Spatio-temporal vernier acuity

The study of space-time vernier (STV) provides information on the spatio-temporal structure of the visual system in the same way that the classical spatio-spatial vernier (SSV) provides information on its spatial structure. The transposition of a SSV task into a STV one yields the following experimental format: an object (in the present case a Gaussian Blob) drifts with a constant velocity, V, disappears at x0, t0 and reappears after a variable duration delta t at a position x1 +/- delta x with x1 the correct position (given a constant V) and delta x the minimum (positive and negative) spatial offset discriminable from x0, i.e. the STV threshold. Observer's task is to specify whether the reappearance position is ahead of, or behind x1. The STV functions of delta t measured for 1, 5 and 10 deg/s reference velocities are linear with non-zero spatial and temporal intercepts at the origin. We refer to these x and t intercepts as dynamic dmin and tmin. Dynamic dmin is the smallest instantaneous displacement (infinite velocity) discriminable from a continuous drift, V. Dynamic tmin is the shortest 'motion stop' discriminable from the same continuous drift, V. To our knowledge these quantities have not yet been assessed. Estimated dynamic dmin increases with V. whereas tmin is more or less V independent suggesting that the motion sensors presumably involved in the STV task have peak spatial frequencies inversely proportional with V and a temporal frequency characteristic independent of V (at least within the studied range). The observed STV linearity with the spatio-temporal separation implies that the STV task is equivalent to a velocity discrimination. Two additional observations yield support to this conclusion. (i) The slopes of these functions yield velocities very similar to those discriminable from the reference V in a standard V-discrimination experiment. (ii) The predicted STV performances based on a decomposition of the task into two velocity discrimination tasks run as independent experiments are reasonably accurate.     

Effects of imagery on vernier acuity under conditions of induced depth.

Imagery interferes with visual acuity (the "Perky effect") when an image is close to a visual target and both the image and the acuity target are located in the same depth plane. Whether imagery-induced interference occurs when a mental image and a target are separated by induced depth was investigated. Participants projected an image in front of or behind a vernier acuity target on a frontal or back plane suggested by the panels of an outline cube. A drop in accuracy for the target was found when an image was projected in front of, but not behind, the target. Thus, induced depth can influence the Perky effect. By contrast, real lines interfered with the target regardless of perceived depth plane, which is inconsistent with the hypothesis that imagery and perception are equivalent. Results support the hypothesis that images interfere with perception only when the participant must see through an image to obtain information specifying the visual target. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Binocular rivalry: Central or peripheral selective processes?

The traditionally held notion that binocular rivalry reflects central selective processes that take effect subsequent to the analysis of both monocular stimuli contrasts with the currently popular view that the suppressed stimulus suffers inhibition, or blocking, at a relatively peripheral level. The available evidence supports the traditional approach. It is argued that although peripheral responses such as changes in pupil diameter or accommodation may be correlated with rivalry suppression, they may not be held responsible for the suppression itself. Similarly, processes of adaptation and contralateral inhibition are unable to explain binocular rivalry. There is evidence, however, that the suppressed stimulus in rivalry is being fully analyzed and evaluated. Perceptual experience is thereby shown to reflect processes over and above the analysis of sensory information, and binocular rivalry suggests itself as a useful context in which to isolate and investigate these processes. (105 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Orientation dependency for foveal line stimuli: detection and intensity discrimination, resolution, orientation discrimination and vernier acuity

Thresholds were measured for five tasks: line detection, intensity discrimination, two-line resolution, vernier acuity and line-orientation discrimination. For each task, 30 arcmin lines were presented foveally in eight retinal meridians to assess similarities in orientation anisotropies across tasks in the same observer. Three observers were tested. The pattern of the orientation anisotropy differs across tasks. Meridional anisotropies exist in detection, increment discrimination thresholds, and vernier acuity but the classical oblique effect is consistently found only in orientation discrimination.     

Binocular coordination in reading.

Measured the differences in time between the 2 eyes, using laboratory real-time computer methods to detect and measure the time between velocity peaks of binocular saccadic movements in reading. The hypothesis was that instead of being completely conjugate as indicated by prior methods of ocular measurement, the eyes must be coordinated in directional motion by small time differences that govern their feedback guidance and relative velocity. Results with 3 Ss indicate that the time differences between the eyes clustered around 3 values: (a) near synchrony, including no difference and left eye leading by 1 msec.; (b) left eye leading by 7-9 msec.; and (c) left eye leading by 14 msec. These time differences were not related to the difficulty of the reading material, but were changed significantly by 15– horizontal rotation of the reading display. Results change the established views that the eyes are perfectly conjugate in saccadic motion and provide initial suggestive data toward a dynamic feedback doctrine of coordinate eye motion and functional disabilities in visual perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Binocular function clarified

Normal binocular function is defined as the bifoveal connection of the central and peripheral structures of the visual system. Binocular function in strabismus is defined as connections, more or less strong and more or less labile, of the fovea of the fixating eye with the "pseudo-fovea" of the deviating eye including all central and peripheral structures, and this connection represents, in fact, a progress of adaptation of all parameters to the new conditions of vision.     

