Perceptual processing of stereopsis in humans: high-field (3.0-tesla) functional MRI study

Distinct rich and diverse clubs regulate coarse and fine binocular disparity processing: Evidence from stereoscopic task-based fMRI

While cortical regions involved in processing binocular disparities have been studied extensively, little is known on how the human visual system adapts to changing disparity magnitudes. In this paper, we investigate causal mechanisms of coarse and fine binocular disparity processing using fMRI with a clinically validated, custom anaglyph-based stimulus. We make use of Granger causality and graph measures to reveal the existence of distinct rich and diverse clubs across different disparity magnitudes. We demonstrate that Middle Temporal area (MT) plays a specialized role with overlapping rich and diverse characteristics. Next, we show that subtle interhemispheric differences exist across various brain regions, despite an overall right hemisphere dominance. Finally, we pass the graph measures through the decision tree and found that the diverse clubs outperform rich clubs in decoding disparity magnitudes. Our study sets the stage for conducting further investigations on binocular disparity processing, particularly in the context of neuro-ophthalmic disorders with binocular impairments.

Deficits of Visual Cortex Function in Acute Acquired Concomitant Esotropia Patients

Purpose

The purpose of this study was to explore the cortical deficits of patients with acquired concomitant esotropia (AACE) using the resting-state functional magnetic resonance imaging (rs-fMRI) technique.

Methods

Rs-fMRI signals from 25 patients with AACE and 25 matched controls were collected. The repeated-measures analysis of variance (RM-ANOVA) test and two-sample t-test were used to investigate statistical differences of the amplitudes of low-frequency fluctuation (ALFF) signals and correlation analysis was performed to validate the relationship of signal change and clinical features.

Results

The AACE group showed decreased ALFF in both hemispheres symmetrically (t = 0.38, P = 0.71), with peak t in both middle occipital gyrus. The ALFF signal from the upper left inferior frontal gyrus was negatively correlated with the age of onset (r = 0.62, P = 0.0008), and the ALFF signal from the right superior temporal gyrus was negatively correlated with the near work hours (r = 0.63, P = 0.0008). The ALFF signal in the left fusiform gyrus was positively correlated with both near (r = 0.48, P = 0.01) and far (r = 0.44, P = 0.03) deviation, whereas it was only positively correlated with far deviation (r = 0.44, P = 0.03) in the right. Besides, the age of onset and the near work hour were independent factors of signal changes.

Conclusions

Using the ALFF signal of rs-fMRI, we found functional deficits in the primary visual cortex and dorsal pathway in patients with AACE. There were functional changes in the fusiform gyrus, and the greater the deviation angle, the higher the changing level. These findings reveal the association of AACE and the visual center, giving us more clues about the treatment of AACE.

Altered Spontaneous Brain Activity Patterns and Functional Connectivity in Adults With Intermittent Exotropia: A Resting-State fMRI Study

The purpose of this study is to investigate brain functional changes in patients with intermittent exotropia (IXT) by analyzing the amplitude of low-frequency fluctuation (ALFF) of brain activity and functional connectivity (FC) using resting-state functional magnetic resonance imaging (rs-fMRI). There were 26 IXT patients and 22 age-, sex-, education-, and handedness-matched healthy controls (HCs) enrolled who underwent rs-fMRI. The ALFF, fractional ALFF (fALFF) values in the slow 4 and slow 5 bands, and FC values were calculated and compared. The correlations between ALFF/fALFF values in discrepant brain regions and clinical features were evaluated. Compared with HCs, ALFF/fALFF values were significantly increased in the right angular gyrus (ANG), supramarginal gyrus (SMG), inferior parietal lobule (IPL), precentral gyrus (PreCG), and the bilateral inferior frontal gyri (IFG), and decreased in the right precuneus gyrus (PCUN), left middle occipital gyrus (MOG), and postcentral gyrus (PoCG) in IXT patients. The Newcastle Control Test score was negatively correlated with ALFF values in the right IFG (r = −0.738, p < 0.001). The duration of IXT was negatively correlated with ALFF values in the right ANG (r = −0.457, p = 0.049). Widespread increases in FC were observed between brain regions, mainly including the right cuneus (CUN), left superior parietal lobule (SPL), right rolandic operculum (ROL), left middle temporal gyrus (MTG), left IFG, left median cingulate gyrus (DCG), left PoCG, right PreCG, and left paracentral gyrus (PCL) in patients with IXT. No decreased FC was observed. Patients with IXT exhibited aberrant intrinsic brain activities and FC in vision- and eye movement-related brain regions, which extend current understanding of the neuropathological mechanisms underlying visual and oculomotor impairments in IXT patients.

