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PubMed2003

Occlusion cues resolve sudden onsets into morphing or line motion, disocclusion, and sudden materialization.

An abrupt appearance of a new stimulus, or sudden onset, has several possible perceptual interpretations. The change may reflect an object new to the scene or instead be caused by disocclusion of a pre-existing object. Alternatively, the sudden onset may be interpreted as the morphing of a pre-existing figure (as in "line motion"). Previous work has focused on the morphing percept to the exclusion of other interpretations of sudden onsets. This paper supports the idea that morphing, and the other interpretations of sudden onsets, reflect occlusion cues indicating the most likely cause of the stimulus. Consider a line segment that appears abruptly. The data herein show that when the segment has already been represented as present in the scene(via amodal completion), its onset is likely to be perceived as a disocclusion event, with no appearance of morphing. Even when individual frames do not support amodal completion, dynamic (although motionless) cues can favor the disocclusion interpretation, again vetoing the perception of line motion. Some final demonstrations address sudden materialization, in which previously unseen objects suddenly appear. Again there is ambiguity in that sudden materialization and disocclusion can be caused by image changes that are locally identical. Remote cues to occlusion are shown to give these stimuli distinct appearances. The existence of these ambiguities, and the role of occlusion cues in resolving them, has implications for theories of motion perception and attentional capture.

Attention↗
PubMed1997

Comparing the visual deficits of a motion blind patient with the visual deficits of monkeys with area MT removed.

The performance of a 'motion blind' patient on a series of tasks in which the perception of motion played an essential or no role was compared with that of a human subject with normal vision and with that of macaque monkeys in which cortical visual area MT had been removed and adjacent areas damaged. The patient experienced difficulties on those tasks in which the perception of motion was essential, but was unimpaired on those tasks that did not require it. Similarly, the tasks which the 'motion blind' patient found impossible or difficult were precisely those tasks on which monkeys lacking area MT performed poorly. Similarly, the tasks on which the patient performed well also presented no difficulties for the animals lacking cortical area MT. The close correlation between the pattern of visual perceptual impairments in the patient and monkeys indicates that the patient's inability to perceive most forms of visual movement is attributable to total loss of, or extensive damage to, a cortical visual area that is the human equivalent of area MT and perhaps its adjacent areas.

Adult↗
PubMed1986

Motion selectivity in macaque visual cortex. III. Psychophysics and physiology of apparent motion.

We have conducted physiological and psychophysical experiments to identify possible neural substrates of the perception of apparent motion. We used identical sequences of flashed stimuli in both sets of experiments to better compare the responses of cortical neurons and psychophysical observers. Physiological data were obtained from two cortical visual areas, striate cortex (V1) and the middle temporal area (MT). In the previous paper we presented evidence that neuronal thresholds for direction selectivity in extrastriate area MT were similar to psychophysical thresholds for motion perception at the largest effective interflash interval, and thus speed, for a given eccentricity. We now examine physiological and psychophysical thresholds for a broad range of speeds to determine whether such a correspondence exists for speeds below the upper threshold considered in the previous paper. Stimuli were presented in stroboscopic motion of constant apparent speed while the spatial and temporal interflash intervals were systematically varied. For each neuron we measured the largest spatial interval that elicited directionally selective responses at each of several apparent speeds. We calculated the composite performance of neurons in both MT and V1 by averaging the spatial interval necessary for direction selectivity at each apparent speed. We employed the same apparent-motion stimuli for psychophysical experiments with human subjects in which we measured the spatial interval necessary for the perception of motion over a similar range of apparent speeds. We obtained a composite profile of psychophysical performance by averaging thresholds across subjects at each apparent speed. For high apparent speeds, physiological data from MT, but not V1, corresponded closely to the psychophysical data as suggested in the preceding paper. For low apparent speeds, however, physiological data from MT and V1 were similar to each other and to the psychophysical data. It would appear, therefore, that neurons in either V1 or MT could mediate the perceptual effect at low speeds, whereas MT is a stronger candidate for this role at high speeds. We suggest that the neuronal substrate for apparent motion may be distributed over multiple cortical areas, depending upon the speed and spatial interval of the stimulus.

