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PubMed2003

An illusion of coherent global motion arising from single brief presentations of a stationary stimulus.

We describe a new illusion in which a single stationary stimulus appears to undergo coherent global motion. Contrast relationships between the stimulus elements suggest the illusion arises via processing of Off- and On-channel signals that remain independent until after passing through low-level motion detectors. We propose that patterns of activation resulting from biphasic temporal impulse response functions in the magnocellular pathway are the basis of the illusion, and describe a model to account for the illusory motion percept.

Computer Graphics↗
PubMed2006

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.

Adult↗
PubMed2002

Neural mechanisms of saccadic suppression.

In normal vision our gaze leaps from detail to detail, resulting in rapid image motion across the retina. Yet we are unaware of such motion, a phenomenon known as saccadic suppression. We recorded neural activity in the middle temporal and middle superior temporal cortical areas during saccades and identical image motion under passive viewing conditions. Some neurons were selectively silenced during saccadic image motion, but responded well to identical external image motion. In addition, a subpopulation of neurons reversed their preferred direction of motion during saccades. Consequently, oppositely directed motion signals annul one another, and motion percepts are suppressed.

Animals↗
PubMed1992

Competing motion paths in sequence of random dot patterns.

Global motion perception from a sequence of random dot patterns has been studied by means of the competition technique which consists of making a normally less salient motion path in a superimposed multiple-path stimulus more powerful by adding luminous energy to elements forming this path. The perceived motion direction of a sequence of random dot patterns can be dramatically changed by increasing luminance of some fraction of dots leaving all spatial and temporal intervals between dots unchanged. The threshold luminance increment delta I that is required in order to change the perceived motion direction indicates that differently oriented local motion vectors are resolved into a single common motion vector along which the whole pattern appears to move. An inverse spatial proximity rule was discovered: within a certain spatial limit the motion strength of a particular motion path is proportional to the distance between stimulus elements forming this path.

Humans↗
PubMed2000

Dichoptic plaids may rival, but their motions can integrate.

When the eyes view incompatible images, binocular rivalry usually results: image constituents in corresponding parts of the monocular visual fields are not perceived simultaneously. We asked naive undergraduates to view dichoptic, dioptic, and monoptic plaids. The dichoptic images evoked strong binocular rivalry when contrast was high, especially if the component gratings were set in motion. Nevertheless, the subjects' visual systems integrated the motion information across the two eyes, producing a unitary motion percept that did not reflect the image in either eye alone. By manipulating the relative spatial scale of the gratings, we affected how well the motion cohered: the results were remarkably similar between dichoptic and traditional dioptic plaids. By manipulating the relative speed of the gratings, we systematically affected the perceived direction of motion of the plaids; these results were also remarkably similar for dichoptic and dioptic plaids. Thus, the motion analysis of dichoptic and dioptic plaids is proceeding according to very similar rules, even though the dichoptic images are incompatible and evoke binocular rivalry.

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↗
PubMed1987

Retinal and extraretinal information in movement perception: how to invert the Filehne illusion.

During a pursuit eye movement made in darkness across a small stationary stimulus, the stimulus is perceived as moving in the opposite direction to the eyes. This so-called Filehne illusion is usually explained by assuming that during pursuit eye movements the extraretinal signal (which informs the visual system about eye velocity so that retinal image motion can be interpreted) falls short. A study is reported in which the concept of an extraretinal signal is replaced by the concept of a reference signal, which serves to inform the visual system about the velocity of the retinae in space. Reference signals are evoked in response to eye movements, but also in response to any stimulation that may yield a sensation of self-motion, because during self-motion the retinae also move in space. Optokinetic stimulation should therefore affect reference signal size. To test this prediction the Filehne illusion was investigated with stimuli of different optokinetic potentials. As predicted, with briefly presented stimuli (no optokinetic potential) the usual illusion always occurred. With longer stimulus presentation times the magnitude of the illusion was reduced when the spatial frequency of the stimulus was reduced (increased optokinetic potential). At very low spatial frequencies (strongest optokinetic potential) the illusion was inverted. The significance of the conclusion, that reference signal size increases with increasing optokinetic stimulus potential, is discussed. It appears to explain many visual illusions, such as the movement aftereffect and center-surround induced motion, and it may bridge the gap between direct Gibsonian and indirect inferential theories of motion perception.

Adult↗
PubMed2006

Polarization contrast and motion detection.

Form and motion perception rely upon the visual system's capacity to segment the visual scene based upon local differences in luminance or wavelength. It is not clear if polarization contrast is a sufficient basis for motion detection. Here we show that crayfish optomotor responses elicited by the motion of images derived from spatiotemporal variations in e-vector angles are comparable to contrast-elicited responses. Response magnitude increases with the difference in e-vector angles in adjacent segments of the scene and with the degree of polarization but the response is relatively insensitive to the absolute values of e-vector angles that compose the stimulus. The results indicate that polarization contrast can support visual motion detection.

Animals↗
PubMed2002

Sensory information processing in neuroleptic-naive first-episode schizophrenic patients: a functional magnetic resonance imaging study.

