Human V5 demonstrated by magnetoencephalography using random dot kinematograms of different coherence levels

Akinetopsia: A Systematic Review

ABSTRACT

Selective motion blindness, also known as akinetopsia, is infrequently reported in the literature. Hence, little is known about the condition including its causes, time course, pathophysiology, and current diagnostic methods. In this investigation, we comprehensively surveyed the literature using a systematic review to identify each reported case of the condition. The purpose of this study was to provide an exhaustive catalog of every published occurrence to date to identify and discuss trends, commonalities, and differences among them. Our results revealed distinct characteristics for the various etiologies of this phenomenon in addition to a shared pathophysiologic pathway among them.

Associations Between Autism Spectrum Quotient and Integration of Visual Stimuli in 9-year-old Children: Preliminary Evidence of Sex Differences

PURPOSE

The dorsal stream vulnerability hypothesis posits that the dorsal stream, responsible for visual motion and visuo-motor processing, may be particularly vulnerable during neurodevelopment. Consistent with this, autism spectrum disorder (ASD) has been associated with deficits in global motion integration, though deficits in ventral stream tasks, such as form identification, have also been reported. In the current study, we examined whether a similar pattern of results is found in a cohort of 381 children born with neurodevelopmental risk factors and exhibiting a wide spectrum of caregiver-reported autistic traits.

METHODS

We examined the associations between global motion perception, global form perception, fine motor function, visual-motor integration, and autistic traits (autism spectrum quotient, AQ) using linear regression, accounting for possible interactions with sex and other factors relevant to neurodevelopment.

RESULTS

All assessments of dorsal stream function were significantly associated with AQ such that worse performance predicted higher AQ scores. We also observed a significant sex interaction, with worse global form perception associated with higher AQ in boys (n = 202) but not girls (n = 179).

CONCLUSION

We found widespread associations between dorsal stream functions and autistic traits. These associations were observed in a large group of children with a range of AQ scores, demonstrating a range of visual function across the full spectrum of autistic traits. In addition, ventral function was associated with AQ in boys but not girls. Sex differences in the associations between visual processing and neurodevelopment should be considered in the designs of future studies.

Assessment of Visual Function and Performance in Paralympic Judo for Athletes with Vision Impairment

SIGNIFICANCE

Paralympic judo currently requires all athletes to compete against each other in one class irrespective of their level of vision impairment (VI). Recent evidence suggests that multiple classes are required to enhance fairness, yet it remains unclear how many classes are necessary and what vision tests should be used to define those classes.

PURPOSE

The aim of this study was to quantify the relationship between vision and performance in judo for individuals with VI. The results were expected to inform the development of evidence-based criteria to structure Paralympic judo competition.

METHODS

The visual function of 53 elite VI judokas was assessed using a test battery that included tests of visual acuity (VA), contrast sensitivity, light sensitivity, depth perception, motion perception, visual search, and central visual field. Performance was assessed by measuring the ratio of fights won across all competitions the participants took part in in the 2 years before and after vision testing. Pearson correlation coefficients and decision tree analyses were used to determine the relationship between vision and performance. Partial correlations were also conducted to determine the unique ability of each measure of visual function to predict judo performance.

RESULTS

Visual acuity was the best predictor of judo performance and remained the only visual function related to performance when controlling for correlations between VA and other visual functions. Decision tree analyses suggested to split athletes into two groups for more legitimate competition, using a cutoff point around 2.6 logMAR. Within each of the two resulting subgroups, no correlations remained between any of the visual functions and performance.

CONCLUSIONS

The results of this study suggest that VI judo competition should be split into separate categories for partially sighted and functionally blind athletes. The inclusion of visual functions in addition to VA does not improve the ability to predict performance in VI judo.

Visual motion integration of bidirectional transparent motion in mouse opto-locomotor reflexes

Visual motion perception depends on readout of direction selective sensors. We investigated in mice whether the response to bidirectional transparent motion, activating oppositely tuned sensors, reflects integration (averaging) or winner-take-all (mutual inhibition) mechanisms. We measured whole body opto-locomotor reflexes (OLRs) to bidirectional oppositely moving random dot patterns (leftward and rightward) and compared the response to predictions based on responses to unidirectional motion (leftward or rightward). In addition, responses were compared to stimulation with stationary patterns. When comparing OLRs to bidirectional and unidirectional conditions, we found that the OLR to bidirectional motion best fits an averaging model. These results reflect integration mechanisms in neural responses to contradicting sensory evidence as has been documented for other sensory and motor domains.

Effects of Temporal Expectations on the Perception of Motion Gestalts

Gestalt psychology has traditionally ignored the role of attention in perception, leading to the view that autonomous processes create perceptual configurations that are then attended. More recent research, however, has shown that spatial attention influences a form of Gestalt perception: the coherence of random-dot kinematograms (RDKs). Using ERPs, we investigated whether temporal expectations exert analogous attentional effects on the perception of coherence level in RDKs. Participants were presented fixed-length sequences of RDKs and reported the coherence level of a target RDK. The target was indicated immediately after its appearance by a postcue. Target expectancy increased as the sequence progressed until target presentation; afterward, remaining RDKs were perceived without target expectancy. Expectancy influenced the amplitudes of ERP components P1 and N2. Crucially, expectancy interacted with coherence level at N2, but not at P1. Specifically, P1 amplitudes decreased linearly as a function of RDK coherence irrespective of expectancy, whereas N2 exhibited a quadratic dependence on coherence: larger amplitudes for RDKs with intermediate coherence levels, and only when they were expected. These results suggest that expectancy at early processing stages is an unspecific, general readiness for perception. At later stages, expectancy becomes stimulus specific and nonlinearly related to Gestalt coherence.

