Neural correlates of confidence during decision formation in a perceptual judgment task.

When we make a decision, we also estimate the probability that our choice is correct or accurate. This probability estimate is termed our degree of decision confidence. Recent work has reported event-related potential (ERP) correlates of confidence both during decision formation (the centro-parietal positivity component; CPP) and after a decision has been made (the error positivity component; Pe). However, there are several measurement confounds that complicate the interpretation of these findings. More recent studies that overcome these issues have so far produced conflicting results. To better characterise the ERP correlates of confidence we presented participants with a comparative brightness judgment task while recording electroencephalography. Participants judged which of two flickering squares (varying in luminance over time) was brighter on average. Participants then gave confidence ratings ranging from "surely incorrect" to "surely correct". To elicit a range of confidence ratings we manipulated both the mean luminance difference between the brighter and darker squares (relative evidence) and the overall luminance of both squares (absolute evidence). We found larger CPP amplitudes in trials with higher confidence ratings. This association was not simply a by-product of differences in relative evidence (which covaries with confidence) across trials. We did not identify postdecisional ERP correlates of confidence, except when they were artificially produced by pre-response ERP baselines. These results provide further evidence for neural correlates of processes that inform confidence judgments during decision formation.

Larger error negativity peak amplitudes for accuracy versus speed instructions may reflect more neuro-cognitive alignment, not more intense error processing.

Understanding human error processing is a highly relevant interdisciplinary goal. More than 30 years of research in this field have established the error negativity (Ne) as a fundamental electrophysiological marker of various types of erroneous decisions (e.g. perceptual, economic) and related clinically relevant variations. A common finding is that the Ne is more pronounced when participants are instructed to focus on response accuracy rather than response speed, an observation that has been interpreted as reflecting more thorough error processing. We challenge this wide-spread interpretation by demonstrating that when controlling for the level of non-event-related noise in the participant-average waveform and for single-trial peak latency variability, the significant speed-accuracy difference in the participant-average waveform vanishes. This suggests that the previously reported Ne differences may be mostly attributable to a more precise alignment of neuro-cognitive processes and not (only) to more intense error processing under accuracy instructions, opening up novel perspectives on previous findings.

Divergent effects of absolute evidence magnitude on decision accuracy and confidence in perceptual judgements.

Whether people change their mind after making a perceptual judgement may depend on how confident they are in their decision. Recently, it was shown that, when making perceptual judgements about stimuli containing high levels of 'absolute evidence' (i.e., the overall magnitude of sensory evidence across choice options), people make less accurate decisions and are also slower to change their mind and correct their mistakes. Here we report two studies that investigated whether high levels of absolute evidence also lead to increased decision confidence. We used a luminance judgment task in which participants decided which of two dynamic, flickering stimuli was brighter. After making a decision, participants rated their confidence. We manipulated relative evidence (i.e., the mean luminance difference between the two stimuli) and absolute evidence (i.e., the summed luminance of the two stimuli). In the first experiment, we found that higher absolute evidence was associated with decreased decision accuracy but increased decision confidence. In the second experiment, we additionally manipulated the degree of luminance variability to assess whether the observed effects were due to differences in perceived evidence variability. We replicated the results of the first experiment but did not find substantial effects of luminance variability on confidence ratings. Our findings support the view that decisions and confidence judgements are based on partly dissociable sources of information, and suggest that decisions initially made with higher confidence may be more resistant to subsequent changes of mind.

The relationship between response dynamics and the formation of confidence varies across the lifespan.

