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At least 1,531 records · Page 85Linked to original sources
PubMed1998

A rotational stereoscopic 3-dimensional movement aftereffect.

A stereoscopic rotational movement aftereffect (MAE) and a stereoscopic bi-directional MAE were generated by rotation of a cyclopean random dot cylinder in depth and by movement of two cyclopean random dot planes in opposite directions, respectively. Cross-adaptational MAEs were also generated on each other, but not with stimuli lacking any disparity. Cross-adaptation MAEs were generated between stereoscopic and non-stereoscopic random dot stimuli moving in the one X/Y plane. Spontaneous reversals in direction of movement were observed with bistable stimuli lacking disparity. Two models of the middle temporal area were considered which might explain both the stereoscopic MAEs and the spontaneous reversals.

Adaptation, Ocular↗
PubMed1999

Evidence for a mechanism sensitive to the speed of cyclopean form.

We measured Weber fractions for discriminating the speed of cyclopean gratings and Weber fractions for discriminating the speed of luminance gratings. Of our 14 observers, five were unable to see the cyclopean grating sufficiently well to discriminate its speed. One observer experienced great difficulty in discriminating the speed of cyclopean gratings, even though her threshold for detecting cyclopean gratings was low, and even though she discriminated the speed of luminance gratings on the basis of the task-relevent variable. But several observers based their speed discriminations on trial-to-trial variations of the task-relevent variable while ignoring associated trial-to-trial variations in all task-irrelevant variables (specifically: displacement; temporal frequency; spatial frequency; and presentation duration). We conclude that the visual systems of these observers contain a specialized neural mechanism for the speed of cyclopean gratings that supports acute discriminations of speed (Weber fractions were as low as 0.05-0.07).

Differential Threshold↗
PubMed2006

The role of familiarity in the recognition of static and dynamic objects.

Although the perception of our world is experienced as effortless, the processes that underlie object recognition in the brain are often difficult to determine. In this chapter, we review the effects of familiarity on the recognition of moving or static objects. In particular, we concentrate on exemplar-level stimuli such as walking humans, unfamiliar objects and faces. We found that the perception of these objects can be affected by their familiarity; for example the learned view of an object or the learned dynamic pattern can influence object perception. Deviations in the viewpoint from the familiar viewpoint, or changes in the temporal pattern of the objects can result in some reduction of efficiency in the perception of the object. Furthermore, more efficient sex categorization and crossmodal matching were found for familiar than for unfamiliar faces. In sum, we find that our perceptual system is organized around familiar events and that perception is most efficient with these learned events.

Discrimination, Psychological↗
PubMed2006

The effectiveness of disruptive coloration as a concealment strategy.

Our understanding of camouflage has been developing for over 100 years. Several underlying principles have emerged. Background pattern matching, or crypsis, is insufficient to conceal objects because of edge information. Other strategies exist to disrupt the continuity of extended edges. These strategies are reviewed. We pay particular attention to the theory of disruptive coloration, which predicts that high-contrast elements located at the object edge will mask the perception of a target as belonging to a certain category of object, in spite of the fact that the edge elements are independently visible. Although this strategy has long been assumed to be effective, there has been a lack of supportive data involving the perception of targets by nonhuman animals. We present evidence, from a field study, in support of the notion that disruptive coloration reduces the chances of bird predation of artificial "moths."

Adaptation, Biological↗
PubMed1989

Movement and novelty of a square wave display affect 2-deoxyglucose uptake in the rat visual system.

The [14C]2-deoxy-glucose (2-DG) autoradiographic technique revealed that movement and novelty of a visual display affected rat visual system metabolic activity. Hooded rats were monocularly tested in a surround consisting of patterns of black and white, horizontal and vertical, square wave gratings of different spatial frequencies. For one group this display remained immobile ('stationary' group), and for the other group the display intermittently rotated at 1.5 rpm ('moving' group). Each of these main groups was subdivided such that half had six sessions of prior exposure to the test display ('experienced' group) and half had no prior exposure ('novel' group). The movement groups showed relatively greater 2-DG uptake than the stationary groups in the superior colliculus and in the caudal lateral posterior nucleus, while the novel groups showed greater uptake than the experienced groups in visual cortex.