An Event-Related Potential Study of the Neural Response to Inferred Motion in Visual Images of Varying Coherence

A vivid sense of motion can be inferred from static pictures of objects in motion. Like perception of real motion (RM), viewing photographs with implied motion (IM) can also activate the motion-sensitive visual cortex, including the middle temporal complex (hMT+) of the human extrastriate cortex. Moreover, extrastriate cortical activity also increases with motion coherence. Based on these previous findings, this study examined whether similar coherence level-dependent activity in motion-sensitive human extrastriate cortex is seen with IM stimuli of varying coherence. Photographic stimuli showing a human moving in four directions (left, right, toward, or away from the viewer) were presented to 15 participants. The coherence of the stimuli was manipulated by changing the percentage of pictures implying movement in one direction. Electroencephalographic data were collected while participants viewed IM or counterpart non-IM stimuli. The P2 response of extrastriate visual cortex (source located at hMT+) increased bilaterally with coherence level in the IM conditions but not in the non-IM conditions. This finding demonstrates that extrastriate visual cortical responses are progressively activated as motion coherence increases, even when motion is inferred, providing new support for the view that the activity of human motion-sensitive extrastriate visual cortex can be modulated by top-down perceptual influences in addition to its well-established role in processing bottom-up sensory signals.

Directional Visual Motion Is Represented in the Auditory and Association Cortices of Early Deaf Individuals

Individuals who are deaf since early life may show enhanced performance at some visual tasks, including discrimination of directional motion. The neural substrates of such behavioral enhancements remain difficult to identify in humans, although neural plasticity has been shown for early deaf people in the auditory and association cortices, including the primary auditory cortex (PAC) and STS region, respectively. Here, we investigated whether neural responses in auditory and association cortices of early deaf individuals are reorganized to be sensitive to directional visual motion. To capture direction-selective responses, we recorded fMRI responses frequency-tagged to the 0.1-Hz presentation of central directional (100% coherent random dot) motion persisting for 2 sec contrasted with nondirectional (0% coherent) motion for 8 sec. We found direction-selective responses in the STS region in both deaf and hearing participants, but the extent of activation in the right STS region was 5.5 times larger for deaf participants. Minimal but significant direction-selective responses were also found in the PAC of deaf participants, both at the group level and in five of six individuals. In response to stimuli presented separately in the right and left visual fields, the relative activation across the right and left hemispheres was similar in both the PAC and STS region of deaf participants. Notably, the enhanced right-hemisphere activation could support the right visual field advantage reported previously in behavioral studies. Taken together, these results show that the reorganized auditory cortices of early deaf individuals are sensitive to directional motion. Speculatively, these results suggest that auditory and association regions can be remapped to support enhanced visual performance.

Age-Related Changes in Global Motion Coherence: Conflicting Haemodynamic and Perceptual Responses

Our aim was to use both behavioural and neuroimaging data to identify indicators of perceptual decline in motion processing. We employed a global motion coherence task and functional Near Infrared Spectroscopy (fNIRS). Healthy adults (n = 72, 18-85) were recruited into the following groups: young (n = 28, mean age = 28), middle-aged (n = 22, mean age = 50), and older adults (n = 23, mean age = 70). Participants were assessed on their motion coherence thresholds at 3 different speeds using a psychophysical design. As expected, we report age group differences in motion processing as demonstrated by higher motion coherence thresholds in older adults. Crucially, we add correlational data showing that global motion perception declines linearly as a function of age. The associated fNIRS recordings provide a clear physiological correlate of global motion perception. The crux of this study lies in the robust linear correlation between age and haemodynamic response for both measures of oxygenation. We hypothesise that there is an increase in neural recruitment, necessitating an increase in metabolic need and blood flow, which presents as a higher oxygenated haemoglobin response. We report age-related changes in motion perception with poorer behavioural performance (high motion coherence thresholds) associated with an increased haemodynamic response.

An fMRI study of coherent visual motion processing in children and adults

There is a large corpus of brain imaging studies examining the dorsal visual pathway, especially area V5/MT during visual motion perception. However, despite evidence suggesting a protracted development of the dorsal visual stream, and a role of this pathway in neurodevelopmental disorders, V5/MT has not been characterized developmentally. Further, experiential factors such as reading acquisition may play a modulating role in any age-dependent changes. Here we used a coherent visual motion detection task to examine V5/MT activity and connectivity in typical participants in two studies: a Cross- Sectional Study comparing adults and children; and a Longitudinal Study of 2nd graders followed into 3rd grade. In the Cross-Sectional Study, a whole-brain analysis revealed no differences between the two groups, whereas a region of interest (ROI) approach identified greater activation in left (right trending) V5/MT in adults compared to children. However, when we measured V5/MT activation individually for each participant, children and adults showed no difference in the location or intensity of activation, although children did exhibit relatively larger extent of V5/MT activation bilaterally. There was also relatively greater functional connectivity in the children between left and right occipitotemporal cortex, including V5/MT. The Longitudinal Study revealed no changes in V5/MT activation for any measures of activation or functional connectivity from 2nd to 3rd grade. Finally, there was no evidence of an association between reading and V5/MT over time, nor predictive power of V5/MT activity for later reading. Together, our results indicate similar V5/MT activity across age groups, with relatively greater extent of V5/MT activation and functional connectivity in children relative to adults, bilaterally. These differences were not apparent over the time course of one year, suggesting that these developmental changes occur over a more protracted period.

