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PubMed1997

Isoluminance and chromatic motion perception throughout the visual field.

Isoluminance and chromatic motion perception for red/green gratings were measured throughout an 80 deg visual field. Generally, the red/green isoluminance values changed with increasing eccentricity, i.e., observers increased the red luminance contrast for a fixed green luminance contrast. Enlarging the target size (to compensate for the cone density changes with eccentricity) and decreasing the spatial frequency (to compensate for receptive field property changes with eccentricity) did not change the isoluminance values within the central 20 deg, but the isoluminance ratios decreased beyond 20 deg. Our manipulations did not entirely compensate for a given eccentricity, which implies the need for a post-receptoral scaling function for the perception of drifting chromatic stimuli. Further, the results for isoluminance show heterogeneity between the visual field meridians where the red to green luminance ratio tends to be greater in the superior visual field. In our present conditions, chromatic motion was always perceived (up to 40 deg of eccentricity), but sensitivity generally decreased with increasing eccentricity. The inferior visual field was found to be the most sensitive to chromatic motion. We propose that the lower visual field and not the superior visual field is specialized for colour motion information.

Color Perception↗
PubMed1994

Neural network approaches to visual motion perception.

This paper concerns certain difficult problems in image processing and perception: neurocomputation of visual motion information. The first part of this paper deals with the spatial physiological integration by the figure-ground discrimination neural network in the visual system of the fly. We have outlined the fundamental organization and algorithms of this neural network, and mainly concentrated on the results of computer simulations of spatial physiological integration. It has been shown that the gain control mechanism, the nonlinearity of synaptic transmission characteristic, the interaction between the two eyes, and the directional selectivity of the pool cells play decisive roles in the spatial physiological integration. In the second part, we have presented a self-organizing neural network for the perception of visual motion by using a retinotopic array of Reichardt's motion detectors and Kohonen's self-organizing maps. It has been demonstrated by computer simulations that the network is able to learn to solve the ambiguities given by local motion detection mechanism. The resultant self-organized configuration in the output layer is resembling direction selective columns which first appear in area MT of the primate visual system. It has been explored that the spatio-temporal coherences, mapping, cooperation, competition, and Hebb rule are the basic neural principles for visual motion perception.

Animals↗
PubMed1993

Motion perception with spatiotemporally matched chromatic and achromatic information reveals a "slow" and a "fast" motion system.

Recent reports dealing with apparent motion challenged the standard view according to which motion processing should be impossible if the visual attributes matched across space and time are processed in independent channels (the similarity principle). The present work examines this possibility insofar as it relates to the spatiotemporal combination of pure chromatic and pure luminance information. The data indicate that the "similarity principle" is indeed infringed at low (< or = 2.5 Hz, i.e. velocities of 2.5 deg/sec for spatial modulations of 1 c/deg, in this study) but not at high (> or = 7.5 Hz) temporal frequencies. The fact that colour and luminance may or may not combine to yield motion perception depending on their temporal modulation reconciliates contradictory results in the literature and supports the idea of two motion systems, a "fast"/specific one, integrating information only from similar subunits, and a "slow"/unspecific one, integrating information across dissimilar subunits (in the present case, across the chromatic and achromatic "domains"). This dichotomy is also supported by the finding that chromatic reverse-phi (i.e. with equiluminant, red and green stimuli) can be observed at medium temporal frequencies but is replaced by direct motion at low temporal frequencies, presumably within the range of the "slow"/unspecific system. Using a modified "minimum motion" technique (referred to as the Reverse-Phi equiluminance method) we present data allowing to assess the relative weights of the two systems as a function of temporal frequency.

Color Perception↗
PubMed1998

Complex motion perception and its deficits.

Within the hierarchy of motion perception, the dorsolateral middle superior temporal area (MSTd) is optimally suited for the analysis of the complex motion patterns that are directly useful for visually guided behaviour (e.g. computation of heading). Recent electrophysiological and psychophysical evidence suggests the existence of 'detectors' in MSTd that are specialised for complex motion patterns and advocates the necessity of combining retinal and extraretinal signals received by MSTd neurones for the accurate perception of heading. In some neurological patients, of which only a small number have been reported to date, lesions involving the human homologue of MST have devastating effects on their ability to navigate in their surroundings. It has been reported that these patients have impaired performance of psychophysical tasks of complex motion discrimination.

Animals↗
PubMed1990

Assimilation and contrast in motion perception: explorations in cooperativity.

