Letter-case-specific priming in the right cerebral hemisphere with a form-specific perceptual identification task.

In a form-specific perceptual identification task, subjects identify and write letter strings in the same letter case as they appear on a computer display. Letter-case-specific repetition priming was observed in this task when test items were presented directly to the right hemisphere, but not when they were presented directly to the left hemisphere, similar to results in previous word-stem completion experiments. This pattern of results was not obtained in a standard perceptual identification task. Results indicate that a specific visual-form subsystem, but not an abstract visual-form subsystem, operates more effectively in the right hemisphere than in the left, and task demands greatly affect which subsystems are recruited in different priming tests.