The effect of dot speed and density on the development of global motion perception

The purpose of this study was to investigate the effect of dot speed and dot density on the development of global motion perception by comparing the performance of adults and children (5–6 years old) on a direction-discrimination task. Motion coherence thresholds were measured at two dot speeds (1 and 4 deg/s) and three dot densities (1, 15, 30 dots/deg²). Adult coherence thresholds were constant at approximately 9%, regardless of speed or density. Child coherence thresholds were significantly higher across conditions, and were most immature at the slow speed and at the sparse density. Thus, the development of global motion perception depends heavily on stimulus parameters. This finding can account for some of the discrepancy in the current developmental literature. Our results, however, caution against making general claims about motion deficits in clinical populations based on only a single measurement at a specific combination of speed and density.     

Orientation discrimination for objects defined by relative motion and objects defined by luminance contrast

A bar-shaped area within a pattern of random dots was demarcated by moving the dots within the bar at a velocity equal and opposite to the velocity of dots outside the bar. Orientation discrimination for this motion-defined dotted bar was compared with orientation discrimination for a contrast-defined dotted bar that was created by switching off all dots outside the bar. Orientation discrimination was approximately as acute (approx. 0.5 deg) for a motion-defined bar as for a contrast-defined dotted bar, provided that dot contrast and speed were both high. Furthermore, this 0.5 deg discrimination compares with the most acute values reported for sharp-edged lines and sinewave gratings. For the motion-defined bar discrimination fell off rapidly when dot contrast was reduced, but remained acute for the contrast-defined bar for a further reduction of 0.6 log units. Thus, there was a 4:1 range of contrasts over which discrimination had collapsed for the motion-defined bar but remained acute for the contrast-defined bar. For the motion-defined bar discrimination also fell off rapidly at low dot speeds, but was almost unaffected by speed for the contrast-defined bar. These findings bear on the question whether orientation of motion-defined and contrast-defined bars are analyzed by the same or by different neural mechanisms, and pose a challenge for current theories of orientation discrimination.     

Defective processing of motion-defined form in the fellow eye of patients with unilateral amblyopia.

The following three measurements were made on a group of 20 pediatric and 5 adult patients with unilateral amblyopia: (1) speed threshold for recognizing motion-defined dotted letters; (2) recognition acuity for isolated solid letters of 4% contrast; and (3) Snellen line acuity for high-contrast letters. Normal limits were established with a group of 30 pediatric and 10 adult control subjects. The main finding was that, in amblyopic children, a high percentage (83%, 15 of 18) of fellow eyes showed a degraded ability to recognize motion-defined letters, even though Snellen acuity and 4% letter acuity were normal for age. The fellow eyes of all nine patients with strabismic amblyopia showed this pattern of loss, as did four of six fellow eyes of patients with anisometropic amblyopia and two of three fellow eyes of patients with anisometropic plus strabismic amblyopia. Only two clinically unaffected eyes were normal for motion-defined letters. These eyes belonged to patients with anisometropic amblyopia. Eighteen of the 19 previously amblyopic eyes tested were abnormal for motion-defined letters even though Snellen acuity was within normal limits for 6 of these eyes. In adults, only one of five fellow eyes failed the motion-defined letter test. It was concluded that the degradation of form perception associated with amblyopia can be different for luminance-defined and motion-defined form and that defective processing of motion-defined form is common in the fellow eyes of children with unilateral amblyopia.     

Visual acuity for optotypes made visible by relative motion

There are several visual mechanisms for analyzing spatial information additional to the much researched mechanism sensitive to luminance contrast. We describe a Snellen-type acuity test for motion-defined (MD) letters. Acuity for these MD letters collapsed at dot speeds slower than 0.05 deg/s, but acuity for contrast-defined (CD) letters was unaffected by speed over the entire 0 to 0.3 deg/s range used. Acuity was a power function of presentation duration for both kinds of letter, but the exponent was higher for MD than for CD letters. Acuity for MD letters was comparatively unaffected by dot density from 50 to 0.05%, below which it suddenly collapsed to zero. On the other hand, acuity for CD letters progressively fell as dot density was reduced from 50%, and below about 0.5% approximated acuity for MD letters.     

