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PubMedDate not supplied

Influence of motion on chromatic detection.

Intense scrutiny has been focused on whether chromatic stimuli contribute to motion perception. The present study considers a related but different question: how does motion affect chromatic detection? Detection thresholds were measured for a disk that underwent a brief (13.3 ms) chromatic change in the L/(L+M) chromatic direction. The disk's presentation sequence and speed (0-16 deg/s) were manipulated. In the coherent presentation sequence, the disk moved smoothly along a circular path centered on the fixation point. In the random presentation sequence, the disk appeared randomly at positions along the circular path. In both types of sequences, the disk underwent a brief chromatic change midway through the temporal presentation sequence. Threshold was elevated in the coherent condition compared to the random condition, and threshold decreased with an increase in speed. The threshold elevation observed in the coherent presentation sequence can be accounted for by temporal integration. The decrease in threshold with an increase in speed can be accounted for by spatial integration. The results, therefore, can be explained by spatiotemporal integration, without invoking a neural mechanism specialized for motion.

Color Perception↗
PubMed2002

Visual motion stimulation, but not visually induced perception of self-motion, biases the perceived direction of verticality.

Large-field torsional optokinetic stimulation is known to affect the perceived direction of gravity with verticality judgements deviating towards the direction of visual stimulus rotation. The present study aimed to replicate this effect and to examine it further by subjecting participants to optokinetic stimulation in roll, resulting in spontaneous alternations between the perception of object-motion and that of contradirectional self-motion (vection), as reported by the subjects. Simultaneously, subjects were oscillated laterally in a flight simulator and indicated their perception of postural verticality. Results confirmed that rotation of the visual environment in the frontal plane biases the perceived orientation of gravity towards the direction of visual stimulus motion. However, no differential effect of perceptual state on postural verticality was obtained when contrasting verticality judgements made during the perception of object-motion with those obtained during reported self-motion perception. This finding is likely to reflect a functional segregation of central nervous visual-vestibular subsystems that process the perception of self-tilt and that of self-rotation to some degree independently.

Adult↗
PubMed2000

What limits the contribution of second-order motion to the perception of surface shape?

Both motion and stereopsis can be derived from contrast as well as luminance defined stimuli. It is currently assumed that these two different sources of information about objects feed into one common stage. Thus it would not be expected that their role in visual perception would be different. Here we show that although motion can be carried by contrast-defined elements, such motion is not used to define three-dimensional (3D) surfaces. A similar effect has been reported in stereopsis; although such contrast-defined elements can give signed disparity signals they nevertheless do not contribute to the percept of shape. We show that the reason for this lies in the inability of the second order signals to cohere or bind across space/spatial scales rather than a characteristic of the elementary motion signals per se.

Contrast Sensitivity↗
PubMed2001

Depth thresholds of motion parallax as a function of head movement velocity.

The lower parallactic depth threshold is determined by (a) the ratio of relative image velocity to head velocity when the head moves fast (>13 cm/s) and (b) the motion threshold when the head moves slow (<13 cm/s). These two results are explained by a single system that codes the ratio of relative image velocity to head velocity, using the same image velocity signal as that used for motion perception. In this explanation, ratios coded from low relative image velocities, which are slightly higher than the motion threshold, produce a perception of depth only when the head moves slowly.

Depth Perception↗
PubMed1990

The influence of spatial frequency on perceived temporal frequency and perceived speed.

Speed matching experiments were conducted using drifting gratings of different spatial frequencies in order to assess the influence of spatial frequency on perceived speed. It was found that gratings of high spatial frequency appear to drift more slowly than low spatial frequency gratings of the same actual velocity. The perceived temporal frequency of a counterphase grating similarly declines as spatial frequency increases. The previously reported effect of temporal frequency on perceived spatial frequency probably does not contribute to these phenomena. Our results suggest that the motion sensors thought to operate within different spatial frequency ranges have different velocity transfer functions, a fact not incorporated in existing computational models of motion perception.

Contrast Sensitivity↗
PubMed1995

Attention-generated apparent motion.

Motion perception mechanisms have recently been divided into three categories. First-order mechanisms primarily extract motion from moving objects or features that differ from the background in luminance. Second-order mechanism extract motion from moving properties, such as a moving area of flicker in which there is no difference in mean luminance between target and background. These first- and second-order motion mechanisms are primarily monocular. The existence of purely binocular, interocular and various other unusual kinds of apparent motion has promoted conjectures of a third-order mechanism, but there has been no clear suggestion as to the actual computations that such a mechanism might perform. Here we demonstrate 'alternating feature' stimuli that produce apparent motion only when the observer selectively attends to one of the embedded features in the display. The latent motion in the alternating feature stimuli is invisible to first- or second-order motion mechanisms, and the direction of apparent motion depends on the particular feature attended. These findings suggest the mechanism of third-order motion: the locations of the most significant features are registered in a salience map, and motion is computed directly from this map.

