ON LANGUAGE LATERALITY IN NORMAL DEXTRALS AND SINISTRALS - RESULTS FROM THE BILATERAL OBJECT NAMING LATENCY TASK

Rasmussen and Milner [N. Y. Acad. Sci. Vol. 299, pp. 355-379, 1977] pu blished data on late-lesioned (after age 6) epileptic patients who had suffered left hemisphere lesions. They estimated that left hemisphere dominance occurred in 96% of dextrals and 70% of sinistrals. These fi gures have been regarded as valid estimates for normal dextrals and si nistrals. We administered the Bilateral Object Naming Latency Task, a verbal tachistoscopic task with very good psychometric properties, to 188 dextral and 72 sinistral normals. Results showed that 93.6% of the dextrals and 80.3% of the sinistrals were left hemisphere dominant. A consideration of results from a number of carefully conducted dichoti c listening studies suggests, as do present results, that the 70% left -dominance estimate of Rasmussen and Milner for normal sinistrals may be too low by about 10%. It is suggested that 'bilateral dominance', p resent in 15% of the epileptic sinistrals of Rasmussen and Milner, may be much less common in normal sinistrals.