Social cues conveyed by the human face, such as eye gaze direction, are evaluated even before they are consciously perceived. While there is substantial individual variability in such evaluation, its neural basis is unknown. Here we asked whether individual differences in preconscious evaluation of social face traits were associated with local variability in brain structure. Adult human participants (n = 36) monocularly viewed faces varying in dominance and trustworthiness, which were suppressed from awareness by a dynamic noise pattern shown to the other eye. The time taken for faces to emerge from suppression and become visible (t2e) was used as a measure of potency in competing for visual awareness. Both dominant and untrustworthy faces resulted in slower t2e than neutral faces, with substantial individual variability in these effects. Individual differences in t2e were correlated with gray matter volume in right insula for dominant faces, and with gray matter volume in medial prefrontal cortex, right temporoparietal junction and bilateral fusiform face area for untrustworthy faces. Thus, individual differences in preconscious social processing can be predicted from local brain structure, and separable correlates for facial dominance and untrustworthiness suggest distinct mechanisms of preconscious processing.
Individual differences in the structure of parietal and prefrontal cortex predict the stability of bistable visual perception. However, the mechanisms linking such individual differences in brain structures to behaviour remain elusive. Here we demonstrate a systematic relationship between the dynamics of brain activity, cortical structure and behaviour underpinning bistable perception. Using fMRI in humans, we find that the activity dynamics during bistable perception are well described as fluctuating between three spatially distributed energy minimums: visual-area-dominant, frontal-area-dominant and intermediate states. Transitions between these energy minimums predicted behaviour, with participants whose brain activity tend to reflect the visual-area-dominant state exhibiting more stable perception and those whose activity transits to frontal-area-dominant states reporting more frequent perceptual switches. Critically, these brain activity dynamics are correlated with individual differences in grey matter volume of the corresponding brain areas. Thus, individual differences in the large-scale dynamics of brain activity link focal brain structure with bistable perception.
During binocular rivalry, visual perception alternates spontaneously between two different monocular images. Such perceptual reversals are slowed or halted if stimuli are presented intermittently with inter-stimulus intervals larger than ~400 ms--a phenomenon called stabilization. Often, the neural correlates of reversal and stabilization are studied separately, and both phenomena in turn are studied separately from the neural correlates of conscious perception. To distinguish the neural correlates of perceptual content, stabilization and reversal, we recorded MEG signals associated with each in the same group of healthy humans observing repeated trials of intermittent presentation of a dichoptic stimulus. Perceptual content correlated mainly with modulation of stimulus-specific activity in occipital/temporal areas 150-270 ms after stimulus onset, possibly reflecting inhibition of the neural populations representing the suppressed image. Stability of perception reflected a gradual build-up of this modulation across at least 10 trials and was also, to some extent, associated with parietal activity 40-90 ms and 220-270 ms after stimulus onset. Perceptual reversals, in contrast, were associated with parietal (150-270 ms) and temporal (150-210 ms) activity on the trial before the reversal and a gradual change in perception-specific activity in occipital (150-270 ms) and temporal (220-420 ms) areas across at least 10 trials leading up to a reversal. Mechanistically, these findings suggest that stability of perception during rivalry is maintained by modulation of activity related to the two monocular images, and gradual adaptation of neuronal populations leads to instability that is eventually resolved by signals from parietal and late sensory cortices.
Structural brain differences in relation to expertise have been demonstrated in a number of domains including visual perception, spatial navigation, complex motor skills and musical ability. However no studies have assessed the structural differences associated with representational skills in visual art. As training artists are inclined to be a heterogeneous group in terms of their subject matter and chosen media, it was of interest to investigate whether there would be any consistent changes in neural structure in response to increasing representational drawing skill. In the current study a cohort of 44 graduate and post-graduate art students and non-art students completed drawing tasks. Scores on these tasks were then correlated with the regional grey and white matter volume in cortical and subcortical structures. An increase in grey matter density in the left anterior cerebellum and the right medial frontal gyrus was observed in relation to observational drawing ability, whereas artistic training (art students vs. non-art students) was correlated with increased grey matter density in the right precuneus. This suggests that observational drawing ability relates to changes in structures pertaining to fine motor control and procedural memory, and that artistic training in addition is associated with enhancement of structures pertaining to visual imagery. The findings corroborate the findings of small-scale fMRI studies and provide insights into the properties of the developing artistic brain.
The ability to estimate durations varies across individuals. Although previous studies have reported that individual differences in perceptual skills and cognitive capacities are reflected in brain structures, it remains unknown whether timing abilities are also reflected in the brain anatomy. Here, we show that individual differences in the ability to estimate subsecond and suprasecond durations correlate with gray matter (GM) volume in different parts of cortical and subcortical areas. Better ability to discriminate subsecond durations was associated with a larger GM volume in the bilateral anterior cerebellum, whereas better performance in estimating the suprasecond range was associated with a smaller GM volume in the inferior parietal lobule. These results indicate that regional GM volume is predictive of an individual's timing abilities. These morphological results support the notion that subsecond durations are processed in the motor system, whereas suprasecond durations are processed in the parietal cortex by utilizing the capacity of attention and working memory to keep track of time.
Can subjective belief about one's own perceptual competence change one's perception? To address this question, we investigated the influence of self-efficacy on sensory discrimination in two low-level visual tasks: contrast and orientation discrimination. We utilised a pre-post manipulation approach whereby two experimental groups (high and low self-efficacy) and a control group made objective perceptual judgments on the contrast or the orientation of the visual stimuli. High and low self-efficacy were induced by the provision of fake social-comparative performance feedback and fictional research findings. Subsequently, the post-manipulation phase was performed to assess changes in visual discrimination thresholds as a function of the self-efficacy manipulations. The results showed that the high self-efficacy group demonstrated greater improvement in visual discrimination sensitivity compared to both the low self-efficacy and control groups. These findings suggest that subjective beliefs about one's own perceptual competence can affect low-level visual processing.
