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A simple and inexpensive apparatus makes possible the feeding of nonliving objects to the toad. The device is used to demonstrate the perception of apparent or "induced" motion. Two methods are successful: (i) toad and food moving together at a constatnt velocity in a stationary environment; (ii) toad and food stationary with the environment moving. The phenomena are similar to those found in human beings.
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Williams syndrome (WS) is a rare genetic disorder that results in profound spatial cognitive deficits. We examined whether individuals with WS have intact perception of biological motion, which requires global spatial integration of local motion signals into a unitary percept of a human form. Children with WS, normal mental-age-matched children, and normal adults viewed point-light-walker (PLW) displays portraying a human figure walking to the left or right. Children with WS were as good as or better than control children in their ability to judge the walker's direction, even when it was masked with dynamic noise that mimicked the local motion of the PLW lights. These results show that mechanisms underlying the perception of at least some kinds of biological motion are unimpaired in children with WS. They provide the first evidence of selective sparing of a specialized spatial system in individuals with a known genetic impairment.
CONCLUSION: Our results indicate that the illusion of self-motion is a significant factor leading to spatial disorientation. OBJECTIVE: Under normal circumstances, self-motion is perceived in response to motion of the head and body. However, under certain conditions, such as virtual reality environments, visually induced self-motion can be perceived even though the subject is not actually moving, a phenomenon known as "vection". The aim of this study was to examine the possible influence of illusory self-rotation (circular vection) on postural adjustments. MATERIAL AND METHODS: The subjects were 10 young females with no history of ocular or vestibular disease. Video-motion analysis was applied to measure postural movements during vertical optokinetic stimulation. RESULTS: For most subjects, movement of the visual surroundings induced head and body displacements in the same direction as that of the visual stimulus, regardless of the onset of self-motion perception. However, there was a significant increase in postural instability after the subjects began to perceive false self-motion in the opposite direction to that of the visual stimulus.
In recent years the idea of parallel and independent processing streams for different visual attributes has become a guiding principle for linking the organization, architecture and function of the visual system. Findings concerning the segregation of motion and color information have been at the forefront of the evidence in favor of the parallel processing scheme. A number of studies have shown that motion perception is impaired for isoluminant stimuli, which are thought to isolate the color system. However, there are now many studies, the results of which are incompatible with the simple idea of segregated pathways. We propose two processing streams for motion that differ mostly in their temporal characteristics. Although neither of the two motion streams is color-blind, as was originally suggested, they differ radically in the way they process color information. The view that we propose provides a framework that reconciles a number of seemingly contradictory results. Evidence to support the new framework comes from psychophysical, physiological and lesion studies.
In this study, we examined the contribution of the orientation of moving objects to perception of a streaming/bouncing motion display. In three experiments, participants reported which of the two types of motion, streaming or bouncing, they perceived. The following independent variables were used: orientation differences between Gabor micropatterns (Gabors) and their path of motion (all the experiments) and the presence/absence of a transient tone (Experiment 1), transient visual flash (Experiment 2), or concurrent secondary task (Experiment 3) at the coincidence of Gabors. The results showed that the events at coincidence generally biased responses toward the perception of bouncing. On the other hand, alignment of Gabors with their motion axes significantly reduced the frequency of bounce perception. The results also indicated that an object whose orientation was parallel to its motion path strengthened the spatiotemporal integration of local motion signals along a straight motion path, resulting in the perception of streaming. We suggest that the effect of collinearity between Gabors and their motion path is relatively free from the effect of attention distraction.
The central hypothesis of the work is that the dimension of control-no control plays an important role in motion sickness. Although it is generally agreed that having control over a moving vehicle greatly reduces the likelihood of motion sickness, few studies have addressed this issue directly, and the theoretical explanation for this phenomenon is not completely clear. In this study, we equated groups differing in controllability for head movement, vision, activity, and predictability, which have often been suggested in the literature as explanations for the driver's immunity to motion sickness. Twenty-two pairs of yoked subjects were exposed to nauseogenic rotation. One subject of each pair had control over the rotation and head movements, while the other was exposed passively to the same motion stimulus. Subjects who had control reported significantly fewer motion sickness symptoms and less of a decrement in their well-being, as compared to the yoked subject without control. The results are discussed in relation to Reason's sensory rearrangement theory and the concept of feed-forward mechanisms in motion perception.