The effects of age on the spatial and temporal integration of global motion

The purpose of this study was to determine the relative contributions of local element speed and/or spatial displacement to age-related deficits in global motion processing. Motion coherence thresholds (79% correct) were measured for discriminating the direction of translational random dot kinematograms (RDKs) as a function of dot speed and spatial displacement across the adult lifespan (20–79 years). Age-related impairments in global motion processing were only apparent in observers 70–79 years of age. In agreement with previous studies, we found an age-related impairment at low (0.625 deg/s) and high speeds (10 deg/s). However, these effects were heavily mediated by dot spatial displacement. Motion coherence thresholds were also most markedly elevated in women aged over 70 years. These findings suggest a prominent role of spatial integration in global motion processing. Moreover, global motion perception appears to be relatively well preserved until around 70 years of age.     

Asymmetrical perception of motion smear in infantile nystagmus

Normal observers perceive less motion smear if a target moves in the opposite direction of a smooth eye movement than if the target moves to produce the same retinal image speed in the same direction as the eye movement. This study investigated whether a similar asymmetrical attenuation of perceived motion smear occurs in observers with infantile nystagmus (IN). Observers (N = 3) viewed a laser spot that moved for 100 or 125 ms to the right or left at a speed between 5 and 60°/s during the slow phase of jerk IN. After each trial, the observer adjusted the length of a bright line to match the extent of the perceived smear. Across observers, the average duration of perceived smear was 39 and 106 ms, respectively, for relative motion of the laser spot in the opposite vs. the same direction as the IN slow phase. In one observer with periodic alternating nystagmus, the direction of spot motion that produced less perceived smear reversed with an alternation in the direction of the IN slow phase. The reduction of perceived motion smear for relative target motion in the opposite direction of IN slow phases is attributed to extra-retinal signals that accompany IN. As during normal eye movements, the reduction of perceived smear for this direction of relative motion should foster the perception of clarity in the stationary visual world.     

The maturation of form and motion perception in school age children

The purpose of the current study was to investigate the maturation of form and motion perception, specifically the component visual abilities involved in the identification of motion-defined form, in children ranging in age from 3 to 12 years. Experiment 1 compared the maturation of motion-defined and texture-defined shape identification. Minimum speed thresholds on the motion-defined shape task decreased until age 7 years. Orientation difference thresholds on the texture-defined shape task decreased until age 11 years. Experiment 2 compared the maturation of global motion and global texture direction discrimination. Coherence thresholds on both tasks were similar in children of all ages and adults. Experiment 3 compared the maturation of direction discrimination on motion coherence and motion displacement tasks. Maximum displacement thresholds (Dmax) increased until age 7 years. The results are discussed with respect to the maturation of M/dorsal and P/ventral visual pathways.     

Location and identity memory of saccade targets

While the memory of objects’ identity and of their spatiotopic location may sustain transsaccadic spatial constancy, the memory of their retinotopic location may hamper it. Is it then true that saccades perturb retinotopic but not spatiotopic memory? We address this issue by assessing localization performances of the last and of the penultimate saccade target in a series of 2-6 saccades. Upon fixation, nine letter-pairs, eight black and one white, were displayed at 3° eccentricity around fixation within a 20° × 20° grey frame, and subjects were instructed to saccade to the white letter-pair; the cycle was then repeated. Identical conditions were run with the eyes maintaining fixation throughout the trial but with the grey frame moving so as to mimic its retinal displacement when the eyes moved. At the end of a trial, subjects reported the identity and/or the location of the target in either retinotopic (relative to the current fixation dot) or frame-based¹ (relative to the grey frame) coordinates. Saccades degraded target’s retinotopic location memory but not its frame-based location or its identity memory. Results are compatible with the notion that spatiotopic representation takes over retinotopic representation during eye movements thereby contributing to the stability of the visual world as its retinal projection jumps on our retina from saccade to saccade.     

Sensitivity to first- and second-order motion and form in children and adults

We compared the sensitivity of adults and children aged 3-10 years to first- and second-order motion and form. For first-order stimuli, at all ages sensitivity was better for motion than form, and motion thresholds were better at 6 Hz than at 1.5 Hz. For second-order stimuli, at all ages sensitivity was better for form than motion, and motion thresholds were better at 0.25 cyc/deg than at 1 cyc/deg. Thresholds became adult-like later for motion than for form and later for first-order than second-order stimuli. For first-order stimuli, the changes with age were larger and more protracted.     

Holistic processing for faces operates over a wide range of sizes but is strongest at identification rather than conversational distances

How does holistic/configural processing, a key property of face perception, vary with distance from an observed person? Two techniques measured holistic processing in isolation from part-based contributions to face perception: salience bias to upright in transparency displays, and a difficult-to-see Mooney face. Results revealed an asymmetric inverted-U-shaped tuning to simulated observer-target distance (stimulus size and viewer-screen distance combinations). Holistic processing peaked at distances functionally relevant for identification during approach (2-10 m; equivalent head size = 6-1.3°), fell off steeply at closer distances functionally relevant for understanding emotional nuances and speech (.25-2 m), and operated over a very wide range of distances (from .46 to 23 m, 47.5-0.6°).     

