Grating detection and orientation discrimination in amblyopia

We examined whether the misperceptions associated with amblyopic visual perception can be revealed under natural viewing conditions by comparing the ability to detect the presence of a grating with the ability to identify the grating orientation.

Grating detection and orientation discrimination performance (horizontal versus vertical) were determined, using stimuli that consisted of sinusoidal gratings of fixed contrast (75%) but with variable spatial frequency. A total of four amblyopic subjects (two strabismic and two non-strabismic) and four age-matched normals participated in the experiment.

Psychometric functions for grating detection and orientation identification were found to be closely matched in the normal subjects and in all four amblyopic subjects, indicating that orientation could be correctly identified at detection threshold.

The absence of orientation uncertainty in the psychophysical data for the amblyopic observers is not consistent with the several previous reports of spatial aliasing in the central field of amblyopes. Our results suggest that non veridical visual perception in central amblyopic vision can not be revealed under natural viewing conditions by comparing the ability to detect the presence of a grating with the ability to identify its orientation. Possible reasons for the failure of this technique to reveal spatial aliasing in amblyopes are discussed.