Individual differences in children's global motion sensitivity correlate with TBSS-based measures of the superior longitudinal fasciculus

Reduced global motion sensitivity, relative to global static form sensitivity, has been found in children with many neurodevelopmental disorders, leading to the "dorsal stream vulnerability" hypothesis (Braddick et al., 2003). Individual differences in typically developing children's global motion thresholds have been shown to be associated with variations in specific parietal cortical areas (Braddick et al., 2016). Here, in 125 children aged 5-12years, we relate individual differences in global motion and form coherence thresholds to fractional anisotropy (FA) in the superior longitudinal fasciculus (SLF), a major fibre tract communicating between parietal lobe and anterior cortical areas. We find a positive correlation between FA of the right SLF and individual children's sensitivity to global motion coherence, while FA of the left SLF shows a negative correlation. Further analysis of parietal cortical area data shows that this is also asymmetrical, showing a stronger association with global motion sensitivity in the left hemisphere. None of these associations hold for an analogous measure of global form sensitivity. We conclude that a complex pattern of structural asymmetry, including the parietal lobe and the superior longitudinal fasciculus, is specifically linked to the development of sensitivity to global visual motion. This pattern suggests that individual differences in motion sensitivity are primarily linked to parietal brain areas interacting with frontal systems in making decisions on integrated motion signals, rather than in the extra-striate visual areas that perform the initial integration. The basis of motion processing deficits in neurodevelopmental disorders may depend on these same structures.

An Extended Normalization Model of Attention Accounts for Feature-Based Attentional Enhancement of Both Response and Coherence Gain

Paying attention to a sensory feature improves its perception and impairs that of others. Recent work has shown that a Normalization Model of Attention (NMoA) can account for a wide range of physiological findings and the influence of different attentional manipulations on visual performance. A key prediction of the NMoA is that attention to a visual feature like an orientation or a motion direction will increase the response of neurons preferring the attended feature (response gain) rather than increase the sensory input strength of the attended stimulus (input gain). This effect of feature-based attention on neuronal responses should translate to similar patterns of improvement in behavioral performance, with psychometric functions showing response gain rather than input gain when attention is directed to the task-relevant feature. In contrast, we report here that when human subjects are cued to attend to one of two motion directions in a transparent motion display, attentional effects manifest as a combination of input and response gain. Further, the impact on input gain is greater when attention is directed towards a narrow range of motion directions than when it is directed towards a broad range. These results are captured by an extended NMoA, which either includes a stimulus-independent attentional contribution to normalization or utilizes direction-tuned normalization. The proposed extensions are consistent with the feature-similarity gain model of attention and the attentional modulation in extrastriate area MT, where neuronal responses are enhanced and suppressed by attention to preferred and non-preferred motion directions respectively.

We report a pattern of feature-based attentional effects on human psychophysical performance, which cannot be accounted for by the Normalization Model of Attention using biologically plausible parameters. Specifically, this prominent model of attentional modulation predicts that attention to a visual feature like a specific motion direction will lead to a response gain in the input-response function, rather than the input gain that we actually observe. In our data, the input gain is greater when attention is directed towards a narrow range of motion directions, again contrary to the model’s prediction. We therefore propose two physiologically testable extensions of the model that include direction-tuned normalization mechanisms of attention. Both extensions account for our data without affecting the previously demonstrated successful performance of the NMoA.

Neural Correlates of the Time Marker for the Perception of Event Timing

While sensory processing latency, inferred from the manual reaction time (RT), is substantially affected by diverse stimulus parameters, subjective temporal judgments are relatively accurate. The neural mechanisms underlying this timing perception remain obscure. Here, we measured human neural activity by magnetoencephalography while participants performed a simultaneity judgment task between the onset of random-dot coherent motion and a beep. In a separate session, participants performed an RT task for the same stimuli. We analyzed the relationship between neural activity evoked by motion onset and point of subjective simultaneity (PSS) or RT. The effect of motion coherence was smaller for PSS than RT, but changes in RT and PSS could both be predicted by the time at which an integrated sensory response crossed a threshold. The task differences could be ascribed to the lower threshold for PSS than for RT. In agreement with the psychophysical threshold difference, the participants reported longer delays in their motor response from the subjective motion onset for weaker stimuli. However, they could not judge the timing of stimuli weaker than the detection threshold. A possible interpretation of the present findings is that the brain assigns the time marker for timing perception prior to stimulus detection, but the time marker is available only after stimulus detection.

Motion perception: a review of developmental changes and the role of early visual experience

Significant controversies have arisen over the developmental trajectory for the perception of global motion. Studies diverge on the age at which it becomes adult-like, with estimates ranging from as young as 3 years to as old as 16. In this article, we review these apparently conflicting results and suggest a potentially unifying hypothesis that may also account for the contradictory literature in neurodevelopmental disorders, such as Autism Spectrum Disorder (ASD). We also discuss the extent to which patterned visual input during this period is necessary for the later development of motion perception. We conclude by addressing recent studies directly comparing different types of motion integration, both in typical and atypical development, and suggest areas ripe for future research.

The steady-state visual evoked potential in vision research: A review

Periodic visual stimulation and analysis of the resulting steady-state visual evoked potentials were first introduced over 80 years ago as a means to study visual sensation and perception. From the first single-channel recording of responses to modulated light to the present use of sophisticated digital displays composed of complex visual stimuli and high-density recording arrays, steady-state methods have been applied in a broad range of scientific and applied settings.The purpose of this article is to describe the fundamental stimulation paradigms for steady-state visual evoked potentials and to illustrate these principles through research findings across a range of applications in vision science.

Motion area V5/MT+ response to global motion in the absence of V1 resembles early visual cortex

Motion area V5/MT+ shows a variety of characteristic visual responses, often linked to perception, which are heavily influenced by its rich connectivity with the primary visual cortex (V1). This human motion area also receives a number of inputs from other visual regions, including direct subcortical connections and callosal connections with the contralateral hemisphere. Little is currently known about such alternative inputs to V5/MT+ and how they may drive and influence its activity. Using functional magnetic resonance imaging, the response of human V5/MT+ to increasing the proportion of coherent motion was measured in seven patients with unilateral V1 damage acquired during adulthood, and a group of healthy age-matched controls. When V1 was damaged, the typical V5/MT+ response to increasing coherence was lost. Rather, V5/MT+ in patients showed a negative trend with coherence that was similar to coherence-related activity in V1 of healthy control subjects. This shift to a response-pattern more typical of early visual cortex suggests that in the absence of V1, V5/MT+ activity may be shaped by similar direct subcortical input. This is likely to reflect intact residual pathways rather than a change in connectivity, and has important implications for blindsight function. It also confirms predictions that V1 is critically involved in normal V5/MT+ global motion processing, consistent with a convergent model of V1 input to V5/MT+. Historically, most attempts to model cortical visual responses do not consider the contribution of direct subcortical inputs that may bypass striate cortex, such as input to V5/MT+. We have shown that the signal change driven by these non-striate pathways can be measured, and suggest that models of the intact visual system may benefit from considering their contribution.