The role of feedback in learning a vernier discrimination task

We compare improvement through training in vernier acuity under different feedback conditions in order to clarify the role of feedback during learning of a perceptual task and to test different (neural network) models of perceptual learning. Improvement of performance is measured in 49 observers under feedback, no feedback, uncorrelated feedback, partial feedback, and block feedback conditions. Correct feedback conditions yield a larger improvement of performance than manipulated and no feedback conditions. Providing feedback that is uncorrelated to the observers' responses prevents learning, while the effect of block feedback does not differ significantly from complete feedback. Our results cannot be explained by learning rules that depend exclusively on an external teacher or by models that propose learning in an exposure-dependent way with unsupervised learning rules but without top-down influences.     

Binocular distance perception.

Binocular distance perception is not veridical. A constant binocular disparity corresponds neither to a constant perceived depth nor to a constant perceived distance ratio. Perceived relative distance depends on physical distance as well as disparity. This implies the existence of an egocentric distance signal. A model is proposed that attributes all of the error in binocular distance perception to a misperception of egocentric distance and a difference in the effective magnifications in the 2 eyes. Perceived distance of near targets exceeds physical distance; perceived distance of far targets is less than physical distance. The model describes a large body of data in which Ss set distances to satisfy various relative perceived distance criteria. The misperception of egocentric distance is also manifested in a variety of experiments in which the S directly indicates perceived egocentric distance. The egocentric distance signal appears to be of extraretinal origin and to be related to the vergence of the eyes. (59 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Binocular visual surface perception

Binocular disparity, the differential angular separation between pairs of image points in the two eyes, is the well-recognized basis for binocular distance perception. Without denying disparity's role in perceiving depth, we describe two perceptual phenomena, which indicate that a wider view of binocular vision is warranted. First, we show that disparity can play a critical role in two-dimensional perception by determining whether separate image fragments should be grouped as part of a single surface or segregated as parts of separate surfaces. Second, we show that stereoscopic vision is not limited to the registration and interpretation of binocular disparity but that it relies on half-occluded points, visible to one eye and not the other, to determine the layout and transparency of surfaces. Because these half-visible points are coded by neurons carrying eye-of-origin information, we suggest that the perception of these surface properties depends on neural activity available at visual cortical area V1.     

Effects of refractive error on detection acuity and resolution acuity in peripheral vision

PURPOSE: To evaluate the effect of refractive error on detection acuity and resolution acuity in peripheral vision. METHODS: Detection acuity, defined as the highest spatial frequency for which luminance gratings can be discriminated from a uniform field, and resolution acuity, defined as the highest spatial frequency for which spatial patterns are perceived veridically, was determined for vertical and horizontal gratings located at 20 degrees, 30 degrees, and 40 degrees of eccentricity. Resolution was also measured for tumbling-E discrimination at these locations. Refractive state of the eye for test targets was manipulated by introducing an ophthalmic trial lens into the line of sight for the stimulus while holding accommodative state fixed. RESULTS: Detection acuity in the periphery varied significantly with the amount of optical defocus, whereas acuity for grating resolution or letter discrimination was unaffected by defocus over a large range (up to 6 D). These results are consistent with the working hypothesis that detection acuity in the periphery is limited by contrast insufficiency under normal viewing conditions, but resolution is limited by ambiguity because of neural undersampling. CONCLUSIONS: The large depth of focus for resolution acuity measured for peripheral vision indicates that spatial resolution is likely to remain sampling-limited even when peripheral refractive errors are not fully corrected, thus relaxing the methodologic requirements for obtaining noninvasive estimates of neural sampling density of the living eye in a clinical setting.     

DYZY-1型大圆锥体游标尺在设备检修中的应用

为解决韶钢大型圆锥体工件外锥面与端面交线尺寸的测量,采用了一种较精确测量的专用量具DYZY-1型大圆锥体游标卡尺．介绍了其结构及在设备检修中的典型应用实例,对其不足也提出了改进意见．     

Moving vernier in amblyopic and peripheral vision: greater tolerance to motion blur

