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PubMed1998

Smooth pursuit eye movements to extraretinal motion signals: deficits in relatives of patients with schizophrenia.

BACKGROUND: Although mounting evidence supports the idea that smooth pursuit abnormality marks the genetic liability to schizophrenia, the precise ocular motor mechanism underlying the abnormality remains unknown. Based on recent findings in schizophrenia, we hypothesize that subtle deficits in the ability to hold online and/or use extraretinal motion information underlie the pursuit abnormality in vulnerable individuals. METHODS: The hypothesis was tested in 69 first-degree, biological relatives of probands with schizophrenia; 26 relatives had schizophrenia spectrum personalities (SSP). Subjects recruited from the community (n=71; 29 with SSP), without a known family history of psychosis, constituted the comparison groups. The traditional smooth pursuit gain measure, which is a ratio of smooth pursuit eye velocity in response to both retinal and extraretinal motion signals and the target velocity, was obtained. In addition, newly developed measures of predictive smooth pursuit (ie, in the presence of only extraretinal motion signals) were obtained. The latter measures were evaluated after the current retinal motion signals were made unavailable by briefly making the target invisible. RESULTS: Relatives, particularly those with SSP, showed significantly poorer predictive pursuit response to extraretinal motion signals (F(2,136)=6.51, P<.005), compared with the community subjects. However, the traditional smooth pursuit gain in response to both retinal and extraretinal motion signals was not different between groups. CONCLUSIONS: These results suggest that relatives of patients with schizophrenia, particularly those with SSP, have specific deficits in predictive pursuit based on only extraretinal motion signals. Normal smooth pursuit gain in response to both retinal and extraretinal motion signals is likely due to compensation based on retinal motion information. The latter suggests normal retinal motion processing and smooth pursuit motor output.

Adolescent↗
PubMed2002

Motion detectors in the locust visual system: From biology to robot sensors.

Motion detectors in the locust optic lobe and brain fall into two categories: neurones that respond selectively to approaching vs. receding objects and neurones that respond selectively to a particular pattern of image motion over a substantial part of the eye, generated by the locust's own movements through its environment. Neurones from the two categories can be differentiated on the basis of their response to motion at a constant velocity at a fixed distance from the locust: neurones of the first category respond equally well to motion in any direction whereas neurones in the second category respond selectively to one preferred direction of motion. Several of the motion detectors of the first category, responding to approaching objects, share the same input organisation, suggesting that it is important in generating a tuning for approaching objects. Anatomical, physiological, and modelling studies have revealed how the selectivity of the response is generated. The selectivity arises as a result of a critical race between excitation, generated when image edges move out over the eye and delayed inhibition, generated by the same edge movements. For excitation to build up, the velocity and extent of edge motion over the eye must increase rapidly. The ultrastructure of the afferent inputs onto the dendrites of collision sensitive neurones reveals a possible substrate for the interaction between excitation and inhibition. This interpretation is supported by both physiological and immunocytochemical evidence. The input organisation of these neurones has been incorporated into the control structure of a small mobile robot, which successfully avoids collisions with looming objects. The ecological role of motion detectors of the second category that respond to image motion over a substantial part of the visual field, is discussed as is the input organisation that generates this selective response. The broad tuning of these neurones, particularly at low velocities (<0.02 degree/s), suggests they may have a role in navigation during migratory flights at altitude. By contrast, their optimum tuning to high-image velocities suggests these motion detectors are adapted for use in a fast flying insect, which does not spend significant time hovering.

Animals↗
PubMed1992

Visual evoked potentials specific for motion onset.