Invisibility of moving objects: a core symptom of motion blindness

Although the higher brain mechanisms of seeing moving objects have been deeply investigated, motion blindness remains a rare and enigmatic symptom. Very few case reports well describe the detailed symptoms and the lesions. We report a case of a patient who presented with invisibility of moving objects, that is, motion blindness resulting from a unilateral right hemispheric lesion. This man, in his 60s, suffered persistent motion blindness from a unilateral right temporoparietal subcortical haemorrhage. He could not see the moving objects, just felt the objects 'disapper' when they began moving. The symptom was observed not only in his daily life but also during investigations in the hospital. To the best of our knowledge, this is the first report of a patient who showed persistent motion blindness with a right unilateral lesion, and only the second one with clinically apparent motion blindness, whose symptoms were similar to those of the first reported case.

Global motion perception in 2-year-old children: a method for psychophysical assessment and relationships with clinical measures of visual function

PURPOSE

We developed and validated a technique for measuring global motion perception in 2-year-old children, and assessed the relationship between global motion perception and other measures of visual function.

METHODS

Random dot kinematogram (RDK) stimuli were used to measure motion coherence thresholds in 366 children at risk of neurodevelopmental problems at 24 ± 1 months of age. RDKs of variable coherence were presented and eye movements were analyzed offline to grade the direction of the optokinetic reflex (OKR) for each trial. Motion coherence thresholds were calculated by fitting psychometric functions to the resulting datasets. Test-retest reliability was assessed in 15 children, and motion coherence thresholds were measured in a group of 10 adults using OKR and behavioral responses. Standard age-appropriate optometric tests also were performed.

RESULTS

Motion coherence thresholds were measured successfully in 336 (91.8%) children using the OKR technique, but only 31 (8.5%) using behavioral responses. The mean threshold was 41.7 ± 13.5% for 2-year-old children and 3.3 ± 1.2% for adults. Within-assessor reliability and test-retest reliability were high in children. Children's motion coherence thresholds were significantly correlated with stereoacuity (LANG I & II test, ρ = 0.29, P < 0.001; Frisby, ρ = 0.17, P = 0.022), but not with binocular visual acuity (ρ = 0.11, P = 0.07). In adults OKR and behavioral motion coherence thresholds were highly correlated (intraclass correlation = 0.81, P = 0.001).

CONCLUSIONS

Global motion perception can be measured in 2-year-old children using the OKR. This technique is reliable and data from adults suggest that motion coherence thresholds based on the OKR are related to motion perception. Global motion perception was related to stereoacuity in children.

ERP evidence for human early visual sensitivity to co-linearity compared to co-circularity

Our complex visual environment is constrained by natural geometric regularities, including spatiotemporal regularity, co-linearity and co-circularity. To investigate human visual processing associated with these regularities we directly compared the neural processes in encoding dynamic co-linearity and co-circularity using event-related potentials (ERPs). By recording ERPs to a target bar presented alone (no context) or in a dynamic sequence of bars following a co-linear or co-circular path, we observed earlier ERPs to targets embedded in co-linear sequence at early (66ms) and later stages (197ms) of post-target processing. In contrast, targets in co-circular sequence only modulated ERPs at later stages of processing. It is proposed that early visual processing may have adapted to efficiently process co-linearity to improve target identification, whereas sensitivity to co-circularity does not occur until later stages of processing. These results have significant impact for understanding brain-behaviour relationships when processing natural geometric regularities.

The effect of dot speed and density on the development of global motion perception

The purpose of this study was to investigate the effect of dot speed and dot density on the development of global motion perception by comparing the performance of adults and children (5-6years old) on a direction-discrimination task. Motion coherence thresholds were measured at two dot speeds (1 and 4deg/s) and three dot densities (1, 15, 30dots/deg(2)). Adult coherence thresholds were constant at approximately 9%, regardless of speed or density. Child coherence thresholds were significantly higher across conditions, and were most immature at the slow speed and at the sparse density. Thus, the development of global motion perception depends heavily on stimulus parameters. This finding can account for some of the discrepancy in the current developmental literature. Our results, however, caution against making general claims about motion deficits in clinical populations based on only a single measurement at a specific combination of speed and density.

Human neural responses involved in spatial pooling of locally ambiguous motion signals

Early visual motion signals are local and one-dimensional (1-D). For specification of global two-dimensional (2-D) motion vectors, the visual system should appropriately integrate these signals across orientation and space. Previous neurophysiological studies have suggested that this integration process consists of two computational steps (estimation of local 2-D motion vectors, followed by their spatial pooling), both being identified in the area MT. Psychophysical findings, however, suggest that under certain stimulus conditions, the human visual system can also compute mathematically correct global motion vectors from direct pooling of spatially distributed 1-D motion signals. To study the neural mechanisms responsible for this novel 1-D motion pooling, we conducted human magnetoencephalography (MEG) and functional MRI experiments using a global motion stimulus comprising multiple moving Gabors (global-Gabor motion). In the first experiment, we measured MEG and blood oxygen level-dependent responses while changing motion coherence of global-Gabor motion. In the second experiment, we investigated cortical responses correlated with direction-selective adaptation to the global 2-D motion, not to local 1-D motions. We found that human MT complex (hMT+) responses show both coherence dependency and direction selectivity to global motion based on 1-D pooling. The results provide the first evidence that hMT+ is the locus of 1-D motion pooling, as well as that of conventional 2-D motion pooling.

