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PubMed2004

Viewing the motion of human body parts activates different regions of premotor, temporal, and parietal cortex.

Activation of premotor and temporoparietal cortex occurs when we observe others movements, particularly relating to objects. Viewing the motion of different body parts without the context of an object has not been systematically evaluated. During a 3T fMRI study, 12 healthy subjects viewed human face, hand, and leg motion, which was not directed at or did not involve an object. Activation was identified relative to static images of the same human face, hand, and leg in both individual subject and group average data. Four clear activation foci emerged: (1) right MT/V5 activated to all forms of viewed motion; (2) right STS activated to face and leg motion; (3) ventral premotor cortex activated to face, hand, and leg motion in the right hemisphere and to leg motion in the left hemisphere; and (4) anterior intraparietal cortex (aIP) was active bilaterally to viewing hand motion and in the right hemisphere leg motion. In addition, in the group data, a somatotopic activation pattern for viewing face, hand, and leg motion occurred in right ventral premotor cortex. Activation patterns in STS and aIP were more complex--typically activation foci to viewing two types of human motion showed some overlap. Activation in individual subjects was similar; however, activation to hand motion also occurred in the STS with a variable location across subjects--explaining the lack of a clear activation focus in the group data. The data indicate that there are selective responses to viewing motion of different body parts in the human brain that are independent of object or tool use.

Adolescent↗
PubMed2006

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.

Adolescent↗
PubMed2005

Eccentric perception of biological motion is unscalably poor.

Accurately perceiving the activities of other people is a crucially important social skill of obvious survival value. Human vision is equipped with highly sensitive mechanisms for recognizing activities performed by others [Johansson, G. (1973). Visual perception of biological motion and a model for its analysis. Perception and Psychophysics, 14, 201; Johansson, G. (1976). Spatio-temporal differentiation and integration in visual motion perception: An experimental and theoretical analysis of calculus-like functions in visual data processing. Psychological Research, 38, 379]. One putative functional role of biological motion perception is to register the presence of biological events anywhere within the visual field, not just within central vision. To assess the salience of biological motion throughout the visual field, we compared the detectability performances of biological motion animations imaged in central vision and in peripheral vision. To compensate for the poorer spatial resolution within the periphery, we spatially magnified the motion tokens defining biological motion. Normal and scrambled biological motion sequences were embedded in motion noise and presented in two successively viewed intervals on each trial (2AFC). Subjects indicated which of the two intervals contained normal biological motion. A staircase procedure varied the number of noise dots to produce a criterion level of discrimination performance. For both foveal and peripheral viewing, performance increased but saturated with stimulus size. Foveal and peripheral performance could not be equated by any magnitude of size scaling. Moreover, the inversion effect--superiority of upright over inverted biological motion [Sumi, S. (1984). Upside-down presentation of the Johansson moving light-spot pattern. Perception, 13, 283]--was found only when animations were viewed within the central visual field. Evidently the neural resource responsible for biological motion perception are embodied within neural mechanisms focused on central vision.

Discrimination, Psychological↗
PubMed2005

Motion processing specialization in Williams syndrome.

Williams syndrome (WS) is a rare genetic disorder characterized by severe spatial deficits and relatively spared language. Although initial research suggested that WS entails a generalized motion processing deficit, later work demonstrated intact biological motion perception in people with WS, reflecting a sparing of a specific motion perception system. The present study examined whether this sparing is unique to biological motion, or extends to other motion tasks as well. WS children and adults and normal controls were tested to examine developmental changes across a variety of motion tasks. Results indicated that WS individuals performed at normal levels for motion coherence and biological motion tasks but had elevated thresholds for the 2-D form-from-motion task, a profile that extended into adulthood. These findings provide evidence that a genetic impairment can lead to a selective motion processing deficit and argue against characterizing WS as including a general motion processing impairment. The nature of the motion deficit is considered, including the implications for WS dorsal/ventral processing.

