Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Access to consciousness of briefly presented visual events is modulated by transcranial direct current stimulation of left dorsolateral prefrontal cortex

Adaptive behaviour requires the ability to process goal-relevant events at the expense of irrelevant ones. However, perception of a relevant visual event can transiently preclude access to consciousness of subsequent events — a phenomenon called attentional blink (AB). Here we investigated involvement of the left dorsolateral prefrontal cortex (DLPFC) in conscious access, by using transcranial direct current stimulation (tDCS) to potentiate or reduce neural excitability in the context of an AB task. In a sham-controlled experimental design, we applied between groups anodal or cathodal tDCS over the left DLPFC, and examined whether this stimulation modulated the proportion of stimuli that were consciously reported during the AB period. We found that tDCS over the left DLPFC affected the proportion of consciously perceived target stimuli. Moreover, anodal and cathodal tDCS had opposing effects, and exhibited different temporal patterns. Anodal stimulation attenuated the AB, enhancing conscious report earlier in the AB period. Cathodal stimulation accentuated the AB, reducing conscious report later in the AB period. These findings support the notion that the DLPFC plays a role in facilitating information transition from the unconscious to the conscious stage of processing

Autonomic arousal and attentional orienting to visual threat are predicted by awareness

The rapid detection and evaluation of threat is of fundamental importance for survival. Theories suggest that this evolutionary pressure has driven functional adaptations in a specialized visual pathway that evaluates threat independently of conscious awareness. This is supported by evidence that threat-relevant stimuli rendered invisible by backward masking can induce physiological fear responses and modulate spatial attention. The validity of these findings has since been questioned by research using stringent, objective measures of awareness. Here, we use a modified continuous flash suppression paradigm to ask whether threatening images induce adaptive changes in autonomic arousal, attention, or perception when presented outside of awareness. In trials where stimuli broke suppression to become visible, threatening stimuli induced a significantly larger skin conductance response than nonthreatening stimuli and attracted spatial attention over scrambled images. However, these effects were eliminated in trials where observers were unaware of the stimuli. In addition, concurrent behavioral data provided no evidence that threatening images gained prioritized access to awareness. Taken together, our data suggest that the evaluation and spatial detection of visual threat are predicted by awareness

Metacognition in decision-making: Exploring age-related changes in confidence

Metacognition is a fundamental human function that supports goal-directed behaviour. By constantly monitoring and evaluating our decisions we are able to detect errors when they occur and adjust the behaviour accordingly. Metacognitive evaluations can be expressed in ratings of decision confidence or error detection reports. Humans are generally capable of forming well-calibrated estimates of their own performance, yet metacognitive abilities have been shown to be specifically affected by healthy ageing. However, the mechanisms underlying this decline remain poorly understood. This thesis aims to investigate the cognitive processes of age-related changes in perceptual metacognitive performance by combining approaches from the fields of error monitoring and decision confidence. For this, we developed a new paradigm for studying the metacognitive evaluation of errors and correct responses that was feasible for adults of all ages. While recording an electroencephalogram (EEG) and response force, a sample of 65 healthy adults from 20 to 76 years made a series of decisions in a modified version of the Flanker task and subsequently indicated how confident they felt about their decision on a four-point scale. Across two studies, conducted in the same large sample, I addressed three specific research questions: first, how is metacognitive performance affected by healthy ageing? Second, what are factors contributing to the observed decline in metacognitive performance? And third, how does an age-related decline in metacognitive performance affect subsequent behaviour? The analysis of behavioural data (Study 1a) showed that metacognitive accuracy declined significantly with older age and that this decline could not be explained by the decline in task performance alone. Independent of age, however, participants adjusted their performance according to their metacognitive evaluation of their previous decision and responded more cautiously after reporting low confidence. The analysis of electrophysiological data (Study 1b) focussed on the modulation of two correlates of error monitoring by confidence and age. The results indicated that the error/correct positivity (Pe/c), a component discussed as a marker of error detection and decision confidence, scaled with reported confidence in errors but did not show the expected modulation by age. The amplitude of the error/correct negativity (Ne/c), a marker of early error monitoring processes, also scaled with reported confidence in errors, but in contrast, was less sensitive to variations in confidence with older age. Finally, Study 2 investigated the effect of age on the relationship between confidence and two response parameters of the initial decision: response time and response force. We replicated a widely reported negative relationship between confidence and response time. Importantly, we showed, for the first time, that confidence was also negatively related to fine-grained changes in peak force, which was intuitively exerted by the participants. Notably, these associations were dependent on the accuracy of the response and changed markedly across age: the relationship between confidence and response time was only found in correct responses and was pronounced with older age, while the relationship between confidence and peak force was only found in errors and only in younger adults. Overall, these findings jointly provide novel insights deepening our understanding of the observed decline in metacognitive performance with older age. A similar modulation of the Pe/c by confidence across the lifespan suggests that the post-decisional process of accumulating evidence about the correctness of a prior decision might generally be intact until old age. Instead, the age-related decline in metacognitive accuracy appears to be related to a multitude of cognitive and neural changes, which might reflect increased noise and hence higher uncertainty in older adults’ computation of confidence. Moreover, I discuss how a metacognitive decline could manifest in real life and how recent findings offer a promising view regarding the effect of training on metacognitive performance

