Visual Perception Tasks Research Articles

The end point of the ventral visual stream: face and non-face perceptual deficits following unilateral anterior temporal lobe damage

While it has been claimed that the ventral visual stream ends in the inferior aspects of the anterior temporal lobe (ATL), little is known about whether this region is important for visual perception. Here the performance of two patients with unilateral ATL damage was assessed across four visual perception tasks that parametrically varied stimulus similarity. Patients performed normally on difficult judgments of circle size or face age but were impaired on face identity and dot pattern matching tasks. Portions of the ATL, most likely the ventral surface, may have a functional role in visual perception tasks requiring detailed configural processing, most commonly used to discern facial identity.

From word superiority to word inferiority: Visual processing of letters and words in pure alexia

Visual processing and naming of individual letters and short words were investigated in four patients with pure alexia. To test processing at different levels, the same stimuli were studied across a naming task and a visual perception task. The normal word superiority effect was eliminated in both tasks for all patients, and this pattern was more pronounced in the more severely affected patients. The relationship between performance with single letters and words was, however, not straightforward: One patient performed within the normal range on the letter perception task, while being severely impaired in letter naming and word processing, and performance with letters and words was dissociated in all four patients, with word reading being more severely impaired than letter recognition. This suggests that the word reading deficit in pure alexia may not be reduced to an impairment in single letter perception.

Neural Correlates of State- and Strength-based Perception

Perceptual judgments can be based on two kinds of information: state-based perception of specific, detailed visual information, or strength-based perception of global or relational information. State-based perception is discrete in the sense that it either occurs or fails, whereas strength-based perception is continuously graded from weak to strong. The functional characteristics of these types of perception have been examined in some detail, but whether state- and strength-based perception are supported by different brain regions has been largely unexplored. A consideration of empirical work and recent theoretical proposals suggests that parietal and occipito-temporal regions may be differentially associated with state- and strength-based signals, respectively. We tested this parietal/occipito-temporal state/strength hypothesis using fMRI and a visual perception task that allows separation of state- and strength-based perception. Participants made same/different judgments on pairs of faces and scenes using a 6-point confidence scale where "6" responses indicated a state of perceiving specific details that had changed, and "1" to "5" responses indicated judgments based on varying strength of relational match/mismatch. Regions in the lateral and medial posterior parietal cortex (supramarginal gyrus, posterior cingulate cortex, and precuneus) were sensitive to state-based perception and were not modulated by varying levels of strength-based perception. In contrast, bilateral fusiform gyrus activation was increased for strength-based "different" responses compared with misses and did not show state-based effects. Finally, the lateral occipital complex showed increased activation for state-based responses and additionally showed graded activation across levels of strength-based perception. These results offer support for a state/strength distinction between parietal and temporal regions, with the lateral occipital complex at the intersection of state- and strength-based processing.

Knowledge corruption for visual perception in individuals high on paranoia

Studies revealed that patients with paranoid schizophrenia display overconfidence in errors for memory and social cognition tasks. The present investigation examined whether this pattern holds true for visual perception tasks.Nonclinical participants were recruited via an online panel. Individuals were asked to complete a questionnaire that included the Paranoia Checklist and were then presented with 24 blurry pictures; half contained a hidden object while the other half showed snowy (visual) noise. Participants were asked to state whether the visual items contained an object and how confident they were in their judgment. Data from 1966 individuals were included following a conservative selection process.Participants high on core paranoid symptoms showed a poor calibration of confidence for correct versus incorrect responses. In particular, participants high on paranoia displayed overconfidence in incorrect responses and demonstrated a 20% error rate for responses made with high confidence compared to a 12% error rate in participants with low paranoia scores. Interestingly, paranoia scores declined after performance of the task.For the first time, overconfidence in errors was demonstrated among individuals with high levels of paranoia using a visual perception task, tentatively suggesting it is a ubiquitous phenomenon. In view of the significant decline in paranoia across time, bias modification programs may incorporate items such as the one employed here to teach patients with clinical paranoia the fallibility of human cognition, which may foster subsequent symptom improvement.

Analysis of EEG signals related to artists and nonartists during visual perception, mental imagery, and rest using approximate entropy.