Motions within one region of the field influence motion seen elsewhere. To explore this phenomenon we used cinematograms comprised of alternating strips within which dots (i) tended to move in one direction, or (ii) moved in random directions (dynamic noise). When alternating strips were narrow, motion in one direction induced a similar direction of illusory motion in the adjoining dynamic noise (assimilation); when alternating strips were wide, motion tended to induce an illusory opposed motion in the dynamic noise (contrast). Since this illusory motion exhibits hysteresis, it probably results from spatially distributed, cooperative processes. The shift from assimilation to contrast, as the cinematogram's strips increase in size, suggests that facilitatory and inhibitory influences of the network extend over different distances.

Contrast Sensitivity↗
PubMed1995

Visual motion perception.

The primate visual motion system performs numerous functions essential for survival in a dynamic visual world. Prominent among these functions is the ability to recover and represent the trajectories of objects in a form that facilitates behavioral responses to those movements. The first step toward this goal, which consists of detecting the displacement of retinal image features, has been studied for many years in both psychophysical and neurobiological experiments. Evidence indicates that achievement of this step is computationally straightforward and occurs at the earliest cortical stage. The second step involves the selective integration of retinal motion signals according to the object of origin. Realization of this step is computationally demanding, as the solution is formally underconstrained. It must rely--by definition--upon utilization of retinal cues that are indicative of the spatial relationships within and between objects in the visual scene. Psychophysical experiments have documented this dependence and suggested mechanisms by which it may be achieved. Neurophysiological experiments have provided evidence for a neural substrate that may underlie this selective motion signal integration. Together they paint a coherent portrait of the means by which retinal image motion gives rise to our perceptual experience of moving objects.

Animals↗
PubMed1993

Barber-pole illusions and plaids: the influence of aperture shape on motion perception.

The barber-pole illusion and its influence on plaid perception were investigated in two experiments to test the following expectations: (i) apertures which bias the perception of grating motion in directions consistent with plaid direction will facilitate plaid perception, and (ii) apertures which bias the perception of grating motion in directions inconsistent with plaid direction will disrupt plaid perception. In experiment 1 the barber-pole illusion was measured as a function of grating orientation (20 degrees, 45 degrees, and 70 degrees, clockwise and counterclockwise from horizontal), and aperture shape (vertical, horizontal; at each of three elongations). Barber-pole illusions reported with 45 degrees gratings increased with increased aperture elongation. However, this was not found with 20 degrees and 70 degrees gratings; these were almost always reported as moving in a direction parallel to the side of the aperture with which the gratings formed angles approaching 90 degrees. In experiment 2 this dependence of barber-pole illusions on the relative orientation between gratings and apertures was also evident with 45 degrees gratings in oblique apertures; only oblique directions of grating motion were reported. The influence of the same apertures on the separate contrast thresholds required for initial plaid coherence and initial plaid decomposition was measured. In experiments 1 and 2, coherence thresholds were unaffected by apertures, contrary to expectation (i). However, in both experiments expectation (ii) was confirmed; decomposition thresholds decreased in apertures which biased perceived direction of gratings towards vertical (plaid direction), and increased in apertures which biased grating motion away from vertical. Adaptation of plaid mechanisms during measurement of decomposition thresholds was proposed to explain the discrepancy between coherence and decomposition data. Taken together, the results were interpreted as reflecting interactions between mechanisms mediating the barber-pole illusion and mechanisms mediating plaid perception.

Humans↗
PubMed1993

Impaired visual motion perception in the contralateral hemifield following unilateral posterior cerebral lesions in humans.

Contrast thresholds for a number of tasks were measured in the contralateral and ipsilateral upper quadrants of the visual field (eccentricity = 10 degrees) before and after an occipito-parietal surgical resection, in one patient, carried out for intractable epilepsy. Postoperatively the contrast thresholds for discriminating the speed of movement of drifting sine-wave gratings were elevated by greater than a log unit in the contralateral field with little or no change in the detection thresholds for the same stimuli. Contrast thresholds for opposite direction-of-motion (DOM) discrimination of a contrast modulated (CMod) grating (a 'non-Fourier' motion stimulus) were also elevated by about a log unit in the contralateral hemifield but thresholds for DOM discrimination of a sine-wave (luminance modulated, LMod) grating were unaffected. Contrast thresholds for orientation discrimination of stationary gratings (a non-motion task) were unaffected. This general pattern of results was found in two other patients following lateral occipital surgical resections. Eight other patients with occipito-temporal (two cases), parietal (three cases) and medial occipital lobe lesions (three cases) showed no difference between the two hemifields on any of the tasks. Comparison of the location of the lesions leads to the conclusion that damage to the lateral occipital gyri is responsible for the pattern of visual deficit observed. Damage to an extra-striate visual area concerned with motion perception (the human homologue of primate V5-MT) may have occurred. There has been no previous description of impairment of motion perception localized to a hemifield in humans. The characteristics of the residual motion perception in these cases is described further in the accompanying article [Plant and Nakayama (1993), Brain, 116, 1337-1353].

