Can a motion-blind patient reach for moving objects?

Continuous theta burst TMS of area MT+ impairs attentive motion tracking

Attentive motion tracking deficits measured using multiple object tracking (MOT) tasks have been identified in a number of neurodevelopmental disorders such as amblyopia and autism. These deficits are often attributed to the abnormal development of high-level attentional networks. However, neuroimaging evidence from amblyopia suggests that reduced MOT performance can be explained by impaired function in motion-sensitive area MT+ alone. To test the hypothesis that a subtle disruption of MT+ function could cause MOT impairment, we assessed whether continuous theta burst stimulation (cTBS) of MT+ influenced MOT task accuracy in individuals with normal vision. The MOT stimulus consisted of four target and four distractor dots and was presented at ±10° eccentricity (right/left hemifield). fMRI-guided cTBS was applied to left MT+. Participants (n = 13, age: 27 ± 3) attended separate active and sham cTBS sessions where the MOT task was completed before, 5-min post- and 30-min post-cTBS. Active cTBS significantly impaired MOT task accuracy relative to baseline for the right (stimulated) hemifield 5-min (10 ± 2% reduction) and 30-min (14 ± 3% reduction) post-stimulation. No impairment occurred within the left (control) hemifield after active cTBS or for either hemifield after sham cTBS. These results highlight the importance of lower level motion processing for MOT, suggesting that a minor disruption of MT+ function alone is sufficient to cause a deficit in MOT performance.

Visual Cortical Area MT Is Required for Development of the Dorsal Stream and Associated Visuomotor Behaviors

The middle temporal (MT) area of the extrastriate visual cortex has long been studied in adulthood for its distinctive physiological properties and function as a part of the dorsal stream, yet interestingly it possesses a similar maturation profile as the primary visual cortex (V1). Here, we examined whether an early-life lesion in MT of marmoset monkeys (six female, two male) altered the dorsal stream development and the behavioral precision of reaching-to-grasp sequences. We observed permanent changes in the anatomy of cortices associated with both reaching (parietal and medial intraparietal areas) and grasping (anterior intraparietal area), as well as in reaching-and-grasping behaviors. In addition, we observed a significant impact on the anatomy of V1 and the direction sensitivity of V1 neurons in the lesion projection zone. These findings indicate that area MT is a crucial node in the development of primate vision, affecting both V1 and areas in the dorsal visual pathway known to mediate visually guided manual behaviors.SIGNIFICANCE STATEMENT Previous studies have identified a role for the MT area of the visual cortex in perceiving motion, yet none have examined its central role in the development of the visual cortex and in the establishment of visuomotor behaviors. To address this, we used a unilateral MT lesion model in neonatal marmosets before examining the anatomic, physiological, and behavioral consequences. In adulthood, we observed perturbations in goal-orientated reach-and-grasp behavior, altered direction selectivity of V1 neurons, and changes in the cytoarchitecture throughout dorsal stream areas. This study highlights the importance of MT as a central node in visual system development and consequential visuomotor activity.

Effect of Visual Field Location on Global Motion Perception: A Developmental Study

Previous work has shown that motion perception in school-age children is similar to that of adults for fast speeds but is immature at slow speeds for stimuli presented in the central visual field. This study examined whether visual field location affects this developmental pattern. We measured left/right and up/down global motion direction discrimination for fast and slow speeds in 7- to 10-year-old children and in adults with stimuli presented to upper, central, or lower visual fields. For left/right direction discrimination, children showed significantly higher (worse) coherence thresholds than adults for slow, but not fast, speeds in the central visual field. In the upper and lower visual fields, children showed significantly higher coherence thresholds than adults for both speeds. For up/down direction discrimination, children showed similar performance to adults for the central visual field. In the upper and lower visual fields, children performed significantly worse than adults; this finding was speed-tuned only for the lower visual field. Thus, children show immature global motion perception in the periphery even when performance in central vision is adult-like. These results enrich our understanding of motion perception development in children with typical vision.