Neural processes for intentional control of perceptual switching: a magnetoencephalography study

This article reports an interesting link between the psychophysical property of intentional control of perceptual switching and the underlying neural activities. First, we revealed that the timing of perceptual switching for a dynamical dot quartet can be controlled by the observers' intention, without eye movement. However, there is a clear limitation to this control, such that each animation frame of the stimulus must be presented for a sufficiently long time length; in other words, the frequency of the stimulus alternation must be sufficiently slow for the control. The typical stimulus onset asynchrony for a 50% level of success was about 275 ms for an average of 10 observers. On the basis of psychophysical property, we designed three experiments for investigating the neural process with a magnetoencephalography. They revealed that: (1) a peak component occurring about 300 ms after a reversal was stronger when the direction of perceived motion was switched intentionally than when it was not switched, and (2) neural components about 30-40 ms and 240-250 ms after the reversal of the stimulus animation were stronger when perception was altered intentionally than when it was switched unintentionally. The 300 ms component is consistent with a previous study about passive perceptual switching (Struber and Herrmann [ 2002]: Cogn Brain Res 14:370-382), but the intentional effect was seemed to be a different component from the well-known P300 component.

Feature-based attention modulates direction-selective hemodynamic activity within human MT

Attending to the spatial location or to nonspatial features of a stimulus modulates neural activity in cortical areas that process its perceptual attributes. The feature-based attentional selection of the direction of a moving stimulus is associated with increased firing of individual neurons tuned to the direction of the movement in area V5/MT, while responses of neurons tuned to opposite directions are suppressed. However, it is not known how these multiplicatively scaled responses of individual neurons tuned to different motion-directions are integrated at the population level, in order to facilitate the processing of stimuli that match the perceptual goals. Using functional magnetic resonance imaging (fMRI) the present study revealed that attending to the movement direction of a dot field enhances the response in a number of areas including the human MT region (hMT) as a function of the coherence of the stimulus. Attending the opposite direction, however, lead to a suppressed response in hMT that was inversely correlated with stimulus-coherence. These findings demonstrate that the multiplicative scaling of single-neuron responses by feature-based attention results in an enhanced direction-selective population response within those cortical modules that processes the physical attributes of the attended stimuli. Our results provide strong support for the validity of the "feature similarity gain model" on the integrated population response as quantified by parametric fMRI in humans.

Topographical frequency dynamics within EEG and MEG sleep spindles

OBJECTIVE

Spindles are rhythmic bursts of 10-16 Hz activity, lasting ∼1 s, occur during normal stage 2 sleep. Spindles are slower in frontal EEG and possibly MEG. The posterior-fast EEG pattern may predominate early in the spindle, and the anterior-slow pattern late. We aimed to determine the proportion of spindles showing this spatio-spectro-temporal interaction for EEG, and whether it occurs in MEG.

METHODS

We recorded high density EEG and MEG from seven healthy subjects during normal stage 2 sleep. High vs. low frequency (12 vs. 14 Hz) power was measured early vs. late (25th-45th vs. 55th-75th duration percentile) in 183 spindle discharges.

RESULTS

The predicted spatio-spectro-temporal interaction was shown by 48% of EEG and 34% of MEG spindles (chance=25%). Topographically, high frequency EEG power was greatest at midline central contacts, and low frequency power at midline frontal. This frequency-specific topography was fixed over the course of the spindle.

CONCLUSIONS

An evolution from posterior-fast to anterior-slow generators commonly occurs during spindles, and this is visible with EEG and to a lesser extent, MEG.

SIGNIFICANCE

The spatio-spectral-temporal evolution of spindles may reflect their possible involvement in coordinating cortical activity during consolidation.

Magnetoencephalography demonstrates multiple asynchronous generators during human sleep spindles

Sleep spindles are approximately 1 s bursts of 10-16 Hz activity that occur during stage 2 sleep. Spindles are highly synchronous across the cortex and thalamus in animals, and across the scalp in humans, implying correspondingly widespread and synchronized cortical generators. However, prior studies have noted occasional dissociations of the magnetoencephalogram (MEG) from the EEG during spindles, although detailed studies of this phenomenon have been lacking. We systematically compared high-density MEG and EEG recordings during naturally occurring spindles in healthy humans. As expected, EEG was highly coherent across the scalp, with consistent topography across spindles. In contrast, the simultaneously recorded MEG was not synchronous, but varied strongly in amplitude and phase across locations and spindles. Overall, average coherence between pairs of EEG sensors was approximately 0.7, whereas MEG coherence was approximately 0.3 during spindles. Whereas 2 principle components explained approximately 50% of EEG spindle variance, >15 were required for MEG. Each PCA component for MEG typically involved several widely distributed locations, which were relatively coherent with each other. These results show that, in contrast to current models based on animal experiments, multiple asynchronous neural generators are active during normal human sleep spindles and are visible to MEG. It is possible that these multiple sources may overlap sufficiently in different EEG sensors to appear synchronous. Alternatively, EEG recordings may reflect diffusely distributed synchronous generators that are less visible to MEG. An intriguing possibility is that MEG preferentially records from the focal core thalamocortical system during spindles, and EEG from the distributed matrix system.

