Multisensory enhancement elicited by unconscious visual stimuli.

The merging of information from different senses (i.e., multisensory integration) can facilitate information processing. Processing enhancements have been observed with signals that are irrelevant to the task at hand, and with cues that are non-predictive. Such findings are consistent with the notion that multiple sensory signals are sometimes integrated automatically. Multisensory enhancement has even been reported with stimuli that have been presented subliminally, though only with meaningful multisensory relations that have already been learned. The question of whether there exist cases where multisensory effects occur without either learning or awareness has, though, not been clearly established in the literature to date. Here, we present a case study of a patient with Posterior Cortical Atrophy, who was unable to consciously perceive visual stimuli with our task parameters, yet who nevertheless still exhibited signs of multisensory enhancement even with unlearned relations between audiovisual stimuli. In a simple speeded detection task, both response speed, and the variability of reaction times, decreased in a similar manner to controls for multisensory stimuli. These results are consistent with the view that the conscious perception of stimuli and prior learning are not always a prerequisite for multisensory integration to enhance human performance.

In-group biases and oculomotor responses: beyond simple approach motivation.

An in-group bias describes an individual's bias towards a group that they belong to. Previous studies suggest that in-group bias facilitates approach motor responses, but disrupts avoidance ones. Such motor biases are shown to be more robust when the out-group is threatening. We investigated whether, under controlled visual familiarity and complexity, in-group biases still promote pro-saccade and hinder anti-saccades oculomotor responses. Participants first learned to associate an in-group or out-group label with an arbitrary shape. They were then instructed to listen to the group-relevant auditory cue (name of own and a rival university) followed by one of the shapes. Half of the participants were instructed to look towards the visual target if it matched the preceding group-relevant auditory cue and to look away from it if it did not match. The other half of the participants received reversed instructions. This design allowed us to orthogonally manipulate the effect of in-group bias and cognitive control demand on oculomotor responses. Both pro- and anti-saccades were faster and more accurate following the in-group auditory cue. Independently, pro-saccades were performed better than anti-saccades, and match judgements were faster and more accurate than non-match judgements. Our findings indicate that under higher cognitive control demands individuals' oculomotor responses improved following the motivationally salient cue (in-group). Our findings have important implications for learning and cognitive control in a social context. As we included rival groups, our results might to some extent reflect the effects of out-group threat. Future studies could extend our findings using non-threatening out-groups instead.

The Neural Basis of Independence Versus Interdependence Orientations: A Voxel-Based Morphometric Analysis of Brain Volume.

Sociocultural research has established independence and interdependence as two fundamental ways of thinking about oneself and the social world. Recent neuroscience studies further demonstrate that these orientations modulate brain activity in various self- and socially related tasks. In the current study, we explored whether the traits of independence and interdependence are reflected in anatomical variations in brain structure. We carried out structural brain imaging on a large sample of healthy participants ( n = 265) who also completed self-report questionnaires of cultural orientations. Voxel-based morphometry analysis demonstrated that a relative focus of independence (vs. interdependence) was associated with increased gray-matter volume in a number of self-related regions, including ventromedial prefrontal cortex, right dorsolateral prefrontal cortex, and right rostrolateral prefrontal cortex. These results provide novel insights into the biological basis of sociocultural orientations.

Exploring the quiet eye in archery using field- and laboratory-based tasks.

The 'quiet eye' (QE)-a period of extended gaze fixation on a target-has been reported in many tasks that require accurate aiming. Longer quiet eye durations (QEDs) are reported in experts compared to non-experts and on successful versus less successful trials. The QE has been extensively studied in the field; however, the cognitive mechanisms underlying the QE are not yet fully understood. We investigated the QEDs of ten expert and ten novice archers in the field and in the laboratory using a computer-based archery task. The computer task consisted of shooting archery targets using a joystick. Random 'noise' (visual motion perturbation) was introduced at high and low levels to allow for the controlled examination of the effects of task complexity and processing demands. In this computer task, we also tested an additional group of ten non-archers as controls. In both field and computer tasks, eye movements were measured using electro-oculography. The expert archers exhibited longer QED compared to the novice archers in the field task. In the computer task, the archers again exhibited longer QEDs and were more accurate compared to non-archers. Furthermore, expert archers showed earlier QE onsets and longer QEDs during high noise conditions compared to the novices and non-archers. Our findings show skill-based effects on QED in field conditions and in a novel computer-based archery task, in which online (visual) perturbations modulated experts' QEDs. These longer QEDs in experts may be used for more efficient programming in which accurate predictions are facilitated by attention control.