In this paper, differences between multichannel EEG signals of artists and nonartists were analyzed during visual perception and mental imagery of some paintings and at resting condition using approximate entropy (ApEn). It was found that ApEn is significantly higher for artists during the visual perception and the mental imagery in the frontal lobe, suggesting that artists process more information during these conditions. It was also observed that ApEn decreases for the two groups during the visual perception due to increasing mental load; however, their variation patterns are different. This difference may be used for measuring progress in novice artists. In addition, it was found that ApEn is significantly lower during the visual perception than the mental imagery in some of the channels, suggesting that visual perception task requires more cerebral efforts.

Using theories of delusion formation to explain abnormal beliefs in Body Dysmorphic Disorder (BDD)

Body Dysmorphic Disorder (BDD) is characterised by overvalued or delusional beliefs of ‘imagined ugliness’. Delusional beliefs have been explained by a number of cognitive theories, including faulty perceptions, biases in attention, and corruption of semantic memory. Atypical aesthetics may also influence beliefs in BDD. In fourteen BDD patients, compared to controls (n=14), we examined these theories of beliefs in a cognitive test battery consisting of perceptual organisation and visual affect perception tasks, a Stroop task using body words, a sentence verification task, a fluency task, and an attractiveness task. BDD patients performed similar to controls on tasks measuring information (bias) processing and aesthetics. However, BDD showed abnormal abilities on semantic processing involving sentence verification and category fluency. There was only a trend finding of impaired performance on perceptual processing tasks in BDD. The findings suggest that the delusional beliefs in BDD may be explained by impaired semantic processing.

DF's visual brain in action: The role of tactile cues

Patient DF, an extensively-tested woman with visual form agnosia from ventral-stream damage, is able to scale her grip aperture to match a goal object's geometry when reaching out to pick it up, despite being unable to explicitly distinguish amongst objects on the basis of their different geometries. Using evidence from a range of sources, including functional MRI, we have proposed that she does this through a functionally intact visuomotor system housed within the dorsal stream of the posterior parietal lobe. More recently, however, Schenk (2012a). The Journal of Neuroscience, 32(6), 2013–2017; Schenk (2012b). Trends in Cognitive Sciences, 16(5), 258–259. has argued that DF performs well in visually guided grasping, not through spared and functioning visuomotor networks in the dorsal stream, but because haptic feedback about the locations of the edges of the target is available to calibrate her grasps in such tasks, whereas it is not available in standard visual perceptual tasks. We have tested this 'calibration hypothesis' directly, by presenting DF with a grasping task in which the visible width of a target varied from trial to trial while its actual width remained the same. According to the calibration hypothesis, because haptic feedback was completely uninformative, DF should be unable to calibrate her grip aperture in this task. Contrary to this prediction, we found that DF continued to scale her grip aperture to the visual width of the targets and did so well within the range of healthy controls. We also found that DF's inability to distinguish shapes perceptually is not improved by providing haptic feedback. These findings strengthen the notion that DF’s spared visuomotor abilities are driven largely by visual feedforward processing of the geometric properties of the target. Crucially, these findings also indicate that simple tactile contact with an object is needed for the visuomotor dorsal stream to be engaged, and accordingly enables DF to execute visually guided grasping successfully. This need for actions to have a tangible endpoint provides an important new modification of the Two Visual Systems theory.

Altered Activity of the Primary Visual Area during Gaze Processing in Individuals with High-Functioning Autistic Spectrum Disorder: A Magnetoencephalography Study

Background: Individuals with autistic spectrum disorder (ASD) demonstrate an impaired ability to infer the mental states of others from their gaze. Thus, investigating the relationship between ASD and eye gaze processing is crucial for understanding the neural basis of social impairments seen in individuals with ASD. In addition, characteristics of ASD are observed in more comprehensive visual perception tasks. These visual characteristics of ASD have been well-explained in terms of the atypical relationship between high- and low-level gaze processing in ASD. Method: We studied neural activity during gaze processing in individuals with ASD using magnetoencephalography, with a focus on the relationship between high- and low-level gaze processing both temporally and spatially. Minimum Current Estimate analysis was applied to perform source analysis of magnetic responses to gaze stimuli. Results: The source analysis showed that later activity in the primary visual area (V1) was affected by gaze direction only in the ASD group. Conversely, the right posterior superior temporal sulcus, which is a brain region that processes gaze as a social signal, in the typically developed group showed a tendency toward greater activation during direct compared with averted gaze processing. Conclusion: These results suggest that later activity in V1 relating to gaze processing is altered or possibly enhanced in high-functioning individuals with ASD, which may underpin the social cognitive impairments in these individuals.

