Sensitivity to synchronicity of biological motion in normal and amblyopic vision

Abstract

Amblyopia is a developmental disorder of spatial vision that results from abnormal early visual experience usually due to the presence of strabismus, anisometropia, or both strabismus and anisometropia. Amblyopia results in a range of visual deficits that cannot be corrected by optics because the deficits reflect neural abnormalities. Biological motion refers to the motion patterns of living organisms, and is normally displayed as points of lights positioned at the major joints of the body. In this experiment, our goal was twofold. We wished to examine whether the human visual system in people with amblyopia retained the higher-level processing capabilities to extract visual information from the synchronized actions of others, therefore retaining the ability to detect biological motion. Specifically, we wanted to determine if the synchronized interaction of two agents performing a dancing routine allowed the amblyopic observer to use the actions of one agent to predict the expected actions of a second agent. We also wished to establish whether synchronicity sensitivity (detection of synchronized versus desynchronized interactions) is impaired in amblyopic observers relative to normal observers. The two aims are differentiated in that the first aim looks at whether synchronized actions result in improved expected action predictions while the second aim quantitatively compares synchronicity sensitivity, or the ratio of desynchronized to synchronized detection sensitivities, to determine if there is a difference between normal and amblyopic observers. Our results show that the ability to detect biological motion requires more samples in both eyes of amblyopes than in normal control observers. The increased sample threshold is not the result of low-level losses but may reflect losses in feature integration due to undersampling in the amblyopic visual system. However, like normal observers, amblyopes are more sensitive to synchronized versus desynchronized interactions, indicating that higher-level processing of biological motion remains intact. We also found no impairment in synchronicity sensitivity in the amblyopic visual system relative to the normal visual system. Since there is no impairment in synchronicity sensitivity in either the nonamblyopic or amblyopic eye of amblyopes, our results suggest that the higher order processing of biological motion is intact.

Symmetry Detection in Visual Impairment: Behavioral Evidence and Neural Correlates

“…Similarly to the case of normal ageing, the deficit in symmetry detection observed in the amblyopic participants may be a manifestation of a broader deficit related to suboptimal high-level visual processing. In line with this, recent evidence has shown that amblyopic individuals require more samples in both eyes to detect biological motion compared to normal control observers [32]. These threshold differences did not depend on low-level losses, but likely reflected losses in feature integration due to undersampling in the amblyopic visual system.…”

Motion perception: a review of developmental changes and the role of early visual experience

“…The amblyopic eyes did exhibit elevated thresholds relative to fellow eyes and controls, but that was attributed to a greater sensitivity to the presence of noise dots rather than a selective impairment in biological motion processing (Thompson et al, 2008 ). Using a different task in which difficulty was controlled by removing dots from the point light displays, instead of adding noise, Luu and Levi ( 2013 ) recently demonstrated similar effects in observers with strabismic and anisometropic amblyopia. Observers had to decide whether two point light stimuli representing two dancers were moving in or out of synchrony with one another.…”

Global processing in amblyopia: a review

“…Although amblyopic eyes did exhibit elevated thresholds relative to fellow eyes and controls, this could be attributed to a greater sensitivity to the presence of noise dots rather than a selective impairment in biological motion processing ( Thompson et al, 2008b ). Recently, Luu and Levi (2013) used a different approach to assess biological motion perception in observers with strabismic and anisometropic amblyopia. They presented point light stimuli representing two dancers and the observers had to decide whether the dancers were moving in or out of synchrony with one another.…”