Characteristics of saccadic intrusions

Primary fixation is never perfectly stable, but is frequently interrupted by slow drifts, microsaccades and saccadic intrusions (SI). SI are involuntary, conjugate movements which take the form of an initial fast movement away from the desired eye position and followed after a short duration, by either a return secondary saccade or a drift. The purpose of this study was to examine the prevalence and metrics of SI in a population of 50 healthy subjects. Using both one and two dimensional recordings we find that all 50 members of the subject group exhibited SI. The SI were bilateral, conjugate and horizontal. No purely vertical SI were detected when examined in three subjects. SI amplitude mean and range was 0.6° ± 0.5°, 0.1°-4.1°; SI frequency mean and range was 18.0 ± 14.3 per min, 1.0-54.8 per min; SI duration mean and range was 225 ± 150, 20-870 ms. The mean SI amplitude and frequency when SI < 0.5° were removed was 0.97° ± 0.56° and 7.0 ± 11.4 per min respectively. Age was positively correlated with SI amplitude (p < 0.01), but there was no correlation between age and SI frequency. Three of four types of SI monophasic square wave intrusions (MSWI), biphasic square wave intrusions (BSWI) and double saccadic pulses (DSP) were found to be exclusively saccadic, whilst the fourth type, the single saccadic pulses (SSP), were confirmed to exhibit a slow secondary component. MSWI were the most frequently observed SI occurring in 47 out of 50 (94%) of the subjects with a mean amplitude, frequency and duration of 0.7° ± 0.5°, 11.5 ± 11.6 per min, and 255 ± 147 ms respectively. Mean amplitudes and frequencies for BSWI (n = 20), SSP (n = 11) and DSP (n = 34) were found to be 0.50° ± 0.2°, 1.2 ± 2.5 per min; 0.40° ± 0.20°, 0.4 ± 1.0 per min and 0.3° ± 0.4°, 5.0 ± 8.7 per min respectively. No differences in MSWI characteristics were found between binocular and monocular viewing. Possible explanations for SI occurrence include experimental viewing conditions, subject fatigue and covert shifts in attention.     

Binocular lens treatment in tree shrews: Effect of age and comparison of plus lens wear with recovery from minus lens-induced myopia

We examined normal emmetropization and the refractive responses to binocular plus or minus lenses in young (late infantile) and juvenile tree shrews. In addition, recovery from lens-induced myopia was compared with the response to a similar amount of myopia produced with plus lenses in age-matched juvenile animals. Normal emmetropization was examined with daily noncycloplegic autorefractor measures from 11 days after natural eye-opening (days of visual experience [VE]) when the eyes were in the infantile, rapid growth phase and their refractions were substantially hyperopic, to 35 days of VE when the eyes had entered the juvenile, slower growth phase and the refractions were near emmetropia. Starting at 11 days of VE, two groups of young tree shrews wore binocular +4 D lenses (n = 6) or −5 D lenses (n = 5). Starting at 24 days of VE, four groups of juvenile tree shrews (n = 5 each) wore binocular +3 D, +5 D, −3 D, or −5 D lenses. Non-cycloplegic measures of refractive state were made frequently while the animals wore the assigned lenses. The refractive response of the juvenile plus-lens wearing animals was compared with the refractive recovery of an age-matched group of animals (n = 5) that were myopic after wearing a −5 D lens from 11 to 24 days of VE. In normal tree shrews, refractions (corrected for the small eye artifact) declined rapidly from (mean ± SEM) 6.6 ± 0.6 D of hyperopia at 11 VE to 1.4 ± 0.2 D at 24 VE and 0.8 ± 0.4 D at 35 VE. Plus 4 D lens treatment applied at 11 days of VE initially corrected or over-corrected the young animals’ hyperopia and produced a compensatory response in most animals; the eyes became nearly emmetropic while wearing the +4 D lenses. In contrast, plus-lens treatment starting at 24 days of VE initially made the juvenile eyes myopic (over-correction) and, on average, was less effective. The response ranged from no change in refractive state (eye continued to experience myopia) to full compensation (emmetropic with the lens in place). Minus-lens wear in both the young and juvenile groups, which initially made eyes more hyperopic, consistently produced compensation to the minus lens so that eyes reached age-appropriate refractions while wearing the lenses. When the minus lenses were removed, the eyes recovered quickly to age-matched normal values. The consistent recovery response from myopia in juvenile eyes after minus-lens compensation, compared with the highly variable response to plus lens wear in age-matched juvenile animals suggests that eyes retain the ability to detect the myopic refractive state, but there is an age-related decrease in the ability of normal eyes to use myopia to slow their elongation rate below normal. If juvenile human eyes, compared with infants, have a similar difficulty in using myopia to slow axial elongation, this may contribute to myopia development, especially in eyes with a genetic pre-disposition to elongate.     

