h~uropsyholoyru, Vol. 31, No 2. pp. 127-136, 1993. Prmted m Great Britain. 0028&3932;93 $6.00+0.00 \p 1993 Pergamon Press Ltd zyxwvutsrqpon DUAL TASK PERFORMANCE BY PATIENTS WITH LEFT OR RIGHT SPEECH DOMINANCE AS DETERMINED BY CAROTID AMYTAL TESTS BRENDA KOSAKA,* MERRILL HISCOCK,? ESTHER STRAUSS,* JUHN A. WADAS and SHERRILL PURVES~ *Department of Psychology, University of Victoria, Victoria, BC, Canada VSW 2Y2; TDepartment of Psychology, University of Houston, Houston, 77204-5341, U.S.A.; fDivision of Neurology, University Hospital, UBC Site, Vancouver, BC, Canada V6T 2Al; and $Department of Neurology, Vancouver General Hospital, Vancouver, BC, Canada V5Z lM9 (Received 13 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFED February 1991: accepted 25 Auyust 1992) Abstract-Patients who had their speech dominance determined by carotid Amytal testing were evaluated with a dual task procedure consisting of reading and finger tapping. As expected, the asymmetry of interference between tasks varied with speech dominance. Patients with left hemisphere speech tended to show greater interference in the right hand whereas patients with right hemisphere speech showed greater interference in the left hand. Since the right hemisphere dominant patients were also right-handed, the results suggest that interference effects are more closely linked to speech than to motor dominance. INTRODUCTION MOST DUAL TASK STUDIES have been conducted with normal subjects (see KINSBOURNE and HISCOCK [ 143 for a review). The efficiency of performing simultaneous tasks is thought to be related to hemispheric specialization for the particular tasks being performed [S, 131. There is some indirect evidence of favour of this notion. For example, when right-handers are asked to read and finger tap at the same time, interference is greater for the right than the left hand. This asymmetry presumably stems from the predominantly left hemispheric control of both activities. The purpose of the present study was to evaluate the validity of this model directly by testing patients who have had their cerebral speech dominance determined by the carotid Amytal test [24, 251. The dual task paradigm has undergone considerable scrutiny [6, 15, 19, 20, 231. One important issue is whether interference effects are related to motor rather than speech dominance. Some studies have found that, regardless of the subject’s hand preference, the dominant hand shows more interference than the non-dominant hand [15, 19, 231. If left- greater-than-right interference in left-handers is a pure reflection of right cerebral dominance for speech, its incidence in those studies would exceed any known incidence figure from carotid Amytal studies [17, 211 or studies of aphasia [4]. Another motor influence that may contaminate the results of dual task studies is the movement of the mouth while reading *Address for reprints: Dr B. Kosaka, Head Injury Assessment Unit, 6951 Westminister Highway, Richmond, BC, Canada V7C lC6. 127