Object and observer motion in the perception of objects by infants.

Sixteen-week-old human infants distinguish optical displacements given by their own motion from displacements given by moving objects, and they use only the latter to perceive the unity of partly occluded objects. Optical changes produced by moving the observer around a stationary object produced attentional levels characteristic of stationary observers viewing stationary displays and much lower than those shown by stationary observers viewing moving displays. Real displacements of an object with no subject-relative displacement, produced by moving an object so as to maintain a constant relation to the moving observer, evoked attentional levels that were higher than with stationary displays and more characteristic of attention to moving displays, a finding suggesting detection of the real motion. Previously reported abilities of infants to perceive the unity of partly occluded objects from motion information were found to depend on real object motion rather than on optical displacements in general. The results suggest that object perception depends on registration of the motions of surfaces in the three-dimensional layout. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation of vestibular and visual oculomotor function

The visual system interacts synergistically with the vestibular system. A normally functioning vestibulo-ocular reflex is necessary but not sufficient for optimum visual acuity during head motion. Studies of dynamic visual acuity, the acuity achieved during relative motion of visual targets or of the observer, indicate that motion of images on the retina markedly compromises vision. The vestibulo-ocular reflex normally provides a substantial measure of stabilization of the retina during head movements, but purely vestibular compensatory eye movements are not sufficiently precise for optimal vision under all circumstances. Other mechanisms, including visual tracking, motor preprogramming, prediction, and mental set, interact synergistically to optimize the gain (eye velocity divided by head velocity) of compensatory head movements. All of these mechanisms are limited in their capacity to produce effective visual-vestibular interaction at higher rotational frequencies and velocities. It is under these conditions that vestibular deficits give rise to symptoms of oscillopsia. Patients having vestibular lesions exploit mechanisms of visual-vestibular interaction to compensate by substitution for deficient vestibular function. Thus, for accurate topographic clinical diagnosis of vestibular lesions, testing conditions should isolate purely vestibular responses. This may be done by testing reflex eye movements during passively generated rotations in darkness, or perhaps by testing during other types of motion under conditions of extreme frequency and velocity sufficient to attenuate the effects of visual-vestibular interaction. This article reviews clinical tests of vestibular function in relation to synergistic interactions with vision.     

Depth perception in motion parallax and stereokinesis.

Perceived depth in the stereokinetic effect (SKE) illusion and in the monocular derivation of depth from motion parallax were compared. Motion parallax gradients of velocity can be decomposed into 2 components: object- and observer-relative transformations. SKE displays present only the object-relative component. Observers were asked to estimate the magnitude and near–far order of depth in motion parallax and SKE displays. Monocular derivation of depth magnitude from motion parallax is fully accounted for by the perceptual response to the SKE, and observer-relative transformations absent in the SKE are of perceptual utility only as determinants of the near–far signing of perceived sequential depth. The amount of depth and rigidity perceived in motion parallax and SKE displays covaries with the projective size of the stimuli. The monocular derivation of depth from motion is mediated by a perceptual heuristic of which the SKE is symptomatic. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The observer-relative velocity field as the basis for effective motion parallax.

Earlier studies of motion parallax found unambiguous relative depth perception when random dot patterns were systematically translated in accordance with either motion of the observer's head or motion of the display scope. The need for such relative motion between an observer and a flow field was examined by placing a flow field in a limited area (window) in a large scope and translating the window relative to the observer. Accuracy in judging surface orientation and quantitative depth estimates were determined by the velocity field relative to the observer and were not measurably affected by whether this field was produced with a stationary or a moving window. Accuracy was consistently higher for smaller ratios of maximum to minimum projected velocities, reaching 100% in one experiment with a 1.12:1 ratio. We conclude that fully effective motion parallax does not require relative motion between the observer's head and the contours of a flow field. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal properties of visual motion signals for the initiation of smooth pursuit eye movements in monkeys