Animals↗
PubMed1996

Perception of direction of visual motion. I. Influence of angular body acceleration and tilt.

We investigated, psychophysically, the influence of body rotation on visual motion direction thresholds for both upright sitting and tilted observers. Four angular accelerations (0, 20, 40 and 60 degrees/s2) were combined with 3 concurrent backward-tilt positions (0, 45 and 90 degrees). This led to combined stimulation of the semicircular canals and otoliths. Vestibular stimulation was combined with a visual motion stimulus. Random-dot kinematograms in which varying percentages of pixels coherently moving to the left were presented upon a background of otherwise randomly moving pixels (random walk). The smallest percentage of coherently moving pixels leading to a clear perception of motion direction represented as the perceptual threshold. Angular accelerations about the longitudinal body axis significantly increased motion-direction thresholds. Concurrent backward tilt did not influence thresholds. These results differ from those of studies in which translational linear acceleration was employed. Our results support the view that it is necessary to distinguish between linear acceleration caused by gravitational forces and that caused by additional linear accelerations about the x-, y-, and z-axes.

Acceleration↗
PubMed1996

Perception of direction of visual motion. II. Influence of linear body acceleration.

We investigated whether linear whole-body acceleration along the interaural y-axis influenced the concurrent perception of visual motion direction as has been shown for angular accelerations. A sled running on air bearings along a 7.5-m track was used to accelerate 18 subjects at two different linear accelerations. These young, healthy volunteers, aged 25.50 +/- 7.38 years, used a joystick to indicate whether or not they perceived visual motion to the left within a random-dot kinematogram continuously presented on a monitor moving with them. The percentage of coherently leftward moving pixels presented for a 640-ms period during acceleration was adjusted according to a Modified Binary Search (MOBS) procedure. Six conditions were tested, two acceleration levels of 1 and 2 m/s2 to both left and right with, at the higher acceleration, two different times of visual motion presentation. Conditions were sequenced by means of a 6 x 6 Latin square balanced for order and carry over. A MANOVA did not show any statistically significant effects either for the independent variables acceleration, velocity, and direction of motion of the sled or for their interactions. The results obtained are in clear contrast to those obtained under rotatory stimulation. We conclude that the otolithic contribution to vestibular-visual motion processing is negligible.

Acceleration↗
PubMed2005

Deficits of motion integration and segregation in patients with unilateral extrastriate lesions.

Functional neuroimaging in human subjects and single cell recordings in monkeys show that several extra-striate visual areas are activated by visual motion. However, the extent to which different types of motion are processed in different regions remains unclear, although neuropsychological studies of patients with circumscribed lesions hint at regional specialization. We, therefore, studied four patients with unilateral damage to different regions of extrastriate visual cortex on a series of visual discrimination tasks that required them, to a different extent, to integrate local motion signals in order to correctly perceive the direction of global motion. Performance was assessed psychophysically and compared with that of control subjects and with the patients' performance with stimuli presented in the visual field ipsilateral to the lesion. The results indicate considerable regional specialization in extra-striate regions for different aspects of motion processing, namely the largest displacement from frame to frame (D-max) that can sustain perception of coherent motion; perception of relative speed; the amount of coherent motion needed to sustain a percept of global motion in a particular direction; the detection of discontinuities within a moving display; the extraction of form from motion. It was also clear that a defect in local motion, i.e. D-max, can be overcome by integrating local motion signals over a longer period of time. Although no patient suffered from only one defect, the overall pattern of results strongly supports the notion of regional specialization for different aspects of motion processing.

Adult↗
PubMed2002

Dividing attention between form and motion during transparent surface perception.

Attending to objects implies the concurrent process of features that are analyzed in different visual subsystems or domains. Previous works have shown that attention cannot be simultaneously directed to the components of motion present in two transparent surfaces [M. Valdés et al., Cognition 66 (1998) B13-B23], even though they occupy overlapping regions of space. In this paper, possible across-domain effects in object-based attention were examined using a conjunction of form and motion in transparent superimposed surfaces. After directing attention to one surface, different combinations of motion and form judgements were performed. If both attributes belonged to the same surface, no interference was found. If the two judgements concerned features from different surfaces, a large performance cost was present for the attribute belonging to the uncued surface. The fact that these effects cut across feature domains supports the integrated competition hypothesis [J. Duncan, Attention and Performance XVI, The MIT Press, 1996, pp. 549-578].