Resolution for spatial segregation and spatial localization by motion signals

We investigated two types of spatial resolution for perceiving motion-defined contours: grating acuity, the capacity to discriminate alternating stripes of opposed motion from transparent bi-directional motion; and alignment acuity, the capacity to localize the position of motion-defined edges with respect to stationary markers. For both tasks the stimuli were random noise patterns, low-pass filtered in the spatial dimension parallel to the motion. Both grating and alignment resolution varied systematically with spatial frequency cutoff and speed. Best performance for grating resolution was about 10 c/deg (for unfiltered patterns moving at 1-4 deg/s), corresponding to a stripe resolution of about 3'. Grating resolution corresponds well to estimates of smallest receptive field size of motion units under these conditions, suggesting that opposing signals from units with small receptive fields (probably located in V1) are contrasted efficiently to define edges. Alignment resolution was about 2' at best, under similar conditions. Whereas alignment judgment based on luminance-defined edges is typically 3-10 times better than resolution, alignment based on motion-defined edges is only 1.1-1.5 times better, suggesting motion contours are less effectively encoded than luminance contours.     

Characteristics of peripheral refractive errors of myopic and non-myopic Chinese eyes

Interest in peripheral refractive errors has increased as it was hypothesized that peripheral hypermetropia might provide a stimulus for axial elongation (Smith et al., 2005), this study was to determine relative peripheral refractive errors (RPRE) of the eyes of a group of Chinese children and adults. Central and peripheral (20°, 30°, 40° at nasal, temporal, superior and inferior meridians of retina) refractive errors were obtained from cyclopleged eyes of 40 children and 42 adults with a Shin-Nippon auto-refractor. Only right eyes were considered. Central spherical equivalent (M) was used to classify the eyes as Moderate Myopia (MM, −3.00 < M ? −6.00 D), Low Myopia (LM, −0.50 ? M ? −3.00 D), Emmetropia (E, −0.50 < M < +0.50 D) and Low Hypermetropia (LH, +0.50 < M ? +2.00 D). RPRE was calculated as the difference in M between the central and peripheral positions. The results showed that in both children and adults, horizontally, the RPRE profile for the MM group had a relative hypermetropic shift and in contrast, the profile for LH demonstrated a relative myopic shift. The difference in the profile between the MM and LH group was significant (p < 0.05). Also, the RPRE profile for MM group was different between adults and children with adult eyes showing greater amount of hypermetropic shift. Vertically, the RPRE profile of all the refractive error groups showed a myopic shift. Off-axis astigmatism increased and horizontally a shift from ‘with the rule’ to ‘against the rule’ astigmatism was observed for all groups. Our observations demonstrated that in Chinese eyes, the myopic group present a hyperopic shift in the periphery, the hypermetropic eye present a myopic shift and the emmetropic eyes present no differences to the fovea, which are similar to those reports in Caucasian eyes. The variations in the RPRE between various refractive error groups can be explained on the basis of eye shape.     

Motion VEPs with simultaneous measurement of perceived velocity

The dependency of the N200 amplitude of the motion-onset VEP evoked by a parafoveal grating of variable speed (0.25 – 13.5 deg/s, corresponding to 0.5 – 27 Hz) and constant contrast (4%) was studied. Additional measurements were made with parafoveally presented gratings of constant speed (2 deg/s, corresponding to 4 Hz) and a variable contrast (0.5 – 64%) before and after adaptation to a stationary or drifting grating. In this latter experiment, simultaneous psychophysical measurements were made of the perceived speed. The amplitude of the N200 wave increased with increasing stimulus speed within the slow speed range up to 1.5 deg/s (corresponding to 3 Hz). Adaptation to a stationary grating had no significant effect on the relationship between the N200 amplitude and stimulus contrast. Contrary to this, adaptation to a slowly drifting grating (1 deg/s, corresponding to 2 Hz) or to a rapidly drifting grating (4 deg/s, corresponding to 8 Hz) reduced the N200 amplitude significantly. Adaptation to a stationary grating slightly reduced the perceived speed of subsequently viewed gratings. Adaptation to a slowly drifting grating increased the perceived speed of the subsequently viewed gratings, whereas adaptation to a rapidly drifting grating decreased the perceived speed. The findings can be best explained by a two-channel model of speed perception. While the motion VEP reflects the sum of both channel activities, the psychophysical measures point to the antagonistic encoding of low and high velocities. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of age, viewing distance and target complexity on static ocular counterroll

