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

Abstract

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.

A neuropsychological dimension for anchoring effects

“…More importantly, with regard to interhemispheric interaction, research indicates that FS þ right-handers more closely resemble non-right-handers than they resemble FS-right-handers (Christman & Propper, 2001;Gorynia & Egenter, 2000;McKeever, VanDeventer, & Suberi, 1973). Niebauer and colleagues have reported that mixed-versus strong-handed differences are routinely enhanced when FS þ participants are excluded from analyses (Niebauer, 2004;Niebauer et al, 2002;. In addition to decreasing error variability, removing FS þ participants from a sample typically reduces the N by approximately 30-40%.…”

“…Comparable findings reviewed earlier include those of Niebauer et al (2002), where people came into the lab believing that the fake arm was not theirs, but, given appropriate visual and tactile information, mixed-handers were more likely to change beliefs and assume ownership of the fake arm. Furthermore, as one's body size and shape changes, one would assume that (given appropriate input from oneself and others) one's body image beliefs would go hand-in-hand.…”

“…As a result, people tended to update their body image representations and assume ''ownership'' of the fake arm in order to make sense of the synchronized visual and tactile stimulation. Niebauer et al (2002) reported that mixed-handers experienced the illusion both more quickly and more vividly than strongly-handed participants, and interpreted this result as reflecting greater disposition toward body image updating in mixed-handers owing to their greater interhemispheric interaction. Interestingly, the data reported by Botvinik and Cohen (1998) also suggested individual differences in this illusion, with some participants reporting the illusion as having a greater intensity than others; these variations may well have arisen at least in part from unmeasured handedness variations in their sample.…”

“…Accordingly, research shows that mixed-handers exhibit a greater ability to engage in right hemisphere-based updating of left hemisphere-based body image representations. Niebauer, Aselage, and Schutte (2002), for example, investigated individual differences in a bodily illusion, adapted from a procedure reported by Botvinik and Cohen (1998). Participants placed their left or right arm on the outside of a partition, preventing them from seeing it.…”

The evolution and genetics of cerebral asymmetry

“…A similar result was reported by Nicholls et al (2005), although Jaspers-Fayer & Peters (2005) found no relationship between handedness and magical ideation, which was nevertheless more prevalent in females with a tendency to left-right confusion, perhaps suggestive of cerebral symmetry. In a similar vein, there is evidence that mixed-handedness is associated with a greater sensitivity to sensory illusions ( Niebauer et al 2002) and a higher risk of schizophrenia (Claridge et al 1998;Upadhyay et al 2004), and strong belief in the paranormal seems to be associated with symmetrical brain activity (Pizzagalli et al 2000). Jaynes (1976) speculated that cerebral asymmetry emerged in the second millennium BC, in response to assorted catastrophes, such as floods, invasions, etc.…”