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PubMed2003

Disorders of motion and depth.

Damage to the human homologue of area MT produces a motion perception deficit similar to that found in the monkey with MT lesions. Even temporary disruption of MT processing with transcranial magnetic stimulation can produce a temporary akinetopsia [127]. Motion perception deficits, however, also are found with a variety of subcortical lesions and other neurologic disorders that can best be described as causing a disconnection within the motion processing stream. The precise role of these subcortical structures, such as the cerebellum, remains to be determined. Simple motion perception, moreover, is only a part of MT function. It undoubtedly has an important role in the perception of depth from motion and stereopsis [112]. Psychophysical studies using aftereffects in normal observers suggest a link between stereo mechanisms and the perception of depth from motion [9-11]. There is even a simple correlation between stereo acuity and the perception of depth from motion [128]. Future studies of patients with cortical lesions will take a closer look at depth perception in association with motion perception and should provide a better understanding of how motion and depth are processed together.

Alzheimer Disease↗
PubMed2003

Dog phobia in a motion-blind patient.

INTRODUCTION: A prominent neurophysiological model of phobia generation holds that specific phobia might result from the uncoupling of unaware subcortical fear responses from aware cortical fear responses. Former responses are thought to be automatic and fast, providing approximate information about the external stimulus, whereas the latter responses are more controlled and allow comparison with previous experience. Since only the cortical pathway carries information available to awareness, this model also accounts for the striking irrationality of specific phobia in humans. METHODS: Here, we report neuropsychological and neuro-ophthalmological findings in a 41-year-old patient who developed severe dog phobia following bilateral parietal lobe damage. RESULTS: The examinations showed a severe deficit in visual motion perception (visual motion blindness or akinetopsia) as well as spatial vision. Importantly, the patient was largely unaware of his visual deficits. CONCLUSION: Based on the present observation it is argued that irrational fear, as found in specific phobia, might not only result from a general uncoupling of aware cortical from unaware subcortical fear responses, but also from a functionally similar dissociation at the cortical level.

Journal Article↗
PubMed1999

Perception of first- and second-order motion: separable neurological mechanisms?

An unresolved issue in visual motion perception is how distinct are the processes underlying "first-order" and "second-order" motion. The former is defined by spatiotemporal variations of luminance and the latter by spatiotemporal variations in other image attributes, such as contrast or depth. Here we describe two neurological patients with focal unilateral lesions whose contrasting perceptual deficits on psychophysical tasks of "first-order" and "second-order" motion are related to the maps of the human brain established by functional neuroimaging and gross anatomical features. We used a relatively fine-grained neocortical parcellation method applied to high-resolution MRI scans of the patients' brains to illustrate a subtle, yet highly specific dissociation in the visual motion system in humans. Our results suggest that the two motion systems are mediated by regionally separate mechanisms from an early stage of cortical processing.

Adult↗
PubMed2002

The roles of static depth information and object-image relative motion in perception of heading.

In a series of 6 experiments, two hypotheses were tested: that nominal heading perception is determined by the relative motion of images of objects positioned at different depths (R. F. Wang & J. E. Cutting, 1999) and that static depth information contributes to this determination. By manipulating static depth information while holding retinal-image motion constant during simulated self-movement, the authors found that static depth information played a role in determining perceived heading. Some support was also found for the involvement of R. F. Wang and J. E. Cutting's (1999) categories of object-image relative motion in determining perceived heading. However, results suggested an unexpected functional dominance of information about heading relative to apparently near objects.

Adolescent↗
PubMed2000

Visual perception of motion and 3-D structure from motion: an fMRI study.

Functional magnetic resonance imaging was used to study the cortical bases of 3-D structure perception from visual motion in human. Nine subjects underwent three experiments designed to locate the areas involved in (i) motion processing (random motion versus static dots), (ii) coherent motion processing (expansion/ contraction versus random motion) and (iii) 3-D shape from motion reconstruction (3-D surface oscillating in depth versus random motion). Two control experiments tested the specific influence of speed distribution and surface curvature on the activation results. All stimuli consisted of random dots so that motion parallax was the only cue available for 3-D shape perception. As expected, random motion compared with static dots induced strong activity in areas V1/V2, V5+ and the superior occipital gyrus (SOG; presumptive V3/V3A). V1/V2 and V5+ showed no activity increase when comparing coherent motion (expansion or 3-D surface) with random motion. Conversely, V3/V3A and the dorsal parieto-occipital junction were highlighted in both comparisons and showed gradually increased activity for random motion, coherent motion and a curved surface rotating in depth, which suggests their involvement in the coding of 3-D shape from motion. Also, the ventral aspect of the left occipito-temporal junction was found to be equally responsive to random and coherent motion stimuli, but showed a specific sensitivity to curved 3-D surfaces compared with plane surfaces. As this region is already known to be involved in the coding of static object shape, our results suggest that it might integrate various cues for the perception of 3-D shape.

