Biomedical subjects

E R Wist

Publications and source records attributed to E R Wist.

At least 19 recordsLinked to original sources

PubMed2000

The scintillating grid illusion during smooth pursuit, stimulus motion, and brief exposure in humans.

The Scintillating Grid Illusion occurs when small white disks are superimposed onto the intersections of a grey-on-black Hermann grid. As a result illusory dark spots are seen at numerous crossings, flashing with each flick of the eye and changing their location and distribution with each saccade. The illusion is absent with steady fixation. The present study shows that saccadic eye movements are not necessary to produce the illusion. Rather, the illusion was also found to occur (i) during smooth pursuit movements when the grid was stationary, (ii) during smooth displacement of the grid with the gaze kept steady, and (iii) during brief exposures of the stationary grid. It is concluded that, while transient stimulation is essential for generating the illusion, reduction in effective luminance contrast resulting from brief exposure and high stimulus speed are responsible for reductions in its strength.

Adult↗

PubMed2000

Dynamic vision based on motion-contrast: changes with age in adults.

Data are presented for a computerized test of dynamic vision in a sample of 1006 healthy subjects aged between 20 and 85 years. The test employed a form-from-motion stimulus: i.e., within a random-dot display, Landolt rings of the same average luminance as their surroundings become visible only when the dots within the ring are moved briefly, while those of the surround remain stationary. Thus, detection of gap location is based upon motion contrast (form-from-motion) rather than luminance contrast. With the size and exposure duration of the centrally presented ring held constant, motion contrast was manipulated by varying the percentage (between 20 and 100%) of moving dots within the ring. Subjects reported gap location (left, right, top, bottom). A gradual decline of dynamic vision with age was found for all motion-contrast levels. Beyond 70 years of age, chance-level performance occurred in almost half of the subjects. The data provide the basis for applications including diagnostic screening for glaucoma, visual disturbances in brain-damaged patients, as well as assessment of the dynamic vision of drivers of motor vehicles and athletes.

Adult↗

PubMed1999

Characteristics of visual evoked potentials generated by motion coherence onset.

Prior studies have shown that an electrophysiological correlate of visual motion processing can be found in the N2, a transient negativity occurring at about 200 ms in the visual evoked potential (VEP). In most of the studies, N2 was triggered by the onset of a coherent motion. Results of our first experiment revealed that topography of the negative potential can be modified by motion direction information. In contrast to the onset of uncorrelated motion of pixels in a random dot kinematogram (RDK) correlated motion leads to an right hemispheric amplitude advantage. Hemispheric differences can be increased when the negativity is triggered by the onset of a coherent motion direction preceded by uncorrelated motion in RDKs. In a second experiment, we examined whether the negativity elicited by direction is related to the strength of the impression of motion direction measured psychophysically. The latter was modified by varying the percentage of correlated moving pixels in the RDK. Increasing the proportion of these 'direction signals' was associated with both an increase in the strength of the impression of motion direction and an increase in VEP amplitude. Mean correlations of electrophysiological and psychophysical data, which exceeded 0.7, revealed a higher sensitivity of the right hemisphere. The close relationship between the global motion impression and VEP negativity indicate that electrophysiological correlates of processing stages within visual motion analysis can be isolated. The recorded negativity seems to be associated primarily with the process of global motion integration.

Adult↗

PubMed1999

Development of dynamic vision based on motion contrast.

The development of dynamic vision was investigated in 400 healthy subjects (200 females and 200 males) aged between 4 and 24 years. The test consisted of a computer-generated random-dot kinematogram in which a Landolt ring was briefly presented as a form-from-motion stimulus. Motion contrast between the ring and background was varied in terms of the percentage of dots moving coherently within the ring in four levels (100%, 50%, 30%, and 20%). The subject's task was to indicate the position of a gap in the ring (left, right, top, bottom). Results show a clear increase in performance with age for all motion contrast levels, with the greatest changes for the lowest levels. Adult performance was reached at the age of 15 years. Luminance-based static acuity measured with the Landolt test was poorly correlated with acuity for its form-from-motion analogue.

Adolescent↗

PubMed1998

Motion evoked brain potentials parallel the consistency of coherent motion perception in humans.

