Direct injection of noise to the visual cortex decreases accuracy but increases decision confidence

Abstract

Rahnev DA, Maniscalco B, Luber B, Lau H, Lisanby SH. Direct injection of noise to the visual cortex decreases accuracy but increases decision confidence. J Neurophysiol 107: 1556 -1563, 2012. First published December 14, 2011 doi:10.1152/jn.00985.2011The relationship between accuracy and confidence in psychophysical tasks traditionally has been assumed to be mainly positive, i.e., the two typically increase or decrease together. However, recent studies have reported examples of exceptions, where confidence and accuracy dissociate from each other. Explanations for such dissociations often involve dual-channel models, in which a cortical channel contributes to both accuracy and confidence, whereas a subcortical channel only contributes to accuracy. Here, we show that a single-channel model derived from signal detection theory (SDT) can also account for such dissociations. We applied transcranial magnetic stimulation (TMS) to the occipital cortex to disrupt the internal representation of a visual stimulus. The results showed that consistent with previous research, occipital TMS decreased accuracy. However, counterintuitively, it also led to an increase in confidence ratings. The data were predicted well by a single-channel SDT model, which posits that occipital TMS increased the variance of the internal stimulus distributions. A formal model comparison analysis that used information theoretic methods confirmed that this model was preferred over single-channel models, in which occipital TMS changed the signal strength or dual-channel models, which assume two different processing routes. Thus our results show that dissociations between accuracy and confidence can, at least in some cases, be accounted for by a single-channel model.

Continuous theta burst transcranial magnetic stimulation reduces resting state connectivity between visual areas

“…To address our second question, the behavioral data were fit with a SDT model inspired by our laboratory's previous work (Rahnev et al 2011(Rahnev et al , 2012. The main idea of the modeling was that, if constant decision criteria between conditions are assumed (Gorea and Sagi 2000), then one expects different effects of decreased signal strength and increased variability.…”

“…For both experiments, we determined the PT on the first day of the respective experiment using a method similar to Rahnev et al (2012). Briefly, we first used a "hunting procedure" to determine the optimal location for stimulation on the occipital cortex.…”

“…More specifically, starting at 30% of the maximum stimulator output, we delivered single-pulse TMS until we reached the lowest intensity at which a subject reported perceiving phosphenes on 5 out of 10 trials; this intensity was chosen as the subject's PT. Throughout this procedure and subsequent application of cTBS, the main axis of the coil was oriented parallel to the sagittal plane, and the coil handle extended ventrally as in our previous work (Rahnev et al 2012).…”

“…We fit the models to the data as done previously (Rahnev et al 2011(Rahnev et al , 2012) using a maximum likelihood estimation approach that has previously been used within a signal detection framework (Dorfman and Alf 1969). The models were fit to the full distribution of probabilities of each response type contingent on each stimulus type.…”

“…We found that occipital cTBS produced decreases in performance and confidence. To address whether this effect was due to a decrease in signal strength, increase in variability, or both, we fitted the behavioral data to a signal detection theoretic model informed by our laboratory's previous work (Rahnev et al 2011(Rahnev et al , 2012. The main idea of the modeling was that, by assuming constant decision criteria between conditions, one could analytically separate the effects of signal strength and signal variability.…”