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PubMed1989

The "motion-blind" patient: low-level spatial and temporal filters.

The "motion-blind" patient previously described by Zihl et al. (1983) was investigated using standard psychophysical procedures with stimuli whose spatial and temporal properties could be separately manipulated. Detection experiments for sinewave grating stimuli of varying spatial and temporal frequency showed sensitivity in this patient to be only slightly impaired. Temporal integration for stimuli of varying spatiotemporal frequency exhibited the expected space-time covariation seen in normal vision. An examination of the suprathreshold discriminative capacity of this patient was undertaken for spatial frequency, contrast, and temporal frequency. Although all of these discriminative functions were impaired, those concerning temporal frequency or velocity were dramatically reduced. No similar loss was seen for spatial frequency discrimination for moving or temporally varying stimuli. No measurable temporal frequency discrimination was present above 6 Hz and no velocity discrimination above 6 degrees/sec. Experiments involving the direction discrimination of suprathreshold drifting gratings of arrays of random dots revealed an inability to perceive direction of movement above a velocity of about 6 degrees/sec. Contrast thresholds contingent on direction of motion of a drifting grating also showed a much greater deficit than simple detection. Apparent motion using 2-flash random dot kinematograms revealed that the residual motion vision of this patient corresponded to the "short-range" motion process of normal vision. This process originally defined by Braddick (1974) operates over restricted space and time intervals. Apparent motion could only be supported by a narrow range of intermediate spatial displacements. These results suggest that this patient does exhibit some residual motion perception, probably corresponding to a severely impaired "short-range" mechanism. The patient's relatively intact ability to perform simple types of discrimination but severe impairment of performance at making judgments relevant to the nature of motion of the same stimuli suggests that while the components necessary for the analysis of motion are intact their more global associations have been disrupted. This implicates an extrastriate locus of the brain damage. Alternative explanations for the nature of the deficit are discussed.

Biomechanical Phenomena↗

PubMed2002

Brain Areas Active during Visual Perception of Biological Motion.

Theories of vision posit that form and motion are represented by neural mechanisms segregated into functionally and anatomically distinct pathways. Using point-light animations of biological motion, we examine the extent to which form and motion pathways are mutually involved in perceiving figures depicted by the spatio-temporal integration of local motion components. Previous work discloses that viewing biological motion selectively activates a region on the posterior superior temporal sulcus (STSp). Here we report that the occipital and fusiform face areas (OFA and FFA) also contain neural signals capable of differentiating biological from nonbiological motion. EBA and LOC, although involved in perception of human form, do not contain neural signals selective for biological motion. Our results suggest that a network of distributed neural areas in the form and motion pathways underlie the perception of biological motion.

Brain Mapping↗

PubMed2006

Spatiotopic selectivity of BOLD responses to visual motion in human area MT.

Many neurons in the monkey visual extrastriate cortex have receptive fields that are affected by gaze direction. In humans, psychophysical studies suggest that motion signals may be encoded in a spatiotopic fashion. Here we use functional magnetic resonance imaging to study spatial selectivity in the human middle temporal cortex (area MT or V5), an area that is clearly implicated in motion perception. The results show that the response of MT is modulated by gaze direction, generating a spatial selectivity based on screen rather than retinal coordinates. This area could be the neurophysiological substrate of the spatiotopic representation of motion signals.

Adult↗

PubMed2005

Disorders of agency in schizophrenia correlate with an inability to compensate for the sensory consequences of actions.

Psychopathological symptoms in schizophrenia patients suggest that the concept of self might be disturbed in these individuals [1]. Delusions of influence make them feel that someone else is guiding their actions, and certain kinds of their hallucinations seem to be misinterpretations of their own inner voice as an external voice, the common denominator being that self-produced information is perceived as if coming from outside. If this interpretation were correct, we might expect that schizophrenia patients might also attribute the sensory consequences of their own eye movements to the environment rather than to themselves, challenging the percept of a stable world. Indeed, this seems to be the case because we found a clear correlation between the strength of delusions of influence and the ability of schizophrenia patients to cancel out such self-induced retinal information in motion perception. This correlation reflects direct experimental evidence supporting the view that delusions of influence in schizophrenia might be due to a specific deficit in the perceptual compensation of the sensory consequences of one's own actions [1, 2, 3, 4, 5 and 6].