Neural Mechanisms of Temporal Resolution of Attention.

The dynamic nature of the world requires that our visual representations are continuously updated. These representations are more precise if there is a narrow time window over which information is averaged. We assess the neural processes of visual updating by testing patients with lesions including inferior parietal cortex, control patients and healthy adults on a continuous visual monitoring task. In Experiment 1, observers kept track of the changing spatial period of a luminance grating and identified the final spatial period after the stimulus disappeared. Healthy older adults and neurological controls were able to perform better than simulated guesses, but only 3 of 11 patients with damage including parietal cortex were able to reach performance that differed from simulated guesses. The effects were unrelated to lesion size. Poor performance on this task is consistent with an inability to selectively attend to the final moment at which the stimulus was seen. To investigate the temporal limits of attention, we varied the rate of stimulus change in Experiment 2. Performance remained poor for some patients even with slow 2.5 Hz change rates. The performance of 4 patients with parietal damage displayed poor temporal precision, namely recovery of performance with slower rates of change.

Structural Organization of the Corpus Callosum Predicts Attentional Shifts after Continuous Theta Burst Stimulation.

Repetitive transcranial magnetic stimulation (rTMS) applied over the right posterior parietal cortex (PPC) in healthy participants has been shown to trigger a significant rightward shift in the spatial allocation of visual attention, temporarily mimicking spatial deficits observed in neglect. In contrast, rTMS applied over the left PPC triggers a weaker or null attentional shift. However, large interindividual differences in responses to rTMS have been reported. Studies measuring changes in brain activation suggest that the effects of rTMS may depend on both interhemispheric and intrahemispheric interactions between cortical loci controlling visual attention. Here, we investigated whether variability in the structural organization of human white matter pathways subserving visual attention, as assessed by diffusion magnetic resonance imaging and tractography, could explain interindividual differences in the effects of rTMS. Most participants showed a rightward shift in the allocation of spatial attention after rTMS over the right intraparietal sulcus (IPS), but the size of this effect varied largely across participants. Conversely, rTMS over the left IPS resulted in strikingly opposed individual responses, with some participants responding with rightward and some with leftward attentional shifts. We demonstrate that microstructural and macrostructural variability within the corpus callosum, consistent with differential effects on cross-hemispheric interactions, predicts both the extent and the direction of the response to rTMS. Together, our findings suggest that the corpus callosum may have a dual inhibitory and excitatory function in maintaining the interhemispheric dynamics that underlie the allocation of spatial attention. SIGNIFICANCE STATEMENT: The posterior parietal cortex (PPC) controls allocation of attention across left versus right visual fields. Damage to this area results in neglect, characterized by a lack of spatial awareness of the side of space contralateral to the brain injury. Transcranial magnetic stimulation over the PPC is used to study cognitive mechanisms of spatial attention and to examine the potential of this technique to treat neglect. However, large individual differences in behavioral responses to stimulation have been reported. We demonstrate that the variability in the structural organization of the corpus callosum accounts for these differences. Our findings suggest novel dual mechanism of the corpus callosum function in spatial attention and have broader implications for the use of stimulation in neglect rehabilitation.

Structural Variability within Frontoparietal Networks and Individual Differences in Attentional Functions: An Approach Using the Theory of Visual Attention.