BACKGROUND: Schizophrenic disorders are thought to involve widespread abnormalities in information processing. The present study used functional magnetic resonance imaging and a simple and robust paradigm that involved auditory and visual activation to examine basic sensory input circuits. Our aim was to determine which stages of the input processing network are disturbed in first-episode schizophrenic patients. METHODS: Twelve neuroleptic-naive inpatients (paranoid subtype) were compared with 11 healthy subjects by means of echo-planar functional magnetic resonance imaging. In a block design, the paradigm included the simultaneous presentation of a moving 6-Hz checkerboard and auditory stimuli in the form of drumbeats. The subjects were asked to simply look and listen. RESULTS: In comparison with control subjects, patients showed reduced activation in the right thalamus, the right prefrontal cortex, and the parietal lobe (restricted to the dorsal visual pathway) bilaterally. There were no notable differences in the primary visual cortex or the object-specific occipitotemporal pathway. In addition, patients presented with a reduced signal change to auditory stimulation in the left acoustic cortex. CONCLUSIONS: The present study supports the concept of widespread cortical and subcortical deficits in schizophrenia. Our findings suggest abnormal functioning early in the information processing and in high-order association cortices already at illness onset, before the administration of medication or the most confounding effects of illness duration. The main regions have been implicated in visual motion perception and discrimination as well as in attention to sensorial events and perceptual synthesis.

Acoustic Stimulation↗
PubMed1994

A role for a low level mechanism in determining plaid coherence.

A number of recent studies have suggested that the "intersection of constraints" model of two dimensional motion perception, put forward by Adelson and Movshon [(1982) Nature, 300, 523-525], is incomplete. Evidence has been mounting that there is a second two-dimensional motion sensitive mechanism which is monocular and which appears to respond directly to the movement of the intersections (or "blobs") in a two-dimensional image. The current study extends these findings by demonstrating that the perceived coherence of a drifting plaid is largely under the control of a monocular mechanism. Prior exposure to a similarly drifting grating or plaid substantially raises the coherence threshold of a test plaid only if the same eye is adapted and tested. The threshold elevation is much more modest if the test plaid is presented to the unadapted eye, suggesting that coherence judgements are primarily based on the activity level of a monocular process--possibly the "blob tracking mechanism". The results of Expt 2 suggest the possibility that this monocular mechanism is inhibited by binocular exposure.

Adaptation, Ocular↗
PubMed2000

A human extrastriate area functionally homologous to macaque V4.

Extrastriate area V4 is crucial for intermediate form vision and visual attention in nonhuman primates. Human neuroimaging suggests that an area in the lingual sulcus/fusiform gyrus may correspond to ventral V4 (V4v). We studied a human neurological patient, AR, with a putative V4v lesion. The lesion does not affect early visual processing (luminance, orientation, and motion perception). However, it does impair hue perception, intermediate form vision, and visual attention in the upper contralateral visual field. Form deficits occur during discrimination of illusory borders, Glass patterns, curvature, and non-Cartesian patterns. Attention deficits occur during discrimination of the relative positions of object parts, detection of low-salience targets, and orientation discrimination in the presence of distractors. This pattern of deficits is consistent with the known properties of area V4 in nonhuman primates, indicating that AR's lesion affects a cortical region functionally homologous to macaque V4.

Animals↗
PubMed1985

Perceptual organization in multistable apparent motion.

Is motion perception based on a local piecemeal analysis of the image or do 'global' effects also play an important role? Use was made of bistable apparent-motion displays in trying to answer this question. Two spots were flashed simultaneously on diagonally opposite corners of a 1 deg wide square and then switched off and replaced by two spots appearing on the other two corners. One can either see vertical or horizontal oscillation and the display is bistable just as a Necker cube is. If several such bistable figures are randomly scattered on the screen and presented simultaneously, then one usually sees the same motion axis in all of them, suggesting the presence of field-like effects for resolving ambiguity in apparent motion. While viewing a single figure observers experience hysteresis: they tend to adhere to one motion axis or the other and can switch the axis only by looking away and looking back after 10-30 s have elapsed. The figure can be switched off and made to reappear at some other random location on the screen and it is then always found to retain its motion axis. Several such demonstrations are presented to show that spatial induction effects in metastable motion displays may provide a particularly valuable probe for studying 'laws' of perceptual organization.

Fixation, Ocular↗
PubMed1995

Using motion perimetry to detect visual field defects in patients with idiopathic intracranial hypertension: a comparison with conventional automated perimetry.

