Spatiotemporal mechanisms for simple image feature perception in normal and amblyopic vision.

We used the method of image classification to investigate the spatiotemporal mechanisms for simple feature perception in normal and amblyopic vision. In the first experiment, we estimated the spatiotemporal mechanism for detecting a luminance increment of a bright bar embedded in spatiotemporal noise for normal and amblyopic observers. The normal template is characterized by a temporal summation zone surrounded by symmetric spatial inhibition zones and followed by a temporal inhibition zone. The abnormal amblyopic template lacks inhibition but shows normal temporal summation. Neither blurring the stimuli in space nor varying the target signal-to-noise ratios caused any significant change in the normal or amblyopic template. However, decreasing the fundamental frequency of the stimuli restored the normal template in the amblyopic eye. Furthermore, the normal periphery demonstrates a spatiotemporal template similar to that of the amblyopic eye. The second experiment mapped the spatiotemporal interaction dynamics of flankers in an orientation discrimination task. For normal peripheral vision, assimilation of the perceived target orientation into the flanker orientation (i.e., crowding) occurs at flanker locations adjacent to the target in space and around or before the target presentation in time. Cueing the target may influence the spatiotemporal interaction map, but the strongest crowding never coincides with the target presentation. The amblyopic spatiotemporal interaction map is similar to that of the normal periphery, except that in general the spatiotemporal interaction is more widely distributed around and after the target presentation. Distant flankers induced "anti-crowding" (repulsion) of perceived orientation in both normal and amblyopic vision.