Neural substrates differentiating global/local processing of bilateral visual inputs

When fixing problems kills personal development: fMRI reveals conflict between Real and Ideal selves

Many coaching approaches aim to change behavior by increasing self-knowledge. However, self-knowledge can be difficult to achieve. One hypothesis (e.g., Jung, Rogers) is that self-knowledge is challenging because there is inherent conflict between different aspects of the self. This hypothesis is foundational to Boyatzis' intentional change theory (ICT). ICT holds that effective coaching requires deliberate sequencing of the client's exploration of different aspects of their self. Coaches initially encourage clients to focus exclusively on their Ideal self. The ICT approach differs from that advocated by most coaching organizations that suggest collaborative goal setting at the start of the coaching engagement, encouraging clients to focus on fixing performance deficits and problematic behaviors-aspects of the Real self. If there is conflict between thinking about Ideal and Real selves, then this strategy will be suboptimal. The hypothesis of attentional conflict therefore has significant implications for coaching practice. Previous findings establish a link between attention to Ideal vs. Real selves and global vs. local visual processing, respectively. This association alone does not imply conflict because, in naturalistic settings, global and local perceptual processes usually work in concert. However, certain stimuli such as Navon figures (letters made from many smaller letters, e.g., a large E made of small R's) create conflict due to incongruence between the global and local features. Does thinking about the self inherently generate conflict, like a Navon figure, or is it more akin to everyday perception? To answer this question the current study uses functional magnetic resonance imaging to examine the overlap in brain activity in young adults between two pairs of otherwise very dissimilar tasks: coaching interactions focused on Ideal vs. Real self; and attention to global vs. local features of Navon figures. Despite the ostensible absence of overlap in the psychological processes involved in these pairs of tasks, we find a remarkable degree of overlap in brain activity. This overlap was pronounced in higher (parietal and temporal) areas known to be involved in resolving attentional conflict. These findings provide compelling biological evidence for inherent conflict between thinking about Ideal and Real selves.

Different levels of visuospatial abilities linked to differential brain correlates underlying visual mental segmentation processes in autism

The neural underpinnings of enhanced locally oriented visual processing that are specific to autistics with a Wechsler's Block Design (BD) peak are largely unknown. Here, we investigated the brain correlates underlying visual segmentation associated with the well-established autistic superior visuospatial abilities in distinct subgroups using functional magnetic resonance imaging. This study included 31 male autistic adults (15 with (AUTp) and 16 without (AUTnp) a BD peak) and 28 male adults with typical development (TYP). Participants completed a computerized adapted BD task with models having low and high perceptual cohesiveness (PC). Despite similar behavioral performances, AUTp and AUTnp showed generally higher occipital activation compared with TYP participants. Compared with both AUTnp and TYP participants, the AUTp group showed enhanced task-related functional connectivity within posterior visuoperceptual regions and decreased functional connectivity between frontal and occipital-temporal regions. A diminished modulation in frontal and parietal regions in response to increased PC was also found in AUTp participants, suggesting heavier reliance on low-level processing of global figures. This study demonstrates that enhanced visual functioning is specific to a cognitive phenotypic subgroup of autistics with superior visuospatial abilities and reinforces the need to address autistic heterogeneity by good cognitive characterization of samples in future studies.

Navigating the link between processing speed and network communication in the human brain

Processing speed on cognitive tasks relies upon efficient communication between widespread regions of the brain. Recently, novel methods of quantifying network communication like 'navigation efficiency' have emerged, which aim to be more biologically plausible compared to traditional shortest path length-based measures. However, it is still unclear whether there is a direct link between these communication measures and processing speed. We tested this relationship in forty-five healthy adults (27 females), where processing speed was defined as decision-making time and measured using drift rate from the hierarchical drift diffusion model. Communication measures were calculated from a graph theoretical analysis of the whole-brain structural connectome and of a task-relevant fronto-parietal structural subnetwork, using the large-scale Desikan-Killiany atlas. We found that faster processing speed on trials that require greater cognitive control are correlated with higher navigation efficiency (of both the whole-brain and the task-relevant subnetwork). In contrast, faster processing speed on trials that require more automatic processing are correlated with shorter path length within the task-relevant subnetwork. Our findings reveal that differences in the way communication is modelled between shortest path length and navigation may be sensitive to processing of automatic and controlled responses, respectively. Further, our findings suggest that there is a relationship between the speed of cognitive processing and the structural constraints of the human brain network.

