Effects Of Retinal Eccentricity Research Articles

The Peripheral Flicker Illusion.

A new illusion is reported. A visual object suddenly appearing on a red background sometimes causes an impression of flicker or double flash. In Experiment 1, a red, green, or blue object was presented on a red, green, blue, or gray background. Participants evaluated the illusion strength in reference to the physical flicker of a gray object presented in central vision. The results show that the green or blue object presented on the red background caused the illusion. In Experiment 2, the effect of retinal eccentricity on the illusion was tested. The results showed that the illusion was weak in central vision but became stronger as the retinal eccentricity of the objects’ presentation increased. In Experiment 3, optimal luminance conditions for the illusion were explored with the green and blue objects. The illusion was strong when object luminance was lower than background luminance and the optimal luminance for the blue object was lower than that for the green object. We propose a tentative theory for the illusion and discuss its cause.

Perceiving Collision Impacts in Alzheimer's Disease: The Effect of Retinal Eccentricity on Optic Flow Deficits.

The present study explored whether the optic flow deficit in Alzheimer’s disease (AD) reported in the literature transfers to different types of optic flow, in particular, one that specifies collision impacts with upcoming surfaces, with a special focus on the effect of retinal eccentricity. Displays simulated observer movement over a ground plane toward obstacles lying in the observer’s path. Optical expansion was modulated by varying . The visual field was masked either centrally (peripheral vision) or peripherally (central vision) using masks ranging from 10° to 30° in diameter in steps of 10°. Participants were asked to indicate whether their approach would result in “collision” or “no collision” with the obstacles. Results showed that AD patients’ sensitivity to was severely compromised, not only for central vision but also for peripheral vision, compared to age- and education-matched elderly controls. The results demonstrated that AD patients’ optic flow deficit is not limited to radial optic flow but includes also the optical pattern engendered by . Further deterioration in the capacity to extract to determine potential collisions in conjunction with the inability to extract heading information from radial optic flow would exacerbate AD patients’ difficulties in navigation and visuospatial orientation.

The Effect of Retinal Eccentricity on Perceiving Collision Impacts

Three experiments examined the role of central and peripheral vision in collision detection and control of braking. Displays simulated observer movement over a ground plane toward obstacles lying in the observer's path (Experiments 1 & 3) or toward a vertical 2-D plane (Experiment 2). Optical expansion was depicted under the constraint that remains constant throughout the approach. Displays employed in Experiments 1 and 2 were masked centrally (peripheral vision) or peripherally (central vision) with mask size ranging from 10° to 30° in diameter in steps of 5°. Participants responded to the optical pattern engendered by with more consistency in the peripheral vision condition than in the central vision condition. Experiment 3 further examined the peripheral advantage by masking the displayed peripheral region from 20% to 80%. Largely unaffected performance across masked areas of the periphery confirmed that the efficacy of the peripheral retina does not lie in more extensive flow vectors but in its inherent sensitivity to optical consequences engendered by . These results were compared with psychophysical findings in self-motion perception and clinical findings in patients with partial vision loss.

Effects of retinal eccentricity and acuity on global-motion processing

The present study assessed direction discrimination with moving random-dot cinematograms at retinal eccentricities of 0, 8, 22, and 40 deg. In addition, Landolt-C acuity was assessed at these eccentricities to determine whether changes in motion discrimination performance covaried with acuity in the retinal periphery. The results of the experiment indicated that discrimination thresholds increased with retinal eccentricity and directional variance (noise), independent of acuity. Psychophysical modeling indicated that the results for eccentricity and noise could be explained by an increase in channel bandwidth and an increase in internal multiplicative noise.

Effects of retinal eccentricity on the temporal summation of double flashes

Effects of retinal eccentricity on the temporal summation of double flashes

The effect of retinal eccentricity on the discrimination of global motion direction

The effect of retinal eccentricity on the discrimination of global motion direction

Re-evaluating split-fovea processing in word recognition: Effects of retinal eccentricity on hemispheric dominance.

Several studies have claimed that hemispheric asymmetries affect word recognition right up to the point of fixation because each fovea is split precisely at its vertical midline and information presented either side of this midline projects unilaterally to different, contralateral hemispheres. To investigate this claim, four-letter words were presented to the left or right of fixation, either close to fixation entirely in foveal vision (0.15, 0.25, and 0.35 degrees from fixation) or further from fixation entirely in extrafoveal vision (2.00, 2.10, and 2.20 degrees from fixation). Fixation location and stimulus presentation were controlled using an eye-tracker linked to a fixation-contingent display and performance was assessed using a forced-choice task to suppress confounding effects of guesswork. A left hemisphere advantage was observed for words presented in extrafoveal locations but no hemisphere advantage (left or right) was observed for words presented in any foveal location. These findings support the well-established view that words encountered outside foveal vision project to different, contralateral hemispheres but indicate that this division for word recognition occurs only outside the fovea and provide no support for the claim that a functional split in hemispheric processing exists at the point of fixation.