Self-estimation of physical ability in stepping over an obstacle is not mediated by visual height perception: a comparison between young and older adults

Older adults tend to overestimate their step-over ability. However, it is unclear as to whether this is caused by inaccurate self-estimation of physical ability or inaccurate perception of height. We, therefore, measured both visual height perception ability and self-estimation of step-over ability among young and older adults. Forty-seven older and 16 young adults performed a height perception test (HPT) and a step-over test (SOT). Participants visually judged the height of vertical bars from distances of 7 and 1 m away in the HPT, then self-estimated and, subsequently, actually performed a step-over action in the SOT. The results showed no significant difference between young and older adults in visual height perception. In the SOT, young adults tended to underestimate their step-over ability, whereas older adults either overestimated their abilities or underestimated them to a lesser extent than did the young adults. Moreover, visual height perception was not correlated with the self-estimation of step-over ability in both young and older adults. These results suggest that the self-overestimation of step-over ability which appeared in some healthy older adults may not be caused by the nature of visual height perception, but by other factor(s), such as the likely age-related nature of self-estimation of physical ability, per se.

Responses to interocular disparity correlation in the human cerebral cortex

Purpose

Perceiving binocular depth relies on the ability of our visual system to precisely match corresponding features in the left and right eyes. Yet how the human brain extracts interocular disparity correlation is poorly understood.

Methods

We used functional magnetic resonance imaging (fMRI) to characterize brain regions involved in processing interocular disparity correlation. By varying the amount of interocular correlation of a disparity-defined random-dot-stereogram, we concomitantly controlled the perception of binocular depth and measured the percent Blood-Oxygenation-Level-Dependent (%BOLD)-signal in multiple regions-of-interest in the human occipital cortex and along the intra-parietal sulcus.

Results

A linear support vector machine classification analysis applied to cortical responses showed patterns of activation that represented different disparity correlation levels within regions-of-interest in the visual cortex. These also revealed a positive trend between the difference in disparity correlation and classification accuracy in V1, V3 and lateral occipital cortex. Classifier performance was significantly related to behavioural performance in dorsal visual area V3. Cortical responses to random-dot-stereogram stimuli were greater in the right compared to the left hemisphere.

Conclusions

Our results show that multiple regions in the cerebral cortex are sensitive to changes in interocular disparity correlation, and that dorsal area V3 may play an important role in the early transformation of binocular disparity to depth perception.

Comparison of brain activation in response to two dimensional and three dimensional on-line games

OBJECTIVE

The present study assessed the difference in the brain activity of professional gamers (excessive players, but not addicts) in response to playing a 3-dimensional online game with an improved interface.

METHODS

Twenty-three StarCraft I pro gamers and 16 StarCraft II pro gamers were recruited at Chung Ang University Medical Center. Brain activity in response to StarCraft I or II cues was assessed with a 1.5 Tesla Espree MRI scanner.

RESULTS

StarCraft I pro gamers showed significantly greater activity in 4 clusters in response to the video game cues compared to StarCraft II pro gamers: right superior frontal gyrus, right medial frontal gyrus, right occipital lobe, and left medial frontal gyrus. StarCraft II pro gamers showed significantly greater activity in 3 clusters in response to the video game cues compared to StarCraft I pro gamers: left middle frontal gyrus, left temporal fusiform gyrus and left cerebellum.

DISCUSSION

This is the first study to show the difference in brain activity between gamers playing either a 2-dimensional or 3-dimensional online game. Current brain imaging studies may confirm the pro gamers' experience when playing StarCraft II, a 3-dimensional game with an improved interface, relative to playing StarCraft I.

Dorsal visual pathway changes in patients with comitant extropia

Background

Strabismus is a disorder in which the eyes are misaligned. Persistent strabismus can lead to stereopsis impairment. The effect of strabismus on human brain is not unclear. The present study is to investigate whether the brain white structures of comitant exotropia patients are impaired using combined T1-weighted imaging and diffusion tensor imaging (DTI).