Emotional processing in a salient motion context: integration of motion and emotion in both V5/hMT+ and the amygdala

Recent studies have suggested that the extent to which primary task demands draw on attentional resources determines whether or not task-irrelevant emotional stimuli are processed. Another important factor that can bias task-relevant and task-irrelevant stimulus competition is the bottom-up factor of stimulus salience. Here, we investigated the effect of stimulus salience associated with a primary motion task on the processing of emotional face distractors. Faces of different emotional valences were presented within a context of randomly moving dots. Subjects had to detect short intervals of coherent motion while ignoring the background faces. Task salience was manipulated by the level of motion coherence of the dots with high motion coherence being associated with high salience. Using functional magnetic resonance imaging, we show that emotional faces, compared with neutral faces, more strongly interfered with the primary task, as reflected in significant signal decreases in task-related motion area V5/hMT+. In addition, these faces elicited significant signal increases in the left amygdala. Most importantly, task salience was found to further increase amygdala's activity when presented together with an emotional face. Our data support a more general role of the amygdala as a behavioral relevance detector, which flexibly integrates behavioral relevant, salient context information to decode the emotional content of a visual scene.

Visual motion perception deficits due to cerebellar lesions are paralleled by specific changes in cerebro-cortical activity

Recent anatomical studies have revealed strong cerebellar projections into parietal and prefrontal cortex. These findings suggest that the cerebellum might not only play a functional role in motor control but also cognitive domains, an idea also supported by neuropsychological testing of patients with cerebellar lesions that has revealed specific deficits. The goal of the present study was to test whether or not cognitive impairments after cerebellar damage are resulting from changes in cerebro-cortical signal processing. The detection of global visual motion embedded in noise, a faculty compromised after cerebellar lesions, was chosen as a model system. Using magnetoencephalography, cortical responses were recorded in a group of patients with cerebellar lesions (n = 8) and controls (n = 13) who observed visual motion of varied coherence, i.e., motion strength, presented in the peripheral visual field during controlled stationary fixation. Corroborating earlier results, the patients showed a significant impairment in global motion discrimination despite normal fixation behavior. This deficit was paralleled by qualitative differences in responses recorded from parieto-temporal cortex, including a reduced responsiveness to coherent visual motion and a striking loss of bilateral representations of motion coherence. Moreover, the perceptual thresholds correlated with the cortical representation of motion strength on single subject basis. These results demonstrate that visual motion processing in cerebral cortex critically depends on an intact cerebellum and establish a correlation between cortical activity and impaired visual perception resulting from cerebellar damage.

Spatio-temporal tuning of coherent motion evoked responses in 4-6 month old infants and adults

Motion cues provide a rich source of information about translations of the observer through the environment as well as the movements of objects and surfaces. While the direction of motion can be extracted locally these local measurements are, in general, insufficient for determining object and surface motions. To study the development of local and global motion processing mechanisms, we recorded Visual Evoked Potentials (VEPs) in response to dynamic random dot displays that alternated between coherent rotational motion and random motion at 0.8 Hz. We compared the spatio-temporal tuning of the evoked response in 4-6 months old infants to that of adults by recording over a range of dot displacements and temporal update rates. Responses recorded at the frequency of the coherent motion modulation were tuned for displacement at the occipital midline in both adults in infants. Responses at lateral electrodes were tuned for speed in adults, but not in infants. Infant responses were maximal at a larger range of spatial displacement than that of adults. In contrast, responses recorded at the dot-update rate showed a more similar parametric displacement tuning and scalp topography in infants and adults. Taken together, our results suggest that while local motion processing is relatively mature at 4-6 months, global integration mechanisms exhibit significant immaturities at this age.

Visual motion direction is represented in population-level neural response as measured by magnetoencephalography

We investigated whether direction information is represented in the population-level neural response evoked by the visual motion stimulus, as measured by magnetoencephalography. Coherent motions with varied speed, varied direction, and different coherence level were presented using random dot kinematography. Peak latency of responses to motion onset was inversely related to speed in all directions, as previously reported, but no significant effect of direction on latency changes was identified. Mutual information entropy (IE) calculated using four-direction response data increased significantly (>2.14) after motion onset in 41.3% of response data and maximum IE was distributed at approximately 20 ms after peak response latency. When response waveforms showing significant differences (by multivariate discriminant analysis) in distribution of the three waveform parameters (peak amplitude, peak latency, and 75% waveform width) with stimulus directions were analyzed, 87 waveform stimulus directions (80.6%) were correctly estimated using these parameters. Correct estimation rate was unaffected by stimulus speed, but was affected by coherence level, even though both speed and coherence affected response amplitude similarly. Our results indicate that speed and direction of stimulus motion are represented in the distinct properties of a response waveform, suggesting that the human brain processes speed and direction separately, at least in part.

Stimulus-contrast-induced biases in activation order reveal interaction between V1/V2 and human MT+

The luminance contrast of a visual stimulus is known to modulate the response properties of areas V1 and the human MT complex (hMT+), but has not been shown to modulate interactions between these two areas. We examined the direction of information transfer between V1/V2 and hMT+ at different stimulus contrasts by measuring magnetoencephalographic (MEG) responses to moving and stationary stimuli presented centrally or peripherally. To determine the direction of information flow, the different response latencies among stimuli and hemispheres in V1/V2 was compared with those of hMT+. At high contrast, responses to stimulus motion and position began in V1/V2, and were followed in hMT+ with a delay between 34 and 55 ms. However, at low contrast, lateralized responses in hMT+ came first, with those in V1/V2 lagging with a delay of 27 ms. Also, at high contrast, stationary stimuli produced greater responses than motion stimuli in V1/V2, while the reverse was true in hMT+, whose response lagged behind the initial response in V1/V2. The same activation order was found using Mutual Information Analysis of the response variances for each condition. Here, the response variances in hMT+ mimicked and trailed those of V1/V2 at high contrast, whereas the reverse was true at low contrast. Such consistent interactions found using two different methodologies strongly supports a processing link between these two areas. The results also suggest that feedback from hMT+ for low-contrast stimuli compensates for unresolved processing in V1/V2 when the input of a visual image is weak.