The effect of target speed on perception of visual motion direction in a patient with akinetopsia

Although much research has been devoted to the neural correlates of motion perception, the processing of speed of motion is still a topic of discussion. Apart from patient LM, no in-depth clinical research has been done in the past 20 years on this topic. In the present study, we investigated patient TD, who suffered from the rare disorder akinetopsia due to bilateral lesions of V5 after stroke. By means of a Random-Dot-Kinematogram (RDK) in which speed was varied systematically, it was found that TD was impaired in perceiving the direction of movement at speeds exceeding 9 deg/s. Our study suggests that V5 plays an important role in processing high-speed visual motion and further implies that V5 does not play a crucial role in processing low-speed visual motion. A remarkable finding, which has not been shown before, was that TD always reported the opposite direction of the actual movement at a speed of 24 deg/s. This suggests a form of the continuous wagon wheel illusion, which might have been caused by intact brain areas operating at different sampling rates than area V5.

Comparing three portable, tablet-based visuomotor tasks to laboratory versions: An assessment of test validity

The assessment of visuomotor function can provide important information about neurological status. Many tasks exist for testing visuomotor function in the laboratory, but the availability of portable, easy-to-use versions that allow reliable, accurate, and precise measurement of movement timing and accuracy has been limited. We developed a tablet application that uses three laboratory visuomotor tests: the double-step task, interception task, and stop-signal task. We asked the participants to perform both the lab and tablet versions of each task and compared their response patterns across equipment types to assess the validity of the tablet versions. On the double-step task, the participants adjusted to the displaced target adequately in both the lab and tablet versions. On the interception task, the participants intercepted nonaccelerating targets and performed worse on accelerating targets in both versions of the task. On the stop-signal task, the participants successfully inhibited their reaching movements on short stop-signal delays (50–150 ms) more frequently than on long stop-signal delays (200 ms) in both versions of the task. Our findings suggest that the tablet version of each task assesses visuomotor processing in the same way as their respective laboratory version, thus providing the research community with a new tool to assess visuomotor function.

Neural Correlates of Speed-Tuned Motion Perception in Healthy Adults

It has been suggested that slow and medium-to-fast speeds of motion may be processed by at least partially separate mechanisms. The purpose of this study was to establish the cortical areas activated during motion-defined form and global motion tasks as a function of speed, using functional magnetic resonance imaging. Participants performed discrimination tasks with random dot stimuli at high coherence, at coherence near their own thresholds, and for random motion. Stimuli were moving at 0.1 or 5 deg/s. In the motion-defined form task, lateral occipital complex, V5/MT+ and intraparietal sulcus showed greater activation by high or near-threshold coherence than by random motion stimuli; V5/MT+ and intraparietal sulcus demonstrated greater activation for 5 than 0.1 deg/s dot motion. In the global motion task, only high coherence stimuli elicited significant activation over random motion; this activation was primarily in nonclassical motion areas. V5/MT+ was active for all motion conditions and showed similar activation for coherent and random motion. No regions demonstrated speed-tuning effects for global motion. These results suggest that similar cortical systems are activated by slow- and medium-speed stimuli during these tasks in healthy adults.

Visual perception skills: a comparison between patients with Noonan syndrome and 22q11.2 deletion syndrome

Ventral and dorsal streams are visual pathways deputed to transmit information from the photoreceptors of the retina to the lateral geniculate nucleus and then to the primary visual cortex (V1). Several studies investigated whether one pathway is more vulnerable than the other during development, and whether these streams develop at different rates. The results are still discordant. The aim of the present study was to understand the functionality of the dorsal and the ventral streams in two populations affected by different genetic disorders, Noonan syndrome (NS) and 22q11.2 deletion syndrome (22q11.2DS), and explore the possible genotype-phenotype relationships. 'Form coherence' abilities for the ventral stream and 'motion coherence' abilities for the dorsal stream were evaluated in 19 participants with NS and 20 participants with 22q11.2DS. Collected data were compared with 55 age-matched controls. Participants with NS and 22q11.2DS did not differ in the form coherence task, and their performance was significantly lower than that of controls. However, in the motion coherence task, the group with NS and controls did not differ, and both obtained significantly higher scores than the group with 22q11.2DS. Our findings indicate that deficits in the dorsal stream are related to the specific genotype, and that in our syndromic groups the ventral stream is more vulnerable than the dorsal stream.