Partially Overlapping Neural Correlates of Metacognitive Monitoring and Metacognitive Control

Metacognition describes the process of monitoring one’s own mental states, often for the purpose of cognitive control. Previous research has investigated how metacognitive signals are generated (metacognitive monitoring), for example when people (both f/m) judge their confidence in their decisions and memories. Research has also investigated how metacognitive signals are used to influence behavior (metacognitive control), for example setting a reminder (i.e. cognitive offloading) for something you are not confident you will remember. However, the mapping between metacognitive monitoring and metacognitive control needs further study on a neural level. We used fMRI to investigate a delayed-intentions task with a reminder element, allowing human participants to use their metacognitive insight to engage metacognitive control. Using multivariate pattern analysis, we found that we could separately decode both monitoring and control, and, to a lesser extent, cross-classify between them. Therefore, brain patterns associated with monitoring and control are partially, but not fully, overlapping

Methodological Artefacts in Consciousness Science

Consciousness is scientifically challenging to study because of its subjective aspect. This leads researchers to rely on report-based experimental paradigms in order to discover neural correlates of consciousness (NCCs). I argue that the reliance on reports has biased the search for NCCs, thus creating what I call 'methodological artefacts'. This paper has three main goals: first, describe the measurement problem in consciousness science and argue that this problem led to the emergence of methodological artefacts. Second, provide a critical assessment of the NCCs put forward by the global neuronal workspace theory. Third, provide the means of dissociating genuine NCCs from methodological artefacts

Neural correlates of conscious tactile perception: An analysis of BOLD activation patterns and graph metrics

Theories of human consciousness substantially vary in the proposed spatial extent of brain activity associated with conscious perception as well as in the assumed functional alterations within the involved brain regions. Here, we investigate which local and global changes in brain activity accompany conscious somatosensory perception following electrical finger nerve stimulation, and whether there are whole-brain functional network alterations by means of graph metrics. Thirty-eight healthy participants performed a somatosensory detection task and reported their decision confidence during fMRI. For conscious tactile perception in contrast to undetected near-threshold trials (misses), we observed increased BOLD activity in the precuneus, the intraparietal sulcus, the insula, the nucleus accumbens, the inferior frontal gyrus and the contralateral secondary somatosensory cortex. For misses compared to correct rejections, bilateral secondary somatosensory cortices, supplementary motor cortex and insula showed greater activations. The analysis of whole-brain functional network topology for hits, misses and correct rejections, did not result in any significant differences in modularity, participation, clustering or path length, which was supported by Bayes factor statistics. In conclusion, for conscious somatosensory perception, our results are consistent with an involvement of (probably) domain-general brain areas (precuneus, insula, inferior frontal gyrus) in addition to somatosensory regions; our data do not support the notion of specific changes in graph metrics associated with conscious experience. For the employed somatosensory submodality of fine electrical current stimulation, this speaks for a global broadcasting of sensory content across the brain without substantial reconfiguration of the whole-brain functional network resulting in an integrative conscious experience

Neural correlates of conscious tactile perception: An analysis of BOLD activation patterns and graph metrics

Theories of human consciousness substantially vary in the proposed spatial extent of brain activity associated with conscious perception as well as in the assumed functional alterations within the involved brain regions. Here, we investigate which local and global changes in brain activity accompany conscious somatosensory perception following electrical finger nerve stimulation, and whether there are whole-brain functional network alterations by means of graph metrics. Thirty-eight healthy participants performed a somatosensory detection task and reported their decision confidence during fMRI. For conscious tactile perception in contrast to undetected near-threshold trials (misses), we observed increased BOLD activity in the precuneus, the intraparietal sulcus, the insula, the nucleus accumbens, the inferior frontal gyrus and the contralateral secondary somatosensory cortex. For misses compared to correct rejections, bilateral secondary somatosensory cortices, supplementary motor cortex and insula showed greater activations. The analysis of whole-brain functional network topology for hits, misses and correct rejections, did not result in any significant differences in modularity, participation, clustering or path length, which was supported by Bayes factor statistics. In conclusion, for conscious somatosensory perception, our results are consistent with an involvement of (probably) domain-general brain areas (precuneus, insula, inferior frontal gyrus) in addition to somatosensory regions; our data do not support the notion of specific changes in graph metrics associated with conscious experience. For the employed somatosensory submodality of fine electrical current stimulation, this speaks for a global broadcasting of sensory content across the brain without substantial reconfiguration of the whole-brain functional network resulting in an integrative conscious experience