A Comparative Investigation of Wavelet Families for Analysis of EEG Signals Related to Artists and Nonartists During Visual Perception, Mental Imagery, and Rest

Differences between the multichannel EEG signals of artists and nonartists were investigated using wavelet coefficients during visual perception and mental imagery tasks and at rest. The wavelet coefficients were calculated using wavelet functions such as Daubechies (order 1–10), Coiflets (order 1–5), and biorthogonal (order 2.4). Each of the calculated approximation and detail coefficients and their averages, standard deviations, and their energies were separately used for discriminating the two groups. The Davies-Bouldin Index was used for evaluation of the feature space quality. We found that the two groups are discriminable using the wavelet coefficients calculated by all of the studied wavelet functions. It was also observed that level of decomposition does not contribute significantly to discriminability. In addition, we observed no considerable difference between approximation and detail coefficients for discriminating the two groups. It was also found that a distinguishing coefficient may exist am...

‘If you are good, I get better’: the role of social hierarchy in perceptual decision-making

So far, it was unclear if social hierarchy could influence sensory or perceptual cognitive processes. We evaluated the effects of social hierarchy on these processes using a basic visual perceptual decision task. We constructed a social hierarchy where participants performed the perceptual task separately with two covertly simulated players (superior, inferior). Participants were faster (better) when performing the discrimination task with the superior player. We studied the time course when social hierarchy was processed using event-related potentials and observed hierarchical effects even in early stages of sensory-perceptual processing, suggesting early top-down modulation by social hierarchy. Moreover, in a parallel analysis, we fitted a drift-diffusion model (DDM) to the results to evaluate the decision making process of this perceptual task in the context of a social hierarchy. Consistently, the DDM pointed to nondecision time (probably perceptual encoding) as the principal period influenced by social hierarchy.

Investigation of EEG Alpha Rhythm of Artists and Nonartists During Visual Perception, Mental Imagery, and Rest

In this article, differences in alpha power between multichannel EEG signals of artists and nonartists were investigated. The two groups were compared during visual perception, mental imagery, and at-rest conditions. We found no significant differences between the two groups in absolute alpha power at rest. Both absolute and relative alpha power were found to be significantly lower in artists during the visual perception and the mental imagery tasks for some of the channels, suggesting that the cerebral efforts of artists were higher during these conditions. These results indicate that artists considered more features of a painting compared to nonartists. The two groups differed in relative alpha power during the visual perception task compared to the at-rest condition. Relative alpha power values decreased during the visual perception for both groups; however, their variation patterns were different. More significant decreases in relative upper alpha power (10-12Hz) during the visual perception task for ...

Shared attention for smooth pursuit and saccades.

Identification of brief luminance decrements on parafoveal stimuli presented during smooth pursuit improves when a spot pursuit target is surrounded by a larger random dot cinematogram (RDC) that moves with it (Heinen, Jin, & Watamaniuk, 2011). This was hypothesized to occur because the RDC provided an alternative, less attention-demanding pursuit drive, and therefore released attentional resources for visual perception tasks that are shared with those used to pursue the spot. Here, we used the RDC as a tool to probe whether spot pursuit also shares attentional resources with the saccadic system. To this end, we set out to determine if the RDC could release attention from pursuit of the spot to perform a saccade task. Observers made a saccade to one of four parafoveal targets that moved with the spot pursuit stimulus. The targets either moved alone or were surrounded by an RDC (100% coherence). Saccade latency decreased with the RDC, suggesting that the RDC released attention needed to pursue the spot, which was then used for the saccade task. Additional evidence that attention was released by the RDC was obtained in an experiment in which attention was anchored to the fovea by requiring observers to detect a brief color change applied 130 ms before the saccade target appeared. This manipulation eliminated the RDC advantage. The results imply that attentional resources used by the pursuit and saccadic eye movement control systems are shared.