1. Our goal was to assess whether visual motion signals related to changes in image velocity contribute to pursuit eye movements. We recorded the smooth eye movements evoked by ramp target motion at constant speed. In two different kinds of stimuli, the onset of target motion provided either an abrupt, step change in target velocity or a smooth target acceleration that lasted 125 ms followed by prolonged target motion at constant velocity. We measured the eye acceleration in the first 100 ms of pursuit. Because of the 100-ms latency from the onset of visual stimuli to the onset of smooth eye movement, the eye acceleration in this 100-ms interval provides an estimate of the open-loop response of the visuomotor pathways that drive pursuit. 2. For steps of target velocity, eye acceleration in the first 100 ms of pursuit depended on the "motion onset delay," defined as the interval between the appearance of the target and the onset of motion. If the motion onset delay was > 100 ms, then the initial eye movement consisted of separable early and late phases of eye acceleration. The early phase dominated eye acceleration in the interval from 0 to 40 ms after pursuit onset and was relatively insensitive to image speed. The late phase dominated eye acceleration in the interval 40-100 ms after the onset of pursuit and had an amplitude that was proportional to image speed. If there was no delay between the appearance of the target and the onset of its motion, then the early component was not seen, and eye acceleration was related to target speed throughout the first 100 ms of pursuit. 3. For step changes of target velocity, the relationship between eye acceleration in the first 40 ms of pursuit and target velocity saturated at target speeds > 10 degrees /s. In contrast, the relationship was nearly linear when eye acceleration was measured in the interval 40-100 ms after the onset of pursuit. We suggest that the first 40 ms of pursuit are driven by a transient visual motion input that is related to the onset of target motion (motion onset transient component) and that the next 60 ms are driven by a sustained visual motion input (image velocity component). 4. When the target accelerated smoothly for 125 ms before moving at constant speed, the initiation of pursuit resembled that evoked by steps of target velocity. However, the latency of pursuit was consistently longer for smooth target accelerations than for steps of target velocity.(ABSTRACT TRUNCATED AT 400 WORDS)     

Pulfrich effect and the filling in of apparent motion

In the stroboscopic version of the Pulfrich effect a filter is able to induce depth shifts in a target as if the latter were moving continuously, rather than merely occupying a series of discrete positions. This was examined in a further series of experiments, in which a visual alignment technique was used to measure the perceived visual direction of an apparently moving target in intervals between its presentations. Results showed that the target has approximately the visual direction that it would have if it were moving continuously. This "filling in" of apparent motion was shown to occur before the level of stereopsis. The possible influence of tracking eye movements is discussed.     

The aftereffect of tracking eye movements

When observers tracked moving stripes across a background either of stationary stripes, or of stripes moving in the opposite direction, they saw a clear motion aftereffect when the stripes stopped moving. The direction of this aftereffect was opposite to that of the previously tracked stripes, and was thus the same as the direction of the retinal movement of the non-tracked stripes. This aftereffect of tracking was shown not to depend upon slippage of the tracked contours on the retina during tracking, or upon the saccadic phase of optokinetic nystagmus. The effect showed storage over a period of time with the eyes shut. It appears that the effect is due to induced movement, and arises originally from stimulation of the retina by background contours in the tracking phase. This was shown by confining the view of the moving target to one eye, while permitting both eyes to be exposed to background stimulation during tracking. After such stimulation the magnitude of the aftereffect was equal in the two eyes.     

Postsaccadic enhancement of initiation of smooth pursuit eye movements in monkeys