Adult↗
PubMed2005

Impaired perception of self-motion (heading) in abstinent ecstasy and marijuana users.

RATIONALE: Illicit drug use can increase driver crash risk due to loss of control over vehicle trajectory. This study asks, does recreational use of +/-3,4-Methylenedioxymethamphetamine (MDMA; ecstasy) and tetrahydrocannabinol (THC; marijuana) impair cognitive processes that help direct our safe movement through the world? OBJECTIVE: This study assesses the residual effects of combined MDMA/THC use, and of THC use alone, upon perceived trajectory of travel. METHODS: Perception of self-motion, or heading, from optical flow patterns was assessed using stimuli comprising random dot ground planes presented at three different densities and eight heading angles (1, 2, 4 and 8 degrees to the left or right). On each trial, subjects reported if direction of travel was to the left or the right. RESULTS: Results showed impairments in both drug groups, with the MDMA/THC group performing the worst. CONCLUSIONS: The finding that these psychoactive agents adversely affect heading perception, even in recently abstinent users, raises potential concerns about MDMA use and driving ability.

Adult↗
PubMed1985

Perception of orientation of motion as affected by change in divergence of texture, change in size, and in velocity.

When there is relative motion between an observer and a textured surface such as the ground, motion-related visual information is available about the orientation of the surface through vergence of the paths of the elements of the texture, change in their sizes and in their velocities. This experiment determined the perceptual effectiveness of each variable in foveal and peripheral viewing for producing perceptions of three-dimensional motion. The three variables were electronically separated and displayed singly, in all possible pairs, and all together. Subjects communicated their perceptions of degree of perceived surface tilt at the top, bottom, and middle of the display for the eight different combinations of variables because, during pilot work perceived surface bendings were frequently noted where top, bottom, and middle appeared tilted to different extents. All three variables can lead to relatively reliable perceptions of perceived orientation of the plane of motion, with change in velocity being the most powerful determiner. Change in size was the weakest. Certain combinations can lead to perceptions of extreme warping and should be avoided in motion displays. Subjects consistently underestimate the amount of simulated tilt. Foveal viewing was more accurate than peripheral viewing but peripheral performance was adequately consistent as an input channel for some orientation tasks.

Depth Perception↗
PubMed2000

A slowly moving foreground can capture an observer's self-motion--a report of a new motion illusion: inverted vection.

We investigated interactions between foreground and background stimuli during visually induced perception of self-motion (vection) by using a stimulus composed of orthogonally moving random-dot patterns. The results indicated that, when the foreground moves with a slower speed, a self-motion sensation with a component in the same direction as the foreground is induced. We named this novel component of self-motion perception 'inverted vection'. The robustness of inverted vection was confirmed using various measures of self-motion sensation and under different stimulus conditions. The mechanism underlying inverted vection is discussed with regard to potentially relevant factors, such as relative motion between the foreground and background, and the interaction between the mis-registration of eye-movement information and self-motion perception.

Adult↗
PubMed2004

Association of binocular lower visual field impairment, impaired simultaneous perception, disordered visually guided motion and inaccurate saccades in children with cerebral visual dysfunction-a retrospective observational study.

The principal pathways serving higher visual function comprise the dorsal stream and the ventral stream. The dorsal stream runs between the occipital lobes and the parietal lobes and subserves the ability to process the whole visual scene and carry out visually guided movement. The ventral stream runs between the occipital lobes and temporal lobe tissue and primarily subserves visual recognition and memory. These tissues are susceptible to dysfunction in children with brain damage. We report a series of 40 children in whom damage to the brain has led to a common symptom complex affecting vision. Lower visual field loss was frequently elicited. This was associated with impaired ability to make accurate visually guided movement (particularly of the lower limbs) accompanied by impaired simultaneous perception, and in some cases, with inaccurate saccades and in others, impaired perception of movement. These features are consistent with parietal/dorsal stream dysfunction. Difficulty recognising faces and problems with route finding (which are ventral stream functions) were also present in a number of the children. These visual difficulties can be manifest in the presence of normal visual acuity. Recognition of these problems leads to understanding of the child's visual difficulties and facilitates adaptation of curriculum delivery at school.

