Detection of mirror symmetry in random dot patterns at different eccentricities

Differences between central and eccentric vision in the detection of mirror symmetry were investigated using patterns consisting of small dots. In each trial, a dot pattern was flashed for 140 msec and the subject had to decide whether the upper and lower parts of the dot pattern contained mirror symmetric pairs or whether the dots were distributed totally randomly. Detectability of mirror symmetry declined with increasing eccentricity when the retinal size of the dot patterns was constant at different eccentricities and when the size of the patterns in eccentric vision was size-scaled by the cortical magnification factor derived from the frequency of ganglion cells (M-scaling). The drop in detectability was more rapid for constant-size patterns than for M-scaled patterns. The results seem to support the notion that the encoding of positional information in eccentric vision is inferior to that of central vision even when the test patterns are M-scaled.