Adolescent↗
PubMed2006

Feature-based attention influences contextual interactions during motion repulsion.

Visual perception is strongly shaped by the spatial context in which stimuli are presented. Using center-surround configurations with oriented stimuli, recent studies suggest that voluntary attention critically determines which stimuli in the surround affect the percept of the central stimulus. However, evidence for attentional influences on center-surround interactions is restricted to the spatial selection of few among several surround stimuli of different orientations. Here, we extend these insights of center-surround interactions to the motion domain and show that the influence of surround information is critically shaped by feature-based attention. We used motion repulsion as an experimental test tool. When a central target motion was surrounded by a ring of motion, subjects misperceived the direction of the foveal target for particular center-surround direction differences (repulsion condition). Adding an appropriate second motion in the surround counterbalanced the effect, eliminating the repulsion. Introducing feature-based attention to one of the two superimposed directions of motion in the surround reinstated the strong contextual effects. The task relevance of the attended surround motion component effectively induced a strong motion repulsion on the foveally presented stimulus. In addition, the task relevance of the foveal stimulus also induced motion repulsion on the attended surround direction of motion. Our results show that feature-based attention to the surround strongly modulates the veridical perception of a foveally presented motion. The observed attentional effects reflect a feature-based mechanism affecting human perception, by modulating spatial interactions among sensory information and enhancing the attended direction of motion.

Attention↗
PubMed2006

Motion-onset VEPs: characteristics, methods, and diagnostic use.

This review article summarises the research on the motion-onset visual evoked potentials (VEPs) and important motion stimulus parameters which have been clarified. For activation of the visual motion processing system and evocation of the motion-onset specific N2 peak (with latency of 160-200ms) from the extra-striate temporo-occipital and/or parietal cortex, the following stimulus parameters can be recently recommended: low luminance (<ca. 20cd/m(2)) and low contrast (<ca. 10%-sinusoidally modulated) of a moving structure with low velocity and temporal frequency (<ca. 6Hz). A short (up to 200ms) duration of motion and a long (at least 1s) inter-stimulus interval reduce adaptation to motion and predominance of a pattern-related P1 peak. Radial motion (with increasing velocity and decreasing spatial frequency towards the periphery) produces larger reactions as compared to a unidirectional translation. In view of the slow maturation (up to the age of 18 years) and early ageing of the visual motion processing system, the use of age-dependent latency norms may be necessary. Since early or selective involvement of the motion processing system is suspected in some CNS disorders, we suggest an evaluation of the utility of motion-onset VEPs as part of the electrophysiological CNS examination since this method may recognise motion processing involvement better than other methods. Motion-onset VEPs might increase the sensitivity of this examination for diagnosing CNS diseases including Multiple Sclerosis, Neuroborreliosis, Glaucoma, Dyslexia and Encephalopathies.

Central Nervous System Diseases↗
PubMedDate not supplied

Motion perception in glaucoma patients: a review.

Most of the histopathological and psychophysical studies in glaucoma reveal a preferential damage to the magnocellular (M) pathway although a few of them support a damage to the parvocellular (P) pathway as well. In glaucoma, the visual fields are usually evaluated by conventional perimetry. However, it has been demonstrated that 20-40% of ganglion cells are lost before field defects are detected using conventional perimetry. Therefore, new psychophysical tests have recently been designed in order to specifically isolate and evaluate the visual mechanisms that are impaired at the early stages of glaucoma. In this context, several authors have addressed the issue of motion perception under the hypothesis of a predominant damage of the M pathway in glaucoma, and that motion perception is mediated mainly by M pathway. The results of these studies depict a large variation in the percentage of patients showing anomalous motion perception. Overall, motion thresholds are elevated in both glaucoma and ocular hypertensive patients as compared to control subjects, irrespective of the stimulus size and eccentricity. The test which discriminates best between patients and normal subjects is motion perimetry. The visual field defects in glaucoma patients identified by conventional perimetry and motion perimetry are similar, but the sizes of the defects are usually larger with motion perimetry. However, motion tests in central vision have no correlation with visual field defect on conventional perimetry. In glaucoma, loss of performance on motion perception tests does not necessarily support the existence of a specific deficit in the M pathway, because some behavioral studies suggest that the P pathway can also mediate motion perception. It is also difficult to conclude that motion perception is specifically affected in glaucoma because most of these studies do not yield a comparison with other visual functions. Despite these difficulties, localized motion perception tests at eccentricities of more than 15 degrees can be considered as a promising diagnostic tool.