Visuospatial attention allows us to select and act upon a subset of behaviorally relevant visual stimuli while ignoring distraction. Bundesen's theory of visual attention (TVA) (Bundesen, 1990) offers a quantitative analysis of the different facets of attention within a unitary model and provides a powerful analytic framework for understanding individual differences in attentional functions. Visuospatial attention is contingent upon large networks, distributed across both hemispheres, consisting of several cortical areas interconnected by long-association frontoparietal pathways, including three branches of the superior longitudinal fasciculus (SLF I-III) and the inferior fronto-occipital fasciculus (IFOF). Here we examine whether structural variability within human frontoparietal networks mediates differences in attention abilities as assessed by the TVA. Structural measures were based on spherical deconvolution and tractography-derived indices of tract volume and hindrance-modulated orientational anisotropy (HMOA). Individual differences in visual short-term memory (VSTM) were linked to variability in the microstructure (HMOA) of SLF II, SLF III, and IFOF within the right hemisphere. Moreover, VSTM and speed of information processing were linked to hemispheric lateralization within the IFOF. Differences in spatial bias were mediated by both variability in microstructure and volume of the right SLF II. Our data indicate that the microstructural and macrostrucutral organization of white matter pathways differentially contributes to both the anatomical lateralization of frontoparietal attentional networks and to individual differences in attentional functions. We conclude that individual differences in VSTM capacity, processing speed, and spatial bias, as assessed by TVA, link to variability in structural organization within frontoparietal pathways.

Unconscious Familiarity-based Color-Form Binding: Evidence from Visual Extinction.

There is good evidence that early visual processing involves the coding of different features in independent brain regions. A major question, then, is how we see the world in an integrated manner, in which the different features are "bound" together. A standard account of this has been that feature binding depends on attention to the stimulus, which enables only the relevant features to be linked together [Treisman, A., & Gelade, G. A feature-integration theory of attention. Cognitive Psychology, 12, 97-136, 1980]. Here we test this influential idea by examining whether, in patients showing visual extinction, the processing of otherwise unconscious (extinguished) stimuli is modulated by presenting objects in their correct (familiar) color. Correctly colored objects showed reduced extinction when they had a learned color, and this color matched across the ipsi- and contralesional items (red strawberry + red tomato). In contrast, there was no reduction in extinction under the same conditions when the stimuli were colored incorrectly (blue strawberry + blue tomato; Experiment 1). The result was not due to the speeded identification of a correctly colored ipsilesional item, as there was no benefit from having correctly colored objects in different colors (red strawberry + yellow lemon; Experiment 2). There was also no benefit to extinction from presenting the correct colors in the background of each item (Experiment 3). The data suggest that learned color-form binding can reduce extinction even when color is irrelevant for the task. The result is consistent with preattentive binding of color and shape for familiar stimuli.

Brain networks of temporal preparation: A multiple regression analysis of neuropsychological data.

There are only a few studies on the brain networks involved in the ability to prepare in time, and most of them followed a correlational rather than a neuropsychological approach. The present neuropsychological study performed multiple regression analysis to address the relationship between both grey and white matter (measured by magnetic resonance imaging in patients with brain lesion) and different effects in temporal preparation (Temporal orienting, Foreperiod and Sequential effects). Two versions of a temporal preparation task were administered to a group of 23 patients with acquired brain injury. In one task, the cue presented (a red versus green square) to inform participants about the time of appearance (early versus late) of a target stimulus was blocked, while in the other task the cue was manipulated on a trial-by-trial basis. The duration of the cue-target time intervals (400 versus 1400ms) was always manipulated within blocks in both tasks. Regression analysis were conducted between either the grey matter lesion size or the white matter tracts disconnection and the three temporal preparation effects separately. The main finding was that each temporal preparation effect was predicted by a different network of structures, depending on cue expectancy. Specifically, the Temporal orienting effect was related to both prefrontal and temporal brain areas. The Foreperiod effect was related to right and left prefrontal structures. Sequential effects were predicted by both parietal cortex and left subcortical structures. These findings show a clear dissociation of brain circuits involved in the different ways to prepare in time, showing for the first time the involvement of temporal areas in the Temporal orienting effect, as well as the parietal cortex in the Sequential effects.

Biased towards food: Electrophysiological evidence for biased attention to food stimuli.