Media multitasking, or the concurrent consumption of multiple media forms, is increasingly prevalent in today's society and has been associated with negative psychosocial and cognitive impacts. Individuals who engage in heavier media-multitasking are found to perform worse on cognitive control tasks and exhibit more socio-emotional difficulties. However, the neural processes associated with media multi-tasking remain unexplored. The present study investigated relationships between media multitasking activity and brain structure. Research has demonstrated that brain structure can be altered upon prolonged exposure to novel environments and experience. Thus, we expected differential engagements in media multitasking to correlate with brain structure variability. This was confirmed via Voxel-Based Morphometry (VBM) analyses: Individuals with higher Media Multitasking Index (MMI) scores had smaller gray matter density in the anterior cingulate cortex (ACC). Functional connectivity between this ACC region and the precuneus was negatively associated with MMI. Our findings suggest a possible structural correlate for the observed decreased cognitive control performance and socio-emotional regulation in heavy media-multitaskers. While the cross-sectional nature of our study does not allow us to specify the direction of causality, our results brought to light novel associations between individual media multitasking behaviors and ACC structure differences.
Individual differences in adult human brain structure have been found to reveal a great deal of information about variability in behaviors, cognitive abilities and mental and physical health. Driven by such evidence, what contributes to individual variation in brain structure has gained accelerated attention as a research question. Findings thus far appear to support the notion that an individual's brain architecture is determined largely by genetic and environmental influences. This review aims to evaluate the empirical literature on whether and how genes and the environment contribute to individual differences in brain structure. It first considers how genetic and environmental effects may separately contribute to brain morphology, by examining evidence from twin, genome-wide association, cross-sectional and longitudinal studies. Next, evidence for the influence of the complex interplay between genetic and environmental factors, characterized as gene-environment interactions and correlations, is reviewed. In evaluating the extant literature, this review will conclude that both genetic and environmental factors play critical roles in contributing to individual variability in brain structure.
How do our abilities to process number and other continuous quantities such as time and space relate to each other? Recent evidence suggests that these abilities share common magnitude processing and neural resources, although other findings also highlight the role of dimension-specific processes. To further characterize the relation between number, time, and space, we first examined them in a population with a developmental numerical dysfunction (developmental dyscalculia) and then assessed the extent to which these abilities correlated both behaviorally and anatomically in numerically normal participants. We found that (1) participants with dyscalculia showed preserved continuous quantity processing and (2) in numerically normal adults, numerical and continuous quantity abilities were at least partially dissociated both behaviorally and anatomically. Specifically, gray matter volume correlated with both measures of numerical and continuous quantity processing in the right TPJ; in contrast, individual differences in number proficiency were associated with gray matter volume in number-specific cortical regions in the right parietal lobe. Together, our new converging evidence of selective numerical impairment and of number-specific brain areas at least partially distinct from common magnitude areas suggests that the human brain is equipped with different ways of quantifying the outside world.
Visual perception depends strongly on spatial context. A classic example is the tilt illusion where the perceived orientation of a central stimulus differs from its physical orientation when surrounded by tilted spatial contexts. Here we show that such contextual modulation of orientation perception exhibits trait-like interindividual diversity that correlates with interindividual differences in effective connectivity within human primary visual cortex. We found that the degree to which spatial contexts induced illusory orientation perception, namely, the magnitude of the tilt illusion, varied across healthy human adults in a trait-like fashion independent of stimulus size or contrast. Parallel to contextual modulation of orientation perception, the presence of spatial contexts affected effective connectivity within human primary visual cortex between peripheral and foveal representations that responded to spatial context and central stimulus, respectively. Importantly, this effective connectivity from peripheral to foveal primary visual cortex correlated with interindividual differences in the magnitude of the tilt illusion. Moreover, this correlation with illusion perception was observed for effective connectivity under tilted contextual stimulation but not for that under iso-oriented contextual stimulation, suggesting that it reflected the impact of orientation-dependent intra-areal connections. Our findings revealed an interindividual correlation between intra-areal connectivity within primary visual cortex and contextual influence on orientation perception. This neurophysiological-perceptual link provides empirical evidence for theoretical proposals that intra-areal connections in early visual cortices are involved in contextual modulation of visual perception.
Improvement in performance following cognitive training is known to be further enhanced when coupled with brain stimulation. Here we ask whether training-induced changes can be maintained long term and, crucially, whether they can extend to other related but untrained skills. We trained overall 40 human participants on a simple and well established paradigm assessing the ability to discriminate numerosity--or the number of items in a set--which is thought to rely on an "approximate number sense" (ANS) associated with parietal lobes. We coupled training with parietal stimulation in the form of transcranial random noise stimulation (tRNS), a noninvasive technique that modulates neural activity. This yielded significantly better and longer lasting improvement (up to 16 weeks post-training) of the precision of the ANS compared with cognitive training in absence of stimulation, stimulation in absence of cognitive training, and cognitive training coupled to stimulation to a control site (motor areas). Critically, only ANS improvement induced by parietal tRNS + Training transferred to proficiency in other parietal lobe-based quantity judgment, i.e., time and space discrimination, but not to quantity-unrelated tasks measuring attention, executive functions, and visual pattern recognition. These results indicate that coupling intensive cognitive training with tRNS to critical brain regions resulted not only in the greatest and longer lasting improvement of numerosity discrimination, but importantly in this enhancement being transferable when trained and untrained abilities are carefully chosen to share common cognitive and neuronal components.