Glaucoma, Open-Angle↗
PubMed2000

Global motion adaptation.

Image motion is initially detected locally. Local motion signals are then integrated across space in order to specify the global motion of objects or surfaces. It is well known that prolonged exposure to motion causes adaptation at the local motion level. We have investigated whether adaptation also occurs at the global motion level. We have devised a global motion stimulus (a random dot kinematogram) which has equal motion energy in opposite directions but nonetheless gives rise to global motion perception. At the local motion level, adaptation to this stimulus should cause equal adaptation in both directions and should not give rise to an aftereffect. Any aftereffect seen must therefore be attributable to adaptation at the global motion level. We find that following adaptation to this stimulus, judgements of the perceived direction of a test pattern are systematically biased towards the direction opposite to the adapting direction, suggesting that adaptation does occur at a level of visual processing at which global motion is represented.

Adaptation, Physiological↗
PubMed1997

Changes in perceived speed following adaptation to first-order and second-order motion.

To investigate whether or not adaptation to second-order motion can cause changes in perceived speed, measurements of perceived speed were obtained for two varieties of motion: (i) contrast-modulated two-dimensional static noise (second-order motion); and (ii) luminance-modulated noise (first-order motion). The test stimulus (either first-order or second-order) was presented to one side of a central fixation spot and a comparison stimulus (always first-order) was simultaneously presented on the opposite side. The observer's task was to indicate which of the two motion stimuli appeared to drift faster. The perceived speed of the test stimulus was measured with and without prior adaptation to motion on one side of the fixation spot only (that of the test stimulus). The modulation depth of the adaptation stimulus was always half that of the test stimulus and all test patterns were equated for visibility. The pattern of results for second-order motion was similar to that for first-order motion. Typically, adaptation reduced perceived speed, particularly when the adaptation speed was faster than the test speed. However, when the adaptation speed was low relative to the test speed, increases in perceived speed were found. Cross-over adaptation effects between first-order and second-order motion were also observed. Robust velocity aftereffects were found for second-order motion when the noise was dynamic or was high-pass filtered, suggesting that first-order (luminance) artifacts were not responsible for the velocity aftereffects observed. We conclude that the perceived speeds of first-order and second-order motion appear to be encoded in human vision using similar computational principles (but not necessarily utilizing the same mechanism), since the same pattern of results was found for the two varieties of motion.

Adaptation, Physiological↗
PubMed1997

The interaction between stereoscopic and luminance motion.

An interaction in apparent motion between perceived three-dimensional forms defined by stereopsis and local luminous elements is reported. Vertical stripes of cyclopean square gratings were simulated by random-dot stereograms. Alternation of two-frame stereograms whose phases differed by 90 deg caused two kinds of percepts, planes' motion in depth (first-order stereoscopic motion, first-order SM) or lateral motion of gratings (higher-order stereoscopic motion, higher-order SM). Experiment 1 explored the conditions under which higher-order SM frequently arose, as opposed to local luminance-based in-depth motion (first-order SM). The results show that, when the spatial arrangements of two-frame random dots were correlated, higher-order SM dominated for long ISI conditions (ISI > 73 msec). When they were uncorrelated, higher-order SM dominated even under zero ISI conditions. Subjects reported that, when higher-order SM was seen, dots were attached to the surfaces of the moving cyclopean figure (motion capture). Experiment 2 tested which factor caused the domination of higher-order SM under uncorrelated conditions in Experiment 1, the larger distance of dot jump or the varied directions of the dots' motion. The results show that, when the distance of dot jump is large or when the directions of dots' motion are incoherent, higher-order SM arises more frequently. When local first-order motion signals are weakened by appropriate temporal and spatial conditions or by incoherent motion directions, higher-order SM dominates and it captures the motion of dots.