Neurophysiology and neuroanatomy of smooth pursuit: lesion studies

Smooth pursuit impairment is recognized clinically by the presence of saccadic tracking of a small object and quantified by reduction in pursuit gain, the ratio of smooth eye movement velocity to the velocity of a foveal target. Correlation of the site of brain lesions, identified by imaging or neuropathological examination, with defective smooth pursuit determines brain structures that are necessary for smooth pursuit. Paretic, low gain, pursuit occurs toward the side of lesions at the junction of the parietal, occipital and temporal lobes (area V5), the frontal eye field and their subcortical projections, including the posterior limb of the internal capsule, the midbrain and the basal pontine nuclei. Paresis of ipsiversive pursuit also results from damage to the ventral paraflocculus and caudal vermis of the cerebellum. Paresis of contraversive pursuit is a feature of damage to the lateral medulla. Retinotopic pursuit paresis consists of low gain pursuit in the visual hemifield contralateral to damage to the optic radiation, striate cortex or area V5. Craniotopic paresis of smooth pursuit consists of impaired smooth eye movement generation contralateral to the orbital midposition after acute unilateral frontal or parietal lobe damage. Omnidirectional saccadic pursuit is a most sensitive sign of bilateral or diffuse cerebral, cerebellar or brainstem disease. The anatomical and physiological bases of defective smooth pursuit are discussed here in the context of the effects of lesion in the human brain.

Selective attention increases the dependency of cortical responses on visual motion coherence in man

Attention improves visual discrimination and consequently allows to discern stimuli with low signal-to-noise ratios that otherwise would remain undetected. We used magnetoencephalography (MEG) to test whether neuromagnetic responses recorded from occipito-temporal cortex, reflecting the size of visual motion signals embedded in noise (motion coherence), would mirror the perceptual changes induced by attention. Attention directed to a given hemifield increased and decreased the coherence modulation of the MEG response over contralateral and ipsilateral visual cortex, respectively, indicating a change in the neuronal signal-to-noise ratio at the population level.

Abnormalities of coherent motion processing in strabismic amblyopia: Visual-evoked potential measurements

Coherent motion responses of patients with mild to moderate strabismic amblyopia were compared to those of normals using visual-evoked potentials (VEPs). Responses were elicited by dynamic random-dot kinematograms that alternated at 0.83 Hz between globally coherent (left-right) and incoherent (random) motion states. Tuning curves were measured at the first harmonic of the global motion update rate (0.83 Hz) and at the first harmonic of the dot update rate (20 Hz) for spatial displacements 3.1 to 27.9 arcmin (1.6 to 9.3 deg/s). Responses locked to the changes in the global organization of the local direction vectors were an inverted U-shaped function of displacement/speed in the normal-vision observers and in the fellow eyes of the strabismus patients while the tuning function of the amblyopic eyes was shifted to larger displacements/higher speeds. Responses at the dot update rate were reduced in amplitude and altered in timing in both eyes of the patients. The results are consistent with both local and global deficits in motion processing in strabismic amblyopia.

Deficits of visual motion perception and optokinetic nystagmus after posterior suprasylvian lesions in the ferret (Mustela putorius furo)

We recently described an area in the ferret posterior suprasylvian (PSS) cortex characterized by a high proportion of direction selective neurons. To answer the question whether area PSS subserves functions similar to cat posteromediolateral suprasylvian area (PMLS) and monkey medial temporal area (MT) we investigated the contribution of area PSS to visual motion perception and optokinetic nystagmus. Ferrets were tested on global motion detection before and after bilateral lesions involving area PSS and control lesions of other extrastriate visual areas. Following PSS lesions motion coherence thresholds were significantly increased both in pigmented and albino ferrets, whereas control lesions sparing PSS did not affect visual motion perception. Optokinetic nystagmus was strongly reduced to absent after PSS lesions. These results indicate that area PSS is crucial for global motion processing in the ferret and in that sense may be functionally equivalent to PMLS in the cat and area MT in the monkey.

The role of cortical area V5/MT+ in speed-tuned directional anisotropies in global motion perception

Several different directional anisotropies have been found in global motion perception. The purpose of this study was to examine the role of the motion sensitive cortical area V5/MT+ in directional anisotropies for translational flow fields. Experiments 1 and 2 tested direction discrimination and detection of moving random dot patterns. When the speed of motion was 8 deg/s, lower coherence thresholds were found for centripetal relative to centrifugal hemifield motion. When the speed of motion was 1 deg/s, coherence thresholds were similar in all directions. Experiment 3 used fMRI to measure the BOLD response to different directions of motion at speeds of 1 and 8 deg/s. Greater activity was found in V5/MT+ for centripetal motion than for centrifugal motion at both speeds. These results suggest that V5/MT+ does play a role in directional motion anisotropies. This role is discussed with respect to visually-guided reaching and locomotion.

A primer on motion visual evoked potentials

Motion visual evoked potentials (motion VEPs) have been used since the late 1960s to investigate the properties of human visual motion processing, and continue to be a popular tool with a possible future in clinical diagnosis. This review first provides a synopsis of the characteristics of motion VEPs and then summarizes important methodological aspects. A subsequent overview illustrates how motion VEPs have been applied to study basic functions of human motion processing and shows perspectives for their use as a diagnostic tool.

Motion perception deficits in albino ferrets (Mustela putorius furo)

Albino ferrets contrary to their pigmented conspecifics show no optokinetic nystagmus. Therefore, in this study motion perception was compared between pigmented and albino ferrets (Mustela putorius furo) trained to discriminate between coherently moving random dot patterns and dynamic noise stimuli in a two-alternative forced choice task. Fully coherently versus incoherently moving patterns could be distinguished by ferrets of both phenotypes. Motion coherence thresholds, however, were significantly higher in albinos. These results indicate that albino ferrets are not motion blind as could be expected from their total lack of optokinetic reactions. However, they are severely impaired in global motion perception.