Motion perimetry, a method of visual field testing that uses computer graphics to measure motion perception, quantitates a subject's ability to detect a coherent shift in position of dots in a defined circular area against a background of fixed dots. Motion size threshold is defined as the smallest detectable circular target in which dot motion is detected. Subjects respond by touching a computer monitor screen with a light pen, first when they see a target (reaction time) and a second time where motion targets are detected (localization). Reaction time (msec) to the stimulus and localization error (number of pixels from target center) are then calculated and stored. We tested on eye in each of 20 idiopathic intracranial hypertension (IIH) patients and 40 age-matched normal subjects by conventional automated perimetry (Humphrey visual field analyzer, program 24-2) and motion perimetry. Pointwise probability plots of individual abnormal test points for size threshold responses were generated for the IIH patients based on the 95% confidence limits of the normal subject responses. An analysis of the subjects' visual field pairs (motion versus conventional automated perimetry) was performed based on these probability plots. The IIH patients had an elevated mean motion threshold (p < 0.001) and reaction time (p < 0.001) compared with the normal subjects. There were no significant differences for the localization errors. Based on the probability plot analysis, there was good correlation of the visual field defects between the two perimetry tests. In addition, motion perimetry identified nerve fiber bundle-shaped defects in nine patients in whom they were not detected with conventional automated perimetry.

Adult↗
PubMed2003

Effect of element size on stereoscopic apparent motion.

Spatial displacement limits in stereoscopic (cyclopean) apparent motion were measured from sequentially presented two-frame random-depth configurations. Each depth configuration was defined by stereoscopically near or far elements of various sizes. The limits were compared with those in luminance-defined apparent motion. The subject's task was 2-alternative forced-choice of the perceived motion direction of the sequentially presented two-frame random-dot stereograms. The spatial displacement limit below which correct motion perception arose with stereoscopic configurations was larger in proportion to increases in size of elements. The values were almost consistent with those measured by luminance-defined configurations with the same element sizes. This result suggests that the strategy for discrimination of motion direction of random configurations is similar in both stereoscopic and luminance-defined apparent motion.

Depth Perception↗
PubMed2000

Speed and direction of locally-paired dot patterns.

Phenomenal transparency in random-dot kinematograms is abolished when two motion directions are 'locally-balanced' by pairing limited-lifetime dots at each location [Qian, Andersen and Adelson (1994). Journal of Neuroscience, 14, 7357-7366]. Qian et al. also report that locally-paired stimuli appear as directionless flicker when the paired dots differ in their directions by 90 degrees or more. They attribute this to local inhibition between motion detectors more than 45 degrees apart. We investigated perceived motion in such displays, by requiring subjects to make direction and speed judgements with locally-paired stimuli containing two directions 60, 90 or 120 degrees apart. Subjects perceived coherent motion in these displays and made reliable direction judgements, indicating that the two motions are combined rather than interfering destructively. Our results show that the judged motion of locally-paired stimuli is in the vector-average direction of the two components. This vector-averaging rule also applies when the two sets of component dots differ in their velocity. Similarly, speed judgements comply with a vector-averaging rule for a range of speeds as well as for mixed-speed stimuli. These results suggest that the abolition of transparency does not necessarily imply abolition of a global motion percept. The local interaction abolishing transparency is not exclusively inhibitory, at least for directions up to 120 degrees apart, but generates a vector combination of the superimposed motions.

Humans↗
PubMed2003

Neural correlates of cross-modal binding.

Little is known about how the brain binds together signals from multiple sensory modalities to produce unified percepts of objects and events in the external world. Using event-related functional magnetic resonance imaging (fMRI) in humans, we measured transient brain responses to auditory/visual binding, as evidenced by a sound-induced change in visual motion perception. Identical auditory and visual stimuli were presented in all trials, but in some trials they were perceived to be bound together and in others they were perceived as unbound unimodal events. Cross-modal binding was associated with higher activity in multimodal areas, but lower activity in predominantly unimodal areas. This activation pattern suggests that a reciprocal and 'competitive' interaction between multimodal and unimodal areas underlies the perceptual interpretation of simultaneous signals from multiple sensory modalities.

Acoustic Stimulation↗
PubMed1989

Single-unit analysis of pattern-motion selective properties in the middle temporal visual area (MT).

The middle temporal visual area (MT) in macaque extrastriate cortex is characterized by a high proportion of neurons selective for the direction of stimulus motion, and is thus thought to play an important role in motion perception. Previous studies identified a population of cells in MT that appeared capable of coding the motion of whole visual patterns independent of the motions of contours within them (Gizzi et al. 1983; Movshon et al. 1985). These "pattern-motion selective" neurons are unlike motion sensitive cells that have been observed at earlier stages of the visual system. Using very different criteria, we have also previously identified an apparently functionally distinct group of MT neurons (Albright 1984). We predicted that these "Type II" neurons correspond to the pattern-motion neurons. In the present study, we have applied both sets of criteria to individual neurons in MT and found that these two differently defined sets of cells actually form the same population. These results support the idea that MT contributes to a specialized type of motion processing which reflects the integrity of normal perception.

Animals↗
PubMed1990

Influence of visual blur on object-motion detection, self-motion detection and postural balance.

We have compared the influence of visual blurring (either by use of plastic foils or by plus lenses) on detection of object-motion and self-motion, and on visual control of postural balance. Three experiments were performed--in all of which object-motion and self-motion detection latencies (response times) and postural sway (sway path) increased with increasing visual blurring. We conclude that visual blurring either by foils or by glasses affects object- and self-motion perception and postural sway in a similar way.

Attention↗