Interpersonal touch is a fundamental component of social interactions because it can mitigate physical and psychological distress. To reproduce the psychological and physiological effects associated with interpersonal touch, interest is growing in introducing tactile sensations to communication devices. However, it remains unknown whether physical contact with such devices can produce objectively measurable endocrine effects like real interpersonal touching can. We directly tested this possibility by examining changes in stress hormone cortisol before and after a conversation with a huggable communication device. Participants had 15-minute conversations with a remote partner that was carried out either with a huggable human-shaped device or with a mobile phone. Our experiment revealed significant reduction in the cortisol levels for those who had conversations with the huggable device. Our approach to evaluate communication media with biological markers suggests new design directions for interpersonal communication media to improve social support systems in modern highly networked societies.
Recent research indicates that human attention appears inadvertently biased by items that match the contents of working memory (WM). WM-biases can lead to attentional costs when the memory content matches goal-irrelevant items and to attentional benefits when it matches the sought target. Here we used functional and structural MRI data to determine the neural basis of human variation in WM biases. We asked whether human variation in WM-benefits and WM-costs merely reflects the process of attentional capture by the contents of WM or whether variation in WM biases may be associated with distinct forms of cognitive control over internal WM signals based on selection goals. Human ability to use WM contents to facilitate selection was positively correlated with gray matter volume in the left superior posterior parietal cortex (PPC), while the ability to overcome interference by WM-matching distracters was associated with the left inferior PPC in the anterior IPS. Functional activity in the left PPC, measured by functional MRI, also predicted the magnitude of WM-costs on selection. Both structure and function of left PPC mediate the expression of WM biases in human visual attention.
Anthropomorphism is the attribution of human characteristics or behaviour to animals, non-living things or natural phenomena. It is pervasive among humans, yet nonetheless exhibits a high degree of inter-individual variability. We hypothesized that brain areas associated with anthropomorphic thinking might be similar to those engaged in the attribution of mental states to other humans, the so-called theory of mind or mentalizing network. To test this hypothesis, we related brain structure measured using magnetic resonance imaging in a sample of 83 healthy young adults to a simple, self-report questionnaire that measured the extent to which our participants made anthropomorphic attributions about non-human animals and non-animal stimuli. We found that individual differences in anthropomorphism for non-human animals correlated with the grey matter volume of the left temporoparietal junction, a brain area involved in mentalizing. Our data support previous work indicating a link between areas of the brain involved in attributing mental states to other humans and those involved in anthropomorphism.
The brain has limited capacity, and so selective attention enhances relevant incoming information while suppressing irrelevant information. This process is not always successful, and the frequency of such cognitive failures varies to a large extent between individuals. Here we hypothesised that individual differences in cognitive failures might be reflected in inhibitory processing in the sensory cortex. To test this hypothesis, we measured GABA in human visual cortex using MR spectroscopy and found a negative correlation between occipital GABA (GABA+/Cr ratio) and cognitive failures as measured by an established cognitive failures questionnaire (CFQ). For a second site in parietal cortex, no correlation between CFQ score and GABA+/Cr ratio was found, thus establishing the regional specificity of the link between occipital GABA and cognitive failures. We further found that grey matter volume in the left superior parietal lobule (SPL) correlated with cognitive failures independently from the impact of occipital GABA and together, occipital GABA and SPL grey matter volume statistically explained around 50% of the individual variability in daily cognitive failures. We speculate that the amount of GABA in sensory areas may reflect the potential capacity to selectively suppress irrelevant information already at the sensory level, or alternatively that GABA influences the specificity of neural representations in visual cortex thus improving the effectiveness of successful attentional modulation.
Eudaimonic well-being reflects traits concerned with personal growth, self-acceptance, purpose in life and autonomy (among others) and is a substantial predictor of life events, including health. Although interest in the aetiology of eudaimonic well-being has blossomed in recent years, little is known of the underlying neural substrates of this construct. To address this gap in our knowledge, here we examined whether regional gray matter (GM) volume was associated with eudaimonic well-being. Structural magnetic resonance images from 70 young, healthy adults who also completed Ryffs 42-item measure of the six core facets of eudaimonia, were analysed with voxel-based morphometry techniques. We found that eudaimonic well-being was positively associated with right insular cortex GM volume. This association was also reflected in three of the sub-scales of eudaimonia: personal growth, positive relations and purpose in life. Positive relations also showed a significant association with left insula volume. No other significant associations were observed, although personal growth was marginally associated with left insula, and purpose in life exhibited a marginally significant negative association with middle temporal gyrus GM volume. These findings are the first to our knowledge linking eudaimonic well-being with regional brain structure.
Practice-dependent changes in brain structure can occur in task relevant brain regions as a result of extensive training in complex motor tasks and long-term cognitive training but little is known about the impact of visual perceptual learning on brain structure. Here we studied the effect of five days of visual perceptual learning in a motion-color conjunction search task using anatomical MRI. We found rapid changes in gray matter volume in the right posterior superior temporal sulcus, an area sensitive to coherently moving stimuli, that predicted the degree to which an individuals performance improved with training. Furthermore, behavioral improvements were also predicted by volumetric changes in an extended white matter region underlying the visual cortex. These findings point towards quick and efficient plastic neural mechanisms that enable the visual brain to deal effectively with changing environmental demands.