Principal Findings

Thirteen patients with comitant strabismus and twelve controls underwent magnetic resonance imaging (MRI) with acquisition of T1-weighted and diffusion tensor images. T1-weighted images were used to analyze the change in volume of white matter using optimized voxel-based morphology (VBM) and diffusion tensor images were used to detect the change in white matter fibers using voxel-based analysis of DTI in comitant extropia patients. VBM analysis showed that in adult strabismus, white matter volumes were smaller in the right middle occipital gyrus, right occipital lobe/cuneus, right supramarginal gyrus, right cingulate gyrus, right frontal lobe/sub-gyral, right inferior temporal gyrus, left parahippocampa gyrus, left cingulate gyrus, left occipital lobe/cuneus, left middle frontal gyrus, left inferior parietal lobule, and left postcentral gyrus, while no brain region with greater white matter volume was found. Voxel-based analysis of DTI showed lower fractional anisotropy (FA) values in the right middle occipital gyrus and right supramarginal gyrus in strabismus patients, while brain region with increased FA value was found in the right inferior frontal gyrus.

Conclusion

By combining VBM and voxel-based analysis of DTI results, the study suggests that the dorsal visual pathway was abnormal or impaired in patients with comitant exotropia.

Impaired distance perception and size constancy following bilateral occipitoparietal damage

Accurate distance perception depends on the processing and integration of a variety of monocular and binocular cues. Dorsal stream lesions can impair this process, but details of this neurocognitive relationship remain unclear. Here, we tested a patient with bilateral occipitoparietal damage and severely impaired stereopsis. We addressed four related questions: (1) Can distance and size perception survive limitations in perceiving monocular and binocular cues? (2) Are egocentric (self-referential) and allocentric (object-referential) distance judgments similarly impaired? (3) Are distance measurements equally impaired in peripersonal and extrapersonal space? (4) Are size judgments possible when distance processing is impaired? The results demonstrate that the patient's lesions impaired both her distance and size perception, but not uniformly. Her performance when using an egocentric reference frame was more impaired than her performance when using an allocentric reference frame. Likewise, her distance judgments in peripersonal space were more impaired than those in extrapersonal space. The patient showed partial preservation in size processing of novel objects even when familiar size cues were removed.

Symmetry versus repetition in cyclopean vision: A microgenetic analysis

In four experiments, participants had to detect symmetries or repetitions distributed over two depth planes, under presentation times of 200-1000 ms. Structurally corresponding elements were placed in different planes (Experiments 1a and 1b) or in the same plane (Experiments 2a and 2b). Results suggest (a) an ongoing interaction between regularity cues and depth cues, and (b) that efficient detection of symmetry but not of repetition depends on structural correspondences within depth planes. The latter confirms the idea that, to perceptual organization, symmetry is a cue for the presence of one object, whereas repetition is a cue for the presence of multiple objects.

The specificity of cortical region KO to depth structure

Functional MRI studies have identified a cortical region designated as KO between retinotopic areas V3A/B and motion area V5 in human cortex as particularly responsive to motion-defined or kinetic borders. To determine the response of the KO region to more general aspects of structure, we used stereoscopic depth borders and disparate planes with no borders, together with three stimulus types that evoked no depth percept: luminance borders, line contours and illusory phase borders. Responses to these stimuli in the KO region were compared with the responses in retinotopically defined areas that have been variously associated with disparity processing in neurophysiological and fMRI studies. The strongest responses in the KO region were to stimuli evoking perceived depth structure from either disparity or motion cues, but it showed negligible responses either to luminance-based contour stimuli or to edgeless disparity stimuli. We conclude that the region designated as KO is best regarded as a primary center for the generic representation of depth structure rather than any kind of contour specificity.

Diffusion tensor analysis in chronic schizophrenia. A preliminary study on a high-field (3.0T) system

The objective of this study was to delineate further the nature of diffusion anisotropy abnormalities in frontal white matter previously observed in schizophrenic patients using a high-field magnetic resonance imaging (MRI) system. Six schizophrenia patients and six healthy control subjects were examined using a highfield MRI (3.0T) system. In order to confirm previously reported abnormalities in anisotropy, data were first analyzed to determine fractional anisotropy (FA), a frequently utilized general index of anisotropy. Subsequently, the identical data set was subjected to lambda chart analysis (LCA), a newly developed algorithm for diffusion tensor analysis (DTA) that more effectively provides eigenvalue information. Frontal white matter FA was found to be significantly reduced in schizophrenic patients compared to control subjects, confirming previously reported findings. LCA revealed that the decline in FA was due to a disproportionate increase in small eigenvalue components, and not due to a decline in principal eigenvalue components.

