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F H Previc

Publications and source records attributed to F H Previc.

At least 37 records · Page 2Linked to original sources
PubMed1993

Do the organs of the labyrinth differentially influence the sympathetic and parasympathetic systems?

It has long been recognized that the vestibular system plays a major role in autonomic control. The nature of this control remains in dispute, however, as some evidence points to a vestibularly mediated parasympathetic activation, whereas other evidence points to a sympatho-excitatory role for labyrinthine outputs. A theoretical explanation is offered that attempts to resolve this issue by postulating that the utricles exert a predominantly sympatho-excitatory influence via their interactions with brain noradrenergic pathways, while the semicircular canals (and possibly saccules) increase parasympathetic tone via their cholinergic brain stem and cerebellar projections. This explanation is relevant for understanding the vestibular role in orthostatic regulation, motion sickness, oculomotor control, and in many disorders or situations associated with neurochemical or autonomic imbalances.

Animals↗
PubMed1993

The effects of visual depth and eccentricity on manual bias, induced motion, and vection.

The relationship between the effects of visual-surround roll motion on compensatory manual tracking of a central display and the perceptual phenomena of induced motion and vection were investigated. To determine if manual-control biases generated in the direction of surround rotation compensate primarily for the perceived counterrotation of the central display ('induced motion') or the perceived counterrotation of the entire body ('vection'), the depth and eccentricity of the visual surround were varied. In the first experiment, twelve subjects attempted to keep an unstable central display level while viewing rotating visual surrounds in three depth planes: near (approximately 20 cm in front of the central display), coplanar, and far (approximately 21 cm behind the central display). In the second experiment, twelve additional subjects viewed a rotating surround that was presented either in the full visual field (0-110 deg) or in central and peripheral regions of similar width. Manual-control biases and induced motion were shown to be closely related to one another and strongly influenced both by central and by peripheral surround motion at or beyond the plane of fixation. Vection, on the other hand, was shown to be much more dependent on peripheral visual inputs.

Adolescent↗
PubMed1993

Abnormal motoric laterality in strabismus and a hypothesis concerning its neurological origins.

A survey of the literature concerning motoric laterality in strabismus was undertaken. The assessment of manual and ocular dominance was based on a total of eleven studies conducted between 1934 and 1986. The average percentage of right-handedness in strabismics was 73.8%, whereas the average percentage of right-eyedness was 46.9%. Both figures are significantly lower than those obtained for the normal population. It is hypothesized that reduced right dominance in strabismics results from dysfunction of the otoliths and/or their higher brainstem pathways.

Brain Diseases↗
PubMed1993

The effects of background visual roll stimulation on postural and manual control and self-motion perception.

The effects of background visual roll stimulation on postural control, manual control, and self-motion perception were investigated in this study. In the main experiment, 8 subjects were exposed to wide field-of-view background scenes that were tilted and static, continuously rotating, or sinusoidally rotating at frequencies between 0.03 and 0.50 Hz, as well as a baseline condition. The subjects performed either a postural control task (maintain an upright stance) or a manual control task (keep an unstable central display horizontally level). Root-mean square (RMS) error in both the postural and manual control tasks was low in the static tilt condition and extremely high in response to continuous rotation. Although the phases of the postural and manual responses were highly similar, the power and RMS error generated by the sinusoidal visual background stimulation peaked at a lower frequency in the postural task. Vection ratings recorded at the end of the postural and manual trials somewhat paralleled the frequency tuning differences between tasks, which a subsequent experiment showed to be the result of the differential motion of the central display rather than the differential positioning of the subject. In general, these results show that the dynamic characteristics of visual orientation systems vary according to the specific motor and/or perceptual system investigated.

Adult↗
PubMed1992

The relationship between turning behavior and motoric dominance in humans.

This study attempted to correlate turning direction on the stepping test with three measures of motoric dominance--handedness, footedness, and eyedness. 111 high school students performed the stepping test while deprived of visual and auditory cues during a 1-min. interval. Although only slightly more than half of the subjects rotated rightward, the direction and magnitude of turning correlated significantly with footedness and eyedness but not with handedness. Thus, axial turning biases and motoric dominance may partially share a common mechanism, possibly involving vestibular asymmetry.

Adolescent↗
PubMed1992

The effects of dynamic visual stimulation on perception and motor control.