It has been proposed that numerical and temporal information are processed by partially overlapping magnitude systems. Interactions across different magnitude domains could occur both at the level of perception and decision-making. However, their neural correlates have been elusive. Here, using functional magnetic resonance imaging in humans, we show that the right intraparietal cortex (IPC) and inferior frontal gyrus (IFG) are jointly activated by duration and numerosity discrimination tasks, with a congruency effect in the right IFG. To determine whether the IPC and the IFG are involved in response conflict (or facilitation) or modulation of subjective passage of time by numerical information, we examined their functional roles using transcranial magnetic stimulation (TMS) and two different numerosity-time interaction tasks: duration discrimination and time reproduction tasks. Our results show that TMS of the right IFG impairs categorical duration discrimination, whereas that of the right IPC modulates the degree of influence of numerosity on time perception and impairs precise time estimation. These results indicate that the right IFG is specifically involved at the categorical decision stage, whereas bleeding of numerosity information on perception of time occurs within the IPC. Together, our findings suggest a two-stage model of numerosity-time interactions whereby the interaction at the perceptual level occurs within the parietal region and the interaction at categorical decisions takes place in the prefrontal cortex.
Several large imaging-genetics consortia aim to identify genetic variants influencing subcortical brain volumes. We investigated the extent to which genetic variation accounts for the variation in subcortical volumes, including thalamus, amygdala, putamen, caudate nucleus, globus pallidus and nucleus accumbens and obtained the stability of these brain volumes over a five-year period. The heritability estimates for all subcortical regions were high, with the highest heritability estimates observed for the thalamus (.80) and caudate nucleus (.88) and lowest for the left nucleus accumbens (.44). Five-year stability was substantial and higher for larger [e.g., thalamus (.88), putamen (.86), caudate nucleus (.87)] compared to smaller [nucleus accumbens (.45)] subcortical structures. These results provide additional evidence that subcortical structures are promising starting points for identifying genetic variants that influence brain structure.
Previous studies indicate that conscious face perception may be related to neural activity in a large time window around 170-800 msec after stimulus presentation, yet in the majority of these studies changes in conscious experience are confounded with changes in physical stimulation. Using multivariate classification on MEG data recorded when participants reported changes in conscious perception evoked by binocular rivalry between a face and a grating, we showed that only MEG signals in the 120-320 msec time range, peaking at the M170 around 180 msec and the P2m at around 260 msec, reliably predicted conscious experience. Conscious perception could not only be decoded significantly better than chance from the sensors that showed the largest average difference, as previous studies suggest, but also from patterns of activity across groups of occipital sensors that individually were unable to predict perception better than chance. In addition, source space analyses showed that sources in the early and late visual system predicted conscious perception more accurately than frontal and parietal sites, although conscious perception could also be decoded there. Finally, the patterns of neural activity associated with conscious face perception generalized from one participant to another around the times of maximum prediction accuracy. Our work thus demonstrates that the neural correlates of particular conscious contents (here, faces) are highly consistent in time and space within individuals and that these correlates are shared to some extent between individuals.
The ability to estimate duration is essential to human behavior, yet people vary greatly in their ability to estimate time and the brain structures mediating this inter-individual variability remain poorly understood. Here, we showed that inter-individual variability in duration estimation was highly correlated across visual and auditory modalities but depended on the scale of temporal duration. We further examined whether this inter-individual variability in estimating durations of different supra-second time scales (2 or 12?s) was reflected in variability in human brain anatomy. We found that the gray matter volume in both the right posterior lateral sulcus encompassing primary auditory and secondary somatosensory cortex, plus parahippocampal gyrus strongly predicted an individuals ability to discriminate longer durations of 12?s (but not shorter ones of 2?s) regardless of whether they were presented in auditory or visual modalities. Our findings suggest that these brain areas may play a common role in modality-independent time discrimination. We propose that an individuals ability to discriminate longer durations is linked to self-initiated rhythm maintenance mechanisms relying on the neural structure of these modality-specific sensory and parahippocampal cortices.
Synesthesia is a rare condition in which stimulation in one modality leads to a secondary experience in another sensory modality. Varying accounts attribute the condition to either neuroanatomical differences between the synesthetes and non-synesthetes or functional differences in how sensory brain regions interact. This study employed voxel-based morphometry to examine whether synesthetes who experience both grapheme-color and tone-color synesthesia as their evoked sensation show neuroanatomical differences in gray matter volume compared to non-synesthetes. We observed that synesthetes showed an increase in gray matter volume in left posterior fusiform gyrus (FG), but a concomitant decrease in anterior regions of left FG and left MT/V5. These findings imply that synesthesia for color is linked to neuroanatomical changes between adjacent regions of the visual system.
Chemical reactions between hydrogen terminated Si(001)2 x 1 surface and impinging H radical are investigated by means of first-principles molecular-dynamics simulations. Reaction probabilities of abstraction of surface terminating H atom with H2 formation, adsorption onto Si surface and reflection of impinging H atom are analyzed with respect to the kinetic energy of incident H radical. The probabilities of abstraction and adsorption turn out to be ranging from 0.81 to 0.58 and from 0.19 to 0.42, respectively, while that of reflection almost zero. As initial kinetic energy of the impinging atom increases, the reaction probability of abstraction decreases and that of absorption increases. Metastable H-absorbed atomic configurations are also derived by optimizing the structures obtained in the impinging dynamics calculations. They are candidates of the so-called reservoir site which is a key to understand the unity hydrogen coverage observed after an exposure to gaseous H atom ambient despite existing residual vacant sites due to abstraction.
The human brain exhibits remarkable interindividual variability in cortical architecture. Despite extensive evidence for the behavioral consequences of such anatomical variability in individual cortical regions, it is unclear whether and how different cortical regions covary in morphology. Using a novel approach that combined noninvasive cortical functional mapping with whole-brain voxel-based morphometric analyses, we investigated the anatomical relationship between the functionally mapped visual cortices and other cortical structures in healthy humans. We found a striking anticorrelation between the gray matter volume of primary visual cortex and that of anterior prefrontal cortex, independent from individual differences in overall brain volume. Notably, this negative correlation formed along anatomically separate pathways, as the dorsal and ventral parts of primary visual cortex showed focal anticorrelation with the dorsolateral and ventromedial parts of anterior prefrontal cortex, respectively. Moreover, a similar inverse correlation was found between primary auditory cortex and anterior prefrontal cortex, but no anatomical relationship was observed between other visual cortices and anterior prefrontal cortex. Together, these findings indicate that an anatomical trade-off exists between primary sensory cortices and anterior prefrontal cortex as a possible general principle of human cortical organization. This new discovery challenges the traditional view that the sizes of different brain areas simply scale with overall brain size and suggests the existence of shared genetic or developmental factors that contributes to the formation of anatomically and functionally distant cortical regions.
