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The ability to recognize one's own successful cognitive processing, in e.g., perceptual or memory tasks, is often referred to as metacognition. How should we quantitatively measure such ability? Here we focus on a class of measures that assess the correspondence between trial-by-trial accuracy and one's own confidence. In general, for healthy subjects endowed with metacognitive sensitivity, when one is confident, one is more likely to be correct. Thus, the degree of association between accuracy and confidence can be taken as a quantitative measure of metacognition. However, many studies use a statistical correlation coefficient (e.g., Pearson's r) or its variant to assess this degree of association, and such measures are susceptible to undesirable influences from factors such as response biases. Here we review other measures based on signal detection theory and receiver operating characteristics (ROC) analysis that are “bias free,” and relate these quantities to the calibration and discrimination measures developed in the probability estimation literature. We go on to distinguish between the related concepts of metacognitive bias (a difference in subjective confidence despite basic task performance remaining constant), metacognitive sensitivity (how good one is at distinguishing between one's own correct and incorrect judgments) and metacognitive efficiency (a subject's level of metacognitive sensitivity given a certain level of task performance). Finally, we discuss how these three concepts pose interesting questions for the study of metacognition and conscious awareness.

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Unconscious motivation in humans is often inferred but rarely demonstrated empirically. We imaged motivational processes, implemented in a paradigm that varied the amount and reportability of monetary rewards for which subjects exerted physical effort. We show that, even when subjects cannot report how much money is at stake, they nevertheless deploy more force for higher amounts. Such a motivational effect is underpinned by engagement of a specific basal forebrain region. Our findings thus reveal this region as a key node in brain circuitry that enables expected rewards to energize behavior, without the need for the subjects' awareness.Humans tend to adapt the degree of effort they expend according to the magnitude of reward they expect. Such a process has been proposed as an operant concept of motivation (1-3). Motivational processes may be obvious, as when a prospector spends days in extreme conditions seeking gold. The popular view is that motivation can also be unconscious, such that a person may be unable to report the goals or rewards that drive a particular behavior. However, empirical evidence on this issue is lacking, and the potential brain mechanisms involved in converting expected rewards into behavioral activation are poorly understood.We developed an experimental paradigm to visualize unconscious motivational processes, using functional magnetic resonance imaging. A classical approach to trigger unconscious processing is subliminal stimulation, which can be implemented by means of masking procedures. The terminology we use in this report is based on a recent taxonomy (4), in which a process is considered subliminal if it is attended but not reportable. Successful brain imaging studies of subliminal processes have focused so far on processing words (5, 6) as well as emotional stimuli (7,8). In our study, the object of masking was an incentive stimulus for a future action, represented by the amount of reward at stake. The question we asked is whether, and how, the human brain energizes behavior in proportion to subliminal incentives.We developed an incentive force task, using money as a reward: a manipulation that is consistently shown to activate reward circuits in the human brain (9-11). The exact level of motivation was manipulated by randomly assigning the amount at stake as one pound or one penny. Pictures of the corresponding coins were displayed on a computer screen at the beginning of each trial, between two screenshots of "mask" images (Fig. 1). The reportabiity * To whom correspondence should be addressed. E-mail: pessigli@ccr.jussieu.fr. Europe PMC Funders Group Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts of the monetary stakes depended on their display duration, which could be 17,50, or 100ms. The perception of the first two durations was determined as subliminal in a preliminary behavioral test, where subjects reported not seeing anything other than the mask. The third duration was consistently associated with conscious perception of the stimuli a...