Accurate metacognitive judgments, such as forming a confidence judgment, are crucial for goal-directed behavior but decline with older age. Besides changes in the sensory processing of stimulus features, there might also be changes in the motoric aspects of giving responses that account for age-related changes in confidence. In order to assess the association between confidence and response parameters across the adult lifespan, we measured response times and peak forces in a four-choice flanker task with subsequent confidence judgments. In 65 healthy adults from 20 to 76 years of age, we showed divergent associations of each measure with confidence, depending on decision accuracy. Participants indicated higher confidence after faster responses in correct but not incorrect trials. They also indicated higher confidence after less forceful responses in errors but not in correct trials. Notably, these associations were age-dependent as the relationship between confidence and response time was more pronounced in older participants, while the relationship between confidence and response force decayed with age. Our results add to the notion that confidence is related to response parameters and demonstrate noteworthy changes in the observed associations across the adult lifespan. These changes potentially constitute an expression of general age-related deficits in performance monitoring or, alternatively, index a failing mechanism in the computation of confidence in older adults.

Neural correlates of metacognition across the adult lifespan.

Metacognitive accuracy describes the degree of overlap between the subjective perception of one's decision accuracy (i.e. confidence) and objectively observed performance. With older age, the need for accurate metacognitive evaluation increases; however, error detection rates typically decrease. We investigated the effect of ageing on metacognitive accuracy using event-related potentials (ERPs) reflecting error detection and confidence: the error/correct negativity (Ne/c) and the error/correct positivity (Pe/c). Sixty-five healthy adults (20 to 76 years) completed a complex Flanker task and provided confidence ratings. We found that metacognitive accuracy declined with age beyond the expected decline in task performance, while the adaptive adjustment of behaviour was well preserved. Pe amplitudes following errors varied by confidence rating, but they did not mirror the reduction in metacognitive accuracy. Ne amplitudes decreased with age for low confidence errors. The results suggest that age-related difficulties in metacognitive evaluation could be related to an impaired integration of decision accuracy and confidence information processing. Ultimately, training the metacognitive evaluation of fundamental decisions in older adults might constitute a promising endeavour.

Temporal discounting in adolescents and adults with Tourette syndrome.

Tourette syndrome is a neurodevelopmental disorder associated with hyperactivity in dopaminergic networks. Dopaminergic hyperactivity in the basal ganglia has previously been linked to increased sensitivity to positive reinforcement and increases in choice impulsivity. In this study, we examine whether this extends to changes in temporal discounting, where impulsivity is operationalized as an increased preference for smaller-but-sooner over larger-but-later rewards. We assessed intertemporal choice in two studies including nineteen adolescents (age: mean[sd] = 14.21[±2.37], 13 male subjects) and twenty-five adult patients (age: mean[sd] = 29.88 [±9.03]; 19 male subjects) with Tourette syndrome and healthy age- and education matched controls. Computational modeling using exponential and hyperbolic discounting models via hierarchical Bayesian parameter estimation revealed reduced temporal discounting in adolescent patients, and no evidence for differences in adult patients. Results are discussed with respect to neural models of temporal discounting, dopaminergic alterations in Tourette syndrome and the developmental trajectory of temporal discounting. Specifically, adolescents might show attenuated discounting due to improved inhibitory functions that also affect choice impulsivity and/or the developmental trajectory of executive control functions. Future studies would benefit from a longitudinal approach to further elucidate the developmental trajectory of these effects.

Neural correlates of error detection during complex response selection: Introduction of a novel eight-alternative response task.

Error processing in complex decision tasks should be more difficult compared to a simple and commonly used two-choice task. We developed an eight-alternative response task (8ART), which allowed us to investigate different aspects of error detection. We analysed event-related potentials (ERP; N = 30). Interestingly, the response time moderated several findings. For example, only for fast responses, we observed the well-known effect of larger error negativity (Ne) in signalled and non-signalled errors compared to correct responses, but not for slow responses. We identified at least two different error sources due to post-experimental reports and certainty ratings: impulsive (fast) errors and (slow) memory errors. Interestingly, the participants were able to perform the task and to identify both, impulsive and memory errors successfully. Preliminary evidence indicated that early (Ne-related) error processing was not sensitive to memory errors but to impulsive errors, whereas the error positivity seemed to be sensitive to both error types.

Preserved performance monitoring and error detection in left hemisphere stroke.

