Hemisphere-specific processes in letter matching.

Three experiments were designed to investigate outstanding questions concerning the effect of memory load variations on efficiency and coding processes in the left and right cerebral hemispheres. In Experiment 1 subjects were presented with one, two, or three target letters in uppercase or lowercase in central vision, followed by simultaneous bilateral probes requiring a name match response. Twenty young right-handed adults, 10 males and 10 females, acted as subjects. Two main features of the results were as follows: (a) The slope of the linear function relating mean reaction time (RT) and set size was 30% greater for right visual field (RVF)-left-hemisphere probe stimuli under both physical and name identity conditions, and (b) RT for RVF-left-hemisphere probes was greater when the probe was drawn from preterminal serial position in the target list. Experiments 2 and 3 examined the proposition that the results of Experiment 1 reflected asymmetric interference during list acquisition. The results showed that, first, the LVF-right-hemisphere advantage was eliminated or reversed under unilateral probe presentation conditions, and second, the LVF-right-hemisphere advantage for a single, preterminal serial position was insensitive to variations in the interitem interval. The results are thought to be inconsistent with the interference hypothesis. The general implications of the results for existing theories of hemisphere function are discussed.