To evaluate the ability of children with amblyopia to process different kinds of stereoscopic information.

To use behavioural and functional magnetic imaging (fMRI) techniques to examine motion processing in the amblyopic and fellow eyes of children diagnosed with strabismic, anisometropic, or combined amblyopia.

Ho CS, Giaschi DE. (2007) Stereopsis-dependent deficits in maximum motion displacement in strabismic and anisometropic amblyopia.. Vision Research, 47, 2778-2785.

Direction discrimination thresholds for maximum motion displacement (D(max)) have been previously reported to be abnormal in amblyopic children [Ho, C. S., Giaschi, D. E., Boden, C., Dougherty, R., Cline, R., & Lyons, C. (2005). Deficient motion perception in the fellow eye of amblyopic children. Vision Research, 45, 1615-1627; Ho, C. S., & Giaschi, D. E. (2006). Deficient maximum motion displacement in amblyopia. Vision Research, 46, 4595-4603]. We looked at D(max) thresholds for random dot kinematograms (RDKs) biased toward low- or high-level motion mechanisms. D(max) is thought to be limited, for high-level motion mechanisms, by the efficiency of object feature tracking and probability of false matches. To reduce the influence of low-level mechanisms, we determined thresholds also for a high-pass filtered version of the RDKs. Performance did not significantly differ between strabismic and anisometropic groups with amblyopia, although both groups performed significantly worse than the age-matched control group. D(max) thresholds were higher for children with poor stereoacuity. This was significant in both anisometropic and strabismic groups, and more robust for high-pass filtered RDKs than for unfiltered RDKs. The results imply that impairment of the extra-striate dorsal stream is a likely part of the neural deficit underlying both strabismic and anisometropic amblyopia. This deficit appears to be more dependent on extent of binocularity than etiology. Our findings suggest a possible relationship between fine stereopsis, coarse stereopsis, and motion correspondence mechanisms.

Wang J, Ho C, Giaschi D. (2007) Deficient motion-defined and texture-defined figure-ground segregation in amblyopic children. Journal of Pediatric Ophthalmology and Strabismus, 44 (6), 363-371.

Purpose: Motion-defined (MD) form deficits have been reported in the fellow eye and the amblyopic eye of children with amblyopia. These findings implicate possible direction-selective motion processing and/or static figure-ground segregation deficits. Recent evidence suggests that deficient MD form perception in the fellow eye of amblyopic children may not be fully accounted for by a general motion processing deficit. This study investigates the contribution of figure-ground segregation deficits to the MD form perception deficits in amblyopia. Methods: Performance in 6 amblyopic children (5 anisometropic, 1 aniso-strabismic) and 32 control children with normal vision were assessed on MD form, texture-defined (TD) form and global motion tasks. Results: Group performance on MD and TD form tasks were significantly worse in amblyopic children than in control children. Group performance on global motion was not significantly different between the two groups. Conclusions: Our present findings suggest faulty figure-ground segregation mechanisms are likely responsible for the observed MD form perception deficits in amblyopia.

Ho C, Paul P, Asirvatham A, Cavanagh P, Cline R, Giaschi D. (2006) Abnormal spatial selection and tracking in children with amblyopia. Vision Research, 46, 3274-3283.

We assessed 13 children with unilateral amblyopia and 24 age-matched controls on one low-level and four high-level motion tasks. Children with amblyopia showed similar performance to controls in both amblyopic and fellow eyes on the low-level coherence task and two high-level tasks: 2-dot apparent motion and visual search for biological motion targets. Performance on a single-object tracking task was depressed in amblyopic eyes. Performance on a multiple-object tracking task was depressed in both amblyopic and fellow eyes. These results suggest a preservation of low-level motion perception in amblyopia, and a deficit in high-level attentive tracking.

Ho C, Giaschi D, Boden C, Dougherty R, Cline R, Lyons C. (2005) Deficient motion perception in the fellow eye of amblyopic children. Vision Research 45, 1615-1627.

The extent of motion processing deficits and M/dorsal pathway involvement in amblyopia is unclear. Fellow eye performance was assessed in amblyopic children for motion-defined (MD) form, global motion, and maximum displacement (Dmax) tasks. Group performance on MD form was significantly worse in amblyopic children than in control children. Global motion deficits were significantly related to residual binocular function. Abnormally elevated Dmax thresholds were most prevalent in children with anisometropia. Our findings from these three uncorrelated tasks implicate involvement of binocular motion-sensitive mechanisms in the neural deficits of amblyopic children with strabismic, anisometropic, and aniso-strabismic etiologies.

Ho C, Giaschi D (2005) Low-level and high-level maximum motion displacement deficits in amblyopic children. Journal of Vision 5(8):292a.

Direction discrimination thresholds for maximum motion displacement (Dmax) are not fixed values but are highly dependent on stimulus parameters. Dmax increases with reduced dot probability (Boulton & Baker, 1993; Ramachandran & Anstis, 1983) or increased dot size (Cavanagh et al., 1985; Morgan, 1992). It has been theorized that the increase in Dmax under these conditions might reflect a switch in processing from low-level to high-level motion mechanisms in normal observers (Nishida & Sato, 1995; Sato, 1998). The proposed low-level process is reliant on spatial-frequency-tuned motion detectors and the high-level process is mediated by feature matching mechanisms. To determine whether this “switch” in motion mechanisms is observed in amblyopic individuals, thresholds were obtained in both eyes of 9 children with unilateral amblyopia and 9 controls. Each subject performed the task under three random dot display parameters: 20 min size at 5% density (baseline condition), 20 min size at 0.5% density (reduced probability condition), and 1 deg size at 5% density (increased dot size condition). A significant increase in Dmax was observed for displays with reduced dot probability and increased dot size relative to baseline in both groups. However, on the baseline and reduced dot probability conditions, Dmax was significantly lower in both eyes of the amblyopic group compared to the control group. For the increased dot size condition, Dmax was significantly lower in the amblyopic eye but significantly higher in the fellow eye compared to the control group. Extent of binocularity and subtype of amblyopia were not predictive of abnormal performance in this small sample. The results suggest that amblyopic children show the expected shift from low- to high-level motion mechanisms, but both mechanisms appear to be deficient. Our findings implicate abnormal binocular motion processing mechanisms in the neural deficit underlying amblyopia.