We all appreciate that some of our friends and colleagues are more distractible than others. This variability can be captured by pencil and paper questionnaires in which individuals report such cognitive failures in their everyday life. Surprisingly, these self-report measures have high heritability, leading to the hypothesis that distractibility might have a basis in brain structure. In a large sample of healthy adults, we demonstrated that a simple self-report measure of everyday distractibility accurately predicted gray matter volume in a remarkably focal region of left superior parietal cortex. This region must play a causal role in reducing distractibility, because we found that disrupting its function with transcranial magnetic stimulation increased susceptibility to distraction. Finally, we showed that the self-report measure of distractibility reliably predicted our laboratory-based measure of attentional capture. Our findings distinguish a critical mechanism in the human brain causally involved in avoiding distractibility, which, importantly, bridges self-report judgments of cognitive failures in everyday life and a commonly used laboratory measure of distractibility to the structure of the human brain.
Inter-individual variability in perception, thought and action is frequently treated as a source of noise in scientific investigations of the neural mechanisms that underlie these processes, and discarded by averaging data from a group of participants. However, recent MRI studies in the human brain show that inter-individual variability in a wide range of basic and higher cognitive functions - including perception, motor control, memory, aspects of consciousness and the ability to introspect - can be predicted from the local structure of grey and white matter as assessed by voxel-based morphometry or diffusion tensor imaging. We propose that inter-individual differences can be used as a source of information to link human behaviour and cognition to brain anatomy.
It has been argued that both modality-specific and supramodal mechanisms dedicated to time perception underlie the estimation of interval durations. While it is generally assumed that early sensory areas are dedicated to modality-specific time estimation, we hypothesized that early sensory areas such as the primary visual cortex or the auditory cortex might be involved in time perception independently of the sensory modality of the input. To test this possibility, we examined whether disruption of the primary visual cortex or the auditory cortex would disrupt time estimation of auditory stimuli and visual stimuli using transcranial magnetic stimulation (TMS). We found that disruption of the auditory cortex impaired not only time estimation of auditory stimuli but also impaired that of visual stimuli to the same degree. This finding suggests a supramodal role of the auditory cortex in time perception. On the other hand, TMS over the primary visual cortex impaired performance only in visual time discrimination. These asymmetric contributions of the auditory and visual cortices in time perception may be explained by a superiority of the auditory cortex in temporal processing. Here, we propose that time is primarily encoded in the auditory system and that visual inputs are automatically encoded into an auditory representation in time discrimination tasks.
Human behavior depends on the ability to effectively introspect about our performance. For simple perceptual decisions, this introspective or metacognitive ability varies substantially across individuals and is correlated with the structure of focal areas in prefrontal cortex. This raises the possibility that the ability to introspect about different perceptual decisions might be mediated by a common cognitive process. To test this hypothesis, we examined whether inter-individual differences in metacognitive ability were correlated across two different perceptual tasks where individuals made judgments about different and unrelated visual stimulus properties. We found that inter-individual differences were strongly correlated between the two tasks for metacognitive ability but not objective performance. Such stability of an individuals metacognitive ability across different perceptual tasks indicates a general mechanism supporting metacognition independent of the specific task.
Basic aspects of magnitude (such as luminance contrast) are directly represented by sensory representations in early visual areas. However, it is unclear how symbolic magnitudes (such as Arabic numerals) are represented in the brain. Here we show that symbolic magnitude affects binocular rivalry: perceptual dominance of numbers and objects of known size increases with their magnitude. Importantly, variations in symbolic magnitude acted like variations in luminance contrast: we found that an increase in numerical magnitude of adding one lead to an equivalent increase in perceptual dominance as a contrast increment of 0.32%. Our results support the claim that magnitude is extracted automatically, since the increase in perceptual dominance came about in the absence of a magnitude-related task. Our findings show that symbolic, acculturated knowledge about magnitude interacts with visual perception and affects perception in a manner similar to lower-level aspects of magnitude such as luminance contrast.
Oscillatory neuronal activities are commonly observed in response to sensory stimulation. However, their functional roles are still the subject of debate. One-way to probe the roles of oscillatory neural activities is to deliver alternating current to the cortex at biologically relevant frequencies and examine whether such stimulation influences perception and cognition. In this study, we tested whether transcranial alternating current stimulation (tACS) over the primary somatosensory cortex (SI) could elicit tactile sensations in humans in a frequency-dependent manner. We tested the effectiveness of tACS over SI at frequency bands ranging from 2 to 70 Hz. Our results show that stimulation in alpha (10-14 Hz) and high gamma (52-70 Hz) frequency range produces a tactile sensation in the contralateral hand. A weaker effect was also observed for beta (16-20 Hz) stimulation. These findings highlight the frequency dependency of effective tACS over SI with the effective frequencies corresponding to those observed in previous electroencephalography/magnetoencephalography studies of tactile perception. Our present study suggests that tACS could be used as a powerful online stimulation technique to reveal the causal roles of oscillatory brain activities.