Visual motion serves but is not under the purview of the dorsal pathway

Visual motion processing is often attributed to the dorsal visual pathway despite visual motion's involvement in almost all visual functions. Furthermore, some visual motion tasks critically depend on the structural integrity of regions outside the dorsal pathway. Here, based on numerous studies, I propose that visual motion signals are swiftly transmitted via multiple non-hierarchical routes to primary motion-dedicated processing regions (MT/V5 and MST) that are not part of the dorsal pathway, and then propagated to a multiplicity of brain areas according to task demands, reaching these regions earlier than the dorsal/ventral hierarchical flow. This not only places MT/V5 at the same or even earlier visual processing stage as that of V1, but can also elucidate many findings with implications to visual awareness. While the integrity of the non-hierarchical motion pathway is necessary for all visual motion perception, it is insufficient on its own, and the transfer of visual motion signals to additional brain areas is crucial to allow the different motion perception tasks (e.g. optic flow, visuo-vestibular balance, movement observation, dynamic form detection and perception, and even reading). I argue that this lateral visual motion pathway can be distinguished from the dorsal pathway not only based on faster response latencies and distinct anatomical connections, but also based on its full field representation. I also distinguish between this primary lateral visual motion pathway sensitive to all motion in the visual field, and a much less investigated optic flow sensitive medial processing pathway (from V1 to V6 and V6A) that appears to be part of the dorsal pathway. Multiple additional predictions are provided that allow testing this proposal and distinguishing between the visual pathways.

Area V5-a microcosm of the visual brain

Area V5 of the visual brain, first identified anatomically in 1969 as a separate visual area, is critical for the perception of visual motion. As one of the most intensively studied parts of the visual brain, it has yielded many insights into how the visual brain operates. Among these are: the diversity of signals that determine the functional capacities of a visual area; the relationship between single cell activity in a specialized visual area and perception of, and preference for, attributes of a visual stimulus; the multiple asynchronous inputs into, and outputs from, an area as well as the multiple operations that it undertakes asynchronously; the relationship between activity at given, specialized, areas of the visual brain and conscious awareness; and the mechanisms used to “bind” signals from one area with those from another, with a different specialization, to give us our unitary perception of the visual world. Hence V5 is, in a sense, a microcosm of the visual world and its study gives important insights into how the whole visual brain is organized—anatomically, functionally and perceptually.

fMRI evidence of improved visual function in patients with progressive retinitis pigmentosa by eye-movement training

To evaluate changes in the visual processing of patients with progressive retinitis pigmentosa (RP) who acquired improved reading capability by eye-movement training (EMT), we performed functional magnetic resonance imaging (fMRI) before and after EMT. Six patients with bilateral concentric contraction caused by pigmentary degeneration of the retina and 6 normal volunteers were recruited. Patients were given EMT for 5 min every day for 8–10 months. fMRI data were acquired on a 3.0-Tesla scanner while subjects were performing reading tasks. In separate experiments (before fMRI scanning), visual performances for readings were measured by the number of letters read correctly in 5 min. Before EMT, activation areas of the primary visual cortex of patients were 48.8% of those of the controls. The number of letters read correctly in 5 min was 36.6% of those by the normal volunteers. After EMT, the activation areas of patients were not changed or slightly decreased; however, reading performance increased in 5 of 6 patients, which was 46.6% of that of the normal volunteers (p< 0.05). After EMT, increased activity was observed in the frontal eye fields (FEFs) of all patients; however, increases in the activity of the parietal eye fields (PEFs) were observed only in patients who showed greater improvement in reading capability. The improvement in reading ability of the patients after EMT is regarded as an effect of the increased activity of FEF and PEF, which play important roles in attention and working memory as well as the regulation of eye movements.

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We made fMRI measurements for tunnel vision patients.

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After training, increases in activity of FEF were observed in all patients.

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Patients' highly improved reading capability showed increased activity of PEF.

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Improvement in reading is regarded as increased activity of FEF and PEF.

Representational momentum in children born preterm and at term

The term representational momentum (RM) refers to the idea that our memory representations for moving objects incorporate information about movement - a fact that can lead us to make errors when judging an object's location (the RM effect). In this study, we explored the RM effect in a sample of children born very prematurely and a sample born at term. Because preterm children are known to be at risk for problems with motion perception, we anticipated that they would show a weaker or absent RM effect. This prediction was confirmed. In addition, we found that, in both samples of children, 5-6year olds showed a reduced RM effect compared to 7-9year olds. These results demonstrate that the ability to represent motion information in memory shows continued development over this age range, and may help to elucidate factors contributing to problems with fine and gross motor planning and execution that have been observed in the preterm population. We propose that problems affecting the formation, maintenance, or use of predictive models, or motion extrapolation skills, may have cascading effects on the development of other abilities.