Motion-onset visual evoked potentials were studied in 140 subjects by means of motion-onset stimulation either on a television screen or through back projecting via a moving mirror. The motion-onset visual evoked potentials were characterized in 94% of the population by a dominant negative peak with latency in the range of 135-180 ms. Motion-onset visual evoked potentials with a dominant positive peak, as described in the literature, seemed to be a variant of pattern-off visual evoked potentials, caused by the pattern-disappearance effect at the onset of motion with a high temporal frequency (the multiple of the spatial frequency of the structure and the velocity of motion) of more than 6 Hz. Such visual evoked potentials occur mainly when the stimulus is limited to the macular area only. Additionally, other stimulus and recording conditions were found to be suitable for acquiring the specific motion-onset potentials without their contamination by pattern-related components. These conditions were as follows: an aperiodic moving pattern (e.g., random dots) with a low contrast (less than 0.2); a short duration of motion (less than or equal to 200 ms) and a sufficient interstimulus interval (at least five times longer than the motion duration) to decrease the adaptation to motion; and extramacular stimulation and recording of visual evoked potentials from unipolar lateral occipital leads. Such leads should be used because of the lateralization of these visual evoked potentials (mainly to the right occipital area), which is consistent with their assumed extrastriate origin.

Adult↗
PubMed1989

Selective impairment of visual motion interpretation following lesions of the right occipito-parietal area in humans.

A group of eighteen patients selected on the basis of the anatomical locus of the lesion, normal visual acuity and the ability to discriminate visual motion, were assessed on the perception of Julesz Random-Dot stereograms and on three tasks of visual motion interpretation: Speed Discrimination, 3D-Structure-from-Motion and 2D-Form-from-motion. The results on these experimental tasks demonstrate a double dissociation of deficits on the visual analysis of motion and stereopsis in the patients with lesions to the posterior right hemisphere. The right occipital-parietal (ROP) group failed on the Stereopsis task and showed a dramatic impairment on the Speed Comparison and on the Structure-from-Motion experiments. They performed in the normal range, however, on the 2D-Form-from-Motion task. The right occipital-temporal (ROT) group, on the other hand, were severely impaired on the identification of two dimensional forms from motion or stereopsis. In both cases, however, they were able to obtain a coarse segregation of the figure from the background. The ROT group did not present significant deficits on the Speed Discrimination and the Structure-from-Motion tasks. The results are discussed in the light of recent physiological and psychophysical findings, and it is hypothesized that, in the human brain, visual deficits of motion interpretation and of stereopsis are associated with right occipital-parietal lesions.

Adult↗
PubMed1996

A comparison of visual responses to object- and ego-motion in the macaque superior temporal polysensory area.

The responses of visual movement-sensitive neurons in the anterior superior temporal polysensory area (STPa) of monkeys were studied during object-motion, ego-motion and during both together. The majority of the cells responded only to the image of a moving object against a stationary background and failed to respond to the retinal movement of the same object (against the same background) caused by the monkey's ego-motion. All the tested cells continued responding to the object-motion during ego-motion in the opposite direction. By contrast, most cells failed to respond to the motion of an object when the observer and object moved at the same speed and direction (eliminating observer-relative motion cues). The results indicate that STPa cells compute motion relative to the observer and suggest an influence of reference signals (vestibular, somatosensory or retinal) in the discrimination of ego- and object-motion. The results extend observations indicating that STPa cells are selective for visual motion originating from the movements of external objects and unresponsive to retinal changes correlated with the observer's own movements.

Animals↗
PubMed2002

Object motion perception is shaped by the motor control mechanism of ocular pursuit.

