Spatial phase sensitivity of mechanisms mediating discrimination of small orientation differences

Experiments with spatially superimposed gratings have defined mechanisms th at sum signals across spatial frequency bands while mediating discriminatio ns of small differences in orientation. In the present experiments, localiz ed stimuli (Gaussian bars and derivatives of Gaussian bars) occupying diffe rent spatial frequency bands were superimposed in different phase and locat ion relationships to assess the sensitivity of the summing mechanisms to th ese differences. Masking (loss of accuracy when a second component is added as a mask) was unaffected by differences in either phase or location (15 m in separation). Summation (increase in accuracy when both components vary t ogether) occurs for all phase relationships but is reduced by spatial separ ation. (C) 2001 Optical Society of America.