Attention↗
PubMed2006

Anatomical alterations of the visual motion processing network in migraine with and without aura.

BACKGROUND: Patients suffering from migraine with aura (MWA) and migraine without aura (MWoA) show abnormalities in visual motion perception during and between attacks. Whether this represents the consequences of structural changes in motion-processing networks in migraineurs is unknown. Moreover, the diagnosis of migraine relies on patient's history, and finding differences in the brain of migraineurs might help to contribute to basic research aimed at better understanding the pathophysiology of migraine. METHODS AND FINDINGS: To investigate a common potential anatomical basis for these disturbances, we used high-resolution cortical thickness measurement and diffusion tensor imaging (DTI) to examine the motion-processing network in 24 migraine patients (12 with MWA and 12 MWoA) and 15 age-matched healthy controls (HCs). We found increased cortical thickness of motion-processing visual areas MT+ and V3A in migraineurs compared to HCs. Cortical thickness increases were accompanied by abnormalities of the subjacent white matter. In addition, DTI revealed that migraineurs have alterations in superior colliculus and the lateral geniculate nucleus, which are also involved in visual processing. CONCLUSIONS: A structural abnormality in the network of motion-processing areas could account for, or be the result of, the cortical hyperexcitability observed in migraineurs. The finding in patients with both MWA and MWoA of thickness abnormalities in area V3A, previously described as a source in spreading changes involved in visual aura, raises the question as to whether a "silent" cortical spreading depression develops as well in MWoA. In addition, these experimental data may provide clinicians and researchers with a noninvasively acquirable migraine biomarker.

Adult↗
PubMed2002

Vision: the when of perception.

A visual image can be described by its temporal as well as spatial properties. A recent study of the asynchronous colour and motion perception has led to a new view of perceptual synchronisation, in which the temporal structures of events in the external world provide a general explanation of how events are bound or misbound in time.

Color↗
PubMed2005

Stochastic correlative firing for figure-ground segregation.

Segregation of sensory inputs into separate objects is a central aspect of perception and arises in all sensory modalities. The figure-ground segregation problem requires identifying an object of interest in a complex scene, in many cases given binaural auditory or binocular visual observations. The computations required for visual and auditory figure-ground segregation share many common features and can be cast within a unified framework. Sensory perception can be viewed as a problem of optimizing information transmission. Here we suggest a stochastic correlative firing mechanism and an associative learning rule for figure-ground segregation in several classic sensory perception tasks, including the cocktail party problem in binaural hearing, binocular fusion of stereo images, and Gestalt grouping in motion perception.

Acoustic Stimulation↗
PubMed1989

Globally perceived directional flow in static images.

Visual sensitivity to spatial direction has classically been associated with motion perception. Yet humans are adept at deriving directional information in the absence of motion, as when they read maps, or follow arrows or animal tracks. Experiments are reported on the perception of parallel arrow-like forms in which a specific visual sensitivity to static direction is demonstrated. Global processing is operationally defined in terms of the relative discriminability of sets and subsets of stimulus elements; a set of parallel elements and a set in which one element is antiparallel to the rest are shown to be processed globally. The result of this global processing is a static analog of unidirectional optic flow. Global spatial direction differs fundamentally from other perceptions derived from static image processing. It involves long-range interactions in texture arrays, it does not carry information about stimulus location, and it is not reducible to the perception of component stimulus elements. Its likely function is in the construction of the layout of visual space.

Attention↗
PubMed1989

Interattribute apparent motion.

Apparent motion can be seen between two alternating stimuli even if they are defined with respect to their background by attributes other than luminance (such as color, or texture). We measured motion strength as the maximum separation between two alternating stimuli which produced an impression of motion, for conditions in which the two stimuli were defined by the same attribute (intra-attribute) as well as conditions in which they were defined by different attributes (interattribute). The attributes used to define the stimuli were luminance, color, texture, relative motion, or stereopsis. The results indicate that motion was seen for all the intra-attribute conditions about equally well. The results also show that interattribute motion could be seen for all combinations studied. The motion strength in these cases was about 80% of that for the intra-attribute conditions. The process responsible for this motion perception must therefore be able to combine information from different attributes.

Adult↗
PubMed1994

Correspondence-based and energy-based detection of second-order motion in human vision.

