In this study, we investigated 2 possible mechanisms by which interhemispheric interaction (IHI) might facilitate performance. Twenty university students performed 3- and 4-item versions of a less complex physical identity (PI) task in which they decided whether 2 letters were perceptually identical (e.g., ‘A’ and ‘A’) and a more complex name identity (NI) task in which they decided whether 2 letters had the same name (e.g., ‘A’ and ‘a’). Consistent with prior work, IHI facilitated performance more for the relatively complex NI task than for the simpler PI task regardless of how many items were in the display. However, for each task IHI facilitated performance less in the 4-item displays than in the 3-item displays. These results indicate that IHI facilitates performance by allowing (1) a division of processing across the hemispheres, and (2) task-relevant information to be processed by a hemisphere that receives a relatively light processing load. (JINS, 2000, 6, 313–321.)