Depending on the lesion site, a stroke typically affects various aspects of cognitive control. While executing a task, the performance monitoring system constantly compares an intended action plan with the executed action and thereby registers inaccurate actions in case of any mismatch. When errors occur, the performance monitoring system signals the need for more cognitive control, which is most efficient when the subject notices errors rather than processing them subconsciously. The current study aimed to investigate performance monitoring and error detection in a large sample of patients with left hemisphere (LH) stroke. In addition to clinical and neuropsychological tests, 24 LH stroke patients and 32 healthy age-matched controls performed a Go/Nogo task with simultaneous electroencephalography (EEG) measurements. This set-up enabled us to compare performance monitoring at the behavioral and the neural level. EEG data were analyzed using event-related potentials [ERPs; e.g., the error-related negativity (Ne/ERN) and error positivity (Pe)] and additionally more sensitive whole-brain multivariate pattern classification analyses (MVPA). We hypothesized that LH stroke patients would show behavioural deficits in error detection when compared to healthy controls, mirrored by differences in neural signals, in particular reflected in the Pe component. Interestingly, despite clinically relevant cognitive deficits (e.g., aphasia and apraxia) including executive dysfunction (trail making test), we did not observe any behavioral impairments related to performance monitoring and error processing in the current LH stroke patients. Patients also showed similar results for Ne/ERN and Pe components, compared to the control group, and a highly similar prediction of errors from multivariate signals. ERP abnormalities during stimulus processing (i.e., N2 and P3) demonstrated the specificity of these findings in the current LH stroke patients. In contrast to previous studies, by employing a relatively large patient sample, a well-controlled experimental paradigm with a standardized error signaling procedure, and advanced data analysis, we were able to show that performance monitoring (of simple actions) is a preserved cognitive control function in LH stroke patients that might constitute a useful resource in rehabilitative therapies for re-learning impeded functions.

Neural correlates of differential finger gesture imitation deficits in left hemisphere stroke.

Behavioural studies in apraxic patients revealed dissociations between the processing of meaningful (MF) and meaningless (ML) gestures. Consequently, the existence of two differential neural mechanisms for the imitation of either gesture type has been postulated. While the indirect (semantic) route exclusively enables the imitation of MF gestures, the direct route can be used for the imitation of any gesture type, irrespective of meaning, and thus especially for ML gestures. Concerning neural correlates, it is debated which of the visuo-motor streams (i.e., the ventral steam, the ventro-dorsal stream, or the dorso-dorsal stream) supports the postulated indirect and direct imitation routes. To probe the hypotheses that regions of the dorso-dorsal stream are involved differentially in the imitation of ML gestures and that regions of the ventro-dorsal stream are involved differentially in the imitation of MF gestures, we analysed behavioural (imitation of MF and ML finger gestures) and lesion data of 293 patients with a left hemisphere (LH) stroke. Confirming previous work, the current sample of LH stroke patients imitated MF finger gestures better than ML finger gestures. The analysis using voxel-based lesion symptom mapping (VLSM) revealed that LH damage to dorso-dorsal stream areas was associated with an impaired imitation of ML finger gestures, whereas damage to ventro-dorsal regions was associated with a deficient imitation of MF finger gestures. Accordingly, the analyses of the imitation of visually uniform and thus highly comparable MF and ML finger gestures support the dual-route model for gesture imitation at the behavioural and lesion level in a substantial patient sample. Furthermore, the data show that the direct route for ML finger gesture imitation depends on the dorso-dorsal visuo-motor stream while the indirect route for MF finger gesture imitation is related to regions of the ventro-dorsal visuo-motor stream.

Anodal tDCS over left parietal cortex expedites recovery from stroke-induced apraxic imitation deficits: a pilot study.