By using a paradigm based on metacontrast masking, we created experimental conditions in which the subjective report of consciousness differs but the objectively measured ability to discriminate visual targets does not. This approach allowed us to study the neural correlate of consciousness while having performance levels carefully matched in healthy human subjects. A comparison of the neural activity associated with these conditions as measured by functional MRI showed that conscious perception is associated with spatially specific activity in the mid-dorsolateral prefrontal cortex (area 46). Further analysis confirms that this activation is not only free from any performance confound, but is also not driven by differences in the timing of the physical stimuli. Our results suggest that the prefrontal cortex is important for the essentially subjective aspects of conscious perception. masking B lindsight refers to the phenomenon that, after a lesion to the primary visual cortex, a subject can exhibit above-chance performance in detecting or discriminating visual stimuli in a forced-choice setting, despite the lack of acknowledged consciousness of the stimuli (1, 2). In some instances, blindsight subjects can perform at an impressively high level of accuracy (Ͼ80%) in the forced-choice task, even when the subjects believe that they are guessing. This potentially high level of performance makes blindsight an interesting case study for visual consciousness, because it indicates that it is consciousness, but not the basic capacity to process information, that is completely abolished. This dissociation of visual consciousness and performance also allows for the opportunity to compare conditions in which visual consciousness is present in one but not the other while having performance levels matched (3). This approach is particularly promising in regard to the search of the neural correlate of consciousness (NCC) because the resulting difference between the conditions cannot be explained in terms of a mere difference in performance levels. Therefore, the result would be more likely to reflect some essential properties of consciousness per se rather than simply being due to a difference in the effectiveness of information processing in regard to the visual stimuli.Here we try to apply this approach to normal human subjects, and use functional MRI (fMRI) to uncover the NCC. Attempts to unequivocally demonstrate blindsight in normal observers have proved to be controversial, resulting in findings that are sometimes hard to replicate (4-6). However, this difficulty dissolves when we consider the fact that, in brain-imaging studies, a statistical comparison between two conditions is valid so long as the factor in question differs in relative terms: we need not produce conditions in which visual consciousness is either completely present or absent. Instead of looking for a complete dissociation of performance and visual consciousness as in the case of blindsight, we set out to look for a relative difference in the level of v...

We used a recently developed protocol of transcranial magnetic stimulation (TMS), theta-burst stimulation, to bilaterally depress activity in the dorsolateral prefrontal cortex as subjects performed a visual discrimination task. We found that TMS impaired subjects' ability to discriminate between correct and incorrect stimulus judgments. Specifically, after TMS subjects reported lower visibility levels for correctly identified stimuli, as if they were less fully aware of the quality of their visual information processing. A signal detection theory analysis confirmed that the results reflect a change in metacognitive sensitivity, not just response bias. The effect was specific to metacognition; TMS did not change stimulus discrimination performance, ruling out alternative explanations such as TMS impairing visual attention. Together these results suggest that activations in the prefrontal cortex in brain imaging experiments on visual awareness are not epiphenomena, but rather may reflect a critical metacognitive process.

A recent study found that, across individuals, gray matter volume in the frontal polar region was correlated with visual metacognition capacity (i.e., how well one’s confidence ratings distinguish between correct and incorrect judgments). A question arises as to whether the putative metacognitive mechanisms in this region are also used in other metacognitive tasks involving, for example, memory. A novel psychophysical measure allowed us to assess metacognitive efficiency separately in a visual and a memory task, while taking variations in basic task performance capacity into account. We found that, across individuals, metacognitive efficiencies positively correlated between the two tasks. However, voxel-based morphometry analysis revealed distinct brain structures for the two kinds of metacognition. Replicating a previous finding, variation in visual metacognitive efficiency was correlated with volume of frontal polar regions. However, variation in memory metacognitive efficiency was correlated with volume of the precuneus. There was also a weak correlation between visual metacognitive efficiency and precuneus volume, which may account for the behavioral correlation between visual and memory metacognition (i.e., the precuneus may contain common mechanisms for both types of metacognition). However, we also found that gray matter volumes of the frontal polar and precuneus regions themselves correlated across individuals, and a formal model comparison analysis suggested that this structural covariation was sufficient to account for the behavioral correlation of metacognition in the two tasks. These results highlight the importance of the precuneus in higher-order memory processing and suggest that there may be functionally distinct metacognitive systems in the human brain.

Intention is central to the concept of voluntary action. Using functional magnetic resonance imaging, we compared conditions in which participants made self-paced actions and attended either to their intention to move or to the actual movement. When they attended to their intention rather than their movement, there was an enhancement of activity in the pre-supplementary motor area (pre-SMA). We also found activations in the right dorsal prefrontal cortex and left intraparietal cortex. Prefrontal activity, but not parietal activity, was more strongly coupled with activity in the pre-SMA. We conclude that activity in the pre-SMA reflects the representation of intention.