Functional involvement of subcortical structures in global-local processing

The present study examined the involvement of subcortical structures in the processing of global and local information. To this end, we used a stereoscope to present hierarchical stimuli (global shapes composed of local elements) in a dichoptic or a monocular fashion, such that global and local information was either presented to the same eye (same-eye condition) or segregated between the eyes (different-eyes condition). In Experiment 1, the typical global advantage and global-to-local interference were observed for the same-eye presentation condition. On the other hand, no indication of a global advantage or of global-to-local interference emerged in the different-eyes presentation condition. In Experiment 2 we replicated these results, ruling out a possible alternative explanation that the pattern of results observed for the different-eyes presentation condition resulted merely from segregation of the stimulus between the eyes. Rather, the experiment demonstrated that the global-to-local interference was eliminated only when global and local information was segregated between the eyes. Taken together, these findings suggest that processing the global aspect of hierarchical stimuli involves subcortical regions indexed by monocular portions of the visual system.

How the forest interacts with the trees: Multiscale shape integration explains global and local processing

Hierarchical stimuli have been widely used to study global and local processing. Two classic phenomena have been observed using these stimuli: the global advantage effect (we identify the global shape faster) and an interference effect (we identify shape slower when the global and local shapes are different). Because these phenomena have been observed during shape categorization tasks, it is unclear whether they reflect the categorical judgment or the underlying shape representation. Understanding the underlying shape representation is also critical because both global and local processing are modulated by stimulus properties. We performed two experiments to investigate these issues. In Experiment 1, we show that these phenomena can be observed in a same-different task, and that participants show systematic variation in response times across image pairs. We show that the response times to any pair of images can be accurately predicted using two factors: their dissimilarity and their distinctiveness relative to other images. In Experiment 2, we show that these phenomena can also be observed in a visual search task where participant did not have to make any categorical shape judgments. Here too, participants showed highly systematic variations in response time that could be explained as a linear sum of shape comparisons across global and local scales. Finally, the dissimilarity and distinctiveness factors estimated from the same-different task were systematically related to the search dissimilarities observed during visual search. In sum, our results show that global and local processing phenomena are properties of a systematic shape representation governed by simple rules.

Self-Orientation Modulates the Neural Correlates of Global and Local Processing

Differences in self-orientation (or "self-construal") may affect how the visual environment is attended, but the neural and cultural mechanisms that drive this remain unclear. Behavioral studies have demonstrated that people from Western backgrounds with predominant individualistic values are perceptually biased towards local-level information; whereas people from non-Western backgrounds that support collectivist values are preferentially focused on contextual and global-level information. In this study, we compared two groups differing in predominant individualistic (N = 15) vs collectivistic (N = 15) self-orientation. Participants completed a global/local perceptual conflict task whilst undergoing functional Magnetic Resonance Imaging (fMRI) scanning. When participants high in individualistic values attended to the global level (ignoring the local level), greater activity was observed in the frontoparietal and cingulo-opercular networks that underpin attentional control, compared to the match (congruent) baseline. Participants high in collectivistic values activated similar attentional control networks o only when directly compared with global processing. This suggests that global interference was stronger than local interference in the conflict task in the collectivistic group. Both groups showed increased activity in dorsolateral prefrontal regions involved in resolving perceptual conflict during heightened distractor interference. The findings suggest that self-orientation may play an important role in driving attention networks to facilitate interaction with the visual environment.

The local, global, and neural aspects of visuospatial processing in autism spectrum disorders

Behavioral studies have documented a relative advantage in some aspects of visuospatial cognition in autism although it is not consistently found in higher functioning individuals with autism. The purpose of this functional neuroimaging study was to examine the neural activity in high functioning individuals with autism while they performed a block design task that systematically varied with regard to whether a global pattern was present. Participants were 14 adults with high-functioning autism and 14 age and IQ matched typical controls. The task was to identify a missing block in target figures which had either an obvious global shape or was an arbitrary array of blocks. Behavioral results showed intact, but not superior, performance in our participants with autism. A key group difference was that the participants with autism showed reliably greater activation in occipital and parietal regions in both tasks suggesting an increased reliance of the autism group on posterior brain areas to mediate visuospatial tasks. Thus, increased reliance on relatively posterior brain regions in itself may not guarantee superior performance as seen in the present study.