The perception of global coherent motion perception in complex motion patterns containing different direction vectors was investigated. Random dot kinematograms (RDK), plaids and fragmented plaid pattern were presented in which direction vectors of the moving elements were varied. In order to elicit coherent motion perception, all elements were displaced in the same direction (delta0 degrees). In a second condition, fifty percent of the elements were moved diagonally downwards to the left, with the remaining elements moving orthogonally (delta 90 degrees). Simultaneously with psychophysical judgements on the perceived motion direction, visual evoked potentials (VEPs) were recorded at occipital electrode positions. Onset of a global coherent motion was associated with a VEP negativity occurring at about 200 ms. The amplitude of this component was clearly reduced when local ambiguous signals could not be integrated to produce the perception of global coherent motion.

Adult↗

PubMed1998

A computer-assisted test for the electrophysiological and psychophysical measurement of dynamic visual function based on motion contrast.

A new test is described that allows for electrophysiological and psychophysical measurement of visual function based on motion contrast. In a computer-generated random-dot display, completely camouflaged Landolt rings become visible only when dots within the target area are moved briefly while those of the background remain stationary. Thus, detection of contours and the location of the gap in the ring rely on motion contrast (form-from-motion) instead of luminance contrast. A standard version of this test has been used to assess visual performance in relation to age, in screening professional groups (truck drivers) and in clinical groups (glaucoma patients). Aside from this standard version, the computer program easily allows for various modifications. These include the option of a synchronizing trigger signal to allow for recording of time-locked motion-onset visual-evoked responses, the reversal of target and background motion, and the displacement of random-dot targets across stationary backgrounds. In all instances, task difficulty is manipulated by changing the percentage of moving dots within the target (or background). The present test offers a short, convenient method to probe dynamic visual functions relying on surprathreshold motion-contrast stimuli and complements other routine tests of form, contrast, depth, and color vision.

Adolescent↗

PubMed1997

The scintillating grid illusion.

Disk-shaped luminance increments were added to the intersections of a Hermann grid consisting of medium grey bars on a black background. Illusory spots, darker than the background, were perceived as flashing within the white disks with each flick of the eye. This striking phenomenon may be referred to as the scintillating grid illusion. We determined the conditions necessary for cancelling the Hermann grid illusion, as well as the luminance requirements and the size ratio between disks and bars that elicits the scintillation effect. The fact that scanning eye movements are necessary to produce the scintillation effect sets it apart from the Hermann grid illusion.

Eye Movements↗

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↗

PubMed1996

Position and velocity responses from the otoliths and the canals: results from ESA's parabolic flights.

BACKGROUND: Transient (i.e., phasic) bell-shaped vestibularly evoked potentials (VESTEP's) were recorded from the human scalp during whole body rotation about the vertical z-axis using a multi-axis rotary chair (yaw-motion). For pitch-motions about the interaural y-axis, however, a sustained (i.e., tonic) VESTEP was recorded, presumably because of the additional otolithic stimulation. HYPOTHESIS: During microgravity, only phasic VESTEP's were recorded because pitch-motions stimulate only the vertical semicircular canals without otolithic contamination. METHODS: The motion profile applied simulated the form of a natural smooth head movement ("raised cosine"). It was designed to minimize all possible sources of mechanical, electrical, and physiological artifacts. With this motion profile, seated subjects were tilted 90 degrees nose-down or 90 degrees nose-up about their interaural y-axis ("pitch") thus stimulating the vertical semicircular canals and the otoliths. In addition, the raised cosine velocity profile was applied during the microgravity phases of a total of 90 parabolic flight maneuvers, thus stimulating the vertical canals without additional otolithic stimulation. RESULTS: A transient (phasic) bell-shaped VESTEP was found in the Earth-bound laboratory for backward-tilts corresponding to the velocity profile used. For nose-down tilts, however, a sustained (tonic) negativity was found which matched the applied position profile. In microgravity, only the transient bell-shaped responses could be recorded irrespective of tilt direction. CONCLUSION: These results are interpreted in terms of both a position response generated by pitch-down and a velocity response caused by pitch-up motions. This differentiation might prove to be a useful electrophysiological tool in oto-neurological diagnosis to distinguish between otolithic and canal disorders.