Information processing of geometrical features of a surface based on binocular disparity cues: an fMRI study

Cortical areas related to the information processing of binocular disparity-defined geometrical features of a surface, such as depth, orientation and shape are examined by functional magnetic resonance imaging while subjects discriminated these three types of geometrical feature in random dot stereograms. Results indicate that disparity-defined information of depth and that of orientation are processed in the parietal area. Furthermore, the visual system for 3D vision in the parietal area may be organized in a hierarchical manner and the posterior part of the right intraparietal sulcus may be involved in cognitive process of 3D vision. On the other hand, disparity-defined shape information seems to be processed in the occipital visual areas and the crucial involvement of human LOS for this process is suggested.

BOLD response in dorsal areas varies with relative disparity level

Using fMRI, we explored cortical responses to dichoptically presented random-dot (RD) stimuli which formed a checkerboard by means of horizontal disparity (Julesz). Depth reversals occurred every 800 ms by appropriate horizontal shifting of a subset of the RD pattern. We compared cortical blood oxygen level dependent (BOLD) responses of five subjects under conditions with and without binocular disparity. The results indicate that only extrastriate, but not striate, areas responded more to the stimuli with binocular disparity. We further found that the BOLD signal increased with increasing disparity level only in dorsal areas of occipito-parietal and prefrontal cortex. These results suggest that the fMRI BOLD response can reflect the processing of relative binocular disparity in extrastriate cortex.

Stereoscopic processing of absolute and relative disparity in human visual cortex

Stereoscopic vision relies mainly on relative depth differences between objects rather than on their absolute distance in depth from where the eyes fixate. However, relative disparities are computed from absolute disparities, and it is not known where these two stages are represented in the human brain. Using functional MRI (fMRI), we assessed absolute and relative disparity selectivity with stereoscopic stimuli consisting of pairs of transparent planes in depth in which the absolute and relative disparity signals could be independently manipulated (at a local spatial scale). In experiment 1, relative disparity was kept constant, while absolute disparity was varied in one-half the blocks of trials ("mixed" blocks) and kept constant in the remaining one-half ("same" blocks), alternating between blocks. Because neuronal responses undergo adaptation and reduce their firing rate following repeated presentation of an effective stimulus, the fMRI signal reflecting activity of units selective for absolute disparity is expected to be smaller during "same" blocks as compared with "mixed" ones. Experiment 2 similarly manipulated relative disparity rather than absolute disparity. The results from both experiments were consistent with adaptation with differential effects across visual areas such that 1) dorsal areas (V3A, MT+/V5, V7) showed more adaptation to absolute than to relative disparity; 2) ventral areas (hV4, V8/V4alpha) showed an equal adaptation to both; and 3) early visual areas (V1, V2, V3) showed a small effect in both experiments. These results indicate that processing in dorsal areas may rely mostly on information about absolute disparities, while ventral areas split neural resources between the two types of stereoscopic information so as to maintain an important representation of relative disparity.

Representation of stereoscopic structure in human and monkey cortex

Tsao et al. have recently used functional magnetic resonance imaging to compare processing for moving stereoscopic forms in macaque and human brains. Most humans exhibited activation in a swath of lateral occipital areas, extending into the intraparietal sulcus, with a limited version of the same pattern in monkeys. However, neither species showed strong activation of the motion area known as MT in monkey or its human homolog.

Stereopsis activates V3A and caudal intraparietal areas in macaques and humans

Stereopsis, the perception of depth from small differences between the images in the two eyes, provides a rich model for investigating the cortical construction of surfaces and space. Although disparity-tuned cells have been found in a large number of areas in macaque visual cortex, stereoscopic processing in these areas has never been systematically compared using the same stimuli and analysis methods. In order to examine the global architecture of stereoscopic processing in primate visual cortex, we studied fMRI activity in alert, fixating human and macaque subjects. In macaques, we found strongest activation to near/far compared to zero disparity in areas V3, V3A, and CIPS. In humans, we found strongest activation to the same stimuli in areas V3A, V7, the V4d topolog (V4d-topo), and a caudal parietal disparity region (CPDR). Thus, in both primate species a small cluster of areas at the parieto-occipital junction appears to be specialized for stereopsis.