Substantial differences exist in the cognitive styles of liberals and conservatives on psychological measures. Variability in political attitudes reflects genetic influences and their interaction with environmental factors. Recent work has shown a correlation between liberalism and conflict-related activity measured by event-related potentials originating in the anterior cingulate cortex. Here we show that this functional correlate of political attitudes has a counterpart in brain structure. In a large sample of young adults, we related self-reported political attitudes to gray matter volume using structural MRI. We found that greater liberalism was associated with increased gray matter volume in the anterior cingulate cortex, whereas greater conservatism was associated with increased volume of the right amygdala. These results were replicated in an independent sample of additional participants. Our findings extend previous observations that political attitudes reflect differences in self-regulatory conflict monitoring and recognition of emotional faces by showing that such attitudes are reflected in human brain structure. Although our data do not determine whether these regions play a causal role in the formation of political attitudes, they converge with previous work to suggest a possible link between brain structure and psychological mechanisms that mediate political attitudes.
We effortlessly and seemingly instantaneously recognize thousands of objects, although we rarely--if ever--see the same image of an object twice. The retinal image of an object can vary by context, size, viewpoint, illumination, and location. The present study examined how the visual system abstracts object category across variations in retinal location. In three experiments, participants viewed images of objects presented to different retinal locations while brain activity was recorded using magnetoencephalography (MEG). A pattern classifier was trained to recover the stimulus position (Experiments 1, 2, and 3) and category (Experiment 3) from the recordings. Using this decoding approach, we show that an objects location in the visual field can be recovered in high temporal resolution (5 ms) and with sufficient fidelity to capture topographic organization in visual areas. Experiment 3 showed that an objects category could be recovered from the recordings as early as 135 ms after the onset of the stimulus and that category decoding generalized across retinal location (i.e., position invariance). Our experiments thus show that the visual system rapidly constructs a category representation for objects that is invariant to position.
Around 20% of the population exhibits moderate to severe numerical disabilities [1-3], and a further percentage loses its numerical competence during the lifespan as a result of stroke or degenerative diseases . In this work, we investigated the feasibility of using noninvasive stimulation to the parietal lobe during numerical learning to selectively improve numerical abilities. We used transcranial direct current stimulation (TDCS), a method that can selectively inhibit or excitate neuronal populations by modulating GABAergic (anodal stimulation) and glutamatergic (cathodal stimulation) activity [5, 6]. We trained subjects for 6 days with artificial numerical symbols, during which we applied concurrent TDCS to the parietal lobes. The polarity of the brain stimulation specifically enhanced or impaired the acquisition of automatic number processing and the mapping of number into space, both important indices of numerical proficiency [7-9]. The improvement was still present 6 months after the training. Control tasks revealed that the effect of brain stimulation was specific to the representation of artificial numerical symbols. The specificity and longevity of TDCS on numerical abilities establishes TDCS as a realistic tool for intervention in cases of atypical numerical development or loss of numerical abilities because of stroke or degenerative illnesses.
When visual input has conflicting interpretations, conscious perception can alternate spontaneously between competing interpretations . There is a large amount of unexplained variability between individuals in the rate of such spontaneous alternations in perception [2-5]. We hypothesized that variability in perceptual rivalry might be reflected in individual differences in brain structure, because brain structure can exhibit systematic relationships with an individuals cognitive experiences and skills [6-9]. To test this notion, we examined in a large group of individuals how cortical thickness, local gray-matter density, and local white-matter integrity correlate with individuals alternation rate for a bistable, rotating structure-from-motion stimulus . All of these macroscopic measures of brain structure consistently revealed that the structure of bilateral superior parietal lobes (SPL) could account for interindividual variability in perceptual alternation rate. Furthermore, we examined whether the bilateral SPL regions play a causal role in the rate of perceptual alternations by using transcranial magnetic stimulation (TMS) and found that transient disruption of these areas indeed decreases the rate of perceptual alternations. These findings demonstrate a direct relationship between structure of SPL and individuals perceptual switch rate.
Recent developments in transcranial alternating current stimulation (tACS) provide a powerful approach to establish the functional roles of neuronal oscillatory activities in the human brain. Here, we investigated whether tACS can reach and modulate the excitability of the visual cortex in a frequency-dependent manner.
When faced with inconclusive or conflicting visual input human observers experience one of multiple possible perceptions. One factor that determines perception of such an ambiguous stimulus is how the same stimulus was perceived on previous occasions, a phenomenon called perceptual memory. We examined perceptual memory of an ambiguous motion stimulus while applying transcranial magnetic stimulation (TMS) to the motion-sensitive areas of the middle temporal cortex (hMT+). TMS increased the predominance of whichever perceptual interpretation was most commonly reported by a given observer at baseline, with reduced perception of the less favored interpretation. This increased incidence of the preferred percept indicates impaired long-term buildup of perceptual memory traces that normally act against individual percept biases. We observed no effect on short-term memory traces acting from one presentation to the next. Our results indicate that hMT+ is important for the long-term buildup of perceptual memory for ambiguous motion stimuli.
Conscious visual perception can fail in many circumstances. However, little is known about the causes and processes leading to failures of visual awareness. In this study, we introduce a new signal detection measure termed subjective discriminability of invisibility (SDI) that allows one to distinguish between subjective blindness due to reduction of sensory signals or to lack of attentional access to sensory signals. The SDI is computed based upon subjective confidence in reporting the absence of a target (i.e., miss and correct rejection trials). Using this new measure, we found that target misses were subjectively indistinguishable from physical absence when contrast reduction, backward masking and flash suppression were used, whereas confidence was appropriately modulated when dual task, attentional blink and spatial uncertainty methods were employed. These results show that failure of visual perception can be identified as either a result of perceptual or attentional blindness depending on the circumstances under which visual awareness was impaired.