BACKGROUND: To date, specific therapeutic approaches to expedite recovery from apraxic deficits after left hemisphere (LH) stroke remain sparse. Thus, in this pilot study we evaluated the effect of anodal transcranial direct current stimulation (tDCS) in addition to a standardized motor training on apraxic imitation deficits. METHODS: In a rehabilitation hospital, we assessed apraxic, aphasic, and motor deficits in 30 LH stroke patients before and after a five-day standard programme of motor training combined with either anodal (10 min, 2 mA; n = 14) or sham (10 min, 0 mA, n = 16) tDCS applied in a double-blind fashion over left posterior parietal cortex (PPC). Where appropriate, data were analyzed with either t-test, Fisher's exact test, or univariate/ repeated measures ANOVA. RESULTS: Compared to sham tDCS, five sessions of anodal tDCS expedited recovery from apraxic imitation deficits (p < 0.05): Already after 5 days, the anodal tDCS group showed levels of imitation performance that were achieved in the sham tDCS group after 3 months. However, the primary outcome of the study (i.e., anodal tDCS induced improvement of the total apraxia score) failed significance, and there was no significant tDCS effect on apraxia after 3 months. Anodal tDCS improved grip force (of the contra-lesional, i.e., right hand), but had no effect on aphasia. CONCLUSIONS: Data from this pilot study show that repetitive, anodal tDCS over left PPC combined with a standardized motor training expedites recovery from imitation deficits in LH stroke patients with apraxia (relative to sham stimulation). Results suggest that in patients suffering from apraxic imitation deficits a randomized controlled trial (RCT) is warranted that investigates the effects of tDCS applied over PPC in addition to a standardized motor training.

Timing independent spatial motor sequence learning is preserved in left hemisphere stroke.

During neurorehabilitation, the re-learning of motor sequences is crucial for patients with motor deficits, enabling them to master again complex movements. A recent study showed that patients with left hemisphere (LH) stroke exhibited preserved motor sequence learning (as assessed by the serial reaction time (SRT) task) when the timing of the stimuli was comparable in the training and later test phase. However, patients showed significantly smaller learning scores as compared to healthy controls when the temporal delay between the patient's motor response and the following stimulus was randomized in the test phase. We here investigated whether LH stroke patients were able to learn spatial motor sequences even if no predictable temporal information was provided (i.e., adopting random response-stimulus intervals, RSIs) already during the training phase. Twelve right-handed LH stroke patients and 18 right-handed healthy controls performed a SRT task with random RSIs to test incidental learning of a complex spatial motor sequence. Results indicate that, although the learning condition with random RSIs was more difficult than learning with predictable RSIs, LH stroke patients performed as well as healthy controls regarding sequence specific learning. Thus, data show for the first time that LH stroke patients are able to incidentally learn a spatial sequence even when no predictable temporal information is available.

Eyes versus hands: How perceived stimuli influence motor actions.

Many studies showed that biological (e.g., gaze-shifts or hand movements) and non-biological stimuli (e.g., arrows or moving points) redirect attention. Biological stimuli seem to be more suitable than non-biological to perform this task. However, the question remains if biological stimuli do have different influences on redirecting attention and if this property is dependent on how we react to those stimuli. In two separate experiments, participants interact either with a biological or a non-biological stimulus (experiment 1), or with two biological stimuli (gaze-shifts, hand movements)(experiment 2) to which they responded with two different actions (saccade, button press), either in a congruent or incongruent manner. Results from experiment 1 suggest that interacting with the biological stimulus lead to faster responses, compared to the non-biological stimulus, independent of the response type. Results from experiment 2 show longer reaction times when the depicted stimulus was not matching the response type (e.g., reacting with hand movements to a moving object or gaze-shift) compared to a matching condition, while especially the gaze-following condition (reacting with a gaze shift to a perceived gaze shift) led to the fastest responses. These results suggest that redirecting attention is not only dependent on the perceived stimulus but also on the way how those stimuli are responded to.

Error detection across the adult lifespan: Electrophysiological evidence for age-related deficits.

