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Megan Peters; Transcranial magnetic stimulation to visual cortex induces suboptimal introspection. Journal of Vision 2017;17(10):1258. doi: 10.1167/17.10.1258.
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In neurological cases of blindsight, patients with damage to primary visual cortex can discriminate objects but report no visual experience of them. This form of 'unconscious perception' provides a powerful opportunity to study perceptual awareness, but because the disorder is rare, many researchers have sought to induce the effect in neurologically intact observers. One promising approach is to apply transcranial magnetic stimulation (TMS) to visual cortex to induce blindsight (Boyer et al., 2005), but this method has been criticized for being susceptible to criterion bias confounds: perhaps TMS merely reduces internal visual signal strength, and observers are unwilling to report that they faintly saw a stimulus even if they can still discriminate it (Lloyd et al., 2013). Here we applied a rigorous response-bias free 2-interval forced-choice method for rating subjective experience in studies of unconscious perception (Peters and Lau, 2015) to address this concern. We used Bayesian ideal observer analysis to demonstrate that observers' introspective judgments about stimulus visibility are suboptimal even when the task does not require that they maintain a response criterion -- unlike in visual masking. Specifically, observers appear metacognitively blind to the noise introduced by TMS, in a way that is akin to neurological cases of blindsight. These findings are consistent with the hypothesis that metacognitive judgments require observers to develop an internal model of the statistical properties of their own signal processing architecture, and that introspective suboptimality arises when that internal model abruptly becomes invalid due to external manipulations.
Meeting abstract presented at VSS 2017
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