Global motion perception is independent from contrast sensitivity for coherent motion direction discrimination and visual acuity in 4.5-year-old children

Abstract

Global motion processing depends on a network of brain regions that includes extrastriate area V5 in the dorsal visual stream. For this reason, psychophysical measures of global motion perception have been used to provide a behavioral measure of dorsal stream function. This approach assumes that global motion is relatively independent of visual functions that arise earlier in the visual processing hierarchy such as contrast sensitivity and visual acuity. We tested this assumption by assessing the relationships between global motion perception, contrast sensitivity for coherent motion direction discrimination (henceforth referred to as contrast sensitivity) and habitual visual acuity in a large group of 4.5-year-old children (n=117). The children were born at risk of abnormal neurodevelopment because of prenatal drug exposure or risk factors for neonatal hypoglycemia. Motion coherence thresholds, a measure of global motion perception, were assessed using random dot kinematograms. The contrast of the stimuli was fixed at 100% and coherence was varied. Contrast sensitivity was measured using the same stimuli by fixing motion coherence at 100% and varying dot contrast. Stereoacuity was also measured. Motion coherence thresholds were not correlated with contrast sensitivity or visual acuity. However, lower (better) motion coherence thresholds were correlated with finer stereoacuity (ρ=0.38, p=0.004). Contrast sensitivity and visual acuity were also correlated (ρ=-0.26, p=0.004) with each other. These results indicate that global motion perception for high contrast stimuli is independent of contrast sensitivity and visual acuity and can be used to assess motion integration mechanisms in children.

Keywords: At risk infant; Extrastriate visual cortex; Preschool vision assessment; Visual development.

Figure 1

Distribution (n = 117) of (A) motion coherence thresholds (B) log contrast sensitivity for coherent motion direction discrimination (C) visual acuity and (D) stereoacuity.

Figure 2

Relationships between motion coherence thresholds and (A) contrast sensitivity for coherent motion direction discrimination and (B) visual acuity.

Figure 3

Comparison of (A) log contrast sensitivity for coherent motion direction discrimination, (B) visual acuity, and (C) stereoacuity across four quartiles of motion coherence threshold. In panel A, horizontal lines indicate the mean log contrast sensitivity for each quartile of motion coherence threshold. Mean log contrast sensitivity values are given to the right of each data point. The error bars show standard deviation and open circles indicate outliers (values larger or smaller than 1.5 times the interquartile range). In panels B and C, horizontal lines indicate medians with the median value given to the right of each data point. In these panels, error bars show the range and open circles indicate outliers. Absent error bars indicate that no data points (excluding outliers) fell outside of the relevant box plot boundary.

Figure 4

Variation in visual acuity as a function of log contrast sensitivity for coherent motion direction discrimination quartile. Data are shown as in Figure 3B.