Adolescent↗
PubMed2004

A dissociation of motion and spatial-pattern vision in the avian telencephalon: implications for the evolution of "visual streams".

The ectostriatum is a large visual structure in the avian telencephalon. Part of the tectofugal pathway, the ectostriatum receives a large ascending thalamic input from the nucleus rotundus, the homolog of the mammalian pulvinar complex. We investigated the effects of bilateral lesions of the ectostriatum in pigeons on visual motion and spatial-pattern perception tasks. To test motion perception, we measured performance on a task requiring detection of coherently moving random dots embedded in dynamic noise. To test spatial-pattern perception, we measured performance on the detection of a square wave grating embedded in static noise. A double dissociation was revealed. Pigeons with lesions to the caudal ectostriatum showed a performance deficit on the motion task but not the grating task. In contrast, pigeons with lesions to the rostral ectostriatum showed a performance deficit on the grating task but not the motion task. Thus, in the avian telencephalon, there is a separation of visual motion and spatial-pattern perception as there is in the mammalian telencephalon. However, this separation of function is in the targets of the tectofugal pathway in pigeons rather than in the thalamofugal pathway as described in mammals. The implications of these findings with respect to the evolution of the visual system are discussed. Specifically, we suggest that the principle of parallel visual streams originated in the tectofugal pathway rather than the thalamofugal pathway.

Analysis of Variance↗
PubMed2003

Color and motion: which is the tortoise and which is the hare?

Recent psychophysical studies have been interpreted to indicate that the perception of motion temporally either lags or is synchronous with the perception of color. These results appear to be at odds with neurophysiological data, which show that the average response-onset latency is shorter in the cortical areas responsible for motion (e.g., MT and MST) than for color processing (e.g., V4). The purpose of this study was to compare the perceptual asynchrony between motion and color on two psychophysical tasks. In the color correspondence task, observers indicated the predominant color of an 18 degrees x 18 degrees field of colored dots when they moved in a specific direction. On each trial, the dots periodically changed color from red to green and moved cyclically at 15, 30 or 60 deg/s in two directions separated by 180 degrees, 135 degrees, 90 degrees or 45 degrees. In the temporal order judgment task, observers indicated whether a change in color occurred before or after a change in motion, within a single cycle of the moving-dot stimulus. In the color correspondence task, we found that the perceptual asynchrony between color and motion depends on the difference in directions within the motion cycle, but does not depend on the dot velocity. In the temporal order judgment task, the perceptual asynchrony is substantially shorter than for the color correspondence task, and does not depend on the change in motion direction or the dot velocity. These findings suggest that it is inappropriate to interpret previous psychophysical results as evidence that motion perception generally lags color perception. We discuss our data in the context of a "two-stage sustained-transient" functional model for the processing of various perceptual attributes.

Analysis of Variance↗
PubMed1996

How is motion disparity integrated with binocular disparity in depth perception?

Two experiments presented motion disparity conflicting with binocular disparity to examine how these cues determined apparent depth order (convex, concave) and depth magnitude. In each experiment, 8 subjects estimated the depth order and depth magnitude. The first experiment showed the following. (1) The visual system used one of these cues exclusively in selecting a depth order for each display. (2) The visual system integrated the depth magnitude information from these cues by a weighted additive fashion if it selected the binocular disparity in depth order perception and if the depth magnitude specified by motion disparity was small relative to that specified by binocular disparity. (3) The visual system ignored the depth magnitude information of binocular disparity if it selected the motion disparity in depth order perception. The second experiment showed that these three points were consistent whether the subject's head movement or object movement generated motion disparity.

Adult↗