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Dobromir Rahnev, Linda Bahdo, Moniek Munneke, Floris de Lange, Hakwan Lau; Theta-burst transcranial magnetic stimulation to V1 impairs subjective confidence ratings and metacognition. Journal of Vision 2010;10(7):901. doi: 10.1167/10.7.901.
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Lesions to V1 may lead to blindsight - the ability to perform visual tasks despite the absence of visual awareness. Blindsight is a controversial phenomenon, partly because it is a rare condition and researchers rely on verbal reports. Previous work has shown that brain stimulation applied during visual presentation can induce blindsight-like behavior in normal populations. Here we adopt a different approach, capitalizing on a relatively new protocol of stimulation known as theta burst stimulation (TBS). TBS has been shown to suppress visual activity for up to ∼30 minutes. During this period, we can perform intensive psychophysical testings without the tactile and auditory interference caused by brain stimulation. We used post-decisional wagering to objectively assess the effect of TBS on subjective awareness and metacognition. Subjects received TBS to the visual cortex, a control site (Pz), and sham TBS in counter-balanced sessions. Subjects performed a grating orientation task and indicated their confidence. High-confidence responses resulted in higher score when the discrimination was correct but negative score when incorrect. Subjects were told to maximize their overall score. TBS to the visual cortex resulted in a decrease both in performance and confidence. Further, we found that the TBS resulted in a lowered correlation between confidence ratings and accuracy, and this misplacement of confidence ratings led to subjects' failure to maximize their overall score. This impairment of metacognitive ability has previously been shown to be one of the hallmarks of blindsight. The current study shows that TBS to the visual cortex lowers visual performance, subjective confidence ratings, and metacognitive capacity. The fact that TBS is applied before but not during the psychophysical testing means that there is the opportunity to perform brain imaging during the task in order to further characterize the neural mechanisms that underlie these effects.
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