Psychologists have used an inventive combination of techniques to show that the left half of the brain has more self-esteem than the right half. The finding is consistent with earlier research showing that the left hemisphere is associated more with positive, approach-related emotions, whereas the right hemisphere is associated more with negative emotions.
Ryan McKay and colleagues used a version of the self-esteem 'implicit association test' (IAT). This compares how readily participants associate themselves or other people with positive words like 'capable' and negative words like 'boring'. Forty-six participants used keyboard keys to categorise words as self-related (e.g. 'me', 'myself'), other-related ('they', 'themselves'), positive or negative. To take one example, people with high self-esteem should be relatively quicker when the same response key is used to categorise self-words and positive words, than when the same key is used to categorise other-related and positive words.
A key twist to this study is that McKay's team used an auditory version of the IAT - the first time this has ever been done. Specifically, they used so-called 'dichotic presentation' such that when a word was presented via headphones to one ear, the same word was played backwards to the other ear. This has the effect of ensuring that the word is only processed by the hemisphere opposite the presenting ear, thus allowing the participants to perform the IAT test with just one hemisphere at a time.
As you'd expect, a participant's self-esteem as measured via one hemisphere tended to correlate with their self-esteem as measured via the other hemisphere. More intriguingly, however, a consistent finding was that participants clocked up higher self-esteem scores when hearing words via their right ear (processed by the left hemisphere) compared with via their left ear (processed by the right hemisphere).
Critics may point to the language dominance of the left hemisphere as a major confound, but actually this is not relevant - even if the left hemisphere were faster overall, there's no reason it should have shown a specific advantage for associating the self with positive words.
The researchers said further investigations are needed to build on this initial discovery, including lesion studies and brain imaging techniques, which 'would be useful in providing a more fine-grained assessment of the relative activation of the left versus the right hemisphere in the representation and processing of self-esteem and in providing detail concerning anterior/posterior and cortical/subcortical involvement.'
McKay, R., Arciuli, J., Atkinson, A., Bennett, E., & Pheils, E. (2010). Lateralisation of self-esteem: An investigation using a dichotically presented auditory adaptation of the Implicit Association Test. Cortex, 46 (3), 367-373 DOI: 10.1016/j.cortex.2009.05.004