Adult↗
PubMed2004

Strong influence of test patterns on the perception of motion aftereffect and position.

In a completely linear system, the behavior of a square wave pattern can be predicted by its sinusoidal components. However, we observed a complete breakdown of the linear system prediction in the perception of the motion aftereffect (MAE). The duration of the MAE was measured following a one-minute adaptation to a rotating radial grating. Three different luminance patterns were used for both the adaptation and test stimulus: (1) sine wave, (2) square wave, and (3) complex grating with the same Fourier amplitude spectrum as the square wave, but with randomized phases. The sine wave stimulus generated the highest magnitude MAE, followed by the random-phase complex grating, and lastly the square wave grating. To test whether the square wave grating is a weak adaptor or a weak test for the MAE, we performed a cross adaptation experiment in which the sine wave, square wave, and complex gratings were paired in seven ways. Results show that the strength of the MAE critically depended on the test pattern. Regardless of the adaptor, MAE strength is in a decreasing order with the test pattern as sine wave grating, complex grating, and square wave grating. Further experiments ruled out the possibility that differential MAEs between these conditions are due to different peak contrasts in these patterns. Additionally, the MAE from a square wave grating as the test pattern is not accompanied by a significant concurrent shift in the apparent position. Linear system theory cannot predict the magnitude of the MAE using complex gratings. The spatial features of a test stimulus, such as position reliability or luminance uniformity, strongly influence the magnitude of MAE. Sharp edges and local luminance uniformity can greatly reduce MAE.

Adaptation, Ocular↗
PubMed1993

Interaction of vestibular and proprioceptive inputs.

The study investigates the interaction of leg proprioceptive and vestibular afferents for human self-motion perception in space. Stimulation consisted of sinusoidal (0.025-0.4 Hz) and transient horizontal rotations of trunk and head in space (vestibular stimulus, VEST) and of the feet relative to the trunk (leg proprioceptive stimulus, LEG-PROP). Measures of the perception were obtained with the help of a pointing procedure. Leg proprioception. The perception of relative motion between feet and trunk during LEG-PROP was veridical across the frequencies tested and had a low detection threshold (0.2 degree/s). Perception of trunk turning in space. Trunk turning during VEST was underestimated, especially at low frequencies, and the threshold of the perception was > or = 1.0 degree/s. LEG PROP evoked an illusion of trunk turning, which reached a considerable magnitude at low frequencies. During VEST-LEG-PROP combinations, the perception varied monotonously as a function of both inputs. Reflecting the deficiencies of its constituents, it was erroneous with 1 exception. During trunk rotation about the stationary feet, the perception was approximately veridical across frequency and its threshold was down to 0.2 degree/s, suggesting that it was determined essentially by leg proprioception in this condition. These findings resemble those previously obtained for neck proprioception and, therefore, were incorporated into a conceptual model of vestibular-proprioceptive interaction in general. In this model, first an internal notion of foot in space is created by summing the following high-threshold signals: head in space (vestibular), trunk relative to head (neck proprioceptive), and foot relative to trunk (leg proprioceptive). Second, further addition of low-threshold proprioceptive signals of trunk on foot and head on trunk yields the perception of trunk in space and head in space, respectively. Not included in the model is the finding that subjects' perceptual mode may change in certain conditions. When foot excursion exceeds a certain magnitude, for instance, vestibular input alone may determine the self-motion perception.

Adult↗
PubMed1999

Vestibular and vestibulo-proprioceptive perception of motion in the horizontal plane in blindfolded man--I. Estimations of linear displacement.

Perception of linear displacement in the horizontal plane was studied in blindfolded human subjects. Subjects were transported and walked with guidance along 2-6 m straight lines and then had to retrace these paths walking backwards. Subjects solved a double orientational task: firstly, they defined the direction of the backward path and, secondly, estimated its length. Following passive transportation overestimation of shorter distances was observed, which tended towards underestimation with path lengthening. The absolute average error in estimating a 2-m path was 0.4 +/- 0.18 m (M +/- m), a 6-m path -0.2 +/- 0.19 m. Guided subjects constantly overestimated the path length with an averaged error of 0.51 +/- 0.064 m. In defining the direction of the backward path subjects made errors scattered over a range of 0-30 degrees. These errors did not vary in relation to path length. A reverse proportionality was revealed between errors in direction and estimation of path lengths following passive transportation. It is suggested that accuracy in perceiving a linear displacement is dependent upon subjective perception of the preceding change in the trajectory of movement.

