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PubMed1995

Night driving: effects of glare from vehicle headlights on motion perception.

Elderly drivers often experience disability glare at night from the headlights of oncoming vehicles. To assess the effect of glare from vehicle headlights on visual performance for seeing moving targets, experiments were performed at night on a dimly lit road with observers seated in a stationary motor car viewing a computer-generated stimulus display at a distance of 23 m (the stopping distance for 50 kph). The display was set 2 m to the side of a second stationary car whose position on the road was that of an oncoming vehicle with respect to the observer. The headlights of the observer's car were on low-beam while those of those of the opposing car were switched off (contro condition), on lpw-beam or on high-beam. Experiments were performed using mean display luminances of 50 cd/m2 and 0.5 cd/m2. Spatial contrast sensitivity functions for the directional discrimination of drifting (8 Hz sinusoidal gratings were measured using three different viewing conditions: normal vision (binocular visual acuity (BVA) = 6/6); blurred vision (BVA = 6/9-); and simulated intraocular lens opacities (BVA = 6/6-). The data were fitted with an exponential function, which was extrapolated to 100% contrast to estimate dynamic visual acuity. The results show that simulated lens opacities, which have little or no effect on standard day time measures of visual acuity, have a marked effect on night-time measures of contrast sensitivity for moving targets. Taking into account the average luminance of objects lit by road lighting, we estimate that high-beam glare reduces maximum contrast sensitivity by an order of magnitude in persons affected by mild lens opacities, giving a dynamic acuity of 1.0 c/deg (6/180 Snellen equivalent) or less. From this and other studies we argue that there is now a strong case for the introduction of vehicle-licensing sight re-testing at regular intervals in the UK. In addition, we suggest that vehicle-licensing authorities consider the feasibility of introducing sight tests under night-time driving conditions.

Adult↗
PubMed1969

Fundamental properties of intensity, form, and motion perception in the visual nervous systems of Calliphora phaenicia and Musca domestica.

Several classes of interneurons in the optic lobes and brain of the insects, Musca domestica and Calliphora phaenicia, have been studied in detail. Visual stimuli have been categorized on the basis of the properties of intensity, form, and motion. Response characteristics of the classes of neural units are described with respect to these three classes of visual stimuli. While those units that detect motion in select directions have a tonic response, form detection units have a phasic response only. Through correlation of the responses of these classes with visual stimuli, it is shown that these units integrate the responses of other units which have very small visual fields. The small-field units are presumed to integrate the output of a small group of adjacent retinula cells and to respond differentially to intensity, form, and motion. It is shown that the response of both form and motion detection units is independent of the direction of pattern intensity gradation. As a consequence of this independence, it is further shown that failure to detect motion properly must start at a spatial wavelength four times the effective sampling station spacing rather than twice as has been predicted previously.

Animals↗
PubMed2000

Changes in motion perception following oculomotor smooth pursuit adaptation.

The hypothesis that oculomotor smooth pursuit (SP) adaptation is accompanied by alterations in velocity perception was tested by assessing coherence thresholds, using random-dot kinematograms before and after the adaptation paradigm. The results showed that the sensitivity to coherent motion at 10 deg/sec (the initial target velocity during adaptation) was reduced after the SP adaptation, ending up at a level that was between those normally observed for velocities of 10 and 20 deg/sec. This is consistent with an overestimation of the velocity of the coherent motion and suggests that SP adaptation alters not only the oculomotor output, but also the perception of target velocity.

Acceleration↗
PubMed2002

Three-systems theory of human visual motion perception: review and update: comment.

This comment addresses two issues raised by Lu and Sperling [J. Opt. Soc. Am. A 18, 2331 (2001)]. These authors stated that stereomotion (movement of binocular disparity) is processed exclusively by a third-order motion system that involves feature tracking. This comment discusses evidence that clearly shows that stereomotion is processed by a low-level mechanism that does not track features. Lu and Sperling also claimed that motion signals from binocular rivalry have confounded many stereomotion experiments in the past. This comment discusses how stimuli employed in most previous studies of stereomotion processing would not produce rivalry.

Depth Perception↗
PubMed1986

Illusory continuous motion from oscillating positive-negative patterns: implications for motion perception.

