Perceptual salience of global structures and the crowding effect in amblyopia

The crowding effect refers to stronger deficits in linear acuity (e.g., letters in a line) than in single letter acuity in amblyopia. The current work investigated whether the salience of a global structure in which the target for identification is embedded influences the crowding effect in amblyopia.

Compound shapes were presented to the amblyopic and fellow eyes respectively of 12 anisometropic amblyopes. The compound stimuli were presented on either a blank or a cross background so that the salience of global structures were manipulated. Reaction times (RTs) and response error rates were recorded when subjects identified global or local shapes, respectively.

RTs were shorter to global than local shapes for both the amblyopic and the fellow eyes. The global RT advantage was larger for the amblyopic than the fellow eye. Interestingly, when viewing the stimuli with the amblyopic eye, subjects made more errors to local targets when the compound stimuli were presented against the blank than the cross background.

The results suggest that the salience of global structures of visual stimuli contributes to the crowding effect in amblyopia.