With increasing age, cognitive control processes steadily decline. Prior research suggests that healthy older adults have a generally intact performance monitoring system, but show specific deficits in error awareness, i.e., the ability to detect committed errors. We examined the neural processing of errors across the adult lifespan (69 participants; age range 20-72 years) by analysing the error (-related) negativity (Ne/ERN) and the error positivity (Pe) using an adapted version of the Go/Nogo task. At a stable overall error rate, higher age was associated with a greater proportion of undetected errors. While the Ne/ERN was associated with the processing of errors in general, the Pe amplitude was modulated by detected errors only. Furthermore, the Pe amplitude for detected errors was significantly smaller in older adults, in contrast to the Ne/ERN amplitude which did not show age-related changes. Structural path models suggested that through those age-related changes in Pe amplitude, an indirect effect on the performance was observed. Our results confirm and extend previous extreme-group based findings about specific deficits in error detection associated with higher age using age as a continuous predictor. Age-related reductions in Pe amplitude, associated with more undetected errors, are independent of early error processing, as evidenced by the preserved Ne/ERN.

Implicit interactions between number and space in digit-color synesthesia.

In digit-color synesthesia, a variant of grapheme-color synesthesia, digits trigger an additional color percept. Recent work on number processing in synesthesia suggests that colors can implicitly elicit numerical representations in digit-color synesthetes implying that synesthesia is bidirectional. Furthermore, morphometric investigations revealed structural differences in the parietal cortex of grapheme-color synesthetes, i.e., in the brain region where interactions between number and space occur in non-synesthetic subjects. Based upon these previous findings, we here examined whether implicitly evoked numerical representations interact with spatial representations in synesthesia in such a way that even a non-numerical, visuo-spatial task (here: line bisection) is modulated, i.e., whether synesthetes exhibit a systematic bisection bias for colored lines. Thirteen digit-color synesthetes were asked to bisect two sets of lines which were colored in their individual synesthetic colors associated with a small or a large digit, respectively. For all colored line stimuli combined, digit-color synesthetes showed--like control subjects (n = 13, matched for age, gender, IQ and handedness)--a pseudo-neglect when bisecting colored lines. Measuring the color-induced change of the bisection bias (i.e., comparing the biases when bisecting lines colored according to a small number vs those lines corresponding to a large number) revealed that only digit-color synesthetes were significantly influenced by line color. The results provide further evidence for the bidirectional nature of synesthesia and support the concept of a mental number line. In addition, they extend previous reports on bidirectionality in synesthesia by showing that even non-numerical, visuo-spatial performance can be modulated by implicit bidirectional processes.

Altered synaptic plasticity in Tourette's syndrome and its relationship to motor skill learning.

Gilles de la Tourette syndrome is a neuropsychiatric disorder characterized by motor and phonic tics that can be considered motor responses to preceding inner urges. It has been shown that Tourette patients have inferior performance in some motor learning tasks and reduced synaptic plasticity induced by transcranial magnetic stimulation. However, it has not been investigated whether altered synaptic plasticity is directly linked to impaired motor skill acquisition in Tourette patients. In this study, cortical plasticity was assessed by measuring motor-evoked potentials before and after paired associative stimulation in 14 Tourette patients (13 male; age 18-39) and 15 healthy controls (12 male; age 18-33). Tic and urge severity were assessed using the Yale Global Tic Severity Scale and the Premonitory Urges for Tics Scale. Motor learning was assessed 45 minutes after inducing synaptic plasticity and 9 months later, using the rotary pursuit task. On average, long-term potentiation-like effects in response to the paired associative stimulation were present in healthy controls but not in patients. In Tourette patients, long-term potentiation-like effects were associated with more and long-term depression-like effects with less severe urges and tics. While motor learning did not differ between patients and healthy controls 45 minutes after inducing synaptic plasticity, the learning curve of the healthy controls started at a significantly higher level than the Tourette patients' 9 months later. Induced synaptic plasticity correlated positively with motor skills in healthy controls 9 months later. The present study confirms previously found long-term improvement in motor performance after paired associative stimulation in healthy controls but not in Tourette patients. Tourette patients did not show long-term potentiation in response to PAS and also showed reduced levels of motor skill consolidation after 9 months compared to healthy controls. Moreover, synaptic plasticity appears to be related to symptom severity.