Spatial processing of complex stimuli in the amblyopic visual system.

Thresholds for detection and discrimination of the polarity (phase) of repetitive gratings with a ramp luminance profile were compared to sine-wave thresholds in normal and amblyopic observers. In the high-frequency range (4 cy/deg), normal observers detected ramp-wave gratings when the contrast of the fundamental spatial frequency was close to its independent threshold and discriminated the polarity (phase) of the ramp when the second harmonic reached its independent threshold. For the amblyopic eyes, detection of the ramp also occurred when the contrast of the fundamental frequency was near its independent threshold. In contrast, discrimination of the polarity (phase) of the ramp required contrast levels 2 to 10 times greater than needed to detect the second harmonic. The reduced ability of the amblyopic eye to discriminate the polarity of the ramp represents an abnormality in phase processing and appears to be roughly proportional to athe reduced optotype acuity of the amblyopic eyes.