Abstracts

The determination of language dominance is an important issue in the investigation of patients who are epilepsy surgical candidates. Many epilepsy centers use dichotic listening tests such as the Fused Dichotic Words Test (FDWT) for this purpose because they are readily available, repeatable, non-invasive, and are easily administered. There is evidence that language lateralization as determined by dichotic listening shows high agreement with results of intracarotid procedure (IAP) and fMRI ([italic]Epilepsia[/italic] 1999; 40: 47; [italic]Exp Brain Res[/italic] 2002; 145: 166-176). Despite the clinical utility of dichotic listening, the temporal stability of the results in epilepsy patients has not been reported. The purpose of this study was to report the test-retest reliability of the FDWT in patients with focal epilepsy.
The FDWT was administered twice to 33 epilepsy surgical candidates (15 male, 18 female); 30 were right-handed and 3 were left-handed. Mean age was 36.9 yrs (SD = 13.7; range = 9-66 yrs). Mean education level was 12.2 yrs (SD = 2.3) and mean Full Scale IQ was 92.9 (SD = 12.1). Mean test-retest interval was 2.5 days (range = 1-8 days).
The FDWT is a word perception test in which 240 pairs of rhyming words are presented simultaneously, one word to each ear, over earphones. The subject typically perceives only one word and marks it on a multiple-choice response sheet. The most sensitive score is the Miser Asymmetry score, developed specifically for fused lateralization tests. Also analyzed were: Right Ear score, Left Ear score and Total Error score.
Intraclass correlations were conducted between scores at Time 1 and Time 2. Test-retest reliabilities were: r = .86 (p[lt].001) for the Miser Asymmetry score, r = .91 (p [lt] .001) for the Right Ear score, r = .93 (p [lt] .001) for the Left Ear score, and r = .65 (p [lt].001) for Total Error score. At Time 1, 20 subjects were classified as left-hemisphere dominant, 3 were classified as right-hemisphere dominant and 10 obtained scores in the indeterminate range. At Time 2, 18 subjects were classified as left-hemisphere dominant, 2 were classified as right-hemisphere dominant and 13 obtained scores in the indeterminate range. From Time 1 to Time 2, no subjects changed classification from left-hemisphere to right-hemisphere dominance (or vice versa), although 4 subjects changed from unilateral dominance to the indeterminate range (3 from right-hemisphere dominant to indeterminate and 1 from left-hemisphere dominant to indeterminate) and one subject changed from indeterminate to right-hemisphere dominant.
All of the FDWT scores show high test-retest reliability, supporting the temporal stability of this test. Given previous evidence of the classification accuracy of the FDWT, these results support the use of this test in patients undergoing neuropsychological testing as part of a comprehensive presurgical evaluation.