Biomedical subjects

T Banton

Publications and source records attributed to T Banton.

8 recordsLinked to original sources

PubMed1999

Infants' sensitivity to statistical distributions of motion direction and speed.

Adults combine different local motions to form a global percept of motion. This study explores the origins of this process by testing how perturbations of local motion influence infants' sensitivity to global motion. Infants at 6-, 12-, and 18-weeks of age viewed random dots moving with a gaussian distribution of dot directions defined by a mean of 0 degree (rightward) or 180 degrees (leftward) and a standard deviation (SD) of 0, 34, or 68 degrees. A well-practiced observer used infants' optokinetic responses to judge the direction of stimulus motion. Infants were studied both cross-sectionally and longitudinally. Direction discrimination was relatively high at all ages when the SD was 0 degree. When the SD was 34 or 68 degrees, performance declined with age. Adult performance was nearly perfect at these SDs. A similar developmental pattern was found with distributions of dot speed. The decline in infant performance is consistent with the development of both neural tuning and receptive field size. The subsequent improvement by adulthood suggests the development of additional processes such as long-range interactions.

Analysis of Variance↗

PubMed1997

Multiple developmental pathways for motion processing.

PURPOSE: Image flow across the retina can be classified into several types of motion specifying information about spatial layout and self-movement. Adults process these types of motion via different functional pathways. This article investigates the development of these functional pathways. METHODS: The development of sensitivity to several classes of motion is reviewed and correlated with the neural development of the visual system. RESULTS: Different types of motion processing develop at different rates. The clearest example is that sensitivity to direction of translation shows an earlier onset and a different developmental trajectory than sensitivity to shearing motion. In addition, the onset of sensitivity to translation direction and shearing motion coincides with the development of striate laminae 5/6 and 4B, respectively. This earlier development of the deeper striate laminae is also consistent with reports of neonatal direction discrimination in displays undergoing optical expansion and rotation. CONCLUSIONS: Sensitivity to at least two types of motion, translation and shearing, develop in different ways and continue to be processed differently in adulthood. The differential development of sensitivity to these motion types coincides with the laminar development of striate cortex. It thus follows that the nonuniform development of the motion-processing system must be recognized to assess infant motion sensitivity correctly.

Adult↗

PubMed1996

Infants' sensitivity to uniform motion.

Uniform motion across the retina is a powerful cue to the perception of self-motion. In spite of its importance for adaptive functioning, little is known about the early development of uniform motion sensitivity. Six-, 12-, and 18-week-old infants viewed random-dot kinematograms depicting leftward or rightward uniform motion. The display induced optokinetic nystagmus (OKN), which a trained observer used to judge the direction of target motion. Both speed of motion and directional coherence were varied to obtain independent motion detection thresholds. Infants of all three ages could detect uniform motion, and their detection thresholds were constant during this period of development. This is in contrast to the clear improvements in relative motion sensitivity noted previously between 6 and 18 weeks of age with a preferential looking (PL) paradigm. The developmental differences between these studies may result from: (1) separate mechanisms for detecting uniform (absolute) and differential (relative) motion; or (2) separate mechanisms underlying OKN and PL response measures.

Adult↗

PubMed1993

Spatial localization of motion-defined and luminance-defined contours.

Thresholds for the vernier alignment of contours defined by luminance and coherent random-dot motion were measured. The luminance-defined contours were localized with a precision better than the receptor grain, while the motion-defined contours were localized more poorly than this limit. When motion-defined and luminance-defined targets were matched for dot density, vernier thresholds were equivalent at low densities. When the targets were also equated for perceived contrast, the vernier thresholds became equivalent at higher densities as well. These results suggest that the precision with which motion-defined contours are localized is contrast and sample limited. Next, the localization mechanism for motion-defined targets was investigated. Length summation limits were similar for motion-defined and luminance-defined targets, suggesting that these targets could be localized by a common mechanism. Vernier targets were then flanked by two additional bars. Motion-defined flanks interfered with the localization of motion-defined targets and luminance-defined flanks interfered with the localization of luminance-defined targets. However, motion-defined and luminance-defined bars did not interact to produce spatial interference. This result indicates that the mechanisms for localizing luminance-defined and motion-defined targets are independent. We suggest that parallel mechanisms govern the vernier localization of motion-defined and luminance-defined targets.

Contrast Sensitivity↗

PubMed1993

Directional bias in the perception of translating patterns.

Recent findings suggest that the visual system is biased by its past stimulation to detect one direction of motion over others. Three experiments were designed to investigate whether this bias is mediated by the direction or by the velocity of the past stimulation, and whether this bias is offset by contradictory pattern or depth information. Observers were presented with two solid or random-dot patterns that moved across a display screen in antiphase. As the two patterns reached the center of the screen, they became superimposed in such a way that their subsequent directions were ambiguous. Results from experiment 1 showed that the probability of perceiving these patterns as continuing to move in the same directions was significantly greater when they moved at a constant velocity than when they moved at a variable velocity. Results from experiments 2 and 3 revealed that this directional bias was reversed only gradually as an increasing amount of contradictory pattern information was introduced, but that this reversal was quite abrupt when a relatively small amount of contradictory depth information was introduced. Collectively, these results suggest that a directional bias in the perception of moving patterns is mediated not only by the direction of the previous stimulation, but also by the velocity of that stimulation. Moreover, the analyses of pattern and motion information appear relatively independent during the early stages of visual processing, but the analyses of depth and motion information appear considerably more interdependent.

Adult↗

PubMed1993

The perceived strength of motion-defined edges.

Performance on visual tasks involving the use of motion-defined contours is likely to depend on stimulus strength, but presently there are no empirical or experimental assessments of motion-defined contour strength. Therefore, a matching method was used to estimate the strength of suprathreshold motion-defined edges on a luminance-contrast scale. The perceived strength of a motion-defined contour was expressed as an equivalent luminance contrast; this allowed the use of a single scale which accommodates diverse motion-defined stimuli. Motion-defined edge strength estimated in this manner was an inverted U-shaped function of dot density and dot velocity, and spanned at least a fivefold range of edge strengths. For one observer, maximum motion-defined edge strength was equivalent to 79% luminance contrast, at least thirteen times the contrast detection threshold. The results are interpreted via a simple two-stage model for perceiving motion-defined edges.

Contrast Sensitivity↗

PubMed1992

The perceived strength of illusory contours.

Illusory contours are not well understood, partially because a lack of physical substance complicates their specification via physical standards. One solution is to gauge illusory contours with respect to luminance-defined contours, which are easily quantified physically. Accordingly, we chose a metric (perceived contrast) that expresses illusory contour strength in terms of the physical contrast of luminance-defined contours. Using this metric, adult observers adjusted the contrast of a luminance-defined contour until it matched the perceived contrast of an illusory contour. Illusory contour length, inducer size, and inducer contrast all influenced illusory contour strength. The results are adequately explained via low-level visual processes. It appears that matching paradigms can be beneficial in quantitative studies of illusory contours.

Adult↗

PubMed1991

Binocular summation in vernier acuity.

Monocular and binocular abutting line vernier acuities were measured as a function of contrast. Over a range of contrasts from near the line-detection threshold to approximately 20 times threshold, binocular vernier thresholds are lower (better) than monocular thresholds by approximately 50-60%, similar to the binocular improvement found for the detection of both a thin line and a dipole. At higher contrasts the binocular advantage diminishes, apparently as a result of saturation.

Contrast Sensitivity↗