When orthogonal orientations are not processed independently.

We studied the extent to which two gratings, superimposed at orthogonal orientations, are processed independently in making spatial frequency discriminations. Our findings suggest that independence is not preserved in this task, and that it breaks down in two distinct ways: (1) judgments about one component are reduced in accuracy by the presence of the second; and (2) information about the two component gratings is not used independently in making judgments about the compound stimulus formed by them. These results place constraints on the applicability of models that assume information from spatially tuned mechanisms is directly available in performing a discrimination task.