Depth Perception↗
PubMed2003

Impact of impaired wrist motion on hand and upper-extremity performance(1).

PURPOSE: To quantify and compare the disabilities caused by reduced and absent wrist motion using objective measurements of task performance and perceived disability, and to assess the compensatory motions of the shoulder, elbow, forearm, and trunk caused by impaired wrist motion. METHODS: A clinical study of 21 normal subjects was done to measure physical performance and to assess wrist function under conditions of reduced (30 degrees flexion and 30 degrees extension) and nearly absent wrist motion using established physical tests and questionnaires (Disabilities of the Arm, Shoulder, and Hand [DASH], Patient Rated Wrist Evaluation [PRWE], and a study-specific survey). The clinical study also measured compensatory motions of the shoulder, elbow, forearm, and trunk. RESULTS: Average times to perform the Jebsen test and activities of daily living (ADLs) test increased for both motion-restricted conditions of the wrist but did not differ significantly between the conditions. Questionnaire scores regarding function were significantly worse for both motion-restricted conditions and poorest for nearly absent motion. Average compensatory motions in the extremity and trunk statistically increased for both motion-restricted conditions but were not marked and did not differ between the conditions. High variability among subjects occurred in all physical tests and questionnaires for both motion-restricted conditions. CONCLUSIONS: Perceived disability from reduced wrist motion appeared greater than measured functional loss using common physical tests and outcome surveys.

Activities of Daily Living↗
PubMed2003

Processing of global, but not local, motion direction is deficient in schizophrenia.

Visual motion processing is compromised in a substantial proportion of schizophrenic patients, but precise neural mechanisms underlying the motion-processing deficit have not yet been elaborated. The visual motion pathway includes a local and a global processing stage, each of which has distinct neural substrates. Here, we attempt to identify the stage(s) that are implicated in impaired motion processing of schizophrenia-local, global, or both. For schizophrenia patients (n=23) and normal controls (n=26), we measured (1) the thresholds for detecting the motion direction of a random dot pattern, a task that requires global motion processing, and (2) the thresholds for detecting the motion direction of a grating, a task that requires only local motion processing, using psychophysical methods. Schizophrenia patients showed elevated thresholds for detecting the direction of coherent motion, particularly for the high dot-density target. In contrast, schizophrenia patients showed normal thresholds for detecting the direction of motion of a grating. The results indicate that the global, but not the local, processing stage of the visual motion system is compromised in schizophrenia patients, thus implicating motion-sensitive brain areas that possess large receptive fields for spatial and temporal integration, such as Middle Temporal Area/Medial Superior Temporal Area.

Adult↗
PubMed2002

Auditory and visual attention modulate motion processing in area MT+.

Behavioral and physiological studies have established that visual attention to a given feature or location can modulate early visual processing. In the present experiment, we asked whether auditory attention can likewise influence visual processing. We used a visual illusion, the motion aftereffect (MAE), to assess the effects of visual and auditory attention on motion processing in human area MT+. We acquired psychophysical and functional magnetic resonance imaging (fMRI) data while subjects fixated and viewed moving and stationary stimuli in alternating blocks. For each of four motion conditions, we measured the duration of the subsequent MAE, the time for activity in MT+ to return to baseline after motion adaptation (decay time), and the magnitude of MT+ activity during motion adaptation. For each subject, we first obtained measures of motion processing in the absence of attentional demands, by comparing reversing and expanding motion conditions. Subjects perceived the MAE following adaptation to expanding but not reversing motion, as observed previously, and decay times in MT+ were selectively prolonged after expanding motion. We then assessed the effects of performing either a visual or an auditory attentional task during expanding motion adaptation. Performance of the attentional task, whether visual or auditory, produced a significant reduction of subsequent MAE perception and associated decay times in MT+, as compared to expanding motion with fixation only. Both attentional tasks also reduced the magnitude of activation during motion adaptation. These data show that auditory attention, like visual attention, can modify sensory processing at a remarkably early stage of the visual hierarchy.

