Processing deficits of motion of contrast-modulated gratings in anisometropic amblyopia

Abstract

Several studies have indicated substantial processing deficits for static second-order stimuli in amblyopia. However, less is known about the perception of second-order moving gratings. To investigate this issue, we measured the contrast sensitivity for second-order (contrast-modulated) moving gratings in seven anisometropic amblyopes and ten normal controls. The measurements were performed with non-equated carriers and a series of equated carriers. For comparison, the sensitivity for first-order motion and static second-order stimuli was also measured. Most of the amblyopic eyes (AEs) showed reduced sensitivity for second-order moving gratings relative to their non-amblyopic eyes (NAEs) and the dominant eyes (CEs) of normal control subjects, even when the detectability of the noise carriers was carefully controlled, suggesting substantial processing deficits of motion of contrast-modulated gratings in anisometropic amblyopia. In contrast, the non-amblyopic eyes of the anisometropic amblyopes were relatively spared. As a group, NAEs showed statistically comparable performance to CEs. We also found that contrast sensitivity for static second-order stimuli was strongly impaired in AEs and part of the NAEs of anisometropic amblyopes, consistent with previous studies. In addition, some amblyopes showed impaired performance in perception of static second-order stimuli but not in that of second-order moving gratings. These results may suggest a dissociation between the processing of static and moving second-order gratings in anisometropic amblyopia.

Figure 1. Illustration of stimuli used in this experiment.

(a) noise carrier, (b) first-order stimulus, (c) second-order stimulus. All stimuli are presented at screen center, subtended 2.51°×2.51°.

Figure 2. Average contrast sensitivity for the identification of the direction of first-order motion for amblyopic eyes (AE, Circles), non-amblyopic eyes (NAE, Squares), and control eyes (CE, Triangles).

Error bars represent one standard error of the mean.

Figure 3. Averaged contrast sensitivity for carriers in amblyopic eyes, non-amblyopic eyes and control eyes.

AE, amblyopic eyes; NAE, non-amblyopic eyes; CE, control eyes. *, statistically significant (p<0.05); n.s., non-significant (p>0.05). Error bars represent one standard error of the mean.

Figure 4. Average contrast sensitivity for second-order motion and static second-order stimuli for amblyopic eyes (AE, Circles), non-amblyopic eyes (NAE, Squares), and control eyes (CE, Triangles).

Error bars represent one standard error of the mean.

Figure 5. Contrast sensitivity for second-order motion at all carrier contrast levels for each amblyopic subject.

The data points for control eyes (CE, Triangles) were averaged across subjects and temporal frequencies. While the data points for amblyopic eyes (AE, Circles) and non-amblyopic eyes (NAE, Squares) were only averaged across temporal frequencies. Note that for some subjects (S3 and S6) the sensitivity for second-order motion could not be measured at some low carrier contrast levels because of the floor effect. And for some other subjects (S2, S4 and S7) the data could not be measured at the highest carrier contrast levels because in this condition the expected contrast of the noise carriers is larger than 1. Error bars represent one standard error of the mean.

Figure 6. Averaged sensitivity ratios between the amblyopic eyes (AE), non-amblyopic eyes (NAE), and control eyes (CE) for second-order motion (a) and static second-order stimuli (b).

Dash line, the value (1) used in t-test. *, statistically different from 1 (p<0.05) and a mean value lower than 1.