We used random-dot kinematograms to compare the effects of early monocular versus early binocular deprivation on the development of the perception of the direction of global motion. Patients had been visually deprived by a cataract in one or both eyes from birth or later after a history of normal visual experience. The discrimination of direction of global motion was significantly impaired after early visual deprivation. Surprisingly, impairments were significantly worse after early binocular deprivation than after early monocular deprivation, and the sensitive period was very short. The unexpectedly good results after monocular deprivation suggest that the higher centers involved in the integration of global motion profit from input to the nondeprived eye. These findings suggest that beyond the primary visual cortex, competitive interactions between the eyes can give way to collaborative interactions that enable a relative sparing of some visual functions after monocular deprivation.
Many experiments concerned with the role of color in depth and motion perception have applied isoluminant random-dot stereograms and cinematograms. The poor performance in the absence of luminance contrast has been associated with color-blindness of stereopsis and motion perception (Livingstone, M.S. & Hubel, D.H. (1987) J. Neurosci. 7, 3416-3468). Nevertheless, isoluminant stimuli are not fully accepted as appropriate tools in isolating central mechanisms (Logothetis, N.K., Schiller, P.H., Charles, E.R. & Hurlbert, A.C. (1990) Science 247, 214-217). In our experiments we use a broad luminance range to test whether color can contribute to a given mechanism when luminance contrast is present but has a strong "veto" effect from opposite luminance contrast, a condition we named "metaisoluminance." There is no fusion in stereopsis under polarity reversal, when only luminance information is given, and reversed-phi phenomenon is experienced for motion. As a third "matching" task, we included polarity-reversed random-dot Glass-patterns, which exhibit "static flow" and also show pattern reversal. We found that color can counteract the effects of polarity reversal by restoring stereoscopic fusion and reversed phi motion and does it with increased efficiency as the hue contrast increases. We found no such effect of color in Glass-patterns. Thus, we showed that the visual system for binocular depth and motion perception is not color-blind, although correlated hue information under metaisoluminance does not appear to yield shape perception.
Interactions between direction-selective mechanisms for motion were examined in strabismic and anisometropic amblyopia. Amblyopes were found to have a marked reduction in sensitivity to flicker or movement when the amblyopic eye was presented with a combination of two gratings drifting in opposite directions at the same velocity (i.e., a counterphase grating). Sensitivity to flicker of the counterphase grating was improved by preadapting the amblyopic eyes to a single grating which was drifting nasalward, but there was no improvement if the drift of the adapting grating was temporalward. Sensitivity to flicker was also improved by reducing field size from 10 degrees to 3 degrees. However, occluding the central 4 degrees of the 10 degrees field did not significantly alter the sensitivity to flicker. These data suggest that inhibition between motion detectors in the parafovea of amblyopic eyes reduces slow-motion perception in both the parafovea and the fovea. The results also demonstrated a reduction in amblyopic eyes of direction slectivity for motion detection.
Within the exercise and the sports sciences, various "expert observers" rely on visual assessments of movement. Strengths and limitations of unaided observation are outlined based on the biological motion perception literature and related work. The concepts of coordination, control, and action are used to propose an "action prototype" for pattern recognition.
During smooth pursuit eye movement, the perception of target motion appears to come from retinal and extraretinal influences. To explore this, two open-loop conditions (experimental stimuli stabilized at the retina) were used: one to look at the combined effect of retinal and extraretinal signals on perception (using sinusoidal target motion); and the other to look at the characteristics of an extraretinal signal alone (using a complex target and square-wave motion). In both conditions subjects tracked target motion in the dark, and subsequently compared it to motion of a similar target in the light. The main findings of the study are that the magnitude of the extraretinal signal decreases with frequency, and that the retinal and extraretinal signals combine additively. This system appears to involve a transport-time, which could be in the form of a time advance. These features of perception have a variety of implications for motor control.