Animals↗
PubMed2001

Time perception: brain time or event time?

Recent experiments show that synchronous events can appear to an observer to occur at different times. Neural processing time delays are offered as an explanation of these temporal illusions, but equating perceived time with processing time leads to some thorny philosophical problems.

Brain↗
PubMed1999

Perception of self-motion from visual flow.

Accurate and efficient control of self-motion is an important requirement for our daily behavior. Visual feedback about self-motion is provided by optic flow. Optic flow can be used to estimate the direction of self-motion ('heading') rapidly and efficiently. Analysis of oculomotor behavior reveals that eye movements usually accompany self-motion. Such eye movements introduce additional retinal image motion so that the flow pattern on the retina usually consists of a combination of self-movement and eye movement components. The question of whether this 'retinal flow' alone allows the brain to estimate heading, or whether an additional 'extraretinal' eye movement signal is needed, has been controversial. This article reviews recent studies that suggest that heading can be estimated visually but extraretinal signals are used to disambiguate problematic situations. The dorsal stream of primate cortex contains motion processing areas that are selective for optic flow and self-motion. Models that link the properties of neurons in these areas to the properties of heading perception suggest possible underlying mechanisms of the visual perception of self-motion.

Journal Article↗
PubMedDate not supplied

Appetitive responses to computer-generated visual stimuli by the praying mantis Sphodromantis lineola (Burr.).

Tethered adult female praying mantises, Sphodromantis lineola (Burr.), were presented with various computer-generated visual stimuli that moved against patterned or homogeneous white backgrounds in predetermined patterns and at predetermined speeds. The degrees to which the stimulus configurations elicited appetitive behaviors (attempting to approach and/or striking) indicated the relative degrees to which the stimuli were classified as prey. Mantises readily struck at cartoon "crickets" that subtended visual angles as great as 24.5 deg x 62.5 deg, but response rate was suppressed if the stimuli were superimposed on horizontally moving patterned backgrounds. Mantises also displayed appetitive behaviors to moving black squares (edge lengths = 10-47 deg) that moved in predetermined "erratic" paths; however, their response rates were affected by several factors: (1) response rate declined as edge length increased over 10 deg; (2) striking was emitted to stimuli viewed from 23 mm (but not farther) away; and (3) both stimulus displacement rate (distance moved between video frames) and apparent speed (video frame rate) dramatically affected the releasing strength of the stimuli. Finally, mantises responded appetitively to random dot patterns moving synchronously against identically patterned backgrounds and to pairs of black squares moving synchronously against a white background. However, in the latter case, response rate declined as the squares were moved farther apart horizontally or vertically. These and previous results from our laboratory on mantises are congruent with behavioral results obtained from other insects such as flies (Diptera) and dragon flies (Odonata) and suggest that there are neuroanatomical similarities between these groups.

Animals↗
PubMed1987

Sensory and cognitive factors in the processing of visual velocity.

A symmetrical 6 x 6 factorial design of distances and durations served to produce either 36 different moving stimuli (real movement condition) or 36 static displays separately containing the respective stimulus components (cognitive movement condition). Different metric rules underlay the two types of velocity judgments: Perceptual estimations of real movement obeyed a ratio model, whereas conscious estimations of implied movement obeyed an additive model. Valuation operations differed, too; the scales underlying real velocity were nonlinearly related to the even more compressive scales that underlay cognitive velocity. Implications of these results for velocity research are discussed.

Adult↗
PubMed1989

Perception of three-dimensional structure from optic flow without locally smooth velocity.

A common assumption in several analyses of optic flow is that the velocity field must be locally smooth in order to recover relative depth and the structure of surfaces in the environment. This study investigated the appropriateness of this constraint to human perception. In the first experiment, subjects were asked to identify the number of planes present in a display simulating one, two, three, four, or five overlapping, transparent planes. Subjects were able to detect the presence of up to three planes accurately for both horizontal and depth translations. In the second experiment, subjects' judgments of the depth separation of two transparent, overlapping planes increased with the simulated separation. In Experiment 3, subjects were able to determine accurately the sign of depth for two overlapping, transparent surfaces. These results suggest that a smoothness constraint is not required for the analysis of optic flow by human observers. Alternative approaches to the analysis of optic flow are discussed.