It is still a matter of debate whether the control of smooth pursuit eye movements involves an internal drive signal from object motion perception. We measured human target velocity and target position perceptions and compared them with the presumed pursuit control mechanism (model simulations). We presented normal subjects (Ns) and vestibular loss patients (Ps) with visual target motion in space. Concurrently, a visual background was presented, which was kept stationary or was moved with or against the target (five combinations). The motion stimuli consisted of smoothed ramp displacements with different dominant frequencies and peak velocities (0.05, 0.2, 0.8 Hz; 0.2-25.6 degrees /s). Subjects always pursued the target with their eyes. In a first experiment they gave verbal magnitude estimates of perceived target velocity in space and of self-motion in space. The target velocity estimates of both Ns and Ps tended to saturate at 0.8 Hz and with peak velocities >3 degrees /s. Below these ranges the velocity estimates showed a pronounced modulation in relation to the relative target-to-background motion ('background effect'; for example, 'background with'-motion decreased and 'against'-motion increased perceived target velocity). Pronounced only in Ps and not in Ns, there was an additional modulation in relation to the relative head-to-background motion, which co-varied with an illusion of self-motion in space (circular vection, CV) in Ps. In a second experiment, subjects performed retrospective reproduction of perceived target start and end positions with the same stimuli. Perceived end position was essentially veridical in both Ns and Ps (apart from a small constant offset). Reproduced start position showed an almost negligible background effect in Ns. In contrast, it showed a pronounced modulation in Ps, which again was related to CV. The results were compared with simulations of a model that we have recently presented for velocity control of eye pursuit. We found that the main features of target velocity perception (in terms of dynamics and modulation by background) closely correspond to those of the internal drive signal for target pursuit, compatible with the notion of a common source of both the perception and the drive signal. In contrast, the eye pursuit movement is almost free of the background effect. As an explanation, we postulate that the target-to-background component in the target pursuit drive signal largely neutralises the background-to-eye retinal slip signal (optokinetic reflex signal) that feeds into the eye premotor mechanism as a competitor of the target retinal slip signal. An extension of the model allowed us to simulate also the findings of the target position perception. It is assumed to be represented in a perceptual channel that is distinct from the velocity perception, building on an efference copy of the essentially accurate eye position. We hold that other visuomotor behaviour, such as target reaching with the hand, builds mainly on this target position percept and therefore is not contaminated by the background effect in the velocity percept. Generally, the coincidence of an erroneous velocity percept and an almost perfect eye pursuit movement during background motion is discussed as an instructive example of an action-perception dissociation. This dissociation cannot be taken to indicate that the two functions are internally represented in separate brain control systems, but rather reflects the intimate coupling between both functions.

Adult↗
PubMed2003

Early behavior of optokinetic responses elicited by transparent motion stimuli during depth-based attention.

When two visual patterns moving in different directions are superimposed on the same depth plane (transparent motion stimulus), observers perceive transparent surfaces sliding over each other on different depth planes. Simultaneously, an optokinetic response (OKR) occurs so that one of the visual patterns is stabilized on the retina. In this study, we investigated the early behavior of the OKR elicited by transparent motion stimuli while subjects focused their attention on either the near or far surface. Two random dot patterns were superimposed and moved in orthogonal or opposite directions. Subjects were instructed to report the motion direction of the surface on which their attention was focused. The mean latency of initiation of OKR in the case of motion in opposite directions (150 ms) was significantly longer than that in the case of motion in orthogonal directions (100 ms). In the case of motion in orthogonal directions, the distribution of directions of OKR during the initial period, from 100 to 150 ms, was biased toward the mean direction of the two stimulus motions. After 160 ms, the eyes started to pursue a particular motion pattern of which the direction agreed with the far-perceived motion regardless of depth-based attention. Depth-based attention changed the direction of eye movements after 200 ms and eventually made the eyes follow a pattern on which the attention was focused. These results suggest that pursuit eye movement immediately after 160 ms may determine perceptual depth order through change of retinal image motion, because the slow-moving retinal image may be perceived in the far depth plane. Following this process of determination of perceptual depth order, depth-based attention starts to affect OKR.

Adult↗
PubMed2006

The role of human extra-striate visual areas V5/MT and V2/V3 in the perception of the direction of global motion: a transcranial magnetic stimulation study.

Several published single case studies reveal a double dissociation between the effects of brain damage in separate extra-striate cortical visual areas on the perception of global visual motion defined by a difference in luminance (first-order motion) versus motion defined by a difference in contrast (second-order motion). In particular, the medial extrastriate cortical region V2/V3 seems to be crucial for the perception of first-order motion, but not for second-order, whereas a lateral and more anterior portion of the cortex close to the temporo-parieto-occipital junction (in the territory of the human motion area hV5/MT+) seems to be essential only for the perception of second-order motion. In order to test the hypothesis of a functional specialization of different visual areas for different types of motion, we applied repetitive transcranial magnetic stimulation (rTMS) unilaterally over areas V2/V3, V5/MT, or posterior parietal cortex (PPC) while subjects performed a 2AFC task with first- or second-order global motion displays in the contralateral visual field. Results showed a comparable disruption of the two types of motion, with both rTMS over V2/V3 or over MT/V5, and little or no effect with rTMS over PPC. The results suggest that either the previous psychophysical results with neurological patients are incorrect (highly unlikely) or that the lateral and medial regions are directly connected (as they are in macaque monkeys) such that stimulating one automatically affects the other, in this instance disruptively.