Adult↗

PubMed1994

Motion aftereffects with random-dot chequerboard kinematograms: relation between psychophysical and VEP measures.

A random-dot chequerboard kinematogram was used to investigate the effect of motion adaptation both on evoked potentials and on motion aftereffects (MAEs). The experimental paradigm used allowed simultaneous measurement of both variables. Each adaptation period was followed by a series of 5 short test stimuli to which evoked potentials were recorded. Motion aftereffects were observed in the intervals between test stimuli. An inverse relationship between mean N2-P1 amplitude and mean reported MAEs was found as a function of adaptation durations of 1.4, 5.6, and 17.5 s. When the shortest and longest adaptation durations were compared, this relationship held for thirteen of fourteen subjects tested when adaptation-motion and test-motion directions corresponded and for twelve of fourteen subjects when they were opposed. The possibility that the effect of motion adaptation on N2-P1 amplitude was due to local luminance-contrast adaptation is discussed and shown to be unlikely. The suitability of this paradigm for the combined psychophysical and electrophysiological assessment of disturbances in motion perception is discussed.

Adolescent↗

PubMed2000

Directional preponderance in pitch circular vection.

We used optokinetic stimulation (OKS) in eighteen normal adults aged 18-30 years to investigate vertical self-motion perception. In order to induce self-rotation, either a stripe pattern or a random dot pattern was projected onto the inner wall of a hemispherical dome with a diameter of 150 cm. The pattern was rotated either about the subject's vertical axis (yaw) or about the subject's interaural axis (pitch) for 80 s at a constant acceleration of 1 deg/s2. Stimuli were randomly repeated three to four times in each direction. The latency of onset as well as the perceived intensity of circular vection (CV) was measured for each stimulus presentation. CV latencies for upward rotational stimulation were significantly longer than those for downward rotational stimulation under both types of stimulus conditions. There was no significant difference in CV latency between rightward and leftward rotational stimulation. For most subjects, the magnitudes of the perceived CV for rightward rotational stimulation were equal to those for leftward rotational stimulation, whereas the magnitudes of the perceived CV for vertical stimulation showed large intersubject variability. These results provide additional evidence that fundamental differences exist between different types of self-motion. Possible explanations for the directional asymmetry in vertical perception of self-motion will also be discussed.

Adult↗

PubMed2006

Integration of one- and two-dimensional motion signals in infants: evidence from the barber-pole illusion.

Several previous studies in adults have investigated how one- and two-dimensional moving features are integrated into a coherent global motion percept by studying the "barber-pole illusion"; when a one-dimensional moving grating is presented within a rectangular aperture, the two-dimensional line terminators at the edges of the aperture bias the perceived direction of motion toward the longer axis of the aperture. In the current study, we used barber-pole stimuli to investigate the development of motion mechanisms that integrate one- and two-dimensional motion signals. Using a directional eye movement technique, we measured responses to obliquely moving gratings presented within horizontally vs. vertically oriented apertures, in infants (ages 2-5 months) and adults. For all ages, we found that horizontal eye movements were significantly stronger when gratings were presented within horizontal than within vertical apertures, as predicted by the barber-pole illusion. Additionally, we devised a way to infer the "effective shift" in eye movement direction produced by the barber-pole illusion. Using a simple motion integration model, effective shift values were then used to calculate the relative weightings of one- and two-dimensional motion signals to direction coding. The results show that by 2 months of age, infants integrate one- and two-dimensional motion signals, and that the relative weighting of one- and two-dimensional signals remains roughly constant from 2 months of age into adulthood.

Adult↗

PubMed2002

Can spatio-temporal energy models of motion predict feature motion?