Acceleration↗
PubMed1993

Optical information about the severity of upcoming contacts.

The time derivative (tau) of the inverse of the relative rate of optical expansion (tau) may have critical values with potential implications for controlling activity. The present research addresses the particular hypothesis that tau < -0.5 specifies "unsafe" collision courses and tau > or = -0.5 specifies "safe" collision courses. Optical expansion patterns were simulated on a computer with -1.0 < or = tau < 0 and judged as suggesting a "hard" or "soft" collision. tau < -0.5 led to significantly different decisions from tau > or = -0.5, but the critical value of -0.5 was not perceived reliably as soft, a deviation possibly due to discretely approximating continuous functions. Additional experiments evaluated terminal rates of change and display duration and examined the effects of biasing the presented displays toward the soft or the hard end of the tau continuum. The results were consistent with the tau hypothesis.

Acceleration↗
PubMed1993

Things that go bump in the light: on the optical specification of contact severity.

Psychologists are intrigued with the idea that optical variables can specify not only the time until an object impacts an observer but also the severity of the impact. However, the mapping between the optical variables (tau and .tau) and the kinematic variables (velocity, acceleration) has been misstated, erroneously implying that there exist critical values of the optical variables used for locomotion and control. In this commentary, the mathematical relationship between the optical and kinematic variables is reexamined and the erroneous assumptions that have led to the proposal of critical values are show. Also examined are the empirical data on deceleration to approach (particularly from active control paradigms) to assess whether the proposed optical variables are likely candidates for control strategies. Finally, problems associated with numerical approximations to dynamic systems, particularly when analytic solutions exist, are discussed.

Acceleration↗
PubMed1995

Discrimination of coherent motion when local motion varies in speed and direction.

Random-dot cinematograms (RDCs) consist of multiple local motion signals that can vary in direction and speed. These local motion signals can result in coherent motion: the percept of an overall direction and speed of motion in an RDC. Thresholds were obtained for discriminating differences in the strength of coherent motion. Observers were found to easily discriminate the strength of coherent motion on the basis of the elements' direction or speed under optimal conditions. However, a nonreciprocal relation was evident when this discrimination was performed under nonoptimal conditions. Discrimination of coherent motion that was based on the elements' direction was unaffected, but discrimination that was based on speed was impaired. Results indicate that humans are sensitive to small differences in coherent motion strength and suggest that the visual system processes direction and speed information nonreciprocally.

Humans↗
PubMed1977

Impact of oculomotor retraining on the visual perception of curvature.

Observers viewed a computer-generated display consisting of horizontally oriented, concave-up curved lines. The position of these curves was contingent on the horizontal position of the eye so that, in order to change fixation errorlessly, from one point to another on the curve, the eye would have to execute a purely horizontal movement. In Condition H this was achieved by moving the curves horizontally, so that the minimum point was always at the horizontal eye position location, thus simulating the effect of viewing a line through a wedge prism on a contact lens. In Condition V it was achieved by moving the curves vertically so that the point fixated always had the same vertical location. In both conditions eye movements were reprogrammed rapidly to eliminate the vertical components of the saccades that were present at the start. While a small, but significant, amount of perceptual adaptation was obtained in Condition H, none at all was obtained in Condition V. The results are interpreted as not in support of such theories of perceptual adaptation to curvature distortion as require a close relationship between motor learning and perceptual change.

Adaptation, Ocular↗
PubMed2004

Temporal ventriloquism: sound modulates the flash-lag effect.

A sound presented in close temporal proximity to a visual stimulus can alter the perceived temporal dimensions of the visual stimulus (temporal ventriloquism). In this article, the authors demonstrate temporal ventriloquism in the flash-lag effect (FLE), a visual illusion in which a flash appears to lag relative to a moving object. In Experiment 1, the magnitude and the variability of the FLE were reduced, relative to a silent condition, when a noise burst was synchronized with the flash. In Experiment 2, the sound was presented before, at, or after the flash (+/- approximately 100 ms), and the size of the FLE varied linearly with the delay of the sound. These findings demonstrate that an isolated sound can sharpen the temporal boundaries of a flash and attract its temporal occurrence.

Auditory Perception↗