Adult↗
PubMed1998

Direction-specific impairment of motion perception and spatial orientation in downbeat and upbeat nystagmus in humans.

Downbeat and upbeat nystagmus can be classified as central vestibular syndromes in the vertical (pitch) plane of the vestibulo-ocular reflex (VOR) which are defined by ocular motor, perceptual, and postural manifestations. While the ocular motor syndrome was often studied investigations on the perceptual consequences for spatial orientation and motion perception are rare. Subjective visual straight ahead (SVA) and perception of object motion were measured in 11 patients with downbeat (n=6) and upbeat (n=5) nystagmus. Upward deviations of SVA (median +5.2 degrees) were found in downbeat nystagmus, and downward deviations (median -7.8 degrees) in upbeat nystagmus. SVA was deviated toward the slow phase of the vertical nystagmus in the pitch plane and associated with increased fore-aft body sway. Perception of object motion was more severely impaired for vertical (particularly for motion in the direction of slow nystagmus phases) than for horizontal directions in both downbeat and upbeat nystagmus. Impairment of motion perception in the vertical pitch plane of the VOR is beneficial to the extent that it alleviates disturbing oscillopsia due to the involuntary retinal slip. Thus, our findings confirm the hypothesis that downbeat and upbeat nystagmus reflect a central tone imbalance of the VOR in the vertical pitch plane with ocular motor, postural, and perceptual manifestations.

Adult↗
PubMed1999

The mechanism of isoluminant chromatic motion perception.

An isoluminant chromatic display is a color display in which the component colors have been so carefully equated in luminance that they stimulate only color-sensitive perceptual mechanisms and not luminance-sensitive mechanisms. The nature of the mechanism by which isoluminant chromatic motion is perceived is an important issue because color and motion processing historically have been associated with different neural pathways. Here we show that isoluminant chromatic motion (i) fails a pedestal test, (ii) has a temporal tuning function that declines to half-amplitude at 3-6 Hz, and (iii) is perceived equally well when the entire motion sequence is presented monocularly (entire motion sequence to one eye) versus interocularly (the frames of motion sequence alternate between eyes so that neither eye individually could perceive motion). These three characteristics indicate that chromatic motion is detected by the third-order motion system. Based on this theory, it was possible to take a moving isoluminant red-green grating and, by simply increasing the chromatic contrast of the green component, to generate the full gamut of motion percepts, from compelling smooth motion to motion standstill. The perception of motion standstill when the third-order mechanism is nullified indicates that there is no other motion computation available for purely chromatic motion. It follows that isoluminant chromatic motion is not computed by specialized chromatic motion mechanisms within a color pathway but by the third-order motion system at a brain level where binocular inputs of form, color, depth, and texture are simultaneously available and where selective attention can exert a major influence.

Calibration↗
PubMed1995

The functional architecture of human visual motion perception.

UNLABELLED: A powerful paradigm (the pedestal-plus-test display) is combined with several subsidiary paradigms (interocular presentation, stimulus superpositions with varying phases, and attentional manipulations) to determine the functional architecture of visual motion perception: i.e. the nature of the various mechanisms of motion perception and their relations to each other. Three systems are isolated: a first-order system that uses a primitive motion energy computation to extract motion from moving luminance modulations; a second-order system that uses motion energy to extract motion from moving texture-contrast modulations; and a third-order system that tracks features. Pedestal displays exclude feature-tracking and thereby yield pure measures of the first- and second-order systems which are found to be exclusively monocular. Interocular displays exclude the first- and second-order systems and thereby to yield pure measures of feature-tracking. RESULTS: both first- and second-order systems are fast (with temporal frequency cutoff at 12 Hz) and sensitive. Feature tracking operates interocularly almost as well as monocularly. It is slower (cutoff frequency is 3 Hz) and it requires much more stimulus contrast than the first- and second-order systems. Feature tracking is both bottom-up (it computes motion from luminance modulation, texture-contrast modulation, depth modulation, motion modulation, flicker modulation, and from other types of stimuli) and top-down--e.g. attentional instructions can determine the direction of perceived motion.

Attention↗
PubMed1987

Influence of head or trunk oscillations on visually induced self-motion perception in humans.

The influence of concurrent head or trunk movements on optokinetically induced self-motion perception has been investigated by measuring circularvection (CV) latencies. Active head as well as passive trunk oscillation cause an increase in circularvection latency of about 50% as compared to latencies with the head and trunk stationary during full field optokinetic stimulation. The results point towards an intersensory inhibition of self-motion perception.

Adolescent↗
PubMed1998

First- and second-order motion perception in Gabor micropattern stimuli: psychophysics and computational modelling.