Visual Form Perception from Age 20 through 80 Years

We measured performance on a battery of visual form perception tasks for adults sampled evenly from each decade of adult life from 20 to 80 years. Measures were included that are considered to reflect processing at early through intermediate stages of the form processing pathways: collinear facilitation, center-surround contrast effects, global shape discrimination of contours of elements embedded in noise elements, and global shape discrimination in texture (Glass patterns). A total of 38 women and 20 men (mainly Caucasian, low refractive error) participated, aged between 20 and 82 years. With advancing age, contrast sensitivity decreased linearly (B = 0.009, t(56) = 8.14, P < 0.001), perceptual surround suppression of low contrast stimuli embedded in higher contrast surrounds increased (B = -0.006, t(56) = -3.32, P < 0.01), and coherence thresholds for detecting form in Glass patterns increased (B = 0.14, t(56) = 2.53, P = 0.02). Performance between tasks was not correlated. Several aspects of form perception alter gradually throughout the adult lifespan, namely context-dependent perception of contrast, and the extraction of global shape from texture. Our results suggested age-dependent differences under natural viewing conditions that are not predictable by standard clinical measures of visual function, and point to changes in neural function that are ongoing throughout adult life.

EEG reveals an early influence of social conformity on visual processing in group pressure situations

Humans are social beings and often have to perceive and perform within groups. In conflict situations, this puts them under pressure to either adhere to the group opinion or to risk controversy with the group. Psychological experiments have demonstrated that study participants adapt to erroneous group opinions in visual perception tasks, which they can easily solve correctly when performing on their own. Until this point, however, it is unclear whether this phenomenon of social conformity influences early stages of perception that might not even reach awareness or later stages of conscious decision-making. Using electroencephalography, this study has revealed that social conformity to the wrong group opinion resulted in a decrease of the posterior-lateral P1 in line with a decrease of the later centro-parietal P3. These results suggest that group pressure situations impact early unconscious visual perceptual processing, which results in a later diminished stimulus discrimination and an adaptation even to the wrong group opinion. These findings might have important implications for understanding social behavior in group settings and are discussed within the framework of social influence on eyewitness testimony.

A multifocus image fusion method by using hidden Markov model

An image with all objects in focus is desired for human visual perception and computer vision tasks. The multifocus image fusion technique is a solution to fuse images acquired with different focus levels of a scene to obtain a clear fused image. Past approaches such as based on multiscale transformation (MST) are unavoidably lose information due to processing in transform domain and are sensitive to mis-registration. To solve these problems, we propose a hidden Markov model (HMM) based method, which not only uses patches rather than pixels as processing units but also handles each patch in the spatial domain instead of the transform domain. In the proposed method, firstly, the source images are divided into overlapping patches. Then, the fused image is modeled with HMM relying not only on the fidelity, clarity of patches but also on the relationship of adjacent patches. Subsequently, a belief propagation (BP) algorithm is adopted to select the fused patches from the source patches. Finally, these selected patches are integrated into the fused image. The experimental results prove that the proposed method achieves better performance, and is more robust to mis-registration than the MST-based methods.

Comparative Effects of First-Person Shooter Video Game Experience and Brain Stimulation on Threat Detection Learning

