Impaired spatial and binocular summation for motion direction discrimination in strabismic amblyopia

Abstract

Amblyopia is characterised by visual deficits in both spatial vision and motion perception. While the spatial deficits are thought to result from deficient processing at both low and higher level stages of visual processing, the deficits in motion perception appear to result primarily from deficits involving higher level processing. Specifically, it has been argued that the motion deficit in amblyopia occurs when local motion information is pooled spatially and that this process is abnormally susceptible to the presence of noise elements in the stimulus. Here we investigated motion direction discrimination for abruptly presented two-frame Gabor stimuli in a group of five strabismic amblyopes and five control observers. Motion direction discrimination for this stimulus is inherently noisy and relies on the signal/noise processing of motion detectors. We varied viewing condition (monocular vs. binocular), stimulus size (5.3-18.5°) and stimulus contrast (high vs. low) in order to assess the effects of binocular summation, spatial summation and contrast on task performance. No differences were found for the high contrast stimuli; however the low contrast stimuli revealed differences between the control and amblyopic groups and between fellow fixing and amblyopic eyes. Control participants exhibited pronounced binocular summation for this task (on average a factor of 3.7), whereas amblyopes showed no such effect. In addition, the spatial summation that occurred for control eyes and the fellow eye of amblyopes was significantly attenuated for the amblyopic eyes relative to fellow eyes. Our results support the hypothesis that pooling of local motion information from amblyopic eyes is abnormal and highly sensitive to noise.

Concurrent Investigation of Global Motion and Form Processing in Amblyopia: An Equivalent Noise Approach

“…In amblyopia, the deficits at the M-cell level should result in lower sensitivity at both local and global processing stages. But our results and a wide range of studies 13,14,17,41 suggest that the deficits in the motion domain are restricted mostly to the global processing level. Another explanation for the dorsal stream vulnerability in development disorders is due to the late development of the dorsal stream compared with the ventral stream functions.…”

“…The normal internal equivalent noise suggests that local motion processing is intact in both types of amblyopia, in agreement with other studies. 13,14,17,41 The direction sensitive cells stimulated by the amblyopic eye in V1 are also reported to be normal in anisometropic and strabismic primates. 40 Our finding of abnormal global processing in strabismic amblyopia is supported by previous physiological and imaging studies that reported a reduced contribution from the amblyopic eye to extra striate motion areas (MT, MST).…”

Spatial and Global Sensory Suppression Mapping Encompassing the Central 10° Field in Anisometropic Amblyopia

“…A univariate ANOVA conducted on the dichoptic suppression mapping measurements showed significant effects of eccentricity (F [4,88] ¼ 9.284, P < 0.001). Our data showed that there were significant differences among five eccentricities.…”

“…Strabismus (an eye turn), anisometropia (differences in refractive errors), or other causative factors, which occlude the visual axis (form deprivation), 1 can challenge the visual system with differing patterns of visual acuity (VA) and contrast sensitivity losses. 3,4 There is increasing attention now, on the critical role interocular suppression has among amblyopes. [5][6][7][8] Rather than adhering to a traditional monocular therapy in the form of occlusion or penalization, which is challenged by high reoccurrences of residual amblyopia, 9,10 we now aim to provide a proper binocular visual experience during therapy.…”

Visual Motion: From Cortex to Percept

“…Although amblyopia is typically regarded as a disorder of spatial vision, a number of studies have identified deficits in motion perception that appear to be independent of impairments of form perception (see Thompson et al, 2011 for a recent overview). Many of the motion deficits that have been reported are consistent with abnormalities at the level of hMT+ complex.…”