Opposite dependencies on visual motion coherence in human area MT+ and early visual cortex

In order to understand the relationship between brain activity and visual motion perception, knowledge of the cortical areas participating in signal processing alone is insufficient. Rather knowledge on how responses vary with the characteristics of visual motion is necessary. In this study, we measured whole brain activity using magnetoencephalography in humans discriminating the global motion direction of a random dot kinematogram whose strength was systematically varied by the percentage of coherently moving dot elements. Spectral analysis revealed 2 components correlating with motion coherence. A first component in the low-frequency domain ( approximately 3 Hz), linearly increasing with motion coherence, could be attributed to visual cortex including human area middle temporal (MT) +. A second component oscillating in the alpha frequency range and emerging after stimulus offset showed the inverse dependence on motion coherence and arose from early visual cortex. Based on these results, we first of all conclude that motion coherence is reflected in the population response of human extrastriate cortex. Second, we suggest that the occipital alpha activity represents a gating mechanism protecting visual motion integration in later cortical areas from disturbing upcoming signals.

An MEG study into the visual perception of apparent motion in depth

This study investigated (1) the responses associated with the perception of motion in depth induced by a series of scale-changing paradigms, and (2) the locations of the dipoles in the brain elicited by stimuli of motion in depth and in-plane motion. The former was determined using two types of stimulation: real motion and apparent motion in scale (AMS; where two frames with size-changed patterns were presented alternately); and the latter was determined by moving a full-field checkerboard pattern forward or rightward smoothly with the same time course. The results from analyzing magnetoencephalography (MEG) component M160 to differentiate the signals of perception can be summarized as follows: (1) the neurons stimulated by apparent motion (AM) might be similar to those stimulated by a real motion, since there was no statistical difference associated with the signals at M160 and the dipole locations; (2) the perceptional signal of motion in depth seems to be more sensitive when scale-changing information is present; and (3) asymmetrical responses are present in the visual system, with responses being more sensitive to expanding stimuli than to contracting ones, and with the activity being more prominent in the right occipitotemporal area. Overall, this study indicates that the responses evoked by the stimuli causing motion in depth are allocated more to area V3a rather to area V5.

ERPs predict the appearance of visual stimuli in a temporal selection task

In contrast to the visual spatial domain, the effect of attention on sensory processing and stimulus appearance in temporal selection tasks is still controversial. Using a rapid serial visual presentation (RSVP) procedure, we examined whether the stimulus onset asynchrony (SOA) between a color cue and a motion target affects the appearance of the latter. Event-related brain potentials (ERPs) recorded simultaneously allowed us to test whether a change in the targets' appearance is associated with a modulation of the sensory ERP components. In the experimental condition 'SOA', the temporal interval between the cue and the target was varied between 0 and 300 ms. In a control condition, the physical appearance of the motion target was varied (level of coherence: 25-100%) while holding the cue-target SOA constant (300 ms). In trials when the participant detected the target motion, his/her task was to report the strength of the perceived motion on a 5-point scale. In both conditions, the mean rating of the target's appearance increased monotonically with increasing SOA and the level of coherence, respectively. The psychophysical ratings were associated with an increase of a negative deflection about 200 ms (N200) related to the sensory processing of visual motion. The physical variation of motion coherence and the variation of the cue-target SOA affected the N200 response in similar fashion. These results indicate that sensory processing is also modulated by attentional resources in temporal selection tasks which - in turn - affect the appearance of the relevant target stimulus.

Estimation of the timing of human visual perception from magnetoencephalography

To explore the timing and the underlying neural dynamics of visual perception, we analyzed the relationship between the manual reaction time (RT) to the onset of a visual stimulus and the time course of the evoked neural response simultaneously measured by magnetoencephalography (MEG). The visual stimuli were a transition from incoherent to coherent motion of random dots and an onset of a chromatic grating from a uniform field, which evoke neural responses in different cortical sites. For both stimuli, changes in median RT with changing stimulus strength (motion coherence or chromatic contrast) were accurately predicted, with a stimulus-independent postdetection delay, from the time that the temporally integrated MEG response crossed a threshold (integrator model). In comparison, the prediction of RT was less accurate from the peak MEG latency, or from the time that the nonintegrated MEG response crossed a threshold (level detector model). The integrator model could also account for, at least partially, intertrial changes in RT or in perception (hit/miss) to identical stimuli. Although we examined MEG-RT relationships mainly for data averaged over trials, the integrator model could show some correlations even for single-trial data. The model predictions deteriorated when only early visual responses presumably originating from the striate cortex were used as the input to the integrator model. Our results suggest that the perceptions for visual stimulus appearances are established in extrastriate areas [around MT (middle temporal visual area) for motion and around V4 (fourth visual area) for color] approximately 150-200 ms before subjects manually react to the stimulus.

Maturation of luminance- and motion-defined form perception beyond adolescence: a combined ERP and fMRI study

Abilities to discriminate forms defined by motion continue to develop throughout childhood. To investigate late development of the visual motion system, we measured brain activity with event-related EEG potentials (ERPs) and functional magnetic resonance imaging (fMRI) in groups of adolescents (15-17 years) and adults (20-30 years) during a visual form discrimination task--with forms being either defined by motion or luminance contrast. We further explored whether possible developmental changes varied with the degree of motion coherence reflecting maturation specific to global motion processing. Both the fMRI activation patterns and ERP topographies were very similar between adolescents and adults, suggesting that the basic visual networks for processing motion and form are established by the age of 15-17. The ERP response to luminance- and motion-defined forms was dominated by a posterior negativity (N1: 120-270 ms). The N1 of the motion contrast was delayed in adolescents, whereas the N1 of the static condition did not differ between groups. Since the motion-evoked N1 is thought to arise in the middle temporal area MT/V5, our results indicate that visual motion processing in MT continues to get faster, becoming still more efficient during late development. Neither the ERP nor the fMRI results revealed maturation effects specific to motion coherence. This indicates that the specific mechanisms to process global dot motion are already mature in adolescence. The present findings support the view that static perception matures earlier than dynamic perception, and that these visual systems have different developmental courses.