Adult↗
PubMed2006

Space motion sickness.

Motion sickness remains a persistent problem in spaceflight. The present review summarizes available knowledge concerning the incidence and onset of space motion sickness and aspects of the physiology of motion sickness. Proposed etiological factors in the elicitation of space motion sickness are evaluated including fluid shifts, head movements, visual orientation illusions, Coriolis cross-coupling stimulation, and otolith asymmetries. Current modes of treating space motion sickness are described. Theoretical models and proposed ground-based paradigms for understanding and studying space motion sickness are critically analyzed. Prediction tests and questionnaires for assessing susceptibility to space motion sickness and their limitations are discussed. We conclude that space motion sickness does represent a form of motion sickness and that it does not represent a unique diagnostic entity. Motion sickness arises when movements are made during exposure to unusual force backgrounds both higher and lower in magnitude than 1 g earth gravity.

Humans↗
PubMed2001

Independent first- and second-order motion energy analyses of optic flow.

The human visual system contains a functional sub-system that is specialized to extract image motion. The sensitivities of neurons change as one moves higher in the pathway. Initially cells collect responses from small retinal areas but later those local signals are combined to extract global motion; either frontoparallel or radial motion relative to the center of the visual field. This sequence of processing is conducted in parallel by pathways sensitive to the motion of either the first- or second-order luminance statistics of the image. Previously it had been shown that these two pathways were independent at the level at which local motion signals and frontoparallel global motion signals are extracted. In this study independence is tested during the extraction of radial global motion; a process strongly associated with cortical area MST (or V6) and the next logical level in the motion pathway. We find that the two pathways do provide independent estimates of radial motion and are, therefore, independent at all levels of the motion pathway that have been tested to date.

Adult↗
PubMed1984

Illusory motion in visual displays.

The apparent motion of a change in the structure of a random check pattern is studied by spatially masking it with another noise pattern and it is compared with phi motion. A fundamental difference with phi motion is the insensitivity of second order correlators (Reichardt mechanisms) to this apparent motion. The following experimental characteristics distinguish this motion from phi motion: it induces no motion after-effect, it is not transparent to another simultaneous motion, it is strongly influenced by spatial masking and it does not evoke optokinetic nystagmus. A fourth order detector is introduced which is sensitive to this illusory motion as well as to phi motion. Simulation experiments with this detector together with the subjective reports of the observers lead us to the conclusion that human subjects inadvertently treat the coarsest spatial structures as signal and the finest as the disturbing noise.

Adult↗
PubMed1987

Motion capture anisotropy.

Two uncorrelated random dot patterns were superimposed and alternated to produce dynamic incoherent noise. When a low spatial frequency sine wave grating was optically superimposed on this noise and moved in step with the alternation of the two frames, the incoherent motion was masked and all the dots were seen to adhere to the grating and to move with it as a single rigid sheet ("Motion Capture"). Over a wide range of displacements subjects could not discriminate uncorrelated noise which was "captured" from correlated noise patterns which moved physically in the same direction as the grating. In fact the motion signal from the low frequency grating was even strong enough to overcome signals from two correlated random dot patterns which moved in the opposite direction. Capture was not as strong if the direction of dot motion was orthogonal to the direction of grating motion. We conclude that in any dynamic visual scene the motion of certain salient features in the image tends to dominate our perceptual experience. The signal from low frequencies masks or inhibits the signal from the high frequencies. Since the latter now have no motion signal of their own they are assumed to move with the low frequencies. Thus, motion capture suggests an important biological role for long-range apparent motion: the process serves to preserve continuity of object identity while at the same time eliminating spurious motion signals that arise from finer image features. In this manner the visual system solves the "correspondence problem" without benefit from either computation or cognition.