A black and white (positive) grating pattern was superimposed in exact register on its own photographic negative. Four operations were repetitively applied to this positive pattern so that it moved fractionally to the right, grew dimmer, moved back to the left, and grew brighter again. This sequence produced a strong illusion of continuous apparent motion to the right for as long as the cycle was repeated. The small relative motion between the two patterns generated two new illusory effects: enhanced real movement (ERM) and reversed real movement (RRM). The dimming and brightening phases gave rise to reversed apparent movement (RAM). All three effects are attributed to spatial filtering by neural mechanisms, which shifts the effective position of the positive-negative contours.

Color Perception↗
PubMed2005

Self-motion perception from expanding and contracting optical flows overlapped with binocular disparity.

Expanding and contracting patterns were presented on different disparity planes to investigate the role of stereo depth in vection. Experiment 1 tested the effect of stereo depth on inducing vection with expanding and contracting flows on different disparity planes. Subjects reported whether they felt forward or backward self-motion. The results clearly showed the dominance of the background flow in determining one's self-motion direction. Experiment 2 tested the effect of stereo depth on a vection direction using two expanding flows. The center of each expansion was displaced to either horizontal side. The subjects judged in which direction they were going when they felt vection. The results demonstrated that the subjects felt their heading biased toward the direction of the center of the farther expansion while feeling vection. The heading perception from the expanding flow was determined only by the background flow, not by 2-D integration of the retinal motion. The result demonstrates the importance of background flow produced by stereo depth in determining one's self-motion from an expanding/contracting motion.

Depth Perception↗
PubMed2003

Interaction of retinal image and eye velocity in motion perception.

When we move our eyes, why does the world look stable even as its image flows across our retinas, and why do afterimages, which are stationary on the retinas, appear to move? Current theories say this is because we perceive motion by summation: if an object slips across the retina at r degrees/s while the eye turns at e degrees/s, the object's perceived velocity in space should be r + e. We show that activity in MT+, the visual-motion complex in human cortex, does reflect a mix of r and e rather than r alone. But we show also that, for optimal perception, r and e should not summate; rather, the signals coding e interact multiplicatively with the spatial gradient of illumination.

Confidence Intervals↗
PubMed1997

Modulating irrelevant motion perception by varying attentional load in an unrelated task.

Lavie's theory of attention proposes that the processing load in a relevant task determines the extent to which irrelevant distractors are processed. This theory was tested by asking participants in a study to perform linguistic tasks of low or high load while ignoring irrelevant visual motion in the periphery of the display. Although task and distractor were unrelated, both functional imaging of motion-related activity in cortical area V5 and psychophysical measures of the motion aftereffect showed reduced motion processing during high load in the linguistic task. These findings fulfill the prediction that perception of irrelevant distractors depends on the relevant processing load.

Adult↗
PubMed2005

Attention-driven discrete sampling of motion perception.

In movies or on TV, a wheel can seem to rotate backwards, due to the temporal subsampling inherent in the recording process (the wagon wheel illusion). Surprisingly, this effect has also been reported under continuous light, suggesting that our visual system, too, might sample motion in discrete "snapshots." Recently, these results and their interpretation have been challenged. Here, we investigate the continuous wagon wheel illusion as a form of bistable percept. We observe a strong temporal frequency dependence: the illusion is maximal at alternation rates around 10 Hz but shows no spatial frequency dependence. We introduce an objective method, based on unbalanced counterphase gratings, for measuring this phenomenon and demonstrate that the effect critically depends on attention: the continuous wagon wheel illusion was almost abolished in the absence of focused attention. A motion-energy model, coupled with attention-dependent temporal subsampling of the perceptual stream at rates between 10 and 20 Hz, can quantitatively account for the observed data.

Attention↗
PubMedDate not supplied

Motion perception of head or trunk modulates cervico-ocular reflex (COR).

In 15 sitting volunteers with eyes covered the vestibulo- and cervico-ocular reflexes were tested with sinusoidal movements around the vertical axis of the body, at frequencies of 0.05, 0.1 and 0.2 s-1 and a total amplitude of 40 degrees. When the trunk was moved against the fixed head, the subjects described mainly an illusionary head movement at 0.05 s-1, while, at 0.2 s-1 only the trunk movement was perceived. Subjects asked to imagine head motion during COR showed increased eye shifts and total saccadic amplitudes. With concentration on trunk movement perception these values decreased.

Adult↗
PubMed1991

Orientation perception, motion sickness and vertigo: beyond the sensory conflict approach.