Step-ramp target motion evokes a characteristic sequence of presaccadic smooth eye movement in the direction of the target ramp, catch-up targets to bring eye position close to the position of the moving target, and postsaccadic eye velocities that nearly match target velocity. I have analyzed this sequence of eye movements in monkeys to reveal a strong postsaccadic enhancement of pursuit eye velocity and to document the conditions that lead to that enhancement. Smooth eye velocity was measured in the last 10 ms before and the first 10 ms after the first saccade evoked by step-ramp target motion. Plots of eye velocity as a function of time after the onset of the target ramp revealed that eye velocity at a given time was much higher if measured after versus before the saccade. Postsaccadic enhancement of pursuit was recorded consistently when the target stepped 3 degrees eccentric on the horizontal axis and moved upward, downward, or away from the position of fixation. To determine whether postsaccadic enhancement of pursuit was invoked by smear of the visual scene during a saccade, I recorded the effect of simulated saccades on the presaccadic eye velocity for step-ramp target motion. The 3 degrees simulated saccade, which consisted of motion of a textured background at 150 degrees/s for 20 ms, failed to cause any enhancement of presaccadic eye velocity. By using a strategically selected set of oblique target steps with horizontal ramp target motion, I found clear enhancement for saccades in all directions, even those that were orthogonal to target motion. When the size of the target step was varied by up to 15 degrees along the horizontal meridian, postsaccadic eye velocity did not depend strongly either on the initial target position or on whether the target moved toward or away from the position of fixation. In contrast, earlier studies and data in this paper show that presaccadic eye velocity is much stronger when the target is close to the center of the visual field and when the target moves toward versus away from the position of fixation. I suggest that postsaccadic enhancement of pursuit reflects activation, by saccades, of a switch that regulates the strength of transmission through the visual-motor pathways for pursuit. Targets can cause strong visual motion signals but still evoke low presaccadic eye velocities if they are ineffective at activating the pursuit system.     

Self-motion path discrimination: effects of image stabilization

Path-deviation thresholds were measured as the effects of eye movements in the retinal flow were minimized through image stabilization. Thresholds obtained with image stabilization were compared to those obtained with unstabilized viewing to determine whether the elimination of eye movements from the retinal flow improves self-motion judgments. The results showed that, at slow forward speeds, eliminating the retinal effects of eye movements did not improve path-discrimination performance; subjects required more of an angular deviation to discriminate a circular from a straight motion path with image stabilization than with unstabilized viewing. In an effort to understand the results, eye movements were measured in unstabilized viewing conditions, and the measured eye velocities were used to estimate the retinal-image motion. The results showed that, for slow forward speeds, eye movements increased the average retinal speed, independent of the circular flow direction. At fast forward speeds, there was no significant increase in the average retinal-image speed due to eye movements. A parsimonious explanation for the decreased performance with image stabilization at the slow forward speed is that retinal-image motion was too slow to optimally stimulate the visual motion sensors.     

Depth perception as a function of motion parallax and absolute-distance information.

Conducted 3 experiments with 12 observers from a university community to determine whether the visual system calibrates motion parallax according to absolute-distance information in processing depth and to map the range of depth perception as a function of distance and motion parallax. The parallax was created by yoking the relative movement of random dots displayed on a CRT to the movements of the head. In Exp I, at viewing distances of 40 and 80 cm, Ss reported the apparent depth produced by motion parallax equivalent to a binocular disparity of 0.47°. The mean apparent depth at 80 cm was 2.6 times larger than at 40 cm. In Exp II, again at viewing distances of 40 and 80 cm, Ss adjusted the extent of parallax so that the apparent depth was 7.0 cm. The mean extent of parallax at 80 cm was 31% of that at 40 cm. These findings show that the visual system does calibrate motion parallax according to absolute-distance information in processing depth. In Exp III, distances ranged from 40 to 320 cm, and a wide range of parallax was used. As distance and parallax increased, the perception of a rigid 3-dimensional surface was accompanied by rocking motion; perception of depth was replaced by perception of motion in some trials at 320 cm. Moreover, the mean apparent depths were proportional to the viewing distance at 40 and 80 cm but not at 160 and 320 cm. (25 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Aging and the Perception of Depth and 3-D Shape From Motion Parallax.

The ability of younger and older observers to perceive 3-D shape and depth from motion parallax was investigated. In Experiment 1, the observers discriminated among differently curved 3-dimensional (3-D) surfaces in the presence of noise. In Experiment 2, the surfaces' shape was held constant and the amount of front-to-back depth was varied; the observers estimated the amount of depth they perceived. The effects of age were strongly task dependent. The younger observers' performance in Experiment 1 was almost 60% higher than that of the older observers. In contrast, no age effect was obtained in Experiment 2. Older observers can effectively perceive variations in depth from patterns of motion parallax, but their ability to discriminate 3-D shape is significantly compromised. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Disruption of the Saccharomyces cerevisiae YAP3 gene reduces the proteolytic degradation of secreted recombinant human albumin