Sensitivity to stimulus onset and offset in the S-cone pathway

Previous work [Vassilev, А., Mihaylova, M., Racheva, K., Zlatkova, M., & Anderson, R. S. (2003). Spatial summation of S-cone ON and OFF signals: Effects of retinal eccentricity. Vision Research, 43, 2875–2884; Vassilev, A., Zlatkova, M., Krumov, A., & Schaumberger, M. (2000). Spatial summation of blue-on yellow light increments and decrements in human vision. Vision Research, 40, 989–1000] has shown that spatial summation of brief S-cone selective stimuli depends on their polarity, increments or decrements, suggesting involvement of S-ON and OFF pathways, respectively. This assumption was tested in two experiments using a modified two-color threshold method of Stiles to selectively stimulate the S-cones. In the first experiment we measured detection threshold for small 100 ms S-cone selective increments and decrements presented within three types of temporal window, rectangular, ramp onset/rapid offset and rapid onset/ramp offset. The ramp-onset threshold was higher than the ramp-offset threshold regardless of stimulus sign. In the second experiment we measured reaction time (RT) with near-threshold stimuli spatially coincident with the background to avoid spatial contrast. RT distribution for S-cone selective 500 ms increments and decrements was unimodal and followed stimulus onset. An increase of stimulus duration to 1000 and 2000 ms resulted in the appearance of responses following stimulus offset. The results suggest that, for brief S-cone selective increments or decrements, the human visual system is more sensitive to stimulus onset than to stimulus offset. Only for longer stimuli is the offset important, probably due to slow adaptation at a postreceptoral level.

Depth-of-focus of the human eye in the near retinal periphery

Although the depth-of-focus in the foveal region has been well investigated, knowledge regarding the effect of retinal eccentricity on blur detection and sensitivity is limited. In the present study, the depth-of-focus at the fovea and in the near retinal periphery (0°–8°) was assessed psychophysically in 7 human subjects using a 5 mm artificial pupil with accommodation paralyzed. The group mean total depth-of-focus progressively increased linearly from 0.89 D at the fovea to 3.51 D at a retinal eccentricity of 8° at the rate of 0.29 D/degree, with response variability (S.E.M.) remaining relatively constant (±0.17 D). We speculate that the reduced detection and sensitivity to blur in the near periphery may be attributed to retinal topography, sharpness overconstancy, optical aberrations, and visual attention in peripheral vision.

Spatial summation of S-cone ON and OFF signals: Effects of retinal eccentricity

We studied spatial summation for S-cone ON and OFF signals as a function of retinal eccentricity in human subjects. S-cone isolation was obtained by the two-colour threshold method of Stiles, modified by adding blue light to the yellow background. Test stimuli were blue light increments or decrements within a circular area of variable size. These were presented for 100 ms at 0 to 20 deg along the horizontal temporal retinal meridian. Ricco’s area of complete spatial summation was measured from the threshold vs. area curves. This was nearly constant and approximately the same for both types of stimuli within the 0–5 deg range and increased beyond this range. The decremental area increased faster, suggesting that separate mechanisms, presumably ON and OFF, integrate S-cone increments and decrements. The results appear to provide new evidence for the existence of separate S-cone ON and OFF pathways. We compare the data with known morphology of primate retina and assume that, if S-cone decrements are detected via separate OFF cells, these should differ in density and dendritic field size from the S-cone ON cells, but only in the retinal periphery.

The discrimination of blur in peripheral coloured borders

Our interest is in measuring the threshold for blur, for long borders at well-defined retinal eccentricities between large fields of colour. Our method is to precisely match a centrally fixated sharp-edged disk of one colour against a surround of another, using the minimum distinct border criterion. We then measure the amount of added Gaussian blur that makes the sharp step-edged border just noticeably different. The selected colours are small fixed chromatic deviations of 500 msec duration from an adaptive low photopic or mesopic white. The effects of retinal eccentricity are striking. Blur thresholds are large for yellow-blue borders centrally (at 1.25° eccentricity) and extremely large for red-green borders peripherally (at 20°). Blur thresholds are generally larger for isoluminous chromatic borders than for a low contrast achromatic border. Accurate Rovamo-Virsu M-scaling is limited to photopic achromatic borders.

Equating character-identification performance across the visual field

The effect of retinal eccentricity on stimulus identification was investigated by measuring observers' ability to identify digits of various sizes presented briefly at different locations in their visual fields. The stimuli were either presented one at a time or presented in pairs with each member of the pair at a different eccentricity and having a different size. Stimulus-response confusion matrices were used to calculate the information transmitted by each character as a function of stimulus size and retinal eccentricity. Linearly scaling stimulus size with retinal eccentricity yields equal information transmission across each subject's visual field. There was no difference between the amounts of information transmitted when the targets were presented alone and when they were transmitted in pairs. For small target sets, therefore, the amount of information transmitted from the screen to the observer can be approximated as the sum of the information at the separate locations.

