Hemispheric interaction and consciousness: degree of handedness predicts the intensity of a sensory illusion.

It has been suggested that the two cerebral hemispheres play different roles in the maintenance and updating of an individual's beliefs. In particular it has been suggested that the left hemisphere (LH) forms consistent beliefs, whereas the right hemisphere (RH) monitors for inconsistencies or anomalies in reference to these beliefs. If some threshold of inconsistencies is detected, the role of the RH is to update the LH's belief system accordingly. Handedness may reflect the degree to which the two hemispheres exchange information such that the more strongly handed an individual is, the less interhemispheric communication may take place, thus attenuating this updating process. Two studies were carried out that confronted participants with conflicting, anomalous sensory information by tapping on both the participant's real hand and a fake hand in synchrony. One conclusion would be to update the LH belief system to include the fake hand as their own and consciously experience the taps as coming from the fake hand. It was predicted that this experience would vary with handedness such that the more strongly handed a participant was, the less they would experience the sensory illusion. Study 1 supported this, with more strongly handed participants reporting lesser degrees of the illusion. A second study replicated this effect and included a variable that measured the time it took for a participant to experience the illusion. A non-significant trend was present such that more strongly handed participants were slower to experience the illusion. Last, although the illusion was felt equally in both the left and right hand conditions, correlations between handedness and the illusion were only present in the left hand condition. A model of how interhemispheric interaction may function in maintaining beliefs and consciousness is presented.