuli could lead to the opposite patterns of result depending on the nature of the task: inhibition in global location tasks, and facilitation in feature analysis tasks. These may correspond to "where" vs "what" or "action" vs "recognition" pathways neurophysiologically.

Contrast sensitivity and coherent motion detection measured at photopic luminance levels in dyslexics and controls

Development dyslexics perform differently from controls on a number of low level visual tasks. We carried out three experiments to explore some of these differences. Dyslexics have been found to have reduced luminance contrast sensitivity at mesopic luminance levels. We failed to replicate this finding at photopic luminance levels. We also compared the (photopic) coherent motion detection thresholds of groups of child and adult dyslexics with those of age matched controls. Dyslexics were significantly less sensitive to motion. The results are discussed in relation to a recent suggestion that developmental dyslexia may be associated with a magnocellular visual deficit.

Suppressive effects of peripheral flicker on foveal bichromatic mixture thresholds

Increment thresholds were determined for bichromatic mixtures of 660 and 520 nm (red + green), and 440 or 460 and 570 nm (blue + yellow). These measurements were made against a 1000-td white background that was surrounded by a larger, luminance matched annulus that appeared steady or flickered at 10 Hz. Targets were circular spots that subtended 60 and 15 min arc and had durations of 10 and 200 msec. All mixture thresholds with the steady surround were non-additive. The flickered surround gave rise to a periphery effect (PE), in the form of elevated mixture thresholds compared to those using the steady surround, for both red + green and blue + yellow mixtures when the 60 min arc, 10 msec spot was used. A PE was not consistently observed for the other three stimulus conditions. We propose the non-additive results indicate parvocellular (P-) pathway involvement in detection, which occurred under all stimulus conditions tested. Furthermore, that the PE were found when mixture stimuli were large, and brief indicates magnocellular (M-) pathway involvement in detection.

The effects of peripheral flicker on foveal spectral sensitivity

A flickering surround reduced sensitivity to large, briefly flashed monochromatic stimuli superimposed on a steady white background, compared to sensitivity measured when the surround was steady. The flickering surround had no effect on stimuli that were large and of long duration or small in size. Increasing the diameter of the background reduced the magnitude of the effect, but did not eliminate it.

Dynamic noise backgrounds facilitate target fading

With strict fixation, a small uniform target of medium contrast, placed at 10 deg eccentricity, faded much faster when presented on a dynamic random noise background than on either a static random noise background or a uniform background of the same luminance. Time to first disappearance was between 10 and 16 sec when the background was dynamic, 26 sec when it was static, and 57 sec when it was uniform. Times were shortest for temporal noise frequencies of the background between 3.5 and 15 Hz. These findings are unexpected: the frequent change of pixel contrast at the edge of the target should perceptually enhance the border, make it less susceptible to local adaptation, and prevent fading. Instead, dynamic random noise facilitates, rather than suppresses fading. Three potential mechanisms are discussed: edge perturbation, jerk effect and surround induction.

Specific effects of the benzodiazepine midazolam on visual receptive fields in light and dark adapted human subjects

Psychophysical experiments in humans have revealed similar characteristics of visual receptive fields as were found in cats and monkeys from retinal ganglion cell recordings. In addition, in some retinal ganglion cells of cats the GABA antagonist bicuculline decreases the activity of the inhibitory surround. These findings led to two predicitions: 1) benzodiazepines will selectively increase the inhibitory surround of human visual receptive fields, 2) after dark adaptation, no free GABA will be available in the synapses and benzodiazepines will have no effect on the visual system. Characteristics of human receptive fields were determined by subthreshold summation: the contrast threshold of a vertical line was measured dependent on the distance of two parallel flanking lines whose contrast was below threshold. Both hypotheses were confirmed: the threshold in the inhibitory region of receptive fields was specifically increased in a dose-dependent manner by midazolam PO (7.5 mg: P < 0.05; 15 mg: P < 0.01). In dark-adapted subjects no effect of midazolam was found. Control experiments with atropine (1 mg IV), sulpiride (100 mg IM), and levodopa (100 mg PO) showed no specific effect. The visual system may be a model to bridge the gap between animal and human psychopharmacology.

The shift effect can be elicited with both foveal and peripheral masks

Foveal target detection thresholds are elevated by presenting a counterphasing, vertical squarewave grating in the peripheral retina. This psychophysical "shift effect" has been considered to be an analogue of the neurophysiological "periphery effect" first described by McIlwain (1964; Journal of Neurophysiology, 27, 1154-1173). Physiological response properties of cells from the retina and lateral geniculate nucleus of cat and primate visual systems predict that sensitivity thresholds should also be elevated for peripheral targets in the presence of a foveal counterphasing mask. In these experiments, contrast sensitivities for human observers were obtained using a two-interval forced-choice procedure for peripheral target sinusoids in the presence of a foveal counterphasing mask. A suppressive shift effect was elicited by the foveal counterphasing squarewave mask, but only for counterphasing peripheral sinusoids. Masking was only obtained at the lowest spatial frequencies for both the peripheral and foveal shift effects.

