Orientation unbound: dissociation of identity and orientation under rapid serial visual presentation

Participants were shown rapid sequences of three letters, flanked by digits, each rotated 0 degree, 90 degrees, 180 degrees, or 270 degrees clockwise from upright. In Experiment 1, the participants tried to report the letter that matched the orientation of an arrow, presented either before (before task) or after (after task) the sequence. A third task (total task) required them to report all of the letters. Accuracy for individual letters was significantly better in the total task than in the before task, and better in the before task than in the after task, suggesting particular difficulty in binding orientation to identity. In Experiment 2, the participants were given letter probes and were asked to indicate the orientation of the probed letter. Although report was above chance, there were frequent illusory conjunctions. Since perception of orientation must depend on prior establishment of identity, our results suggest that orientation and identity may become unbound during processing and are held in parallel storage systems.