The role of the left hemisphere in decision-making

The role of the left hemisphere in decision-making processes in choice reactions to unstructured visual stimuli (Bisiach, Mini, Sterzi and Vallar, 1982) was further investigated in normal right-handed individuals. Subjects were required to provide a motor response to lateralized single dots, abstaining from giving a response when two dots were shown. In the first study, in which the disruptive effects of concurrent articulatory activity were assessed, the decision required integration of information provided to both hemispheres, as the no-go stimulus was constituted by two dots symmetrically positioned, one in each half-field. In the second study, all information relevant to the decision was available to each hemisphere, as the no-go stimulus was represented by two dots in either half-field. Since in both experiments the decision mechanism remained located in the left hemisphere, the following conclusions are drawn: (i) the right hemisphere is unable to fulfil the demands of the present decision-making task, even when either a secondary task interferes with left hemisphere processes or it has direct acces to all the relevant information; this suggests a pattern of absolute hemispheric specialization; (ii) the left hemisphere decision-making process does not rely upon any sort of articulatorily-based "inner speech" component.