This paper examines the perception of first- and second-order motion in human vision. In an extension of previous work by Boulton and Baker [J.B. Boulton, C.L. Baker, Motion detection is dependent on spatial frequency not size, Vision Res., 31 (1991) 77-87; J.B. Boulton, C.L. Baker, Different parameters control motion perception above and below a critical density, Vision Res., 33 (1993) 1803-1811], the direction of two-frame apparent motion is measured for stimuli composed of Gabor or Gaussian micropatterns. Three conditions are investigated. Condition 1 is that used by Boulton and Baker, in which motion is defined by the displacement of Gabor micropatterns. In condition 2, motion is defined by the displacement of Gaussian micropatterns. In condition 3, the envelopes of Gabor micropatterns are displaced while their carriers remain static. Using sparsely distributed micropatterns, direction judgements in all three conditions are determined by the spacing of the micropatterns. With a dense stimulus, direction judgements vary as a function of displacement in qualitatively different ways for the three conditions. The psychophysical results are predicted by a two-channel computational model. In one channel, motion is calculated directly from stimulus luminance, while in the other it is preceded by a texture-grabbing operation. The relative activities of the two channels dictates which governs direction judgements for any given stimulus.

Computer Simulation↗
PubMed2001

Neural correlates of chromatic motion perception.

A variety of psychophysical and neurophysiological studies suggest that chromatic motion perception in the primate brain may be performed outside the classical motion processing pathway. We addressed this provocative proposal directly by assessing the sensitivity of neurons in motion area MT to moving colored stimuli while simultaneously determining perceptual sensitivity in nonhuman primate observers. The results of these studies demonstrate a strong correspondence between neuronal and perceptual measures. Our findings testify that area MT is indeed a principal component of the neuronal substrate for color-based motion processing.

Animals↗
PubMed2000

Motion perception at scotopic light levels.

Although the spatial and temporal properties of rod-mediated vision have been extensively characterized, little is known about scotopic motion perception. To provide such information, we determined thresholds for the detection and identification of the direction of motion of sinusoidal grating patches moving at speeds from 1 to 32 deg/s, under scotopic light levels, in four different types of observers: three normals, a rod monochromat (who lacks all cone vision), an S-cone monochromat (who lacks M- and L-cone vision), and four deuteranopes (who lack M-cone vision). The deuteranopes, whose motion perception does not differ from that of normals, allowed us to measure rod and L-cone thresholds under silent substitution conditions and to compare directly the perceived velocity for moving stimuli detected by either rod or cone vision at the same light level. We find, for rod as for cone vision, that the direction of motion can be reliably identified very near to detection threshold. In contrast, the perceived velocity of rod-mediated stimuli is reduced by approximately 20% relative to cone-mediated stimuli at temporal frequencies below 4 Hz and at all intensity levels investigated (0.92 to -1.12 log cd m(-2)). Most likely, the difference in velocity perception is distal in origin because rod and cone signals converge in the retina and further processing of their combined signals in the visual cortex is presumably identical. To account for the difference, we propose a model of velocity, in which the greater temporal averaging of rod signals in the retina leads to an attenuation of the motion signal in the detectors tuned to high velocities.

Color Vision Defects↗
PubMed1990

Consequences of spatial sampling for human motion perception.

This paper describes evidence for spatial aliasing in human motion perception. For a certain range of spatial frequencies, interference fringes drifting across the extrafoveal retina resemble two-dimensional spatial noise drifting in the opposite direction. For retinal locations within 10 deg of the fovea, the perceived direction of motion is veridical up to spatial frequencies near the cone Nyquist frequency, reverses between one and two times the cone Nyquist frequency, and sometimes reverses back to the correct direction at still higher frequencies. Thus two "motion nulls", or spatial frequencies at which the direction of motion is ambiguous, are typically observed at each retinal eccentricity. A computational model is described in which sinusoidal gratings are sampled by a cone mosaic and the direction of motion of the filtered output is computed. The model predicts that the second motion null, but not the first, should be relatively immune to postreceptoral processing and should roughly equal twice the cone Nyquist frequency. This prediction is confirmed by psychophysical experiments, providing a new technique to estimate cone spacing in the living human eye.

Discrimination, Psychological↗
PubMed1995

Motion perception deficits in glaucomatous optic neuropathy.

The mechanisms mediating impaired motion perception in glaucoma were investigated. Direction discrimination thresholds for low (4.2 deg/sec) and high (12.5 deg/sec) velocity random-dot kinematograms were measured in controls and patients with glaucoma or ocular hypertension. Thresholds were elevated significantly in glaucoma patients and individual ocular hypertensives. Threshold elevations were not due to blur or pupil size. After compensating for motion reversals, high but not low velocity thresholds remained elevated. Only high velocity thresholds correlated with differential luminance sensitivity. A hypothesis that different mechanisms mediate glaucoma-induced deficits at high and low velocities is presented.

Adult↗