Spatial contrast sensitivity: effects of peripheral field stimulation during monocular and dichoptic viewing

This report examines whether a radial grating with a blank 2 deg central aperture viewed with one eye can affect contrast sensitivity for foveally-viewed, counterphasing or stationary, sine-wave gratings seen with the other eye. We find that the moving radial grating preferentially raises the threshold for the low spatial frequencies of the counterphasing but not the stationary foveal stimulus. These results closely parallel recent primate electrophysiological work which suggests that visual stimulation of the peripheral field with a moving radial grating can activate inhibitory corticofugal influences on lateral geniculate neurons. The current data are evaluated in terms of a model which suggests that the peripheral stimulus activates corticofugal mechanisms.

Spatial frequency selectivity of remote pattern masking

Sudden movement of a high contrast grating in peripheral retina selectively reduces the sensitivity of human observers to low spatial frequency sinusoidal gratings, presented at the fovea. The suppression is similar to that observed using spots as targets. It is suggested that both these effects result from masking by the physiological periphery effect.

Effects of high-contrast peripheral patterns on the detection threshold of sinusoidal targets

Detection thresholds of sinusoidal gratings in the simultaneous presence of high-contrast peripheral masking stimuli partially overlapping the test gratings were determined as a function of the separation between the center of the test grating and the peripheral stimulus by a two-alternative forced-choice method. The results showed that the threshold-elevating effect of simultaneously present peripheral masking stimuli depends on how much of the test grating is left unexposed. An additional experiment, in which the detection thresholds in the absence of the peripheral stimulus were determined as a function of the number of cycles of the test grating, enabled us to show that the threshold-elevating effect is somewhat higher than the effect of simply cutting the test grating down in size. The threshold-elevating effects caused by high-contrast peripheral masking stimuli can be explained in terms of a lateral inhibition and a probability summation across space, taking into account the nonuniform sensitivity across the visual field.

Visual masking by flickering surrounds

Observers detected drifting sine-wave gratings presented in a circular 3 dia test field which was surrounded by a 3.25 degrees wide annulus. Forced choice contrast thresholds were measured with surrounds consisting of a steady field of light or uniform sinusoidal flicker. The flickering surround raised detection thresholds only for gratings with spatial frequencies below 2-4 c/deg. Variations on the basic experiment revealed that: (1) low spatial frequency gratings drifting through the surround masked detection of uniform flicker presented to the center; (2) masking did not depend greatly on the drift rate of the test grating but could not be obtained with stationary targets; (3) flicker restricted to either the top or side borders of the test field was a sufficient condition to produce masking; (4) the size of the masking effect decreased with center-surround separation. These results suggest a destructive interaction between transient mechanisms subserving neighboring regions of the visual field.

Foveal inhibition and facilitation caused by remote grating jerks: interaction between long-range and short-range effects

Periodic oscillation of a luminance grating imaged upon the peripheral retina reduces the threshold visibility of a foveally presented test spot. This new effect has been named the "jerk effect". The present investigation is concerned with the effect of a single jerk of the remote grating on threshold sensitivity. Foveal sensitivity changes were measured for different delays between grating jerk and test spot presentation. For 0.38 degrees, 100 ms test spot, long-range transient inhibition was found for all delays, with a maximal effect between 0 and 30 ms delay. By combining the jerk effect with the Westheimer paradigm, both facilitatory and inhibitory long-range effects could be demonstrated. For facilitation to occur, it was necessary that the steady background extended into the sensitization zone of the Westheimer area. Inhibition was the only result for smaller backgrounds. Reduced visibility is consistent with the hypothesis that peripheral transient mechanisms inhibit foveal sustained mechanisms. Enhanced visibility indicates that thresholds depend on an interaction between foveal-sustained and foveal-transient units. Transient peripheral stimulation and steady backgrounds of increasing diameter change the balance of inhibitory and facilitatory processes between these units.

Remote pattern reversal reduces the proximal negative response of the goldfish retina

1. Using the eyecup preparation, proximal negative responses (PNR) to small test spots of different irradiance were recorded with (a) a stationary peripheral black and white grating surrounding the test spot, and (b) with contrast reversal of the same grating. In the latter case, the PNR-amplitude was reduced by a magnitude that was dependent on the frequency of contrast reversal. The reduction was maximum (approximately 50%) for a frequency of 8-10 Hz. 2. The attenuation was constant for PNR-amplitudes greater than half the maximum value, but increased for smaller responses. The fact that the intensity-response curve was not merely shifted towards higher values on the log intensity axis, indicates that the suppression was an effect neither of stray light nor of adaptive processes in the distal retina. 3. The effect of a single shift of the grating (by half a cycle) on the PNR was studied at different delays between grating shift and test spot presentation. Strong suppression of the PNR was found for delays between 100 ms (shift preceding test spot) and -50 ms (test spot preceding grating shift), with a maximum at about 30 ms. 4. This long-range effect of peripheral transient stimulation is of inhibitory nature, and probably related to Werblin's windmill effect.