Motion in the retinal image may occur either in the form of spatiotemporal variations in luminance (first-order motion) or as spatiotemporal variations in characteristics derived from luminance, such as contrast (second-order motion). Second-order motion patterns were employed in an attempt to establish the principles used for the detection of image motion in the human visual system. In principle, one can detect motion at a high level of visual analysis by identifying features of the image and tracking their positions (correspondence-based detection) or at a low level by analysis of spatiotemporal luminance variations without reference to features (intensity-based detection). Prevailing models favor the latter approach, which has been adapted to account for the visibility of second-order motion by postulation of a stage of rectification that precedes motion energy detection [J. Opt. Soc. Am. A 5, 1986 (1988)]. In two experiments it is shown that second-order motion is indeed detected normally by use of the strategy of transformation plus energy detection but that detection can also be achieved by use of the feature-correspondence strategy when the intensity strategy fails. In the first experiment, a stimulus is employed in which opposite directions of motion perception are predicted by the two strategies. It is shown that normally the direction associated with motion energy in the rectified image is seen but that the direction associated with feature motion is seen when the energy system is disabled by the use of an interstimulus interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Contrast Sensitivity↗
PubMed2003

Spatial and temporal visual properties of single neurons in the feline anterior ectosylvian visual area.

The spatial and temporal visual sensitivity to drifting sinusoidal gratings was studied in 75 neurons of the feline anterior ectosylvian visual area (AEV). Extracellular single-unit recordings were performed in halothane-anesthetized (0.6%), immobilized, artificially ventilated cats. Most cells were strongly sensitive to the direction of drifting gratings. The mean value of the direction tuning widths was approximately 90 deg. Most of the cells (69 of the 75 cases) displayed rather narrowly tuned band-pass characteristics in the low spatial frequency range, with a mean optimal spatial frequency of 0.2 cycles/degree (c/deg). The mean spatial bandwidth was 1.4 octaves. The remainder of the units was low-pass tuned. A majority of the units responded optimally to high temporal frequencies (mean 6.3 Hz), although some cells did exhibit preferences for every examined temporal frequency between 0.6 Hz and 10.8 Hz. The temporal frequency-tuning functions mostly revealed a band-pass character with a mean temporal bandwidth of 1.1 octaves. Our results demonstrate that the neurons along the anterior ectosylvian sulcus display particular spatial and temporal characteristics. The AEV neurons, with their preference for low spatial frequencies and with their fine spatial and temporal tuning properties, seem to be candidates for special tasks in motion perception.

Animals↗
PubMed1981

On the relativity of perceived motion.

Perceived stability of the visual world during eye movements is traditionally explained as due to the presence of extraretinal signals, equal in magnitude to retinal signals. Motion is perceived when the two signals differ. An experiment is reported in which motion thresholds were measured during smooth pursuit eye movements. The results show that the traditional view is incomplete. Motion is only perceived when the two signals differ by at least a just noticeable difference (JND), the magnitude of which depends on ocular velocity and is independent of the direction of stimulus motion relative to the eyes. The data lead to the rejection of theories according to which ocular velocity is under-represented in extraretinal signals. In addition they show that retinal image motion carries no information about stimulus motion. Perceived motion, direction and velocity are relative concepts. They depend on the JND and therefore they are relative to extraretinal signals. This principle explains the Filehne illusion and even predicts the Aubert-Fleischl phenomenon. A similar analysis can be applied to understand vestibular effects on motion perception.

Differential Threshold↗
PubMed1990

How the visual system detects changes in the direction of moving targets.

To determine how the visual system represents information about change in target direction, we studied the detection of such change under conditions of varying stimulus certainty. Target direction was either held constant over trials or was allowed to vary randomly. When target direction was constant the observer could be certain about that stimulus characteristic; randomizing the target direction rendered the observer uncertain. We measured response times (RTs) to changes in target direction following initial trajectories of varying time and distance. In different conditions, the observer was uncertain about either the direction of the initial trajectory, or the direction of change or both. With brief initial trajectories in random directions, uncertainty about initial direction elevated RTs by 50 ms or more. When the initial trajectories were at least 500 ms, this directional uncertainty ceased to affect RTs; then, only uncertainty about the direction of change affected RTs. We discuss the implications of these results for (i) schemes by which the visual system might code directional change; (ii) the visual integration time for directional information; and (iii) adaptational processes in motion perception.

Attention↗
PubMed1991

Percepts of rigid motion within and across apertures.

Humans consistently err in their percepts of rotational motion viewed through an aperture. Such errors provide insight into the constraints observers use to interpret retinal images. In the 1st of 2 experiments, Ss consistently perceived the fixed center of rotation for an unmarked line viewed through an aperture as located on the line, regardless of its actual location. Accuracy greatly improved with visible line endings. This finding was extended to explain why a square appears nonrigid when it rotates behind a partial occluder. This illusion may result from observers misperceiving the center of rotation of the unmarked square sides. In this situation, Ss seemed unable to apply an object rigidity constraint across apertures. These findings support a conceptualization of the visual system in which consistent local information must be clearly present before prior knowledge can be used to interpret retinal stimulation.

Attention↗