We have previously shown that 2 mA of transcranial direct current stimulation (tDCS) of the right inferior cortex improved sensitivity ( d’) during learning and 24-hour retention of a complex visual perceptual learning task, independent of changes in response bias ( ß) (Falcone et al., 2012). Because some participants in that study had video game experience, the current study investigated the effect of three different levels of video game experience on the learning rate for the same perceptual task: non-video game players (NVGPs), gamers with low 1st person shooter gaming expertise (Low-1stVGPs), and gamers with high 1st person shooter gaming expertise (High-1stVGPs). There were graded group differences in d’ but not in ß by the end of the training: NVGPs had the lowest sensitivity, Low-1stVGPs intermediate, and High-1stVGPs the highest. The High-1stVGPs group had significantly higher perceptual sensitivity than the NVGPs group and, while not statistically significant, there was a clear trend of a higher perceptual sensitivity for the High-1stVGPs group over the Low-1stVGPs. In addition, the rate of learning in the High-1stVGP was comparable to that of the group receiving 2 mA tDCS. While the High-1stVGP group had a slightly lower d’ value by the end of training, it was not significantly different from that of the 2 mA tDCS group. The results indicate that 1st person shooter videogame experience and brain stimulation have comparable beneficial effects on complex perceptual learning. Both types of effects have been attributedto enhancement of visual attention. Thus, even greater benefits for augmenting learning might be possible by administering tDCS to individuals with 1st person shooter videogame experience.

Motor-reduced visual perceptual abilities and visual-motor integration abilities of Chinese learning children

This study investigated the relationship between motor-reduced visual perceptual abilities and visual-motor integration abilities of Chinese learning children by employing the Developmental Test of Visual Perception (Hammill, Pearson, & Voress, 1993), in which both abilities are measured in a single test. A total of 72 native Chinese learners of age 5 participated in this study. The findings indicated that the Chinese learners scored much higher in the visual-motor integration tasks than in motor-reduced visual perceptual tasks. The results support the theory of autonomous systems of motor-reduced visual perception and visual-motor integration and query current beliefs about the prior development of the former to the latter for the Chinese learners. To account for the Chinese participants’ superior performance in visual-motor integration tasks over motor-reduced visual perceptual tasks, the visual-spatial properties of Chinese characters, general handwriting theories, the motor control theory and the psychogeometric theory of Chinese character-writing are referred to. The significance of the findings is then discussed.

Transcranial Direct Current Stimulation Augments Perceptual Sensitivity and 24-Hour Retention in a Complex Threat Detection Task

We have previously shown that transcranial direct current stimulation (tDCS) improved performance of a complex visual perceptual learning task (Clark et al. 2012). However, it is not known whether tDCS can enhance perceptual sensitivity independently of non-specific, arousal-linked changes in response bias, nor whether any such sensitivity benefit can be retained over time. We examined the influence of stimulation of the right inferior frontal cortex using tDCS on perceptual learning and retention in 37 healthy participants, using signal detection theory to distinguish effects on perceptual sensitivity (d′) from response bias (ß). Anodal stimulation with 2 mA increased d′, compared to a 0.1 mA sham stimulation control, with no effect on ß. On completion of training, participants in the active stimulation group had more than double the perceptual sensitivity of the control group. Furthermore, the performance enhancement was maintained for 24 hours. The results show that tDCS augments both skill acquisition and retention in a complex detection task and that the benefits are rooted in an improvement in sensitivity (d′), rather than changes in response bias (ß). Stimulation-driven acceleration of learning and its retention over 24 hours may result from increased activation of prefrontal cortical regions that provide top-down attentional control signals to object recognition areas.

EEG-fMRI Based Information Theoretic Characterization of the Human Perceptual Decision System

The modern metaphor of the brain is that of a dynamic information processing device. In the current study we investigate how a core cognitive network of the human brain, the perceptual decision system, can be characterized regarding its spatiotemporal representation of task-relevant information. We capitalize on a recently developed information theoretic framework for the analysis of simultaneously acquired electroencephalography (EEG) and functional magnetic resonance imaging data (fMRI) (Ostwald et al. (2010), NeuroImage 49: 498–516). We show how this framework naturally extends from previous validations in the sensory to the cognitive domain and how it enables the economic description of neural spatiotemporal information encoding. Specifically, based on simultaneous EEG-fMRI data features from n = 13 observers performing a visual perceptual decision task, we demonstrate how the information theoretic framework is able to reproduce earlier findings on the neurobiological underpinnings of perceptual decisions from the response signal features' marginal distributions. Furthermore, using the joint EEG-fMRI feature distribution, we provide novel evidence for a highly distributed and dynamic encoding of task-relevant information in the human brain.

Philippe G. Schyns

Philippe G. Schyns