Discrimination, Psychological↗
PubMed1991

Time-till-breakdown and VEP measures of short-range apparent motion.

Varying short-range apparent motion (AM) stimulus displacements from 2.7 to 21.6 min it was found that VEP amplitudes varied as a function of the limits for short-range AM described using time-till-breakdown as a behavioural measure of AM strength. This VEP amplitude difference was, however, in the reverse direction to that predicted as the "motion" condition elicited lower VEP amplitude responses than the "non-motion" conditions (which did not significantly differ from each other). This direction of VEP amplitude difference was supported by an intensive study of a single subject. The "breakdown effect" enabled VEPs to be gathered during periods in which the subjective experience was of either coherent lateral motion, or breakdown (incoherent motion) without changing any stimulus parameter. The VEP component identified in expt 2, as predicted, was of lower amplitude during motion with respect to periods of breakdown. The results of these experiments are discussed in terms of describing motion and breakdown in short-range AM displays as "coherent" and "incoherent" motion, rather than as "motion" and "non-motion".

Adult↗
PubMed1993

Isolating the effect of one-dimensional motion signals on the perceived direction of moving two-dimensional objects.

A considerable body of evidence suggests the existence of a two-stage mechanism for the detection of global motion. In the first stage the motion of elongated contours is extracted and then at the second stage these one-dimensional (1D) motion signals are combined. What is the nature of the computation carried out in combining the 1D motion signals towards forming a global motion percept? We devised a set of stimuli that differentiate between different possible computations. In particular, they distinguish between a velocity-space construction (such as intersection of constraints) and a linear computation such as vector averaging. In addition, these stimuli do not contain two-dimensional (2D) motion signals such as line intersections, that allow unambiguous determination of global velocity. Stimuli were presented in uncrossed disparity relative to the aperture through which they were presented, to reduce the effect of line terminator motion. We found that subjects are unable to detect the veridical global direction of motion for these stimuli. Instead, they perceive the stimulus pattern to be moving in a direction which reflects the average of its 1D motion components. Our results suggest that the visual system is not equipped with a mechanism implementing a velocity-space computation of global motion.

Humans↗
PubMed1993

Surface segmentation mechanisms and motion perception.

Two studies are presented which explore how depth information is determined from conditions of transparency and whether this information combines with other depth information to determine the segmenting of motion information on the basis of likely surface boundaries. The first study explored how binocular disparity combines with monocular depth cues associated with transparency to determine whether subjects see one or multiple surfaces in depth in static displays. When transparency provided a depth cue that was consistent with binocular disparity, depth discrimination thresholds were at normal levels. However, if transparency was inconsistent with the binocular disparity, depth discrimination thresholds were elevated, indicating that subjects had difficulty seeing distinct surfaces lying in separate depth planes. Moreover, threshold elevations were found to correspond to the reductions in contrast between the intersecting contours of the stimulus, suggesting that the strength of perceived depth from transparency is the result of attenuated responses from competing contrast sensitive T-junction mechanisms responsible for the detection of opaque occlusion. A second experiment explored whether the grouping of local motion signals relied on surface interpretations that result from the interaction of transparency and disparity. Surface interpretations were manipulated in moving plaids by combining transparent layering and binocular disparity to show that the motion arising from contours is grouped together (pattern motion) when these cues support the existence of a single surface, and is segregated (component motion) when they support separate surfaces. When these cues were consistent, only small disparity differences were required for the gratings to appear as separately moving surfaces. However, when they were inconsistent, greater disparities were required (about a factor of 2 greater). Taken together, these studies demonstrate that the grouping of local motion information is not resolved within the motion system alone. Information seemingly unrelated to motion processing, namely surface segmentation cues, is used to determine whether or not motion information arising from various contours is pooled together to determine a single motion.

Cues↗
PubMed1993

What happens if it changes color when it moves?: psychophysical experiments on the nature of chromatic input to motion detectors.