Aberrant functional organization within and between resting-state networks in AD

Altered functional characteristics have been reported in amnestic mild cognitive impairment (aMCI) and Alzheimer's disease (AD); nonetheless, comprehensive analyses of the resting-state networks (RSNs) are rare. This study combined multiple imaging modalities to investigate the functional and structural changes within each RSN and between RSNs in aMCI/AD patients. Eight RSNs were identified from functional MRI data from 35 AD, 18 aMCI and 21 normal control subjects using independent component analysis. We compared functional connectivity (FC) within each RSN and found decreased FC in the several cognitive-related RSNs in AD, including the bilateral precuneus of the precuneus network, the posterior cingulate cortex and left precuneus of the posterior default mode network (DMN), and the left superior parietal lobule of the left frontoparietal network (LFP). We further compared the grey matter volumes and amplitudes of low-frequency fluctuations of these regions and found decreases in these measures in AD. Importantly, we found decreased inter-network connectivity between the visual network and the LFP and between the anterior and posterior DMNs in AD. All indices in aMCI patients were numerically between those of controls and AD patients. These results suggest that the brain networks supporting complex cognitive processes are specifically and progressively impaired over the course of AD, and the FC impairments are present not only within networks but also between networks.

Superior parietal lobule dysfunction in a homogeneous group of dyslexic children with a visual attention span disorder

A visual attention (VA) span disorder has been reported in dyslexic children as potentially responsible for their poor reading outcome. The purpose of the current paper was to identify the cerebral correlates of this VA span disorder. For this purpose, 12 French dyslexic children with severe reading and VA span disorders and 12 age-matched control children were engaged in a categorisation task under fMRI. Two flanked and isolated conditions were designed which both involved multiple-element simultaneous visual processing but taxed visual attention differently. For skilled readers, flanked stimuli processing activated a large bilateral cortical network comprising the superior and inferior parietal cortex, the inferior temporal cortex, the striate and extrastriate visual cortex, the middle frontal cortex and the anterior cingulate cortex while the less attention-demanding task of isolated stimuli only activated the inferior occipito-temporal cortex bilaterally. With respect to controls, the dyslexic children showed significantly reduced activation within bilateral parietal and temporal areas during flanked processing, but no difference during the isolated condition. The neural correlates of the processes involved in attention-demanding multi-element processing tasks were more specifically addressed by contrasting the flanked and the isolated conditions. This contrast elicited activation of the left precuneus/superior parietal lobule in the controls, but not in the dyslexic children. These findings provide new insights on the role of parietal regions, in particular the left superior parietal lobule, in the visual attention span and in developmental dyslexia.

The inversion effect in visual word form processing

Reading is one of the best well-practiced visual tasks for modern people. We investigated how the visual cortex analyzes spatial configuration in written words by studying the inversion effect in Chinese character processing. We measured the psychometric functions and brain activations for upright real-characters and non-characters and their inverted (upside down) versions. In the psychophysical experiment, the real-characters showed an inversion effect at both 1 degrees and 4 degrees eccentricities, while the non-characters showed no inversion effect for all eccentricities tested. In the functional magnetic resonance image (fMRI) experiment, the left fusiform gyrus and a small area in the bilateral lateral occipital regions showed a significant differential activation between upright and inverted real-characters. The bilateral fusiform gyri also show differential activation between upright real- and non-characters. The dorsal lateral occipital regions showed character-selective activation when compared with scrambled lines. The result suggested that the occipitoparietal regions may analyze the local features of an object regardless of its familiarity. Therefore, the lateral occipital regions may play an intermediate role in integrating the local information in an object. Finally, the fusiform gyrus plays a critical role in analyzing global configurations of a visual word form. This is consistent with the notion that the human visual cortex analyzes an object in a hierarchical way.

Activation patterns in visual cortex reveal receptive field size-dependent attentional modulation

Because our brain cannot process all visual information that enters it, we usually pay attention to only a specific aspect of our visual world. Selective visual attention modulates brain activation in cortical areas corresponding to the attended spatial location. However, visual attention has also been associated with the modulation of activation in different brain areas depending on the relevant spatial scale. In this study, we establish a link between attended spatial scale and receptive field size. We demonstrate that attention to a large or a small object in a visual scene increases activation specifically in brain regions with correspondingly large or small receptive field sizes. To analyze and visualize differential brain activation in contiguous cortical areas we used a mapping strategy evaluating the modelling parameters (beta) from functional magnetic resonance imaging data analysis. Assessment of the course of these parameters along traces in different directions in the visual cortex strengthens our conclusion that selective visual attention modulates brain areas with specific neuronal receptive field size properties corresponding to the task at hand. This also confirms predictions of models of selective attention, that attentional modulation of visual processing critically depends on the receptive field size of neurons across the visual cortex.