Clinical experience on 3.0 T systems in Niigata, 1996 to 2002

High-field human magnetic resonance imaging (MRI) systems developed over the recent years have contributed significantly to the field of functional MRI and multinuclear spectroscopy. As more experience is gained, it has become apparent that high-field systems, especially those at 3.0 T, possess significant advantages in the clinical setting over conventional MRI systems. High-field MRI is promising as an all-in-one system for both structural and functional assessments. This review summarizes the exciting features of clinical imaging based on our cumulative 6-year experience on various 3.0 T systems.

Stereoscopic processing in the human brain as a function of binocular luminance rivalry

We investigated the neural substrates of a recent model of human stereodepth perception by obtaining measurements of regional cerebral blood flow (rCBF) using PET. Subjects experienced the perceptual properties of stereopsis by viewing rival-luminance stereograms displaying an identical random-dot pattern in their central portion while the backgrounds exhibited correspondent dots contrasting in black/white luminance. The stereoscopic vision induced by retinal luminance rivalry coincided with a significant elevation of rCBF in the dorsal visual pathway. Area V5 (MT) was activated bilaterally by the experimental condition while the remaining active loci were restricted to the right hemisphere. The neural sites that responded to this novel stereoscopic stimulus are similar to those activated by traditional stereograms containing horizontal disparities.

Cortical reorganization in patients with subcortical hemiparesis: neural mechanisms of functional recovery and prognostic implication

OBJECT

A systematic investigation on cortical reorganization in patients with hemiparesis of a subcortical origin, with special emphasis on functional correlates, was conducted using functional magnetic resonance (fMR) imaging performed on a 3-tesla system specifically optimized for fMR imaging investigation.

METHODS

The study group included 46 patients with hemiparesis (25 with right and 21 with left hemiparesis) and 30 age-matched healthy volunteers as controls. All study participants were originally right handed. The characteristics of the lesion were putaminal hemorrhage in 19 patients, thalamic hemorrhage in 10 patients, and striatocapsular bland infarction in 17 patients. Functional recovery in subcortical hemiparesis showed two distinct phases of the recovery process involving entirely different neural mechanisms. Phase I is characterized by the process of recovery and/or reorganization of the primary system. Successful recovery of this system is typically reached within 1 month after stroke onset. Its clinical correlate is a rapid recovery course and significant recovery of function within 1 month of stroke onset. Failure of recovery of the primary system shifts the recovery process to Phase II, during which reorganization involving the ipsilateral pathway takes place. The clinical correlate of Phase II is a slow recovery course with variable functional outcome.

CONCLUSIONS

Effective functional organization of the ipsilateral pathway, as identified by linked activation of the ipsilateral primary sensorimotor cortex and contralateral anterior lobe of the cerebellum, is correlated with a good prognostic outcome for patients in the slow recovery group. A high degree of connectivity between supplementary motor areas, bilaterally, appears to influence functional recovery adversely.

Functional MRI of self-controlled stereoscopic depth perception

Stereoscopic depth perception was studied in healthy young adults using fMRI imaging at 2.0 T. In a novel paradigm we compared the cortical activation elicited by single-image stereograms which create alternating 2D and 3D percepts (event-related analysis triggered on the self-controlled switches between the two percepts) with the activation caused by a more conventional approach contrasting pairs of stereoscopic images with pairs of identical images (block design). The data show a distributed network of cortical areas embedded within the visual pathways that included about one-quarter of the cortical surface activated by 2D visual stimulation and about one-half of the area activated by 3D percepts based on stereoscopic image pair. 3D perception recruited mostly neuronal populations in higher order visual areas: whereas about 40% of the visually activated locations along the intraparietal sulcus were also activated by 3D perception based on single-image stereograms (resp. 90% stereoscopic images), only 10% such overlap was found in striate cortex. The study revealed no sup-port for a right-hemispheric lateralization of depth perception.

Common neural processing regions for dynamic and static stereopsis in human parieto-occipital cortices

We performed functional magnetic resonance imaging to identify the neural processing regions in the parieto-occipital cortices for human dynamic and static stereopsis. The subjects were ten ophthalmologists professionally trained to do microscopic surgery. Visual stimuli for dynamic or static stereopsis were performed with solid stereograms displayed in the image guides of a binocular visual stimulation device that we developed. The dorsal occipital portion and the superior parietal lobule (i.e. dorsal parieto-occipital portion) were activated not only in static stereopsis, but also in dynamic stereopsis. The activation showed a right hemispherical dominancy. On the other hand, the temporo-occipital junction (i.e. human MT (middle temporal area) / MST (medial superior temporal area) complex) was activated in dynamic stereopsis. This demonstrates that the dorsal parieto-occipital portion is a common neural processing region for dynamic and static stereopsis.