Adult↗

PubMed1995

Processing of visual motion direction in the fronto-parallel plane in the stationary or moving observer.

To examine the effect of concurrent self-motion on the perception of the direction of object-motion, random-dot kinematograms were employed in which the strength of the directional signal was manipulated by varying the percentage of coherently moving pixels. The subject's task was to indicate the motion direction of briefly presented displays while undergoing whole body rotations with angular accelerations of 0, 5, 15, or 45 degrees/s2. The perception of the direction of visual motion in the horizontal plane was impaired only when visual and vestibular motion directions were incongruous. The impairment increases with both increasing angular acceleration and decreasing percentage of coherently moving pixels. For object-motion in the vertical plane, an impairment was found for both congruous and incongruous combination of visual and vestibular stimulation, although not as pronounced for the latter (i.e., visual upward, vestibular downward stimulation, and vice versa). These results are discussed in terms of postnatal development and neurophysiological optimization processes resulting from intersensory 'updating' through every-day experience of object-motion during self-motion.

Acceleration↗

PubMed1994

Motion aftereffects with random-dot chequerboard kinematograms: relation between psychophysical and VEP measures.

A random-dot chequerboard kinematogram was used to investigate the effect of motion adaptation both on evoked potentials and on motion aftereffects (MAEs). The experimental paradigm used allowed simultaneous measurement of both variables. Each adaptation period was followed by a series of 5 short test stimuli to which evoked potentials were recorded. Motion aftereffects were observed in the intervals between test stimuli. An inverse relationship between mean N2-P1 amplitude and mean reported MAEs was found as a function of adaptation durations of 1.4, 5.6, and 17.5 s. When the shortest and longest adaptation durations were compared, this relationship held for thirteen of fourteen subjects tested when adaptation-motion and test-motion directions corresponded and for twelve of fourteen subjects when they were opposed. The possibility that the effect of motion adaptation on N2-P1 amplitude was due to local luminance-contrast adaptation is discussed and shown to be unlikely. The suitability of this paradigm for the combined psychophysical and electrophysiological assessment of disturbances in motion perception is discussed.

Adolescent↗

PubMed1993

Identification of the visual motion area (area V5) in the human brain by dipole source analysis.

The retinal periphery of nine healthy subjects was stimulated with computer-generated random-dot kinematograms. These stimuli provided almost isolated visual motion information and minimal position cues. Pattern-reversal stimuli at the same location in the visual field were used for control. Stimulus-related electrical brain activity was recorded from 29 scalp electrodes. Total mean and individual data were analyzed with a spatiotemporal multiple dipole model. The scalp potentials showed a different spatial distribution for motion and pattern stimulation in the time range of 160-200 ms. In this epoch, the predominant motion-related source activity was localized in the region of the contralateral occipital-temporal-parietal border. A significant ipsilateral source activity was not found. The predominant source activity related to the pattern stimulus occurred in the same epoch. The corresponding equivalent dipole was localized more medially and deeper in the brain. The orientation of these major dipole activities was markedly different. These dipoles appeared to represent activity of distinct extrastriate areas, in contrast to earlier activity which was modelled by more posterior dipoles in the occipital lobe. The latter dipoles were at comparable contralateral locations and had similar peak activities around 100 ms, suggesting an origin in the striate cortex.

Adult↗

PubMed1993

MARDER--multi-axes rotation device for experimental research. A new concept for investigations of the vestibular, oculomotor, and visual systems of humans in three-dimensional space.

A hydraulically driven, digitally servo-controlled multi-axes rotary chair is described. This device generates motion profiles with the subjects head in the center of rotation mainly in order to adequately stimulate the semicircular canals which are sensitive sensors for angular accelerations. This newly developed apparatus allows for motion stimuli which are below the vestibular threshold up to accelerations of 12 rad/s2 (688 degrees/s2) and is thus suitable for a variety of experiments in the field of vestibular, oculomotor, and intersensory research in 3-dimensional space.

Acceleration↗

PubMed1990

Impairment of auditory processing by simultaneous vestibular stimulation: psychophysical and electrophysiological data.