In real-life situations, such as during locomotion, or while driving a vehicle, it is necessary to maintain visual fixation and tracking in the presence of the visual flow of the surroundings, which represents a potentially adequate stimulus for the elicitation of optokinetic nystagmus. The present study is concerned with the influence of vestibular disorders, whether pathological or experimentally induced, on those cortically controlled fixation mechanisms, predominantly in the smooth pursuit system, which are involved in suppressing optokinetic information. The study examines the possibility of obtaining an objective measure to assist in counselling patients with unilateral vestibular loss on their vehicle driving ability. To this end, the influence of optokinetic and vestibular stimulation on the execution of smooth pursuit target tracking was measured by recording eye movements during a combination of standard pursuit tasks (0.25, 0.5 and 1 Hz sinusoidal) against standard optokinetic striped backgrounds (0, 30 and 60 degrees/sec). The influence of vestibular imbalance, induced in healthy subjects (n = 35) by unilateral caloric irrigation, and caused by unilateral vestibular loss (in five patients), was also examined under these conditions. During induced vestibular imbalance in normal subjects, and to a greater extent in the tested patients, significant deficits in smooth pursuit gain and increases in saccade frequency were observed during target pursuit against an optokinetic background. Moreover, the findings indicate that the most sensitive parameter for the influence of vestibular optokinetic stimuli on smooth pursuit is frequency of saccades, rather than the gain factor. The tests described here are appropriate for clinical and medico-legal assessment of the influence of vestibular disorder on vehicle driving.     

Distractor interference during smooth pursuit eye movements.

When 2 targets for pursuit eye movements move in different directions, the eye velocity follows the vector average (S. G. Lisberger & V. P. Ferrera, 1997). The present study investigates the mechanisms of target selection when observers are instructed to follow a predefined horizontal target and to ignore a moving distractor stimulus. Results show that at 140 ms after distractor onset, horizontal eye velocity is decreased by about 25%. Vertical eye velocity increases or decreases by 1°/s in the direction opposite from the distractor. This deviation varies in size with distractor direction, velocity, and contrast. The effect was present during the initiation and steady-state tracking phase of pursuit but only when the observer had prior information about target motion. Neither vector averaging nor winner-take-all models could predict the response to a moving to-be-ignored distractor during steady-state tracking of a predefined target. The contributions of perceptual mislocalization and spatial attention to the vertical deviation in pursuit are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pursuit eye movements and the depth-movement phenomenon in dynamic visual noise

The ability to generate voluntary pursuit eye movements in the absence of retinal-contour motion cues was assessed on the basis of observers' perceptions of depth and motion when they viewed dynamic visual noise with a filter over one eye. The results indicated that the depth-movement phenomenon yielded robust pursuit with the velocity an inverse function of filter density. These data suggest that retinal-contour motion cues are not necessary and that perceived motion is sufficient to drive pursuit.     

Directional organization of eye movement and visual signals in the floccular lobe of the monkey cerebellum

The floccular lobe of the monkey is critical for the generation of visually-guided smooth eye movements. The present experiments reveal physiological correlates of the directional organization in the primate floccular lobe by examining the selectivity for direction of eye motion and visual stimulation in the firing of individual Purkinje cells (PCs) and mossy fibers. During tracking of sinusoidal target motion along different axes in the frontoparallel plane, PCs fell into two classes based on the axis that caused the largest modulation of simple-spike firing rate. For "horizontal" PCs, the response was maximal during horizontal eye movements, with increases in firing rate during pursuit toward the side of recording (ipsiversive). For "vertical" PCs, the response was maximal during eye movement along an axis just off pure vertical, with increases in firing rate during pursuit directed downward and slightly contraversive. During pursuit of target motion at constant velocity, PCs again fell into horizontal and vertical classes that matched the results from sinusoidal tracking. In addition, the directional tuning of the sustained "eye velocity" and transient "visual" components of the neural responses obtained during constant velocity tracking were very similar. PCs displayed very broad tuning approximating a cosine tuning curve; the mean half-maximum bandwidth of their tuning curves was 170-180 degrees. Other cerebellar elements, related purely to eye movement and presumed to be mossy fibers, exhibited tuning approximately 40 degrees narrower than PCs and had best directions that clustered around the four cardinal directions. Our data indicate that the motion signals encoded by PCs in the monkey floccular lobe are segregated into channels that are consistent with a coordinate system defined by the vestibular apparatus and eye muscles. The differences between the tuning properties exhibited by PCs compared with mossy fibers indicate that a spatial transformation occurs within the floccular lobe.     