Adult↗
PubMed1981

Perception of motion using blur pattern information in the moderate and high-velocity domains of vision.

A series of studies of visual orientation at blurring velocities is integrated ans summarized. Surfaces moving rapidly in depth were simulated and sensitivities of observers to depth-related geometric parameters of the resulting blur patterns, such as divergence and curvature, were measured. Examples of some ecological analyses of these parameters as sources of visual orientation information are given. The results indicate that human sensitivity to a number of blur pattern variables is high enough to be useful in guidance of locomotion. It was also found that some of the information about motion contained in blur patterns may actually be form information. It appears that visual motion processing may involve a complex interplay of visual form and motion analysing systems.

Discrimination, Psychological↗
PubMed2005

The detection of motion in chromatic stimuli: pedestals and masks.

This study seeks to clarify the reasons for some of the differences in the published data on chromatic motion perception, and to provide further support for the existence of a low-level motion mechanism sensitive to purely chromatic change. Observers discriminated the direction of motion of displaced sinusoidal gratings in the presence of a static grating mask (or pedestal). Each component of the stimulus was independently described in cardinal colour space and calibrated for subjective equiluminance using multiple methods. The motion structure, stimulus size, temporal frequency, contrast, relative phase and chromatic properties were all varied parametrically and the data cast in terms of predictions made by two different theoretical approaches to the test-mask combination. The vast majority of the data were well explained by a low-level motion mechanism sensitive to the motion of foveally-placed chromatic stimuli. Data consistent with either higher-level motion perception or a luminance-like signal were found outside the fovea and when the stimulus properties did not otherwise favour chromatic motion perception. There was some explanation of inconsistencies in previously published data and a strong suggestion that previous results showing pedestal-like behaviour for these stimulus combinations were a special case rather than a general result.

Color Perception↗
PubMed2000

Perception of Fourier and non-Fourier motion by larval zebrafish.

A moving grating elicits innate optomotor behavior in zebrafish larvae; they swim in the direction of perceived motion. We took advantage of this behavior, using computer-animated displays, to determine what attributes of motion are extracted by the fish visual system. As in humans, first-order (luminance-defined or Fourier) signals dominated motion perception in fish; edges or other features had little or no effect when presented with these signals. Humans can see complex movements that lack first-order cues, an ability that is usually ascribed to higher-level processing in the visual cortex. Here we show that second-order (non-Fourier) motion displays induced optomotor behavior in zebrafish larvae, which do not have a cortex. We suggest that second-order motion is extracted early in the lower vertebrate visual pathway.

Animals↗
PubMed1985

Perception of motion in equiluminous kinematograms.

Two fields of random dots that were identical except for a slight shift in a central square region were presented in rapid alternation. This produced a vivid impression of a square moving back and forth above the background. When the kinematogram is presented in equiluminous red/green, the motion of the central region can still be seen, although over a narrower range of alternation rates, interstimulus intervals, and displacements than for black/white presentation. The perception of motion for equiluminous stimuli indicates that colour and motion can be analyzed conjointly by the visual system. However, as originally reported by Ramachandran and Gregory, the segregation of the oscillating central square from the background is lost at equiluminance. This segregation process therefore appears to be colour-blind.

Color Perception↗
PubMed1991

Purely chromatic perception of motion in depth: two eyes as sensitive as one.

Motion hyperacuity (phase) thresholds were measured for both lateral and stereoscopic oscillatory motion in both luminance and equiluminant red/green gratings of 2 cycles per degree. Thresholds for lateral chromatic motion did not exhibit the inhibitory fall-off at low temporal frequencies that was found for luminance motion. Phase thresholds for purely chromatic motion were substantially higher than those for luminance gratings, in proportion to the ratio of cone signal modulation, but they could be predicted from the corresponding contrast sensitivities for both types of stimulus. Stereomovement thresholds in luminance gratings showed the stereomovement suppression effect relative to monocular motion sensitivity previously reported for line stimuli, but purely chromatic gratings did not. Together with the lack of an inhibitory fall-off, these results imply that chromatic and luminance motion are processed by different neural pathways, and that the chrominance pathway is capable of supporting a strong percept of stereoscopic motion from purely chromatic gratings.

Attention↗