Transcranial magnetic stimulation to visual cortex induces suboptimal introspection

Abstract

Blindsight patients with damage to the visual cortex can discriminate objects but report no conscious visual experience. This provides an intriguing opportunity to allow the study of subjective awareness in isolation from objective performance capacity. However, blindsight is rare, so one promising way to induce the effect in neurologically intact observers is to apply transcranial magnetic stimulation (TMS) to the visual cortex. Here, we used a recently-developed criterion-free method to conclusively rule out an important alternative interpretation of TMS-induced performance without awareness: that TMS-induced blindsight may be just due to conservative reporting biases for conscious perception. Critically, using this criterion-free paradigm we have previously shown that introspective judgments were optimal even under visual masking. However, here under TMS, observers were suboptimal, as if they were metacognitively blind to the visual disturbances caused by TMS. We argue that metacognitive judgments depend on observers’ internal statistical models of their own perceptual systems, and introspective suboptimality arises when external perturbations abruptly make those models invalid -- a phenomenon that may also be happening in actual blindsight.

Tuned normalization in perceptual decision-making circuits can explain seemingly suboptimal confidence behavior

“…The Tuned Normalization model can account for effects of evidence accumulation noise on task performance and confidence. (a) Rahnev and colleagues (Rahnev et al, 2012) showed that occipital TMS decreased performance but increased confidence in a visual discrimination task, in line with other studies showing similar effects as a result of TMS (Rahnev et al, 2012b;Peters et al, 2017a), inattention (Rahnev et al, 2011), and microstimulation (Fetsch et al, 2014) colleagues (Zylberberg et al, 2016). (a) The authors showed that increased stimulus volatility leads to similar objective performance but increased confidence ratings, especially at low objective performance levels.…”

“…While this optimal 'probability correct' account of confidence has enjoyed significant empirical support, it seems difficult for it to account for cases where task performance and confidence dissociate (Rahnev et al, 2011(Rahnev et al, , 2012bKoizumi et al, 2015;Maniscalco et al, 2016;Samaha et al, 2016;Peters et al, 2017a;Odegaard et al, 2018). Seemingly suboptimal behaviors have also been observed in post-decisional perceptual judgments other than confidence (Stocker and Simoncelli, 2008;Luu and Stocker, 2018), leading these authors to hypothesize that these suboptimalities may stem from limitations on computational (i.e., neural) resources or a drive towards self-consistent behavior.…”

“…It has been reported that TMS to visual cortex reduces human observers' ability to perform an objective discrimination task, but increases their confidence/visibility judgments (Rahnev et al, 2012b;Peters et al, 2017a). Another similar approach used attention to manipulate the precision of the perceptual signal (Rahnev et al, 2011).…”

“…We hypothesized that these effects all depend on a similar computational mechanism, and that the Tuned Normalization model would likely be able to predict them all. To test this, we simulated a discrimination task in which stimulus strength remained constant across two conditions, but one condition had increased levels of additive noise in evidence accumulation (Table 3), mimicking the effects of TMS (Rahnev et al, 2012b;Peters et al, 2017a), inattention (Rahnev et al, 2011), and microstimulation (Fetsch et al, 2014). We present the results in comparison to figures reproduced from Rahnev et al (Rahnev et al, 2012b), since they provide a succinct summary of this behavioral effect (Figure 4a).…”

“…Our simulation capturing the effect of increased perceptual noise due to TMS, inattention, or microstimulation focused on the representative study of (Rahnev et al, 2012b), which is conceptually similar to (Fetsch et al, 2014), (Peters et al, 2017a), and (Rahnev et al, 2011) discrimination tasks. In (Rahnev et al, 2012b), subjects performed a visual discrimination task in a control condition (vertex TMS) and a condition introducing increased perceptual noise (occipital TMS).…”