Current "spatio-temporal energy" models of how we perceive pattern motion have been very successful in helping us to understand the mechanisms of motion perception. Although they have been supported by a large number of physiological and psychological studies, they have so far not provided a complete explanation for a number of results. These results emerge from experiments concerned with predicting perceived motion direction from patterns comprising two or more components. It has been suggested that these results are more consistent with an earlier type of model based on the motion of two-dimensional features. This paper briefly describes how three generic spatio-temporal energy models have been extended to predict motion derived from two-component stimuli. A new model is then presented that utilises similar architecture to the two-stage spatial-temporal energy model proposed by Adelson and Movshon (Nature 300 (1982) 523). The first stage is a spatial temporal filtering stage and the second stage computes the intersection of constraints (IOC), an important constraint used in combining motion information across two or more components. In the model presented here the second stage is different. A directional spatial second derivative is used to extract zero-crossings at the component level, i.e. gratings. If any zero-crossing falls in the same spatial position for two or more components its displacement is tracked using a nearest neighbour match. Tracking these 'intersecting zero-crossings' essentially computes the IOC but also provides other properties that predict non-IOC motion, and second-order component motion. Surprising new insights are described into how current spatio-temporal energy models may also account for these results. However, unlike the model presented here, they rely on operations carried out on the two-dimensional pattern.

Contrast Sensitivity↗

PubMed1996

Motion discrimination of single targets: comparison of preliminary findings in normal subjects and patients with glaucoma.

BACKGROUND: Luminance, global motion and flicker sensitivities are affected in patients with primary open-angle glaucoma. Although no theoretical model has been put forward to explain the observed reduction in sensitivity in this patient group, these findings have often been attributed to diffuse and selective loss of large optic nerve fibres. METHODS: Movement processing was investigated using an optical projection system that generates smooth, continuous motion with control of speed, displacement and motion direction. Motion-displacement and direction-discrimination thresholds were measured in eight normal subjects and in three patients with diagnosed glaucoma. At each speed tested, targets were presented for a range of displacements and thresholds were extracted after probit analysis. The measurements were carried out both foveally and at 19 degrees in the periphery and provided the data necessary to develop and optimise a model of motion perception based on multiple time delays for the correlation of signals that map progressively more distant parts of the visual field. RESULTS: Our preliminary findings show that direction discrimination can be at chance level even for large displacements when motion is detected 80% of the time. Model simulations show that specific changes in the spatial sampling interval and the speed of transmission of the motion signals involved can cause the observed reduction in motion sensitivity and direction discrimination in patients with glaucoma. CONCLUSIONS: A model for motion detection and direction discrimination of single targets has been proposed to account for the measured functional relationship between motion displacement thresholds and target speed in normal subjects. Tested patients with glaucoma show reduced motion sensitivity and poor discrimination of motion direction. The type of degraded performance observed experimentally in glaucoma patients is also predicted by the model. Such predictions require specific changes in model parameters that may be indicative of changes in the retina caused by the disease.

Adult↗

PubMed2001

Brain activity evoked by inverted and imagined biological motion.

Previous imaging research has identified an area on the human posterior superior temporal sulcus (STS) activated upon viewing biological motion. The current experiments explore the relationship between neural activity within this region and perceptual experience. Biological motion perception is orientation dependent: inverting point-light animations make them more difficult to see. We measured activity levels within this region as observers viewed inverted point-light animations. We also measured neural activity while observers imagined biological motion and compared it to that measured while observers viewed the animations. In both experiments we found that the BOLD response was modulated with perceptual experience. Viewing inverted biological motion activated posterior STS more than scrambled motion, but less than upright biological motion. Mental imagery of biological motion was also sufficient to activate this region in most of our observers, but the level of activity was weaker than during actual viewing of the motion animations.

Female↗

PubMedDate not supplied

Monocular mechanisms determine plaid motion coherence.

Although the neural location of the plaid motion coherence process is not precisely known, the middle temporal (MT) cortical area has been proposed as a likely candidate. This claim rests largely on the neurophysiological findings showing that in response to plaid stimuli, a subgroup of cells in area MT responds to the pattern direction, whereas cells in area V1 respond only to the directions of the component gratings. In Experiment 1, we report that the coherent motion of a plaid pattern can be completely abolished following adaptation to a grating which moves in the plaid direction and has the same spatial period as the plaid features (the so-called "blobs"). Interestingly, we find this phenomenon is monocular: monocular adaptation destroys plaid coherence in the exposed eye but leaves it unaffected in the other eye. Experiment 2 demonstrates that adaptation to a purely binocular (dichoptic) grating does not affect perceived plaid coherence. These data suggest several conclusions: (1) that the mechanism determining plaid coherence responds to the motion of plaid features, (2) that the coherence mechanism is monocular, and thus (3), that it is probably located at a relatively low level in the visual system and peripherally to the binocular mechanisms commonly presumed to underlie two-dimensional (2-D) motion perception. Experiment 3 examines the spatial tuning of the monocular coherence mechanism and our results suggest it is broadly tuned with a preference for lower spatial frequencies. In Experiment 4, we examine whether perceived plaid direction is determined by the motion of the grating components or the features. Our data strongly support a feature-based model.