A set of research findings is described that deals with three principal laboratory measures of visual orientation (vection and postural and manual control). Two studies are highlighted, one of which compared the latencies of vection and visually induced postural change and the other of which investigated manual tracking under visually disorienting conditions. The first study showed that although vection and postural change are somewhat related to each other (for example, both were greater in response to roll and pitch as opposed to linear visual motion), the onset of vection is delayed by several seconds relative to the initiation of visually induced postural shifts. The second study showed that manual biases induced by visual roll motion are not overcome using a thumb-and-forefinger (pyramidal) motor strategy, and may not be equivalent to the "giant hand" illusion that is believed to reflect the predominance of the vestibulospinal (extrapyramidal) motor pathways during extreme spatial disorientation. These and other findings indicate that various visual orientation effects may involve at least partially independent mechanisms.

Humans↗
PubMed1992

Visual scene effects on the somatogravic illusion.

This study attempted to determine which visual scene cues are most effective in overcoming the somatogravic illusion (SGI), a form of spatial disorientation that occurs when a shift in the resultant gravitoinertial force vector created by a sustained linear acceleration is misinterpreted as a change in pitch or bank attitude. Nine subjects were exposed to a gravitoinertial force shift of -30 degrees in the pitch plane, both with their eyes closed and while viewing computer-generated visual scenes through a wide field-of-view head-mounted display. The scenes depicted acceleration over a shoreline by means of horizon, texture, perspective, and color cues that were presented both in isolation and in various combinations. None of the scenes significantly reduced the magnitude of the SGI relative to the eyes-closed (baseline) pitch illusion, even though the textured scenes produced some linear vection. It remains to be established whether low-cost head-mounted visual displays can reliably reduce the magnitude of the SGI and other spatially disorienting illusions.

Acceleration↗
PubMed1991

A general theory concerning the prenatal origins of cerebral lateralization in humans.

The origins of cerebral lateralization in humans are traced to the asymmetric prenatal development of the ear and labyrinth. Aural lateralization is hypothesized to result from an asymmetry in craniofacial development, whereas vestibular dominance is traced to the position of the fetus during the final trimester. A right-ear sensitivity advantage may contribute to a left-hemispheric advantage in speech perception and language functions, whereas left-otolithic dominance may independently promote right-sided motoric dominance and a right-hemispheric superiority in most visuospatial functions. The emergence of handedness is linked to the assumption of an upright posture in the early hominids, whereas the failure to develop clear vestibular asymmetry may underlie the poor motoric lateralization found in several neurodevelopmental disorders.

Afferent Pathways↗
PubMed1991

A test of thumb and index finger control in overcoming a visual analogue of the giant hand illusion.

Anecdotal evidence suggests that a thumb and index finger grip might facilitate recovery from the manifestation of spatial disorientation known as the giant hand phenomenon. Sixteen pilots volunteered as subjects in an experiment that compared the effectiveness of the thumb and index finger versus the whole hand technique to overcome a visually-induced analogue of the giant hand phenomenon. Thumb and index finger control produced greater stability overall, but did not overcome the specific tracking bias induced by a background visual roll stimulus. Various hypotheses are discussed as to why the thumb and index finger technique was ineffective in the present instance.

Adult↗
PubMed1987

Origins and implications of frequency-doubling in the visual evoked potential.

The origins and implications of frequency-doubling (i.e., the dominance of the 4th-harmonic response instead of the reversal response) in the visual evoked potential (VEP) were investigated. Previous research demonstrated that frequency-doubling occurs in humans when sinusoidal but not square-wave luminance modulation is used to elicit the VEP, but little else is known about this intriguing phenomenon. Six adult humans viewed luminance and chromatic gratings that were presented using three different spatiotemporal combinations: 4 c/deg-3 Hz, 4 c/deg-6 Hz, and 12 c/deg-3 Hz. VEP's were recorded monopolarly from Oz using an ear reference and were subjected to a Fourier analysis. The results showed that frequency-doubling occurred only using sinusoidal luminance contrasts at 4 c/deg-3 Hz, although the relative strength of higher harmonic responses was greater for both sine- and square-wave luminance contrasts relative to their chromatic counterparts. Many hypotheses can be put forth to account for VEP frequency-doubling (none of which is entirely satisfactory); however, a plausible view is that this phenomenon is related to the magnocellular-parvocellular distinction. In general, the presence of frequency-doubling and other harmonic distortions may preclude the scalp-recorded steady-state VEP to suprathreshold luminance contrasts from describing accurately the spatiotemporal transfer characteristics of the human visual system.

Adult↗
PubMed1987

Color-specific effects of intense laser exposure on visual evoked potentials in rhesus monkeys.