Acoustic Stimulation↗
PubMed1999

Characteristics of visual evoked potentials generated by motion coherence onset.

Prior studies have shown that an electrophysiological correlate of visual motion processing can be found in the N2, a transient negativity occurring at about 200 ms in the visual evoked potential (VEP). In most of the studies, N2 was triggered by the onset of a coherent motion. Results of our first experiment revealed that topography of the negative potential can be modified by motion direction information. In contrast to the onset of uncorrelated motion of pixels in a random dot kinematogram (RDK) correlated motion leads to an right hemispheric amplitude advantage. Hemispheric differences can be increased when the negativity is triggered by the onset of a coherent motion direction preceded by uncorrelated motion in RDKs. In a second experiment, we examined whether the negativity elicited by direction is related to the strength of the impression of motion direction measured psychophysically. The latter was modified by varying the percentage of correlated moving pixels in the RDK. Increasing the proportion of these 'direction signals' was associated with both an increase in the strength of the impression of motion direction and an increase in VEP amplitude. Mean correlations of electrophysiological and psychophysical data, which exceeded 0.7, revealed a higher sensitivity of the right hemisphere. The close relationship between the global motion impression and VEP negativity indicate that electrophysiological correlates of processing stages within visual motion analysis can be isolated. The recorded negativity seems to be associated primarily with the process of global motion integration.

Adult↗
PubMed1997

Interactions between colour and motion in image segmentation.

BACKGROUND: . An important early stage in visual processing is image segmentation, in which similar regions are grouped together and segregated from dissimilar regions, so that distinct objects ultimately may be located and recognized. In the natural world, objects are simultaneously characterized by colour, motion, texture and other visual attributes. How does the human visual system combine these attributes to segment the image? Although colour and motion information are conveyed by distinct functional streams from retina to visual cortex, there is increasing evidence for early and substantial cross-talk between the streams. Here, we explore psychophysical evidence for interactions between colour and motion in image segmentation. RESULTS: . Observers performed forced-choice segmentation tasks on random-dot stimuli. The dots in the vertical target figure were distinguished from the background dots by a different distribution of speeds or colours. To explore interactions between motion and colour segmentation, we added motion noise to the colour signal (or vice versa) by assigning all dots speeds (or colours) drawn from one of several noise distributions. Motion noise severely affects segmentation by colour. Motion noise defined by a broad distribution of speeds degrades colour segmentation, but a two-speed motion distribution (half moving up, half moving down) facilitates colour segmentation. Control experiments prove that the facilitatory effect is not caused by integrating colour information over different frames, nor can it be explained by probability summation over the two planes of moving dots. Colour noise also affects motion segmentation, but under a more restricted range of conditions, and not in a facilitatory way. CONCLUSIONS: . Colour and motion information interact at early stages during image segmentation, before decisions based on either cue in isolation are made. The robust bipolar effects of motion information on segmentation by colour indicate that the establishment of motion-defined surfaces takes primacy, and that such surfaces constitute important primitives for further processing.

Choice Behavior↗
PubMed1992

Are there separate ON and OFF channels in fly motion vision?