Recent psychophysical studies have shown that perceived timings of events can be dissociated from their physical temporal relationship. In the flash-lag effect (FLE), a flash presented at the same spatiotemporal position as a continuously moving stimulus is perceived to lag behind the moving stimulus. In the present study, we report a peculiar condition in which FLE does not occur even when the position of a moving object is estimated at the moment of a transient event. In a series of experiments, we compared perceived timings and processing delays for appearance of a new object against feature changes of an existing object. We found that perceived timing of the appearance of a new object is delayed compared to the perception of feature changes updating the properties of an object. Our results suggest the construction of a new object representation requires additional time to establish a stable neuronal representation.
Across cultures, social relationships are often thought of, described, and acted out in terms of physical space (e.g. "close friends" "high lord"). Does this cognitive mapping of social concepts arise from shared brain resources for processing social and physical relationships? Using fMRI, we found that the tasks of evaluating social compatibility and of evaluating physical distances engage a common brain substrate in the parietal cortex. The present study shows the possibility of an analytic brain mechanism to process and represent complex networks of social relationships. Given parietal cortexs known role in constructing egocentric maps of physical space, our present findings may help to explain the linguistic, psychological and behavioural links between social and physical space.
Biological motion detection is both commonplace and important, but there is great inter-individual variability in this ability, the neural basis of which is currently unknown. Here we examined whether the behavioral variability in biological motion detection is reflected in brain anatomy. Perceptual thresholds for detection of biological motion and control conditions (non-biological object motion detection and motion coherence) were determined in a group of healthy human adults (n=31) together with structural magnetic resonance images of the brain. Voxel based morphometry analyzes revealed that gray matter volumes of left posterior superior temporal sulcus (pSTS) and left ventral premotor cortex (vPMC) significantly predicted individual differences in biological motion detection, but showed no significant relationship with performance on the control tasks. Our study reveals a neural basis associated with the inter-individual variability in biological motion detection, reliably linking the neuroanatomical structure of left pSTS and vPMC with biological motion detection performance.
Visual perception can be modulated by sounds. A drastic example of this is the sound-induced flash illusion: when a single flash is accompanied by two bleeps, it is sometimes perceived in an illusory fashion as two consecutive flashes. However, there are strong individual differences in proneness to this illusion. Some participants experience the illusion on almost every trial, whereas others almost never do. We investigated whether such individual differences in proneness to the sound-induced flash illusion were reflected in structural differences in brain regions whose activity is modulated by the illusion. We found that individual differences in proneness to the illusion were strongly and significantly correlated with local grey matter volume in early retinotopic visual cortex. Participants with smaller early visual cortices were more prone to the illusion. We propose that strength of auditory influences on visual perception is determined by individual differences in recurrent connections, cross-modal attention and/or optimal weighting of sensory channels.
Loneliness is the distressing feeling associated with the perceived absence of satisfying social relationships. Loneliness is increasingly prevalent in modern societies and has detrimental effects on health and happiness. Although situational threats to social relationships can transiently induce the emotion of loneliness, susceptibility to loneliness is a stable trait that varies across individuals [6-8] and is to some extent heritable. However, little is known about the neural processes associated with loneliness (but see [12-14]). Here, we hypothesized that individual differences in loneliness might be reflected in the structure of the brain regions associated with social processes. To test this hypothesis, we used voxel-based morphometry and showed that lonely individuals have less gray matter in the left posterior superior temporal sulcus (pSTS)--an area implicated in basic social perception. As this finding predicted, we further confirmed that loneliness was associated with difficulty in processing social cues. Although other sociopsychological factors such as social network size, anxiety, and empathy independently contributed to loneliness, only basic social perception skills mediated the association between the pSTS volume and loneliness. Taken together, our results suggest that basic social perceptual abilities play an important role in shaping an individuals loneliness.
Humans form beliefs asymmetrically; we tend to discount bad news but embrace good news. This reduced impact of unfavorable information on belief updating may have important societal implications, including the generation of financial market bubbles, ill preparedness in the face of natural disasters, and overly aggressive medical decisions. Here, we selectively improved peoples tendency to incorporate bad news into their beliefs by disrupting the function of the left (but not right) inferior frontal gyrus using transcranial magnetic stimulation, thereby eliminating the engrained "good news/bad news effect." Our results provide an instance of how selective disruption of regional human brain function paradoxically enhances the ability to incorporate unfavorable information into beliefs of vulnerability.
Professional ball game players report the feeling of the ball slowing-down before hitting it. Because effective motor preparation is critical in achieving such expert motor performance, these anecdotal comments imply that the subjective passage of time may be influenced by preparation for action. Previous reports of temporal illusions associated with action generally emphasize compensation for suppressed sensory signals that accompany motor commands. Here, we show that the time is perceived slowed-down during preparation of a ballistic reaching movement before action, involving enhancement of sensory processing. Preparing for a reaching movement increased perceived duration of a visual stimulus. This effect was tightly linked to action preparation, because the amount of temporal dilation increased with the information about the upcoming movement. Furthermore, we showed a reduction of perceived frequency for flickering stimuli and an enhanced detection of rapidly presented letters during action preparation, suggesting increased temporal resolution of visual perception during action preparation. We propose that the temporal dilation during action preparation reflects the function of the brain to maximize the capacity of sensory information-acquisition prior to execution of a ballistic movement. This strategy might facilitate changing or inhibiting the planned action in response to last-minute changes in the external environment.