Color-specific visual impairments following exposure to intense laser flashes were investigated using visual evoked potentials (VEPs) recorded from four anesthetized rhesus monkeys. Steady-state VEPs were recorded from the primary visual cortex in response to counterphasing high-contrast sine-wave gratings composed of either luminance contrast (red-black, green-black, and blue-black) or chromatic contrast (red-green). The effects of laser flashes in the red (647 nm), green (514 nm), and blue (476 nm) regions of the visible spectrum were assessed. Only slight wavelength-specific effects were demonstrated, primarily for the red-black grating relative to the other two luminance gratings. Recovery functions for VEPs to the red-green chromatic grating were similar to those of the three luminance gratings. The results are discussed in terms of nonopponent (luminance) and opponent (chromatic) processing.

Animals↗
PubMed1986

Visual evoked potentials to luminance and chromatic contrast in rhesus monkeys.

The spatial and temporal tuning of the luminance and chromatic systems were investigated using visual evoked potentials (VEPs) recorded from rhesus monkeys. VEPs were recorded from eight bipolar electrodes which were chronically implanted in the foveal projection region of area 17 in two monkeys. They were elicited by luminance (yellow-black) and chromatic (red-green) since-wave gratings which varied in spatial frequency (1, 4, 8 and 12 c/deg) and temporal frequency (3, 6, 10 and 15 Hz). The findings showed that chromatic VEPs exhibit low-pass tuning in both the spatial and temporal domains, whereas luminance VEPs exhibit bandpass tuning in the spatial domain and low-pass tuning in the temporal domain. The spatial tuning findings are consistent with the psychophysical literature, while the low-pass temporal tuning shown by the luminance VEPs was attributed to various cancellations and distortions in the suprathreshold VEP at high flicker rates and to the effects of the anesthesia.

Animals↗
PubMed1985

Visual evoked potential correlates of laser flashblindness in rhesus monkeys I. Argon laser flashes.

The visual evoked potential (VEP) in four rhesus monkeys was used to assess the transient loss of visual function resulting from single 100-ms argon laser flashes (476.5 and 514.5 nm) whose energy levels did not exceed the maximum permissible exposure (MPE). VEP's were elicited by high-contrast square-wave test gratings which were phase-reversed at a frequency of 6 Hz, and were recorded using bipolar electrodes implanted in the foveal projection region of area 17. The parameters which were investigated included (1) flash size (focused vs. expanded), (2) position of the electrode's receptive field relative to the position of the flash (0, 1.5, 3.0, and 4.5-deg separation), (3) flash exposure level (50, 5.0, and 0.5% of the MPE), (4) peak wavelength of the test grating (454, 540, and 630 nm), and (5) spatial frequency of the test grating (1.0, 4.0, 6.0, and 12.0 c/deg). The results of the flash-size experiment revealed that the expanded flash, whose retinal diameter was approximately 750 microns, eliminated or severely attenuated the VEP for a longer duration than did the focused flash and also resulted in a more gradual recovery function. The combined results of the flash position and energy level experiments indicated that the effective energy of the focused flash declined rapidly beyond 1.5 deg, but still approximated 4% of its maximum value as far as 4.5 deg from its center. Few, if any, wavelength-specific effects were observed after exposure to either the 476.5- or 514.5-nm flashes, even when the energy of the flashes was reduced to a small fraction of the MPE. Finally, the flash effect was considerably longer in duration for the 12.0 c/deg grating relative to the low and intermediate frequency gratings. In general, the findings suggest that the focused and expanded argon laser flashes produce a VEP suppression whose time course and other characteristics correlate well with those associated with behaviorally observed flashblindness in humans after exposure to intense noncoherent flashes.

Animals↗
PubMed1985

Visual evoked potential correlates of laser flashblindness in rhesus monkeys. II. Doubled-neodymium laser flashes.

The effects of Q-switched (20-ns) doubled-neodymium (Nd-2) laser flashes upon the visual evoked potential (VEP) of two rhesus monkeys were studied and compared with the effects of 100-ms argon laser flashes described previously. VEP's were recorded under barbiturate anesthesia using bipolar electrodes chronically implanted in foveal striate cortex, and were elicited by 6-Hz phase-reversing gratings. The parameters which were investigated included the retinal area and energy level of the flash, and the wavelength, spatial frequency, and contrast of the test grating. The effects produced by the Q-switched pulses at 50% of the maximum permissible exposure (MPE) were smaller in magnitude than those produced by the longer duration argon flashes. The reduced effects of the Nd-2 pulses were attributed to the lower energy contained in these flashes, as dictated by the MPE standards. In other respects, the Nd-2 flash effects closely paralleled the argon effects. The results of the various experiments suggest that VEP decrements produced by long and short flashes are similar at equal energy levels, despite the fact that the shorter flashes are believed to produce considerably less pigment bleaching.

Animals↗