Right hemisphere language processing: Studies with normal subjects.

This project was concerned with the nature of the language ability within the right cerebral hemisphere (RH), and in particular with the idea that the RH possesses a selective ability to process highly imageable words - the RH imageability hypothesis. Nine experiments are reported in which word stimuli were presented tachistoscopically to the lateral visual fields. In Experiments 1-5 the accuracy of lateral word recognition, with oral responding, was assessed. The prediction that performance asymmetry would vary as a function of word imageability was not fulfilled, and the results suggested that several previously published studies, which have hitherto been regarded as supporting the RH imageability hypothesis, may be discounted on artifactual grounds. The design of Experiment 6 incorporated a comparative judgement task, and manual reaction time functions were plotted separately for each visual field. A rationale was developed which enabled clearcut inferences to be made concerning the hemispheric locus of the decision stage in this task. Results clearly indicated that the task of deciding which of two imageable nouns refers to the larger object is limited to the left hemisphere. Thus the results of Experiments 1-6 were consistent in suggesting that the right hemisphere does not possess a selective ability to process highly imageable words. In the remaining experiments lateral differences in performance on category matching tasks were explored. Although variation in performance asymmetry as a function of word imageability was observed in some conditions, a complex pattern of results emerged which was only very weakly supportive of the RH imageability hypothesis. The implications of these findings for the overall status of the RH imageability hypothesis were discussed.