The purpose of this study was to examine the hypothesis that higher stimulus velocities could be tolerated in amblyopic and normal peripheral vision. The basis for this hypothesis is that a shift in the spatial scale of processing appears to account for the degradation in vernier acuity for moving stimuli in normal vision, and, to a large degree for the degradation in vernier acuity for stationary stimuli in amblyopic and peripheral vision. Vernier thresholds were determined using a pair of long abutting lines, for velocities ranging between 0 and 8 deg/sec. Comparisons were made between non-amblyopic and amblyopic eyes in two amblyopic observers, and between central and peripheral (5 and 10 deg) vision in two normal observers. We analyzed our threshold vs velocity data using an equivalent noise analysis, and defined the knee of the function, the point at which vernier threshold is elevated by a factor of square root of 2, as the "critical velocity" beyond which image motion degrades vernier acuity. Critical velocities were found to be higher in amblyopic than in nonamblyopic eyes; and higher in peripheral than central vision. Our results are consistent with the predictions from the shift in spatial scale notion--that higher velocity of image motion can be tolerated because of the shift in sensitivity toward lower spatial-frequency filter mechanisms in amblyopic and normal peripheral vision.     

Binocular rivalry: ambiguities resolved

For over 100 years, binocular rivalry was seen as the result of competition between the two eyes, involving reciprocal suppression of retinal inputs. Now it emerges that rivalry reflects alternating perceptual interpretations that are represented in the firing patterns of cells in the temporal visual cortex.     

Binocular fixation disparity in single word displays.

It has been claimed that the recognition of words displayed in isolation is affected by the precise location at which they are fixated. However, this putative role for fixation location has yet to be reconciled with the finding from reading research that binocular fixations are often misaligned and, therefore, more than 1 location in a word is often fixated simultaneously. The accuracy and alignment of binocular fixations during single word processing have not been assessed previously. To investigate this issue, words were presented for lexical decision at locations around a central fixation point. Eye-tracking data revealed that participants often fixated inaccurately and that fixations were frequently misaligned, but that this did not affect word recognition. The findings show that binocular fixation disparity is pervasive even in single word displays and a potential source of confound for research into effects of fixation location on word recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Binocular matching of dissimilar features in phantom stereopsis

Previously we have demonstrated that quantitative depth perception can be elicited from a stereogram that lacks contrast defined binocular corresponding elements (phantom stereopsis). In this report, we use computer simulation to demonstrate that it is biologically plausible for some known binocular cortical cell types to combine non-conventional matching features. Therefore, binocular matching processes based on the responses of these cells could be a conventional one, namely, looking for similar response patterns in the two eyes. While at cell types we simulated gave identical disparity outputs to the conventional stereogram, they responded differently to the phantom stereogram. Processes other than low-level disparity detectors may have to be invoked in order to achieve a unique depth solution.     

Binocular correlates of the direction of motion in depth

Two binocular cues to the direction of an object's motion in depth are the ratio (phi R/phi L) between the velocities of the object's retinal images in the right and left eyes and the ratio (phi/gamma) between the velocity of the binocularly-fused image of the object and the rate of change of disparity. We report that the apparent direction of motion in depth of a monocularly-camouflaged target can be varied by altering the ratio phi/gamma. Because no monocular motion signal is available in this case, we conclude that the ratio phi/gamma is a sufficient cue to the direction of motion in depth. This is not to deny that the phi R/phi L cue might be used in the everyday visual situation where monocular velocities phi R and phi L are available to the brain.     

Dynamic visual acuity as related to age, sex, and static acuity.

What effects ability to follow visually a moving target? How about static acuity? Using equipment, including slides, to study static acuity, with 236 Ss, it was concluded that this does not predict it. "The exact nature of those factors other than static acuity that influence dynamic acuity are not yet known, but it is probable that they involve the efficiency of the entire oculo-motor system." From Psyc Abstracts 36:01:3LK11B. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of measures of visual acuity in infants: Teller acuity cards and sweep visual evoked potentials

PURPOSE: This study compares the development of acuity in the same infants during one testing session using Teller acuity cards (TAC) and sweep visual evoked potentials (sVEP). We asked whether different testing methods in two centers would produce different developmental time courses. METHODS: Forty-eight infants were tested in two centers. The standard procedure for TAC was used. For sVEP acuity, the amplitude response curve derived from time-locked cortical activity was used to extrapolate to zero response, giving an acuity estimate for each infant. RESULTS: sVEP acuity was generally higher than TAC acuity. The rate of development was steeper for TAC than sVEP acuity with TAC starting at a much lower level. The ratio of sVEP to TAC acuity decreased exponentially with age reaching an asymptote of about 1.44 at 6 months. CONCLUSIONS: Results were indistinguishable between centers suggesting that comparison of acuity measures obtained using variations of these methods across centers is possible.     

Automated clinical visual acuity testing

We developed a method for testing visual acuity using a general-purpose microcomputer which displays visual acuity targets on a television monitor, controls a staircase psychophysical testing procedure, and provides a printed record of mean visual acuity and standard deviation. This automated procedure can be used to increase the precision of clinical visual acuity testing and to determine if changes in a patient's visual acuity are statistically significant.