The present review is aimed at analyzing and discussing some of the cortical mechanisms possibly involved in the perception of object motion and object localization in the visual field. A comprehensive approach to these topics would be beyond the scope of this work. The highest priority, therefore, will be given to the cortical machinery involved in these processes, while very little (or nothing at all) will be said on the possible role played by subcortical structures such as the lateral geniculate nucleus and the superior colliculus which, albeit not directly involved in perception, might contribute to it.
OBJECTIVE: Our aim was to investigate the influence of optokinetically induced rotatory self-motion sensation (circular vection [CV]) on asymmetries in real and representational space in normal subjects. BACKGROUND: Vestibular and optokinetic stimulation (particularly when accompanied by rightward CV) can reduce left-sided hemineglect in patients. METHOD: Twenty healthy right-handed men were administered a line bisection (LB) task and a stimulus-response compatibility task monitoring mental representation of space (the RULER task). The RULER task required speeded unimanual decisions ("smaller than 6?" vs. "larger than 6?") to foveally presented numbers between 1 and 11. Both tasks were performed in a baseline condition (no stimulation) and with full-field optokinetic stimulation to induce CV to either side. RESULTS: The bisection marks of both hands were shifted significantly to the left during leftward CV, introducing a pseudoneglect for the left and right hands. Rightward CV did not influence LB. In the RULER task, we found a stimulus-response compatibility, namely, faster right-hand responses to large numbers (i.e., 7-11) and faster left-hand responses to small numbers (i.e., 1-5). Although optokinetic stimulation did not significantly affect subjects' representation of space, the overall pattern of observed deviations was strikingly similar to that obtained in LB. CONCLUSIONS: Optokinetic stimulation affects healthy subjects' exploration and, to a lesser extent, their representation of space. In contrast to previous studies in neglect patients and healthy subjects, we found that leftward CV rather than rightward CV induced a leftward deviation of the subjective midpoint. This discrepancy is most likely a consequence of the exclusively peripheral visual field stimulation in our experiment. We suggest that the leftward deviation during rightward CV described in former studies may be due to the cuing effect of the leftward moving dots in the central visual field. In the absence of these central cues, the direction of CV seems to be the main determining factor for observed hemispatial effects.
We usually perceive a stationary, stable world despite coherent visual motion induced by eye movements. This astonishing example of perceptual invariance results from a comparison of visual information with internal reference signals (nonretinal signals) predicting the visual consequences of an eye movement. The important consequence of this concept is that our subjective percept of visual motion reflects the outcome of this comparison rather than retinal image slip. To localize the cortical networks underlying this comparison, we compared magnetoencephalography (MEG) responses under two conditions of pursuit-induced retinal image motion, which were identical physically but--due to different calibrational states of the nonretinal signal prompted under our experimental conditions--gave rise to different percepts of visual motion. This approach allows us to demonstrate that our perception of self-induced visual motion resides in comparably "late" parts of the cortical hierarchy of motion processing sparing the early stages up to cortical area MT/V5 but including cortex in and around the medial aspect of the parietooccipital cortex as one of its core elements.
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We have colour vision because there are three types of cone photoreceptors which are maximally sensitive in the long (L), middle (M) and short (S) wavelength regions of the spectrum. Psychophysical experiments have, however, revealed mechanisms selectively responsive to light modulated in three 'cardinal directions' in colour space. The responses of these mechanisms are determined by algebraic sums of the excitations of the cones. One of these mechanisms is responsive to changes in luminance, its spectral sensitivity being that of the sum of the L and M cones. The other two respond best to isoluminant changes in light. The responses of one of these mechanisms are determined by the difference in the excitations of the L and M cones, and those of the other one determined by the difference between the excitation of the S cones on the one hand and the excitations of the L and M cones on the other. We have obtained quite surprising results concerning the role of these mechanisms in the perception of motion. Drifting gratings modulated along different cardinal directions appear to slip with respect to one another. In contrast, when the directions of the modulations are rotated by 45 degrees in colour space, the gratings cohere. Our results are consistent with the notion that information about movement is analysed within mechanisms maximally responsive along the cardinal directions.