M pathway and areas 44 and 45 are involved in stereoscopic recognition based on binocular disparity

We characterized the visual pathways involved in the stereoscopic recognition of the random dot stereogram based on the binocular disparity employing a functional magnetic resonance imaging (fMRI). The V2, V3, V4, V5, intraparietal sulcus (IPS) and the superior temporal sulcus (STS) were significantly activated during the binocular stereopsis, but the inferotemporal gyrus (ITG) was not activated. Thus a human M pathway may be part of a network involved in the stereoscopic processing based on the binocular disparity. It is intriguing that areas 44 (Broca's area) and 45 in the left hemisphere were also active during the binocular stereopsis. However, it was reported that these regions were inactive during the monocular stereopsis. To separate the specific responses directly caused by the stereoscopic recognition process from the nonspecific ones caused by the memory load or the intention, we designed a novel frequency labeled tasks (FLT) sequence. The functional MRI using the FLT indicated that the activation of areas 44 and 45 is correlated with the stereoscopic recognition based on the binocular disparity but not with the intention artifacts, suggesting that areas 44 and 45 play an essential role in the binocular disparity.

Myths and Truths in functional MRI: A Basic Guide for Practitioners

Since the first successful demonstration of primary visual cortex "activation" by Sokoloff in 1961, activation studies based on regional blood flow alteration became one of the gold standards for neuroscientific investigation. The rapid advancement of non-invasive imaging techniques provided an appropriate stage for the human application of this original method. Following the tremendous success of positron emission tomography (PET) utilizing O(15) labeled H(2)O (H(2)O(15)-PET), the magnetic resonance imaging (MRI) version, which is now referred to as functional MRI (fMRI), was introduced. fMRI is the method created based on the empirical observation that MRI exhibits spontaneous signal alteration associated with blood flow changes. It is now believed that the principle of fMRI is identical to H(2)O(15)-PET, namely, that it is blood flow based in accordance with the well-known Munro-Kellie doctrine which predicts a decline in cerebral venous blood volume secondary to an increase in cerebral arterial blood volume. The method is inherently qualitative and does not provide quantitative information regarding flow alteration. With the growing use of fMRI, however, exponentially increasing well founded criticism questioning the validity of fMRI data has been raised. The majority of validation issues arise during the process of obtaining raw images, which eventually provides raw numerical data for post-processing statistical analysis. This article provides a distillation of the essential knowledge necessary for the non-MR physicist fMRI investigator.

Central Tinnitus: A Case Report

We report a case of acute-onset unilateral tinnitus in a 25-year-old woman. Analysis of imaging studies indicated that the tinnitus was likely caused by an acute hemorrhage of a small cavernous angioma that was located adjacent to the contralateral primary auditory cortex. This case provides substantial support for the concept that central tinnitus might indeed represent a pathologic activation of neural networks of nonspecific auditory perception.

Cortical areas related to attention to 3D surface structures based on shading: an fMRI study

The aim of the present study was to determine which cortical areas are activated in relation to attention to a three-dimensional (3D) structure of a surface based on shading. Cortical activities were examined using functional magnetic resonance imaging while subjects discriminated whether the central part of the surface protruded or was recessed based on shading without any binocular disparity cues. Relatively broad cortical areas including both dorsal and ventral visual pathways were recruited when shading was used as a crucial cue for the perception of the 3D structure of a surface. In these cortical areas, however, the right intraparietal area was shown to be commonly activated in all subjects and in all sessions by multisubject conjunction analysis. These results strongly suggest that the intraparietal area plays an important role in perception of the 3D structure of a surface, even when based only on monocular depth cues without binocular disparity cues.

Asymmetry of parietal lobe activation during piano performance: a high field functional magnetic resonance imaging study

Functional asymmetry of the parietal lobes during piano performance was assessed utilizing independent component-cross correlation-sequential epoch analysis of functional magnetic resonance imaging time series. Eight right handed musically trained subjects played the piano with their right hand, left hand, or both hands as cued by visually presented musical scores. The areas activated included the posterior parietal cortex (PPC) and the primary sensorimotor areas (SM1). While unilateral SM1 activation was correlated to motion of the corresponding contralateral hand, PPC activation was correlated to piano performance irrespective of hand modality. Furthermore, PPC activation exhibited significant asymmetry, with left hemisphere dominance. The results indicate that the left parietal lobe plays a significant role in the cortical processes of piano performance.

