Cue summation in spatial discriminations.

We investigated the extent to which discrimination performance improves when more than a single cue distinguishes two patterns. When two simple gratings differ slightly in spatial frequency, orientation, and/or contrast, the performance of most observers is better in multiple-cue conditions than in single-cue conditions and by an amount indicating Euclidean summation of information. These results are shown to be consistent with discrimination models that integrate information over different, spatially selective pathways. However, little summation is found when the task requires integration of cues across widely separated spatial frequency bands. This result implies that information is integrated only over pathways tuned to a common region of the spatial frequency domain.