Data from neuropsychology and neuroimaging studies indicate hemispheric asymmetries in processing objects global form versus local parts. However the attentional mechanisms subtending visual selection of different levels of information are poorly understood. The classical left hemisphere/local-right hemisphere/global dichotomy has been recently challenged by studies linking the asymmetry of activation in the posterior parietal cortex (PPC) with the relative salience of the stimulus rather than with the local/global level. The present study aimed to assess hemispheric asymmetry in local-global and salience-based selection in hierarchical stimuli by using transcranial direct current stimulation (tDCS). To this end, tDCS has been applied to the PPC of both the hemispheres. Our data revealed that tDCS did affect the selection of the target on the basis of its relative salience in a manner that depended on the tDCS polarity applied to the two hemispheres. This result is in line with previous findings that the left PPC is critically involved in attention for low-salience stimuli in the presence of high-salience distractor information, while right PPC is involved in attending to more salient stimuli. Hemispheric asymmetries were also found in local/global selection. Overall the results suggest that neural activation in the PPC is related to both the salience and the level of stimulus representations mediating responses to hierarchical stimuli. The comparison of the results from Experiments 1 and 2 in local/global-based selection suggests that the effect of stimulation could be completely opposite depending on subtle differences in demands of attentional control (sustained attention vs task switching).
Empathy is a multi-faceted concept consisting of our ability not only to share emotions but also to exert cognitive control and perspective taking in our interactions with others. Here we examined whether inter-individual variability in different components of empathy was related to differences in brain structure assessed using voxel-based morphometry. Following a magnetic resonance imaging (MRI) scan, participants completed the Interpersonal Reactivity Index (IRI). Multiple regression was then used to assess the relationship between individual differences in grey matter volume and individual differences in empathy traits. We found that individual differences in affective empathic abilities oriented towards another person were negatively correlated with grey matter volume in the precuneus, inferior frontal gyrus, and anterior cingulate. Differences in self-oriented affective empathy were negatively correlated with grey matter volume of the somatosensory cortex, but positively correlated with volume in the insula; cognitive perspective taking abilities were positively correlated with grey matter volume of the anterior cingulate; and the ability to empathise with fictional characters was positively related to grey matter changes in the right dorsolateral prefrontal cortex. These findings are discussed in relation to neurocognitive models of empathy.
Transcranial direct current stimulation (tDCS) has been successfully applied to cortical areas such as the motor cortex and visual cortex. In the present study, we examined whether tDCS can reach and selectively modulate the excitability of the frontal eye field (FEF). In order to assess potential effects of tDCS, we measured saccade latency, landing point, and its variability in a simple prosaccade task and in an antisaccade task. In the prosaccade task, we found that anodal tDCS shortened the latency of saccades to a contralateral visual cue. However, cathodal tDCS did not show a significant modulation of saccade latency. In the antisaccade task, on the other hand, we found that the latency for ipisilateral antisaccades was prolonged during the stimulation, whereas anodal stimulation did not modulate the latency of antisaccades. In addition, anodal tDCS reduced the erroneous saccades toward the contralateral visual cue. These results in the antisaccade task suggest that tDCS modulates the function of FEF to suppress reflexive saccades to the contralateral visual cue. Both in the prosaccade and antisaccade tasks, we did not find any effect of tDCS on saccade landing point or its variability. Our present study is the first to show effects of tDCS over FEF and opens the possibility of applying tDCS for studying the functions of FEF in oculomotor and attentional performance.
Expertise in non-visual domains such as musical performance is associated with differences in gray matter volume of particular regions of the human brain. Whether this is also the case for expertise in visual object recognition is unknown. Here we tested whether individual variability in the ability to recognize car models, from novice performance to high level of expertise, is associated with specific structural changes in gray matter volume. We found that inter-individual variability in expertise with cars was significantly and selectively correlated with gray matter volume in prefrontal cortex. Inter-individual differences in the recognition of airplanes, that none of the participants had expertise with, were correlated with structural variability of regions bordering the visual cortex. These results highlight the role of prefrontal regions outside the visual cortex in accessing and processing visual knowledge about objects from the domain of expertise and suggest that expertise in visual object recognition may entail structural changes in regions associated with semantic knowledge.
Moral sentiment has been hypothesized to reflect evolved adaptations to social living. If so, individual differences in moral values may relate to regional variation in brain structure. We tested this hypothesis in a sample of 70 young, healthy adults examining whether differences on two major dimensions of moral values were significantly associated with regional gray matter volume. The two clusters of moral values assessed were "individualizing" (values of harm/care and fairness) and "binding" (deference to authority, in-group loyalty, and purity/sanctity). Individualizing was positively associated with left dorsomedial pFC volume and negatively associated with bilateral precuneus volume. For binding, a significant positive association was found for bilateral subcallosal gyrus and a trend to significance for the left anterior insula volume. These findings demonstrate that variation in moral sentiment reflects individual differences in brain structure and suggest a biological basis for moral sentiment, distributed across multiple brain regions.
In the Simon task, a conflict arises because irrelevant spatial information competes for response selection either facilitating or interfering with performance. Responses are faster when stimulus and response position correspond than when they do not. The FEFs, which have long been characterized for their role in oculomotor control, are also involved in the control of visuospatial attention when eye movements are not required. This study was aimed at investigating whether the FEFs contribute to spatial conflict. Double-pulse TMS was applied to the FEF of either left or right hemisphere during the execution of a Simon task at different time windows after the onset of the visual stimulus. A suppression of the Simon effect was observed after stimulation of the FEF for stimuli appearing in the contralateral hemifield when TMS was applied to the left hemisphere after stimulus onset (0-40 and 40-80 msec). A reduction of the correspondence effect was observed after right FEF TMS for stimuli presented in the left visual hemifield when stimulation was delivered in the 80-120 msec range after stimulus onset. These outcomes indicate that the FEF play a critical role in encoding spatial attribute of a stimulus for response priming, which is the prerequisite for response conflict in the Simon task. Moreover, our finding that the left FEF have a dominant role during spatial conflict extends the idea of the left-hemisphere lateralization of the motor network in action selection by suggesting that the FEF may constitute part of this network.
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