Implicit identification of irrelevant local objects interacts with global/local processing of hierarchical stimuli

This work aimed at studying interactions between automatic object identification and global/local perceptual processing. We designed a paradigm in which participants were presented with pairs of hierarchically organized items, composed of global forms made up of local forms. Both global and local forms could represent either objects or non-objects. Subjects were instructed to detect whether the two hierarchical items composing a pair were identical or different. In a dissimilar pair, items differed at one level (target level), the other level, made of similar forms on both sides, was irrelevant to perform the task. We hypothesized that the automatic identification of object could affect the global precedence principle defined by Navon. In agreement with our hypothesis, we found that when the irrelevant level was made of objects, the global precedence effect was reversed. In contrast, the irrelevant level had no effect when the target level included only objects, or when the irrelevant level was made of non-object, the global precedence principle was being preserved in these cases. This interaction is compatible with the existence of two distinct processes working in parallel, namely automatic identification and structural analysis, that could either interfere or act together for the detection of differences.

Neural correlates of within-level and across-level attention to multiple compound stimuli

Event-related potentials (ERPs) were recorded to investigate the neural mechanisms of attention to the same or different levels of two compound letters presented concurrently in the left and right visual fields, respectively. Relative to the condition when attention was allocated to the global level of one compound stimulus and the local level of another one (across-level attention), attention to the same level of the two compound stimuli (within-level attention) increased an early positivity between 100 and 140 ms (P1) over the occipito-parietal cortex. A long-latency positivity between 320 and 560 ms (P3) over the central-parietal area was also increased in the within-level relative to across-level attention conditions. The ERP results suggest that, relative to across-level attention, within-level attention to multiple compound stimuli facilitates both early sensory-perceptual processing and late process of stimulus evaluation and identification in hierarchical analysis.

Attentional modulation of perceptual grouping in human visual cortex: functional MRI studies

When presented with a complex visual scene, our visual system has to organize the discrete entities present into useful perceptual units. The current work investigated the neural substrates of perceptual grouping defined by Gestalt laws of proximity and similarity of shape, and whether the neural substrates underlying perceptual grouping are modulated by task relevance and spatial attention. In visual discrimination tasks, subjects identified the orientations of perceptual groups formed by proximity or similarity of local elements or alternatively identified colors of either dots around the grouped stimuli or the fixation cross. Using functional magnetic resonance imaging (fMRI), we identified that the calcarine cortex was involved in proximity grouping but not in the grouping process defined by similarity of shape. Moreover, we showed evidence that the neural correlates of proximity grouping in the calcarine cortex were weakened when the elements were of low task relevance and fell outside an attended area of field. The findings reveal the neural basis for basic grouping operations, as well as illustrating how attention and proximity grouping interact in human visual cortex.

Neural mechanisms of global/local processing of bilateral visual inputs: an ERP study

OBJECTIVE

Examine the neural mechanisms of global/local processing of multiple hierarchical stimuli.

METHODS

Event-related brain potentials (ERPs) were recorded from adults who selectively attended to the global or local level of two compound letters that were simultaneously presented in the left and right visual fields, respectively. The compound stimuli were either broadband in spatial frequency (SF) spectrum or contrast balanced to remove low SFs. Subjects were asked to detect the presence of a global or local target that might appear in either the left or the right visual field in separate blocks of trials.

RESULTS

Attention to the local level of broadband stimuli elicited a positivity over lateral occipital sites at 80-120 ms (P1) with larger amplitude than those in the global attention condition. However, global attention produced an enhanced positivity at 240-320 ms (P2) over lateral occipital sites relative to local attention. Both the P1 and P2 waves in the global condition were of larger amplitudes over the left than right hemispheres. Contrast balancing eliminated the P1 and P2 effects and modulated the hemispheric asymmetry of the long-latency occipital positivity.

CONCLUSIONS

The results provide ERP evidence for modulations of neural activities in the visual cortex by global/local attention to concurrently presented multiple compound letters. Moreover, the modulation of brain activities by global/local attention depends upon the presence of low SFs in the compound stimuli.

SIGNIFICANCE

The ERP results of this study contribute to the understanding of neural mechanisms of the processing of simultaneously-presented multiple compound stimuli.