Current theoretical issues central to the understanding of pathological disorientation (vertigo) are addressed through a critical review of research into perceptual disorientation in healthy subjects (motion sickness). Investigations inspired by the 'sensory conflict' model of orientation perception typically paid insufficient attention to higher-order meaningful properties of the environment, purposive activity, and individual differences in sensorimotor experience and skill. These factors are incorporated into an alternative 'active perception' approach, which characterizes perception of orientation as arising from interactions between intra-individual variables and the perceptual properties and sensorimotor demands of the environments encountered. It follows that vertigo is a form of disability which can only be properly assessed in the broader context of a range of relevant attributes of the patient, and his or her activities and environment. Analysis of the principles governing responses to disorienting conditions identifies several factors relevant to the assessment and rehabilitation of vertiginous patients.

Female↗
PubMed1980

Analogue models of motion perception.

An object moving in discrete spatial jumps is difficult to distinguish from a continuously moving object, provided the time between jumps is not too great. The extent of this perceived continuity may be measured by probing the perceived spatial location at times between the target jumps, by either a vernier alignment or a stereoscopic technique. As the time between jumps increase the accuracy of spatial interpolation falls, until finally the object is seen only at its actual spatial locations. These results can be analysed in the frequency domain by treating the signal for apparent motion as the analogue of a periodic waveform containing relatively low frequencies (the continuous motion) and higher frequencies giving rise to the discreteness of the motion. If such an input has the higher frequencies progressively removed by physical filtering, it is perceived ads increasingly continuous. The fact that such filtering is not necessary for perceived continuity when the discrete jumps occur at rates greater than about 30 Hz suggests that frequencies greaster than that limit are removed by the visual system itself.

Cognition↗
PubMed1992

[Ambulatory autonomy and visual motion perception in a case of almost total cortical blindness].

A 37-year-old man experienced cortical blindness following a bilateral stroke in the territory of the posterior cerebral arteries. Four years later, the measurement of visual field defects (Goldmann perimeter) showed persistence of bilateral blindness with a 2-degree preservation of macular vision and a perifoveal sparing between 10 to 30 degrees of eccentricity in the left inferior quadrant. Despite this visual impairment, the subject was able to perform visually-guided locomotion. Moreover he consciously perceived visual motion in the blind parts of his visual field. CT and MRI showed a lesion involving most of the striated cortex. The visual cortex located in the internal occipito-parital regions was relatively spared. The contribution of this structure to extra-striated vision of motion is discussed.

Adult↗
PubMed1978

Subjective Lorentz transformations and the perception of motion.

It has been known for some 40 years that the perceived velocity of a moving object does not correspond to its physical velocity. It is also known that the perceived length and temporal duration of a moving objects is affected by its physical velocity. In this paper it is argued that such phenomenal distortions can be embedded in a model for motion perception that involves the concepts of moving frames, Lorentz transformations, perceived length contractions, and time dilations. Experimental results support this model and indicate that c, the maximum perceivable velocity of movement, plays a crucial role in determining motion effects.

Humans↗
PubMed1998

Cognitive evoked potentials related to visual perception of motion in human subjects.

A method was tested for simultaneous recordings of evoked potentials from the secondary visual cortex (mediotemporal) and from the brain cognitive areas (fronto-central). Visual moving stimulations with cognitive tasks seem to be suitable for combined examination of visual motion perception and cognitive processes based on the magnocellular system activity. This arrangement enhances the analysis of visual information processing and evaluation of central nervous system functions.

Adult↗
PubMed1997

The effect of moderately increased CO2 concentration on perception of coherent motion.

BACKGROUND: Several studies have shown that some aspects of vision are impaired when exposed to higher than normal CO2 concentrations in air. The effect of moderately increased CO2 concentration on coherent motion perception, however, has not been studied. HYPOTHESIS: Studies in neurophysiology and cell biology have provided evidence that higher than normal CO2 concentration in air affects cell activities from the retina to the cortex, including the V1 area in the visual cortex. We predicted that motion perception may be impaired by moderately increased CO2, since the V1 area is a gateway for visual motion information processing. The purpose of the present work was to investigate the effect of 2.5% CO2 concentration in air on coherent motion perception. METHODS: Random dot cinematograms were generated by a computer and served as visual stimuli. A whole-room indirect calorimeter was used for the accurate measurement and control of CO2 concentration in air, and served as the experimental environment. A two-interval-forced choice (2IFC) psychophysical procedure was employed to obtain psychometric functions. RESULTS: For all three subjects, psychometric functions were shifted to the right when exposed to 2.5% CO2 in breathing air, compared to those using fresh air. CONCLUSION: This finding implies that human ability in detecting coherent motion can be temporally impaired when CO2 concentration in air is raised to 2.5%.

Aerospace Medicine↗