Fixation disparity vs. binocular fixation misalignment.

Conventional fixation disparity was compared with the corresponding foveal fixation misalignment measured by a recently developed method based on the effect of retinal eccentricity on the width of the border enhancement band. Unlike procedures using binocular nonius alignment, the method is not subject to adaptive changes in perceived direction. Forced convergence and divergence stimulation served as the independent variable. It was found that conventional fixation disparity represents only a small, constant fraction of the misalignment through the greater portion of the vergence range. However, when the misalignment is restricted to a small, central portion of the foveola, this relation changes drastically, and the fixation disparity can then be much larger than the fixation misalignment. During perfect fixation alignment of the foveal centers, there is always a significant amount of fixation disparity present. It is suggested that the large differences between fixation disparity and fixation misalignment are due to a fundamental, perceptual mechanism that is always at work during binocular vision, changing the relation between retinal location and perceived visual direction.

Information processing in near peripheral vision.

The present study required that Ss name briefly exposed single lower-case letters that were presented at a total of 24 locations (8 meridians X 3 retinal eccentricities, 0.5 degrees, 2.75 degrees, and 5.0 degrees from a central fixation point, 0 degrees). One group of 12 Ss received a set size (load) of 2 letters, and another group of 12 Ss received a set size (load) of 24 letters. Ss given the larger load were significantly less accurate and significantly slower (longer vocal latencies) in naming the letters. In addition, significant main effects of retinal eccentricity and meridian were found. Ss performed more poorly as the stimuli were presented more eccentrically. Also, performance tended to be somewhat poorer above and below the fixation point than it did left or right of fixation. There was also some tendency toward a right visual field superiority. Unlike an earlier study, there was little evidence in favor of a "tunnel vision" interpretation, which would have required an interaction of load X retinal eccentricity. Possible reasons for the different results from the two studies are discussed in terms of a levels-of-processing interpretation.

Effects of retinal eccentricity on displacement thresholds for unidirectional and oscillatory stimuli

Motion sensitivity was determined for line stimuli undergoing unidirectional and oscillatory displacements at various retinal eccentricities. Oscillatory motions of short duration were found to produce consistently greater motion thresholds than unidirectional stimuli at each eccentricity tested. Increasing retinal eccentricity elevated motion thresholds similarly for both forms of stimulus motion. The observed differences between unidirectional and oscillatory stimuli are attributed to differences in the temporal summation of the two forms of stimuli at short durations. These findings also suggest that differences in motion sensitivity between central and peripheral vision are quantitative rather than qualitative.

Relation of brightness to threshold for light-adapted and dark-adapted rods and cones: effects of retinal eccentricity and target size.

'Equal-brightness' functions of retinal eccentricity and target diameter were measured by a matching procedure, and compared with the corresponding threshold functions for four different adaptation conditions: light-adapted cones (LAC), dark-adapted cones (DAC), light-adapted rods (LAR) and dark-adapted rods (DAR). The separation between log brightness matches and log thresholds decreased with eccentricity and increased with target size for all adaptation conditions, but overall separation was substantially greater for the DAR condition than for the other three. A two-channel model of achromatic brightness is proposed to explain the results. The model assumes 'strong' and 'weak' channels, which contribute unequally to brightness. These channels are tentatively identified with tonic and phasic classes of retinal ganglion cells.

The effects of retinal eccentricity and orientation on perceived length.

An experiment was performed to examine the effects of line orientation and retinal locus on the perceived length of a single line. Thirty-five male and female undergraduate volunteers each monocularly judged the length of five test lines presented in two orientations (horizontal and vertical) at five different retinal loci. Displacement of horizontal lines from the fovea on either the horizontal or vertical meridian produced decreases in perceived size. The perceived length of vertical lines, however, decreased only with displacements on the vertical meridian.

The visual stimulus for saccadic eye movements in human observers.

Three experiments are reported in which the salience of visual stimuli is assessed by finding which of two competing peripheral stimuli elicit a saccade when both are presented simultaneously with the use of paradigm due to Love-Schoen. The first experiment shows how salience is affected by position in the visual field. A strong effect of retinal eccentricity is found which is compared with the cortical magnification factor. Additionally directional biases occur. The second experiment shows that temporal change appears to be significant in eliciting a saccade rather than any specific properties related to movement. The third experiment shows that contour at high spatial frequencies does not affect salience. An area of 4 cycles deg-1 high-contrast square-wave grating possesses the same salience as an equivalent area with identical, constant, space average luminance. Taken together, the results suggest that salience might be accountable for in terms of the activation of transient channels in the visual system.

The effect of retinal eccentricity on the Broca-Sulzer phenomenon

The effect of retinal eccentricity on the Broca-Sulzer phenomenon

Spatial and chromatic interactions in the lateral geniculate body of the rhesus monkey.

Spatial and chromatic interactions in the lateral geniculate body of the rhesus monkey.