Estimating heading during real and simulated eye movements

The ability to judge heading during tracking eye movements has recently been examined by several investigators. To assess the use of retinal-image and extra-retinal information in this task, the previous work has compared heading judgments with executed as opposed to simulated eye movements. For eye movement velocities greater than 1 deg/sec, observers seem to require the eye-velocity information provided by extra-retinal signals that accompany tracking eye movements. When those signals are not provided, such as with simulated eye movements, observers perceive their self-motion as curvilinear translation rather than the linear translation plus eye rotation being presented. The interpretation of the previous results is complicated, however, by the fact that the simulated eye movement condition may have created a conflict between two possible estimates of the heading: one based on extra-retinal solutions and the other based on retina-image solutions. In four experiments, we minimized this potential conflict by having observers judge heading in the presence of rotations consisting of mixtures of executed and simulated eye movements. The results showed that the heading is estimated more accurately when rotational flow is created by executed eye movements alone. In addition, the magnitude of errors in heading estimates is essentially proportional to the amount of rotational flow created by a simulated eye rotation (independent of the total magnitude of the rotational flow). The fact that error magnitude is proportional to the amount of simulated rotation suggests that the visual system attributes rotational flow unaccompanied by an eye movement to a displacement of the direction of translation in the direction of the simulated eye rotation.     

Local and global representations of velocity: transparency, opponency, and global direction perception

Human subjects can perceive global motion or motions in displays containing diverse local motions, implying representation of velocity at multiple scales. The phenomena of flexible global direction judgments, and especially of motion transparency, also raise the issue of whether the representation of velocity at any one scale is single-valued or multi-valued. A new performance-based measure of transparency confirms that the visual system represents directional information for each component of a transparent display. However, results with the locally paired random-dot display introduced by Qian et al, show that representations of multiple velocities do not coexist at the finest spatial scale of motion analysis. Functionally distinct scales of motion processing may be associated with (i) local motion detectors which show a strong winner-take-all interaction; (ii) spatial integration of local signals to disambiguate velocity; (iii) selection of reliable velocity signals as proposed in the model of Nowlan and Sejnowski; (iv) object-based or surface-based representations that are not necessarily organised in a fixed spatial matrix. These possibilities are discussed in relation to the neurobiological organisation of the visual motion pathway.     

Promoting physical activity in women: the new challenges

The optokinetic nystagmus is a phylogenetically old reflexive reaction of the eyes to the movements of the visual surroundings. Two components can be distinguished: (1) the direct one is considered to represent a cortically transmitted loop through the posterior parietal areas: MT and MST; (2) the indirect component passes through brain stem nuclei. One of them is the pretectal nucleus of the optic tract in which we found neurons related to the velocity of the moving pattern. Since in neurons of the oculomotor nuclei the neuronal activity is related to eye position, integration must take place somewhere in the circuit. The brain stern-mediated indirect component is influenced by the vestibular organs, not only by semicircular canals but also by otoliths.     

Learned stimulation in space and motion perception.

Argues that in the perception of distance, depth, and visual motion, a single property is often represented by 2 or more stimuli. Two instances of such redundant stimulation are discussed: (a) the various stimuli that represent visual motion and (b) the 2 forms of stimulation by which binocular parallax evokes stereoscopic depth perception. In the case of visual motion, simultaneous operation of redundant stimulation has raised questions concerning the basis of experienced motion and the conditions under which different motion processes are combined. Experiments are described that suggest that some redundant stimuli owe their existence to simple associative learning. Evidence is reviewed that shows that binocular parallax causes stereoscopic depth by means of 2 different perceptual processes. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)