The aim of the experiments reported here was to demonstrate auditory-vestibular interaction both on a psychophysical and on an electrophysiological basis in humans. These results correspond to those recently obtained during simultaneous visual and vestibular stimulation and illustrate experimentally the importance of auditory information processing in spatial orientation. Time to detect the motion of a sound source is significantly increased when simultaneous vestibular stimulation is induced by passive sinusoidal head oscillations. This effect increased with the peak acceleration of the vestibular stimulus (197, 790 and 1777 degrees/s2). Vestibular influence on general auditory information processing without the quality of (object-) motion could be electrophysiologically demonstrated by means of brainstem auditory evoked potentials. The amplitude of component V generated by the inferior colliculi or by neuronal structures located slightly lower in the auditory tract was significantly reduced during concurrent vestibular stimulation. This neuronal brainstem area is a predominant location of biconvergent vestibulo-auditory neurons mediating intersensory information processing at an early neuronal level.

Adolescent↗

PubMed1990

Electrophysiological evidence for visual-vestibular interaction in man.

The aim of the experiments reported here was to confirm electrophysiologically the results of psychophysical experiments, which demonstrated that thresholds for object-motion detection are significantly raised during both concurrent active or passive sinusoidal head oscillations and during visually induced self-motion perception (circularvection, CV). This intersensory inhibition could now be demonstrated electrophysiologically by recording visual motion evoked potentials both during concurrent sinusoidal head oscillations and during visually induced apparent self-motion of the objectively stationary subject. Recordings of visual contrast reversal evoked potentials failed to reveal such an interaction. Perceptual phenomena with multisensory stimulation are well described in the literature. Berthoz et al. demonstrated the dominant influence of the visual channel on vestibular thresholds such that the detection of a suprathreshold vestibular stimulation was clearly impaired by a simultaneously moving visual pattern inducing linearvection and vice versa. Comparable results are reported for circularvection. Evidence for inhibitory interaction between object-motion and simultaneous self-motion perception also exists. Electrophysiological data on intersensory interaction in humans have only been reported between electrical stimulation of a limb and its concurrent movement by means of scalp-recorded somatosensory-evoked potentials (SSEPs) (e.g. refs. 3, 5). Electrophysiological evidence for the interaction of visual object-motion and vestibular self-motion perception in humans has never been reported in the literature thus far, though Hood and Kayan demonstrated that retinal image motion makes a contribution to the vestibularly evoked bioelectric response.

Adult↗

PubMed1984

Interaction between perceived self-motion and object-motion impairs vehicle guidance.

When one is riding in a vehicle, perceptual thresholds for motion of objects are significantly elevated above those determined under corresponding but simulated conditions in the laboratory without concurrent self-motion perception. Authorities on road traffic accidents should thus consider an additional perceptual time of at least 300 milliseconds for detecting critical changes in headway beyond the usual reaction time. Detection times thus corrected consequently lead to an alteration of our conception of safe intervehicle distances in a convoy. This elevation of thresholds for object-motion during self-motion, with its consequences for visual control of vehicle guidance, can be seen as a disadvantageous side effect of an otherwise beneficial space-constancy mechanism, which provides us with a stable world during locomotion.

Automobile Driving↗

PubMed1983

Oscillopsia and retinal slip. Evidence supporting a clinical test.

A clinical bedside test for oscillopsia is described for patients suffering from an acute deficiency of compensatory eye movements due either to inappropriate pursuit eye movements or a defective vestibulo-ocular reflex (VOR). This test involves quantitative measurement of the amplitude of apparent image motion (oscillopsia) during head oscillations with frequencies of 1 or 2 Hz, +/- 20 deg amplitude. It was found that normals show no oscillopsia at 1 Hz whereas patients with acute disorders do. In subacute diseases of eye-head co-ordination, however, recordings of head and eye movements revealed a dissociation between net retinal slip and oscillopsia, with the magnitude of the latter being appreciably smaller than the former. This was interpreted as indicating a central suppression mechanism initiated by the acute eye movement deficiency. The results are discussed in terms of an inhibitory interaction between self and object motion perception which produces elevated thresholds for the detection of image motion.

Adult↗