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Matthew Davidson, Olga Felsovalyi, Amy Trongnetrpunya, Xiuyuan Wang, Hakwan Lau, Thomas Thesen; Different physiological correlates for perceptual decisions and confidence ratings support multi-stage theories. Journal of Vision 2011;11(11):879. doi: 10.1167/11.11.879.
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Both human and animal observers are capable of giving meaningful subjective ratings (e.g., confidence) in perceptual tasks. Recently, neurons have been identified in primate parietal cortex that code for both confidence and accuracy (Kiani & Shadlen, Science, 2009). However, current psychophysical models suggest that subjective ratings may depend on a later stage that is dissociable from the decision regarding stimulus identity (Pleskac & Busemeyer, Psych. Rev., 2010; Maniscalco et al., J. Vis., 2010).
To test for a dissociation, we asked subjects to discriminate between degraded pictures of faces versus houses, and rate their confidence in each trial. We capitalized on the opportunity to directly record electrical activity from the cortex in presurgical epilepsy patients. This method, unlike conventional EEG, allows us to effectively examine activity at high gamma frequencies (>60 Hz), which are known to closely reflect localized neuronal processing in humans.
Like Kiani & Shadlen (2009), we identified activity in the parietal cortex that commonly reflects confidence and accuracy. However, such common activity was found in the prefrontal cortex too. In early sensory regions, we also found a dissociation between confidence and accuracy, with early occipital activity (150–250 ms) most crucial for accuracy and later inferotemporal activity (250–400 ms) more important for confidence.
We have previously shown that attention can enhance discrimination accuracy but, counter-intuitively, lowers confidence (Rahnev et al., J. Vis., 2009). We capitalized on this effect to further distinguish between mechanisms for confidence and accuracy. Here we examined pre-stimulus neural activity, as this may reflect spontaneous fluctuation of attention. Consistent with our previous findings, we found that trials with higher theta band (4–7 Hz) power in the prefrontal cortex were associated with lower confidence, but a trend for higher accuracy.
Taken together, our results suggest that subjective confidence may depend on late stage mechanisms that are distinct from basic perceptual decision making.
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