Independent dimension-weighting mechanisms for visual selection and stimulus identification.

Observers respond faster when the task-relevant perceptual dimension (e.g., color) repeats across consecutive trials relative to when it changes. Such dimension repetition benefits (DRBs) occur in different tasks, from singleton feature search to feature discrimination of a stimulus presented on its own. Here, we argue that the DRBs observed in different tasks originate from distinct mechanisms: preselective weighting of dimension-specific feature contrast signals and, respectively, postselective stimulus processing. The multiple-weighting-systems hypothesis predicts significant DRBs across trials of different tasks that share the same weighting mechanism, but not across tasks involving different mechanisms. Experiments 1, 2, and 3 examined DRBs across localization and detection tasks (both involving feature contrast computations); across detection and identification tasks (which presumably involved different weighting systems); and across identification and discrimination tasks (both involving stimulus identification). As expected, significant DRBs were observed across different tasks in Experiments 1 and 3, but not in Experiment 2. These findings support the multiple-weighting-systems hypothesis.