We investigated the neural mechanisms involved in bias for food stimuli in our visual environment using event related lateralized (ERL) responses. The participants were presented with a cue (food or non-food item) to either identify or hold in working memory. Subsequently, they had to search for a target in a 2-item display where target and distractor stimuli were each flanked by a picture of a food or a non-food item. The behavioural data showed that performance was strongly affected by food cues, especially when food was held in WM compared to when the cues were merely identified. The temporal dynamics of electrophysiological measures of attention (the N1pc and N2pc) showed that the orienting of attention towards food stimuli was associated with two different mechanisms; an early stage of attentional suppression followed by a later stage of attentional orienting towards food stimuli. In contrast, non-food cues were associated only with the guidance of attention to or away from cued stimuli on valid and invalid trials. The results demonstrate that food items, perhaps due to their motivational significance modulate the early orienting of attention, including an initial suppressive response to food items.

Lesion-symptom mapping of self-prioritization in explicit face categorization: distinguishing hypo- and hyper-self-biases.

People make faster familiarity decisions for their own face compared with a familiar other. Lesion studies diverge on whether this self-face prioritization (SFP) effect is associated with functional processes isolated in the left or right hemispheres. To assess both decreases (hypo-) and increases (hyper-) in SFP after brain lesion, we asked patients with chronic deficits to perform familiarity judgments to images of their own face, a familiar other, or unfamiliar faces. Of 30 patients, 7 showed hypo- and 6 showed hyper-self-bias effects, comparing responses with their own faces versus responses with a familiar other. Hyper-self-bias correlated with reduced executive control function and, at a neural level, this was associated with lesions to the left prefrontal and superior temporal cortices. In contrast, reduced self-prioritization was associated with damage to the right inferior temporal structures including the hippocampus and extending to the fusiform gyrus. In addition, lesions affecting fibers crossing the right temporal cortex, potentially disconnecting occipital-temporal from frontal regions, diminished the self-bias effect. The data highlight that self-prioritized face processing is linked to regions in the right hemisphere associated with face recognition memory and it also calls on executive processes in the left hemisphere that normally modulate self-prioritized attention.

The salient self: the left intraparietal sulcus responds to social as well as perceptual-salience after self-association.

Perceptual learning is associated with experience-based changes in stimulus salience. Here, we use a novel procedure to show that learning a new association between a self-label and a neutral stimulus produces fast alterations in social salience measured by interference when targets associated with other people have to be selected in the presence of self-associated distractors. Participants associated neutral shapes with either themselves or a friend, over a short run of training trials. Subsequently, the shapes had to be identified in hierarchical (global-local) forms. The data show that giving a shape greater personal significance by associating it with the self had effects on visual selection equivalent to altering perceptual salience. Similar to previously observed effects linked to when perceptually salient distractors are ignored, effects of a self-associated distractor also increased activation in the left intraparietal cortex sulcus. The results show that self-associations to sensory stimuli rapidly modulate neural responses in a manner similar to changes in perceptual saliency. The self-association procedure provides a new way to understand how personal significance affects behavior.

Coupling social attention to the self forms a network for personal significance.

Prior social psychological studies show that newly assigned personal significance can modulate high-level cognitive processes, e.g., memory and social evaluation, with self- and other-related information processed in dissociated prefrontal structure: ventral vs. dorsal, respectively. Here, we demonstrate the impact of personal significance on perception and show the neural network that supports this effect. We used an associative learning procedure in which we "tag" a neutral shape with a self-relevant label. Participants were instructed to associate three neutral shapes with labels for themselves, their best friend, or an unfamiliar other. Functional magnetic resonance imaging data were acquired while participants judged whether the shape-label pairs were maintained or swapped. Behaviorally, participants rapidly tagged a neutral stimulus with self-relevance, showing a robust advantage for self-tagged stimuli. Self-tagging responses were associated with enhanced activity in brain regions linked to self-representation [the ventral medial prefrontal cortex (vmPFC)] and to sensory-driven regions associated with social attention [the left posterior superior temporal sulcus (LpSTS)]. In contrast, associations formed with other people recruited a dorsal frontoparietal control network, with the two networks being inversely correlated. Responses in the vmPFC and LpSTS predicted behavioral self-bias effects. Effective connectivity analyses showed that the vmPFC and the LpSTS were functionally coupled, with the strength of coupling associated with behavioral self-biases. The data show that assignment of personal social significance affects perceptual matching by coupling internal self-representations to brain regions modulating attentional responses to external stimuli.