Several lines of evidence indicate that the processing of motion by the primate visual system continues even when a moving stimulus differs from its surroundings by color alone. To illuminate the mechanisms by which our visual system uses color as a token for motion correspondence, we have developed an "apparent motion" paradigm in which red/green sine-wave gratings undergo reversal of chromatic contrast sign each time they are displaced in a particular direction. Under such conditions, correspondence based upon conservation of chromatic sign conflicts with correspondence based upon chromatically-defined borders. When these heterochromatic stimuli also possess luminance modulation, motion is always perceived in the direction in which the sign of luminance contrast is preserved. At isoluminance, however, two very different chromatic influences on motion detection are revealed. First, when stimuli undergo small spatial displacements, motion is perceived in the direction of the nearest chromatically-defined border even when the sign of chromatic contrast at that border alternates over time. Under these conditions, motion detectors apparently exploit information about image borders defined by color while sacrificing information about the colors that make up those borders. By contrast, when spatial displacement is large, motion is more apt to be perceived in the direction for which sign of chromatic contrast is preserved. In this instance, information about the polarity of chromatic contrast facilitates motion detection. These results suggest that chromatic signals contributing to motion detection are of two distinct types. This conclusion has implications for the degree of crosstalk between magnocellular and parvocellular processing streams in the primate visual system and it reinforces our understanding of how image features affect the way we see things move.

Color Perception↗
PubMed1995

Perceived motion of contrast-modulated gratings: predictions of the multi-channel gradient model and the role of full-wave rectification.

The paper examines the perception of motion in contrast-modulated sine-wave grating patterns. These non-rigid motion patterns give rise to a spatially-structured motion percept in which perceived speed varies with spatial position. We measured the perceived motion of the low contrast regions of amplitude-modulated gratings as a function of the carrier frequency, the carrier speed, the shape of the modulation signal and the modulation depth. We found that for static carriers perceived speed was greatest in the low contrast regions of the display. The speed of the low contrast regions was underestimated and perceived speed decreased as the spatial frequency of the carrier increased. When the direction of the motion of the carrier was opposite to that of the contrast modulation, the low contrast regions could appear to be stationary. The perceived speed of the contrast modulation increased with modulation depth. The brightness contrast of the carrier grating had little effect on perceived speed of contrast-modulated patterns for average contrasts of over 10%. A motion model which had full-wave rectification as an explicit pre-processing stage followed by low-pass filtering or some other selection criterion, would predict that the motion of contrast-modulated gratings should appear rigid and that the motion of the envelope should be judged correctly. The Multi-channel Gradient Model however predicts both the structured motion field experienced when viewing these second-order motion patterns and the reductions in perceived speed as a function of carrier spatial frequency and carrier speed.

Contrast Sensitivity↗
PubMed1995

Effects of luminance contrast and phase difference on motion assimilation for sinusoidal gratings.

When a sinusoidal (test) grating is displaced horizontally by a phase angle of 180 deg in a two-frame apparent motion display, the perceived direction of motion is ambiguous; the test grating appears to move either to the left or to the right (or to both directions). On the other hand, when the test grating is displaced by 180 deg synchronously with the inducing gratings which, presented above and below the test grating, jump unambiguously in one direction (e.g. displaced by 90 deg), the test grating always appears to move in the same direction as the inducing gratings (motion assimilation). In the present study, the effects of luminance contrast and phase difference on motion assimilation were examined. The proportion of perceived direction of motion (left or right) was measured as a function of phase difference between the test grating in the first and the second frame. The magnitude of motion assimilation was evaluated as the change in the phase difference for which the proportions of observers' response were equal (50%) for both directions. The magnitude of motion assimilation increased with increase in the contrast of the inducing gratings or with decrease in the contrast of the test grating. Also, the magnitude increased as the phase difference of the inducing gratings departed from 180 deg. Based on these results, a quantitative formulation between the magnitude of motion assimilation, and the contrast and the phase difference of the stimulus gratings was derived. Further, a model was proposed which explains the stimulus dependences of motion assimilation in terms of response-integration among local motion detectors.

Contrast Sensitivity↗