Simultaneity window wider in unilateral amblyopia
The parameters of simultaneity window in patients with unilateral amblyopia are affected by disease severity, aetiology and foveal suppression status, a new study shows.
The investigators exposed 17 participants with unilateral amblyopia and 17 controls to a two-alternative forced-choice (2AFC) simultaneity judgement task to characterize the audiovisual (AV) simultaneity window.
During 2AFC task, participants judged a flash-click pair to be either simultaneous or not simultaneous; the stimuli had varying levels of signal onset asynchrony (SOA). The AV simultaneity window width, auditory-lead (click first) threshold, visual-lead (flash first) threshold and point of subjective simultaneity (PSS) were compared between cases and controls.
During binocular viewing, the AV simultaneity width in the amblyopia patients was significantly widened by 37 percent (134 ms; p=0.002) compared to controls. The auditory-lead and visual-lead was wider by 36 (48 ms; p=0.002) and 37 (86 ms; p=0.02) percent, respectively.
Those with moderate amblyopia showed widening of only the auditory-lead threshold by 33 percent (45 ms; p=0.032) compared with controls. The other parameters were not significantly different.
On the other hand, those with severe amblyopia showed broadened auditory-lead threshold (38 percent; p=0.03), visual lead threshold (67 percent; p=0.003) and AV simultaneity window (57 percent; p=0.001) compared to the controls.
Those with anisometropicaetiology had significantly wider auditory-lead threshold (56 percent; p<0.001) and AV simultaneity windows (37 percent; p=0.025) compared with controls. The visual-lead threshold and PSS were not significantly changed.
On the other hand, those with strabismic/mixed aetiologies had larger visual-lead thresholds (32 percent; p=0.032) and AV simultaneity windows (36 percent; p=0.033) compared with controls. The PSS and auditory-lead thresholds were not changed.
Participants with foveal suppression had significantly wider AV simultaneity windows (48 percent; p=0.014) and visual-lead thresholds (68 percent; p=0.011) than controls. In contrast, those without suppression have broader AV simultaneity windows (32 percent; p=0.033) and auditory-lead thresholds (43 percent; p=0.002) compared with controls.