Adaptation, Ocular↗

PubMed2003

Visual motion influences the contingent auditory motion aftereffect.

In this study, we show that the contingent auditory motion aftereffect is strongly influenced by visual motion information. During an induction phase, participants listened to rightward-moving sounds with falling pitch alternated with leftward-moving sounds with rising pitch (or vice versa). Auditory aftereffects (i.e., a shift in the psychometric function for unimodal auditory motion perception) were bigger when a visual stimulus moved in the same direction as the sound than when no visual stimulus was presented. When the visual stimulus moved in the opposite direction, aftereffects were reversed and thus became contingent upon visual motion. When visual motion was combined with a stationary sound, no aftereffect was observed. These findings indicate that there are strong perceptual links between the visual and auditory motion-processing systems.

Attention↗

PubMed1991

Parallel pathways in the visual system: their role in perception at isoluminance.

It has been proposed that the functions of the two major parallel channels of the primate visual system, the color-opponent and the broad-band, can be determined in psychophysical experiments by eliminating luminance but maintaining chrominance information (isoluminance), since under such conditions the broad-band channel is believed to be silenced. To test this proposition we examined the visual functions of monkeys after blocking either of these channels and we also assessed the responses of neurons to isoluminant stimuli in the lateral geniculate nucleus. We show that color, texture, stereopsis and pattern perception in the absence of the color-opponent channel, and flicker and motion perception in the absence of the broad-band channel are compromised. Yet isoluminance functions for stereopsis and texture in the absence of the broad-band channel and for motion in the absence of the color-opponent channel are indistinguishable from normal. Our recordings show that the neuronal responses of the broad-band cells for isoluminant exchange of red and green lights are reduced but not eliminated and that the color-opponent cells also become similarly less responsive under these conditions. We conclude that perceptual losses at isoluminance are not specific for either channel.

Animals↗

PubMed2005

Exposure to a rotating virtual environment during treadmill locomotion causes adaptation in heading direction.

The objective of this study was to investigate the adaptive effects of variation in the direction of optic flow, experienced during linear treadmill walking, on modifying locomotor trajectory. Subjects (n=30) walked on a motorized linear treadmill at 4.0 km h(-1) for 24 min while viewing the interior of a 3D virtual scene projected on to a screen 1.5 m in front of them. The virtual scene depicted constant self-motion equivalent to either (1) walking around the perimeter of a room to one's left (Rotating Room group) or (2) walking down the center of a hallway (Infinite Corridor group). The scene was static for the first 4 min and then constant rate self-motion was simulated for the remaining 20 min. Before and after the treadmill locomotion adaptation period subjects performed five stepping trials. In each trial they marched in place to the beat of a metronome at 90 steps min(-1) for a total of 100 steps while blindfolded in a quiet room. The subject's final heading direction (deg) and final X (fore-aft, cm) and final Y (medio-lateral, cm) positions were measured for each trial. During the treadmill locomotion adaptation period subjects' 3D torso position was measured. We found that subjects in the Rotating Room group, as compared with the Infinite Hallway group: (1) showed significantly greater deviation during post-exposure testing in the heading direction and Y position opposite to the direction of optic flow experienced during treadmill walking; and (2) showed a significant monotonically increasing torso yaw angular rotation bias in the direction of optic flow during the treadmill adaptation exposure period. Subjects in both groups showed greater forward translation (in the +X direction) during the post-treadmill stepping task that differed significantly from their pre-exposure performance. Subjects in both groups reported no perceptual deviation in position during the stepping tasks. We infer that viewing simulated rotary self-motion during treadmill locomotion causes adaptive modification of sensorimotor integration in the control of position and trajectory during locomotion, which functionally reflects adaptive changes in the integration of visual, vestibular, and proprioceptive cues. Such an adaptation in the control of position and heading direction during locomotion, because of the congruence of sensory information, demonstrates the potential for adaptive transfer between sensorimotor systems and suggests a common neural site for processing and self-motion perception and concurrent adaptation in motor output.