Brain strategies for reading in the second language are determined by the first language

Brain activation associated with reading was investigated in ten normal Japanese volunteers (five highly literate in both Japanese and English) and ten American native English speakers (five highly literate in both English and Japanese) in order to determine the neuroanatomic substrates employed in reading the first language (L1), and to determine the effect of L1 on the neurosubstrates involved in reading the second language (L2). The study was performed using blood oxygenation level dependent (BOLD) contrast functional magnetic resonance imaging (fMRI) on a high-field (3.0T) system specifically optimized for fMRI. The activation patterns in Japanese subjects reading Japanese (L1) were substantially different from the patterns obtained in American subjects reading English text (L1). The activation patterns reading L2 were virtually identical to the patterns seen when reading L1 in both Japanese and English natives highly literate in both language systems. The results demonstrated that the neuroanatomical substrates underlying the cognitive processing of reading are differentially determined based on the language system. The study further indicates that the cognitive processes for reading in the second language involve the same cortical structures employed for the first language, supporting the hypothesis that the second language represents the cognitive extension of the first language.

Stereopsis-processing regions in the human parieto-occipital cortex

We performed fMRI on the human parieto-occipital cortex in order to identify the neural processing regions of stereopsis. Visual stimulation for stereopsis was performed with a random-dot stereogram displayed in the image guides of a new binocular visual stimulation device that we developed. Interestingly, regions from the dorsal portion of the occipital lobe to the superior parietal lobule were activated by binocular disparity, while the inferior parietal lobule was not activated. Moreover, these regions were shown as dominant in the right hemisphere. Functional brain mapping revealed that the processing regions of stereopsis were dorsally located in parieto-occipital cortex, and that the superior parietal lobule is an important region for neural processing of human stereopsis.

Receptive field organization of disparity-sensitive cells in Macaque medial superior temporal cortex

Binocular disparities are crucial for building an accurate three-dimensional representation of the peripersonal environment in a viewer-centred frame of reference. Previous studies have shown that visual cells of the medial superior temporal cortex (MST) have large receptive fields and that they are sensitive to disparities present in large surfaces. By using a reverse cross-correlation technique in this study we tested 175 disparity-sensitive units recorded from MST in the awake Macaca mulatta monkey to determine if these large receptive fields are homogeneous in terms of disparity sensitivity. We found that the receptive fields of 50 cells (50 out of 175, 29%) showed subregions with specific disparity sensitivity. These subregions presented eccentricities from 0.8 to 22.3 degrees and their sizes varied from 1.6 to 15.3 degrees 2. This particular receptive field organization represents a suitable mechanism for encoding the location of small objects within our peripersonal space.

Event-related brain potentials during selective attention to depth and form in global stereopsis

To elucidate the discriminating processes of surface depth and boundary form in global stereopsis, event-related brain potentials (ERPs) were investigated by the detection of combinations of the attributes in random sequences. The attentional relevance of depth or form was associated with selection negativities (SNs) over the lateral occipito-temporal regions initiating at about 200 ms post-stimulus. The initial SNs were elicited irrespective of relevance to the other feature; the following parts increased only for stimuli with crossed disparity having the relevant dimension of the other feature, suggesting the independent selection of stereoscopic depth and form followed by the perceptual integration into an object.

Neuroimaging of cognitive functions in human parietal cortex

Functional neuroimaging has proven highly valuable in mapping human sensory regions, particularly visual areas in occipital cortex. Recent evidence suggests that human parietal cortex may also consist of numerous specialized subregions similar to those reported in neurophysiological studies of non-human primates. However, parietal activation generalizes across a wide variety of cognitive tasks and the extension of human brain mapping into higher-order "association cortex" may prove to be a challenge.

Imaging image processing in the human brain

Functional imaging in humans reveals the interplay of the many components of the human visual system: how they process the various types of information contained in the image to recover characteristics of the three-dimensional world surrounding us, but also how, in the course of this process, the retinal image is gradually integrated with non-retinal signals to provide information about the outside world in a format useful to other non-visual brain regions.