BRAIN AND COGNITION 36, 158–192 (1998) ARTICLE NO. BR970951 Relationships between Brain Morphology and Behavioral Measures of Hemispheric Asymmetry and Interhemispheric Interaction Joseph B. Hellige, Kristen B. Taylor, Luis Lesmes, and Suzanne Peterson University of Southern California Thirty adult males identified consonant-vowel-consonant nonword trigrams pro- jected briefly to the left visual field (right hemisphere), the right visual field (left hemisphere) or to both visual fields (and hemispheres) simultaneously. Magnetic resonance images of the brains of these same individuals provided measurements of the length of the Sylvian fissure and surface area of the planum temporale within each hemisphere as well as measurements of the midsagittal area of the corpus callosum. Both behavioral and morphological asymmetries were consistent with those found in previous studies. In addition, there were several relationships between brain morphology and trigram naming. For example, as the length of the right- hemisphere Sylvian fissure increased to become more like the typical length of the left-hemisphere Sylvian fissure, there were fewer errors of trigram identification and attention was distributed more quickly or evenly across the three letters contained in the display. In addition, as the midsagittal area of the corpus callosum increased, the percentage of errors increased on left visual field trials, but not on right visual field or bilateral trials, suggesting that an increase in corpus callosum size may be indicative of greater functional isolation of the two hemispheres.  1998 Academic Press The present study was designed to investigate relationships between cer- tain behavioral measures of brain asymmetry and aspects of brain morphol- ogy. Previous research has identified both behavioral asymmetries and mor- phological asymmetries, including reliable individual variation in both types The research reported in this manuscript was supported in part by a research grant awarded to Joseph B. Hellige from the National Science Foundation (SBR-9507924). Support for the MR images was provided by Grant RO3 MH50940-01A2 awarded to Adrian Raine from the National Institute of Mental Health. We are grateful to Marie Banich, Phil Bryden, Barbara Bulman-Fleming and an anonymous reviewer for helpful comments on an earlier version of the present article. Address correspondence and reprint requests to Joseph B. Hellige, Department of Psychol- ogy, University of Southern California, Los Angeles, CA 90089-1061. E-mail: hellige@rcf. usc.edu. 158 0278-2626/98 $25.00 Copyright  1998 by Academic Press All rights of reproduction in any form reserved.