Bilateral electrodermal activity: Effects of differential hemispheric activation

A considerable number of investigations have been carried out into the relationship between differential hemispheric activation and elecrodermal asymmetry. These have employed a wide range of tasks, whose ability to differentially activate the hemispheres is often questionable. The resulting findings are frequently negative or conflicting (Freixa i Baque et al., 1984; Hugdahl, 1984). Twenty dextral males with no family history of sinistrality took part in the study. Subjects had to make 'same/different' judgements on pairs of upper and/or lower case letters, tachistoscopically presented to the right visual field (RVF) or the left visual field (LVF). There were two conditions for each subject; in the Physical conditions subjects had to judge whether a pair of letters was physically identical (e.g. AA) or different (e.g. Am); in the Nominal condition, subjects had to judge whether a pair of letters was the same in name (e.g. Aa) or different (e.g. Ar). Conditions were counterbalanced between subjects. Subjects were instructed to indicate their judgements as fast as possible by means of a bimanual button press. Bilateral EDA was monitored throughout the task. Reaction time measures revealed the expected left hemisphere advantage in the NOMINAL task, with faster responses associated with RVF presentation. This difference was not demonstrated in the PHYSICAL task. EDA measures paralleled this finding, with the greatest asymmetries occurring in the NOMINAL task during RVF presentation. Overall, right hand skin conductance responses were significantly smaller in conditions involving left hemisphere activation than in those involving right hemisphere activation. Left hand skin conductance responses remained constant. The data are tentatively interpreted in terms of a model involving contralateral inhibitory control of electrodermal activity.