A Neural Decomposition of Visual Search Using Voxel-based Morphometry.

The ability to search efficiently for visual targets among distractors can break down after a variety of brain lesions, but the specific processes affected by the lesions are unclear. We examined search over space (conjunction search) and over time plus space (preview search) in a consecutive series of patients with acquired brain lesions. We also assessed performance on standard neuropsychological measures of visuospatial short-term memory (Corsi Block), sustained attention and memory updating (the contrast between forward and backward digit span), and visual neglect. Voxel-based morphometry analyses revealed regions in the occipital (middle occipital gyrus), posterior parietal (angular gyrus), and temporal cortices (superior and middle temporal gyri extending to the insula), along with underlying white matter pathways, associated with poor search. Going beyond standard voxel-based morphometry analyses, we then report correlation measures of structural damage in these regions and the independent neuropsychological measures of other cognitive functions. We find distinct patterns of correlation in areas linked to poor search, suggesting that the areas play functionally different roles in search. We conclude that neuropsychological disorders of search can be linked to necessary and distinct cognitive functions, according to the site of lesion.

Visual search in depth: The neural correlates of segmenting a display into relevant and irrelevant three-dimensional regions.

Visual perception is facilitated by the ability to selectively attend to relevant parts of the world and to ignore irrelevant regions or features. In visual search tasks, viewers are able to segment displays into relevant and irrelevant items based on a number of factors including the colour, motion, and temporal onset of the target and distractors. Understanding the process by which viewers prioritise relevant parts of a display can provide insights into the effect of top-down control on visual perception. Here, we investigate the behavioural and neural correlates of segmenting a display according to the expected three-dimensional (3D) location of a target. We ask whether this segmentation is based on low-level visual features (e.g. common depth or common surface) or on higher-order representations of 3D regions. Similar response-time benefits and neural activity were obtained when items fell on common surfaces or within depth-defined volumes, and when displays were vertical (such that items shared a common depth/disparity) or were tilted in depth. These similarities indicate that segmenting items according to their 3D location is based on attending to a 3D region, rather than a specific depth or surface. Segmenting the items in depth was mainly associated with increased activation in depth-sensitive parietal regions rather than in depth-sensitive visual regions. We conclude that segmenting items in depth is primarily achieved via higher-order, cue invariant representations rather than through filtering in lower-level perceptual regions.

Antisaccades and executive dysfunction in early drug-naive Parkinson's disease: The discovery study.

BACKGROUND: Cognitive impairment is well recognized in Parkinson's disease (PD), but when it begins to develop is unclear. The aim of this study was to identify early signs of cognitive impairment along with abnormalities in saccadic behavior in newly diagnosed unmedicated PD patients. METHODS: Nineteen drug-naive PD patients and 20 controls were examined using a battery of tests, including an antisaccade task, phonemic and semantic verbal fluencies, and a switching and rule finding task. RESULTS: With simple tasks, no differences were found between the two groups. However, cognitive performance of the two groups diverged with more complex tasks, occurring independently of PD-related motor impairment. Patients exhibited higher antisaccadic error rates and switch costs in the task switching test, and performed significantly worse in the rule finding task. CONCLUSIONS: Certain cognitive domains and saccadic parameters are already significantly impoverished in newly diagnosed Parkinson's patients, even before the initiation of medication.

A significant risk factor for poststroke depression: the depression-related subnetwork.

