Subjects indicated whether or not two letters presented simultaneously to the left or right visual field had the same name. On same-name trials, reaction time was faster when both letters had the same case (physically identical, or PI, pairs) than when they were of different case (name identical, or NI, pairs) and reaction time was faster for left visual field presentations than for right visual field presentations. For left visual field presentations, the letter-case effect was as large on different-name trials as on same-name trials, indicating that the NI-PI difference was not simply a physical identity effect. In contrast, for right visual field presentations, the letter-case effect was restricted to same-name trials. These qualitatively different patterns for the two visual fields are discussed in terms of hypothesized consequences of cerebral hemisphere asymmetry for information processing in the normal brain.
Hellige, J.B., Webster, R. Case effects in letter-name matching: A qualitative visual field difference. Bull. Psychon. Soc. 17, 179–182 (1981).