Can expectancy influence hemispheric asymmetries?

We carried out three experiments with the aim of verifying a critical assum ption of Kinsbourne's (Acta Psychol., 33 (1970), 193-201; Attention and Per formance V, London: Academic press, (1975), pp. 81-96) 'dynamic' attentiona l hypothesis of hemispheric asymmetries, namely, that asymmetries arise onl y when subjects know in advance what type of stimulus and/or cognitive mode they are about to be engaged with. We used a paradigm modified from Posner (J. Exp. Psychol., 109 (1980), 160-174) to study the effects of non-spatia l 'cognitive' cueing on hemispheric asymmetries using a lexical decision an d a visuo-spatial discrimination task (acute vs. obtuse angles). While we d id not find significant overall hemispheric asymmetries with the spatial ma terial, we found a consistent advantage of the left hemisphere in the lexic al decision task. In Experiment 2 where the cue was presented in central vi sion and only the stimuli were lateralised and in Experiment 3 where both c ue and stimuli were lateralised to the same hemisphere, the left hemisphere advantage did not interact with the effect of cueing. In contrast, in Expe riment 4, where only the cue was lateralised and the stimuli were centrally presented, the left hemisphere advantage in the lexical decision task emer ged only following invalid cueing. While the results of Experiments 2 and 3 are not in keeping with Kinsbourne's hypothesis, the result of Experiment 4 shows that some pre-exposural mechanisms may indeed affect the emergence of hemispheric asymmetries. A differential susceptibility in 'disengaging' from the processing mode induced by an invalid cue might represent another interesting example of hemispheric difference. (C) 2001 Elsevier Science Lt d. All rights reserved.