Do we have independent visual streams for perception and action?

The perception-action model proposes that vision-for-perception and vision-for-action are based on anatomically distinct and functionally independent streams within the visual cortex. This idea can account for diverse experimental findings, and has been hugely influential over the past two decades. The model itself comprises a set of core contrasts between the functional properties of the two visual streams. We critically review the evidence for these contrasts, arguing that each of them has either been refuted or found limited empirical support. We suggest that the perception-action model captures some broad patterns of functional localization, but that the specializations of the two streams are relative, not absolute. The ubiquity and extent of inter-stream interactions suggest that we should reject the idea that the ventral and dorsal streams are functionally independent processing pathways.

Contributions of the human temporoparietal junction and MT/V5+ to the timing of interception revealed by transcranial magnetic stimulation

To intercept a fast target at destination, hand movements must be centrally triggered ahead of target arrival to compensate for neuromechanical delays. The role of visual-motion cortical areas is unclear. They likely feed downstream parietofrontal networks with signals reflecting target motion, but do they also contribute internal timing signals to trigger the motor response? We disrupted the activity of human temporoparietal junction (TPJ) and middle temporal area (hMT/V5+) by means of transcranial magnetic stimulation (TMS) while subjects pressed a button to intercept targets accelerated or decelerated in the vertical or horizontal direction. Target speed was randomized, making arrival time unpredictable across trials. We used either repetitive TMS (rTMS) before task execution or double-pulse TMS (dpTMS) during target motion. We found that after rTMS and dpTMS at 100-200 ms from motion onset, but not after dpTMS at 300-400 ms, the button-press responses occurred earlier than in the control, with time shifts independent of target speed. This suggests that activity in TPJ and hMT/V5+ can feed downstream regions not only with visual-motion information, but also with internal timing signals used for interception at destination. Moreover, we found that TMS of hMT/V5+ affected interception of all tested motion types, whereas TMS of TPJ significantly affected only interception of motion coherent with natural gravity. TPJ might specifically gate visual-motion information according to an internal model of the effects of gravity.

Cortical Dynamics of Anticipatory Mechanisms in Interception: A Neuromagnetic Study

Humans demonstrate an amazing ability for intercepting and catching moving targets, most noticeably in fast-speed ball games. However, the few studies exploring the neural bases of interception in humans and the classical studies on visual motion processing and visuomotor interactions have reported rather long latencies of cortical activations that cannot explain the performances observed in most natural interceptive actions. The aim of our experiment was twofold: (1) describe the spatio-temporal unfolding of cortical activations involved in catching a moving target and (2) provide evidence that fast cortical responses can be elicited by a visuomotor task with high temporal constraints and decide if these responses are task or stimulus dependent. Neuromagnetic brain activity was recorded with whole-head coverage while subjects were asked to catch a free-falling ball or simply pay attention to the ball trajectory. A fast, likely stimulus-dependent, propagation of neural activity was observed along the dorsal visual pathway in both tasks. Evaluation of latencies of activations in the main cortical regions involved in the tasks revealed that this entire network of regions was activated within 40 msec. Moreover, comparison of experimental conditions revealed similar patterns of activation except in contralateral sensorimotor regions where common and catch-specific activations were differentiated.

The neural basis of visual body perception

The human body, like the human face, is a rich source of socially relevant information about other individuals. Evidence from studies of both humans and non-human primates points to focal regions of the higher-level visual cortex that are specialized for the visual perception of the body. These body-selective regions, which can be dissociated from regions involved in face perception, have been implicated in the perception of the self and the 'body schema', the perception of others' emotions and the understanding of actions.

The extrastriate cortex distinguishes between the consequences of one's own and others' behavior

The extrastriate body area (EBA) is traditionally considered a category-selective region for the visual processing of static images of the human body. Recent evidence challenges this view by showing motor-related modulations of EBA activity during self-generated movements. Here, we used functional MRI to investigate whether the EBA distinguishes self- from other-generated movements, a prerequisite for the sense of agency. Subjects performed joystick movements while the visual feedback was manipulated on half of the trials. The EBA was more active when the visual feedback was incongruent to the subjects' own executed movements. Furthermore, during correct feedback evaluation, the EBA showed enhanced functional connectivity to posterior parietal cortex, which has repeatedly been implicated in the detection of sensorimotor incongruence and the sense of agency. Our results suggest that the EBA represents the human body in a more integrative and dynamic manner, being able to detect an incongruence of internal body or action representations and external visual signals. In this way, the EBA might be able to support the disentangling of one's own behavior from another's.