The ocular counterroll (OCR) reflex generates partially compensatory torsional eye movements during static head roll tilt. We assessed the influence of age, viewing distance and target complexity on the OCR across the age span (13-63 years; n = 47), by recording eye movements during head-on-body roll tilt (0 ± 40° in 5° steps) while subjects viewed simple vs. complex targets at 0.33 and 1 m. We found that subjects ?31 years had lower gains than those ?30 years, but only for far targets. Consistent with prior reports, far targets elicited higher OCR gains than near targets, and target complexity had no effect on gains, suggesting that visual input is primarily used to maintain vergence during OCR.     

The upper spatial limit for perception of displacement is affected by preceding motion

The upper spatial limit D_max for perception of apparent motion of a random dot pattern may be strongly affected by another, collinear, motion that precedes it [Mateeff, S., Stefanova, M., &. Hohnsbein, J. (2007). Perceived global direction of a compound of real and apparent motion. Vision Research, 47, 1455-1463]. In the present study this phenomenon was studied with two-dimensional motion stimuli. A random dot pattern moved alternately in the vertical and oblique direction (zig-zag motion). The vertical motion was of 1.04° length; it was produced by three discrete spatial steps of the dots. Thereafter the dots were displaced by a single spatial step in oblique direction. Each motion lasted for 57 ms. The upper spatial limit for perception of the oblique motion was measured under two conditions: the vertical component of the oblique motion and the vertical motion were either in the same or in opposite directions. It was found that the perception of the oblique motion was strongly influenced by the relative direction of the vertical motion that preceded it; in the “same” condition the upper spatial limit was much shorter than in the “opposite” condition. Decreasing the speed of the vertical motion reversed this effect. Interpretations based on networks of motion detectors and on Gestalt theory are discussed.     

Perceptual limits of common fate

We studied the perception of a coherently moving group of collinearly arranged dots ("target dots") that traveled orthogonally to their linear orientation within a background of noise dots moving in random yet straight directions at constant speed ("random-direction noise"). Using a 2-interval forced-choice task we obtained coherence thresholds equal to a signal-to-noise ratio of 1-2%. These thresholds are lower than the 4-10% reported in the literature suggesting that the collinear arrangement of the target dots, in addition to movement, provided form information. Weber's Law was found to hold 4-7 target dots. Overall, sensitivity was constant for a broad range of dot speeds up to at least 6.5 deg/s. Lifetime required for optimal perception was 430 ms, far shorter than the threshold duration of 1 s reported for randomly distributed (i.e., nonaligned) target dots [Vis. Res. 41 (2001) 1891]. Angular deviations from parallel between adjacent motion trajectories were tolerated up to 27 deg for divergence and up to 19 deg for convergence. Diverging motion was detected earlier (after 600-800 ms) than converging motion (>1 s). Forced-choice discrimination yielded a higher proportion of correct responses than the actual (i.e., conscious) perception of the coherently moving group of dots. Our results are consistent with findings from neurophysiological recordings and neuroimaging of motion-sensitive neurons in areas V1 and MT showing broad tuning curves for speed and direction of a moving visual stimulus.     

The effects of optical blur on motion and texture perception.

PURPOSE: The purpose of this study is to determine how decreased visual acuity affects performance on tasks of motion and texture perception. METHODS: Positive diopter lenses were used to match three subjects at five levels of decimal visual acuity (DVA) ranging from an uncorrected DVA of 1.6 to the lowest DVA of 0.2. Performance thresholds were determined at each acuity level for five different psychophysical tasks. The tasks assessed the perception of motion-defined form, global motion, maximum motion displacement (Dmax), texture-defined form, and global texture. RESULTS: Reducing visual acuity decreased performance on the tasks of motion-defined form identification, texture-defined form identification, and global texture integration. Performance on the Dmax task improved with a reduction in visual acuity. Performance on the global motion task was unaffected by changes in visual acuity. CONCLUSIONS: Visual acuity should be considered when interpreting the results of developmental or clinical studies of motion and texture perception. The only exception to this is global motion perception, at least when DVA is better than 0.2. The effect of blur on tasks of motion and texture perception may reflect the extent to which high spatial frequency information is required for performance on these tasks.