Adaptation, Physiological↗

PubMed1996

The barberplaid illusion: plaid motion is biased by elongated apertures.

The perceived direction of motion of plaids windowed by elongated spatial Gaussians is biased toward the window's long axis. The bias increases as the relative angle between the plaid motion and the long axis of the window increases, peaks at a relative angle of approximately 45 deg, and then decreases. The bias increases as the window is made narrower (at fixed height) and decreases as the component spatial frequency increases (at fixed aperture size). We examine several models of human motion processing (cross-correlation, motion-energy, intersection-of-constraints, and vector-sum), and show that none of these standard models can predict our data. We conclude that spatial integration of motion signals plays a crucial role in plaid motion perception and that current models must be explicitly expanded to include such spatial interactions.

Adult↗

PubMedDate not supplied

The influence of fixational eye movements on the response of neurons in area MT of the macaque.

We analyzed the relationship between eye movements and neuronal responses recorded from area MT in alert monkeys trained to maintain visual fixation during the presentation of moving patterns. The monkeys made small saccades which moved the eyes with velocities that spanned the sensitivity range of MT neurons. The saccades evoked changes in the neuronal response that depended upon (1) the level of stimulus-evoked activity amidst which the saccade occurred and (2) the direction of the saccade relative to the preferred direction of the neuron. Most notably, saccades were able to suppress stimulus-evoked activity when they caused retinal image flow that opposed the neuron's preference and were able to elicit a response or enhance weak activity when they caused flow in the neuron's preferred direction. On average, the disturbance lasted 40 ms beginning about 40 ms following saccade onset. Using these parameters, we simulated synthetic spike trains from an imaginary pair of similarly tuned neurons and determined that the interneuronal correlation due to saccades should be negligible at all but the lowest ongoing firing rates. This conclusion was supported from our data by the observation that response variance for single MT spike trains was not measurably reduced during periods of stable gaze compared to periods when eye movement exceeded a stability criterion (0.1 deg during 0.5 s). While the intrusions caused by saccades are too short-lived and infrequent to account for the variability of MT neuronal response (counter to the finding in V1 of Gur et al., 1997), the clear directional signal that they carry in area MT suggests that motion perception is not blocked during saccades by suppression at early stages in the visual pathway.

Animals↗

PubMed2004

Visual extinction for motion.

PURPOSE: To alert clinicians to the heretofore undescribed visual behavioral phenomenon of visual extinction limited to motion. METHODS: Neuro-ophthalmological, neuropsychological and neuroimaging assessment of a 57-year-old man with vague visual complaints. RESULTS: Extinction limited to visual motion perception in the left hemifield was demonstrated. The visual defect was attributed to a lesion involving the right occipito-temporo-parietal region in the presence of a left posterior infarction. CONCLUSION: The importance of clinical examination for detection of this specific higher-order visual defect is stressed. The present observation may be helpful in understanding the effects of attention on visual perception and may have important implications for rehabilitation of patients with visual neglect.

Cerebral Infarction↗

PubMed1998

Complex motion stimuli localize higher-order visual processing in normal observers and in patients with parietal lesions.

The present paper illustrates how modern techniques applied in neuroscience can help us to understand the processing of visual information in the human brain and, in turn, how they can be helpful to characterize functional deficits in patients with cortical lesions. Based on theoretical considerations, motion stimuli are developed that require very specific operations to be performed by the visual system. Computational models explaining the processing of these 'Fourier' and 'second-order' motion stimuli are characterized by increasing complexity. The same types of stimuli are used to map the distribution of cortical activity during motion perception by measuring the magnetic and electrical fields on the head surface. Clinical investigations of patients with lesions in the parietal cortex indicate specific deficits in the perception of such stimuli that can be related to the lesion sites.

Action Potentials↗