Visually guided reaching depends on motion area MT+

Visual information is crucial for goal-directed reaching. A number of studies have recently shown that motion in particular is an important source of information for the visuomotor system. For example, when reaching a stationary object, movement of the background can influence the trajectory of the hand, even when the background motion is irrelevant to the object and task. This manual following response may be a compensatory response to changes in body position, but the underlying mechanism remains unclear. Here we tested whether visual motion area MT+ is necessary to generate the manual following response. We found that stimulation of MT+ with transcranial magnetic stimulation significantly reduced a strong manual following response. MT+ is therefore necessary for generating the manual following response, indicating that it plays a crucial role in guiding goal-directed reaching movements by taking into account background motion in scenes.

Deficits in the processing of local and global motion in very low birthweight children

This study evaluated the impact of premature birth on the development of local and global motion processing in a group of very low birthweight (<1500 g), 5- to 8-year-old children. Sensitivity to first- and second-order local motion stimuli and coherence thresholds for global motion in random dot kinematograms were measured. Relative to full-term controls, premature children showed deficits on all three aspects of motion processing. These problems could not be accounted for by stereo deficits, amblyopia, or attentional problems. A history of mild retinopathy of prematurity and/or intraventricular hemorrhage increased risk, but deficits were observed in some children with no apparent ocular or cerebral pathology. It is important to note that, despite the observed group differences, individual profiles of performance did vary; the results suggest that these three forms of motion processing may involve separate neural mechanisms. These findings serve to increase our understanding of the organization and functional development of motion-processing subsystems in humans, and of the impact of prematurity and associated complications on visual development.

The role of V5/MT+ in the control of catching movements: an rTMS study

Milner and Goodale described a model which distinguishes between two visual streams in the brain. It is claimed that the ventral stream serves object recognition (i.e. vision for perception), and the dorsal streams provides visual information for the guidance of action (i.e. vision for action). This model is supported by evidence from the domain of spatial vision, but it remains unclear how motion vision fits into that model. More specifically, it is unclear how the motion complex V5/MT contributes to vision for perception and vision for action. We addressed this question in an earlier study with the V5-lesioned patient LM. Can a motion-blind patient reach for moving objects? We found that she is not only impaired in perceptual tasks but also in catching, suggesting a role for V5/MT+ in vision for both perception and action. However, LM's lesion goes beyond V5/MT+ into more dorsal regions. It is thus possible, that the catching deficit was not produced by damage to V5/MT+ itself. In this case, one would expect that selective interference with V5/MT+ would have no effect on catching. In the present study we tested this prediction by applying rTMS over V5/MT+ of the left hemisphere while healthy subjects were either performing a catching or a reaching task. We found that V5-TMS reduced the speed of the catching but not the reaching response. These results confirm that V5/MT+ is not only involved in perceptual but also in visuomotor tasks.

The role of V5 (hMT+) in visually guided hand movements: an fMRI study

Electrophysiological studies in animals suggest that visuomotor control of forelimb and eye movements involves reciprocal connections between several areas (striate, extrastriate, parietal, motor and premotor) related to movement performance and visuospatial coding of movement direction. The extrastriate area MT [V5 (hMT+) in humans] located in the "dorsal pathway" of the primate brain is specialized in the processing of visual motion information. The aim of our study was to investigate the functional role of V5 (hMT+) in the control of visually guided hand movements and to identify the corresponding cortex activation implicated in the visuomotor tasks using functional magnetic resonance imaging. Eight human subjects performed visually guided hand movements, either continuously tracking a horizontally moving target or performing ballistic tracking movements of a cursor to an eccentric stationary target while fixating a central fixation cross. The tracking movements were back-projected onto the screen using a cursor which was moved by an MRI-compatible joystick. Both conditions activated area V5 (hMT+), right more than left, particularly during continuous tracking. In addition, a large-scale sensorimotor circuit which included sensorimotor cortex, premotor cortex, striatum, thalamus and cerebellum as well as a number of cortical areas along the intraparietal sulcus in both hemispheres were activated. Because activity was increased in V5 (hMT+) during continuous tracking but not during ballistic tracking as compared to motion perception, it has a pivotal role during the visual control of forelimb movements as well.