BACKGROUND: Despite being one of the direct causes of depression, whether stroke-induced neuroanatomical deterioration actually plays an important role in the onset of poststroke depression (PSD) is controversial. We assessed the structural basis of PSD, particularly with regard to white matter connectivity. METHODS: We evaluated lesion index, fractional anisotropy (FA) reduction and brain structural networks and then analyzed whole brain voxel-based lesions and FA maps. To understand brain damage in the context of brain connectivity, we used a graph theoretical approach. We selected nodes whose degree correlated with the Hamilton Rating Scale for Depression score (p < 0.05, false discovery rate-corrected), after controlling for age, sex, years of education, lesion size, Mini Mental State Examination score and National Institutes of Health Stroke Scale score. We used Poisson regression with robust standard errors to assess the contribution of the identified network toward poststroke major depression. RESULTS: We included 116 stroke patients in the study. Fourteen patients (12.1%) had diagnoses of major depression and 26 (22.4%) had mild depression. We found that lesions in the right insular cortex, left putamen and right superior longitudinal fasciculus as well as FA reductions in broader areas were all associated with major depression. Seventeen nodes were selected to build the depression-related subnetwork. Decreased local efficiency of the subnetwork was a significant risk factor for poststroke major depression (relative risk 0.84, 95% confidence interval 0.72-0.98, p = 0.027). LIMITATIONS: The inability of DTI tractography to process fibre crossings may have resulted in inaccurate construction of white matter networks and affected statistical findings. CONCLUSION: The present study provides, to our knowledge, the first graph theoretical analysis of white matter networks linked to poststroke major depression. These findings provide new insights into the neuroanatomical substrates of depression that develops after stroke.

Electrophysiological evidence for enhanced representation of food stimuli in working memory.

Studies from our laboratory have shown that, relative to neutral objects, food-related objects kept in working memory (WM) are particularly effective in guiding attention to food stimuli (Higgs et al. in Appetite, 2012). Here, we used electrophysiological measurements to investigate the neural representation of food versus non-food items in WM. Subjects were presented with a cue (food or non-food item) to either attend to or hold in WM. Subsequently, they had to search for a target, while the target and distractor were each flanked by a picture of a food or non-food item. Behavioural data showed that a food cue held in WM modulated the deployment of visual attention to a search target more than a non-food cue, even though the cue was irrelevant for target selection. Electrophysiological measures of attention, memory and retention of memory (the P3, LPP and SPCN components) were larger when food was kept in WM, compared to non-food items. No such effect was observed in a priming task, when the initial cue was merely identified. Overall, our electrophysiological data are consistent with the suggestion that food stimuli are particularly strongly represented in the WM system.

Haptic shape processing in visual cortex.

Humans typically rely upon vision to identify object shape, but we can also recognize shape via touch (haptics). Our haptic shape recognition ability raises an intriguing question: To what extent do visual cortical shape recognition mechanisms support haptic object recognition? We addressed this question using a haptic fMRI repetition design, which allowed us to identify neuronal populations sensitive to the shape of objects that were touched but not seen. In addition to the expected shape-selective fMRI responses in dorsal frontoparietal areas, we observed widespread shape-selective responses in the ventral visual cortical pathway, including primary visual cortex. Our results indicate that shape processing via touch engages many of the same neural mechanisms as visual object recognition. The shape-specific repetition effects we observed in primary visual cortex show that visual sensory areas are engaged during the haptic exploration of object shape, even in the absence of concurrent shape-related visual input. Our results complement related findings in visually deprived individuals and highlight the fundamental role of the visual system in the processing of object shape.

A dorsal visual route necessary for global form perception: evidence from neuropsychological fMRI.

Hierarchical models of visual processing assume that global pattern recognition is contingent on the progressive integration of local elements across larger spatial regions, operating from early through intermediate to higher-level cortical regions. Here, we present results from neuropsychological fMRI that refute such models. We report two patients, one with lesions to intermediate ventral regions and the other with damage around the intraparietal sulcus (IPS). The patient with ventral damage showed normal behavioral and BOLD responses to global Glass patterns. The patient with IPS damage was impaired in discriminating global patterns and showed a lack of significant responses to these patterns in intermediate visual regions spared by the lesion. However, this patient did show BOLD activity to translational patterns, where local element relations are important. These results suggest that activation of intermediate ventral regions is not necessary to code global patterns; instead global patterns are coded in a heterarchical fashion. High-level regions of dorsal cortex are necessary to generate global pattern coding in intermediate ventral regions; in contrast, local integration processes are not sufficient.