Visual information is processed in a series of subsequent steps. The performance of each of these steps depends not only on the computations it performs itself but also on the representation of the visual surround on which it operates. Here we investigate the consequences of signal preprocessing for the performance of the motion-detection system of the fly. In particular, we analyze whether the retinal input signals are rectified and segregate into separate ON and OFF channels, which then feed independent parallel motion-detection pathways. We recorded the activity of an identified directionally selective interneuron (H1-cell) in response to apparent motion stimuli, i.e. sequential brightness changes at two neighboring locations in the visual field, as well as to brightness changes at only a single location. For apparent motion stimuli, the motion-dependent response component was determined by subtracting from the overall response to the individual stimulus components when presented alone. The following conclusions could be derived: (1) Apparent motion consisting of a sequence of increased or decreased brightness at two locations in the visual field have the same optimum interstimulus time interval (Fig. 3). (2) Sequences of brightness steps of like polarity (either increments or decrements) elicit positive and negative motion-dependent response components when mimicking motion in the cell's preferred and null direction, respectively. The motion-dependent response components are inverted in sign when the brightness steps of a stimulus sequence have a different polarity (Fig. 7). (3) The responses to the beginning and the end of a brightness pulse depend on the pulse duration. For pulse durations of less than 2 s, both events interact with each other (Fig. 9). All of these results do not provide any indication that the fly processes motion information in independent ON and OFF motion detectors. Brightness changes of both signs are rather represented at the input of the same movement detectors, and interactions between signals resulting from both brightness increments and decrements take their sign into account. This type of preprocessing of the retinal input is argued to render a motion-detection system particularly robust against noise.

Animals↗
PubMed1999

Parallel search for conjunctions with stimuli in apparent motion.

A series of experiments was conducted to determine whether apparent motion tends to follow the similarity rule (i.e. is attribute-specific) and to investigate the underlying mechanism. Stimulus duration thresholds were measured during a two-alternative forced-choice task in which observers detected either the location or the motion direction of target groups defined by the conjunction of size and orientation. Target element positions were randomly chosen within a nominally defined rectangular subregion of the display (target region). The target region was presented either statically (followed by a 250 ms duration mask) or dynamically, displaced by a small distance (18 min of arc) from frame to frame. In the motion display, the position of both target and background elements was changed randomly from frame to frame within the respective areas to abolish spatial correspondence over time. Stimulus duration thresholds were lower in the motion than in the static task, indicating that target detection in the dynamic condition does not rely on the explicit identification of target elements in each static frame. Increasing the distractor-to-target ratio was found to reduce detectability in the static, but not in the motion task. This indicates that the perceptual segregation of the target is effortless and parallel with motion but not with static displays. The pattern of results holds regardless of the task or search paradigm employed. The detectability in the motion condition can be improved by increasing the number of frames and/or by reducing the width of the target area. Furthermore, parallel search in the dynamic condition can be conducted with both short-range and long-range motion stimuli. Finally, apparent motion of conjunctions is insufficient on its own to support location decision and is disrupted by random visual noise. Overall, these findings show that (i) the mechanism underlying apparent motion is attribute-specific; (ii) the motion system mediates temporal integration of feature conjunctions before they are identified by the static system; and (iii) target detectability in these stimuli relies upon a nonattentive, cooperative, directionally selective motion mechanism that responds to high-level attributes (conjunction of size and orientation).

Adult↗
PubMed2000

Visual motion integration for perception and pursuit.

To examine the relationship between visual motion processing for perception and pursuit, we measured the pursuit eye-movement and perceptual responses to the same complex-motion stimuli. We show that humans can both perceive and pursue the motion of line-figure objects, even when partial occlusion makes the resulting image motion vastly different from the underlying object motion. Our results show that both perception and pursuit can perform largely accurate motion integration, i.e. the selective combination of local motion signals across the visual field to derive global object motion. Furthermore, because we manipulated perceived motion while keeping image motion identical, the observed parallel changes in perception and pursuit show that the motion signals driving steady-state pursuit and perception are linked. These findings disprove current pursuit models whose control strategy is to minimize retinal image motion, and suggest a new framework for the interplay between visual cortex and cerebellum in visuomotor control.

Humans↗