Biomedical subjects

F H Previc

Publications and source records attributed to F H Previc.

At least 19 recordsLinked to original sources

PubMed2001

Effects of background field-of-view and depth-plane on the oculogyral illusion.

This study examined the effects of background field-of-view and depth plane on the oculogyral illusion. Seven subjects viewed a stationary fixation stimulus during the postrotatory interval following a 45-sec constant-velocity chair rotation. The duration of the illusory movement of the fixation stimulus during the postrotatory interval was measured, along with the duration of the illusion of whole-body rotation (known as the somatogyral illusion) and the duration of the subject's slow-phase vestibular nystagmus. Subjects viewed the fixation stimulus by itself in a No-background condition or when surrounded by six background fields formed by the combination of two fields-of-view (35 degrees and 115 degrees) and three depth-planes (near, coplanar, and far). The different background fields inhibited the oculogyral illusion relative to the No-background condition but did not differ statistically from each other. The somatogyral durations better matched the oculogyral ones than did nystagmus decay, especially when a background field was present. These results suggest that the oculogyral illusion is more related to the experience of whole-body rotation than to oculomotor mechanisms and that the inhibitory effect of a background scene is only modestly affected by its field-of-view and depth plane.

Depth Perception↗

PubMed2001

Target-tilt and vertical-hemifield asymmetries in free-scan search for 3-D targets.

In this study, asymmetries in finding pictorial 3-D targets defined by their tilt and rotation in space were investigated by means of a free-scan search task. In Experiment 1, feature search for cube tilt and rotation, as assessed by a spatial forced-choice task, was slow but still exhibited a characteristic "flat" slope; it was also much faster to upward-tilted cubes and to targets located in the upper half of the search field. Faster search times for cubes and rectangular solids in the upper field, an advantage for upward-tilted cubes, and a strong interaction between target tilt and direction of lighting (upward or downward) for the rectangular solids were all demonstrated in Experiment 2. Finally, an advantage in searching for tilted cubes located in the upper half of the display was shown in Experiment 3, which used a present-absent search task. The results of this study confirm that the upper-field bias in visual search is due mainly to a biased search mechanism and not to the features of the target stimulus or to specific ecological factors.

Adult↗

PubMed2001

Effect of "inside-out" and "outside-in" attitude displays on off-axis tracking in pilots and nonpilots.

BACKGROUND: Pilots employing helmet-mounted displays spend sustained periods of time looking off-axis, necessitating the inclusion of attitude symbology on the helmet to maintain spatial awareness. We examined how fundamentally different attitude references, a moving-horizon ("inside-out") or a moving-aircraft ("outside-in"), affected pilot and nonpilot attitude control when looking on- or off-axis. Both a rear-view and a side-view outside-in perspective were depicted to investigate the effect of control-display compatibility. METHODS: Subjects performed a compensatory pitch-roll tracking task either looking on-axis or 90 degrees off-axis using three symbologies: 1) a compressed pitch ladder with horizon line; 2) a 3-D aircraft representation viewed from the rear; and 3) a 3-D aircraft representation viewed from the side. Tracking error in roll and pitch, control bias, and subjective ratings were collected and analyzed. RESULTS: There was no significant difference in the tracking performance of U.S. Air Force pilots in pitch and roll using the inside-out or outside-in rear-view formats on- and off-axis, although they preferred the inside-out format. Nonpilots tracked significantly better using the outside-in rear-view format, which they also preferred. Both groups tracked poorly using the outside-in side-view format and control-display compatibility had no important effect. CONCLUSIONS: Pilots are equally adept using outside-in and inside-out displays. Given that an outside-in display may better reflect a person's inherent frame of reference for orientation (as evidenced by the nonpilots' superior performance with it), the results seem to indicate that pilots, through experience, have adapted to an inside-out frame of reference.

Accommodation, Ocular↗

PubMed2001

Trends in spatial disorientation research.

Trends in spatial disorientation (SD) research over the past six decades were assessed by means of a literature review using four databases and three SD-related search terms. 347 SD-related papers were identified, 37% of which were in three categories: attitude displays, SD training, and SD incidence. The most dramatic trend was a marked upswing in SD research in the 1990's.

Adolescent↗

PubMed2000

Functional imaging of brain areas involved in the processing of coherent and incoherent wide field-of-view visual motion.

The brain areas involved in processing wide field-of-view (FOV) coherent and incoherent visual stimuli were studied using positron emission tomography (PET). The brains of nine subjects were scanned as they viewed texture patterns moving in the roll plane. Five visual conditions were used: (1) coherent clockwise (CW) wide-FOV (>100 degrees) roll motion; (2) coherent counter-clockwise (CCW) wide-FOV roll motion; (3) wide-FOV incoherent motion; (4) CCW motion confined to the central visual field (approximately 55 degrees); and (5) a stationary control texture. The region most activated by the coherent-motion stimulus relative to the static one was the medial-occipital cortex, whereas both the medial- and lateral-occipital cortices were activated by incoherent motion relative to a static texture. Portions of the retroinsular parietal-temporal cortex, superior insula, putamen, and vestibulocerebellum responded specifically to the coherence of the stimulus, whereas a widespread lateralized activation was observed upon subtracting the CW scans from the CCW scans. The results indicate separate neural regions for processing wide-FOV motion versus stimulus coherence.

Adult↗

PubMed2000

Is "ambient vision" distributed in the brain? Effects of wide-field-view visual yaw motion on PET activation.

Ambient vision comprises the visual functions that are associated with the maintenance of spatial orientation and that depend on peripheral, preconscious visual inputs. Although a limited number of brain areas appear to be activated by coherent wide-field-of-view (WFOV) motion in more than one axis, a diffuse pattern of lateralized brain activity occurs in response to clockwise or counterclockwise ambient visual roll motion. In the present study involving positron emission tomography (PET), a similar finding was shown for rightward versus leftward yaw stimulation. A total of 18 PET scans were obtained from six subjects in response to either leftward or rightward WFOV motion in a collimated display subtending > 100 degrees horizontally. Rightward stimulation elicited mainly activation throughout the right hemisphere, whereas leftward stimulation elicited mainly activation throughout the left hemisphere. These findings provide further evidence that the ambient vision signal is either processed or transmitted throughout the entire brain, as befits a visual function that is fundamental to all other perceptual systems.

Adult↗

PubMed1999

Dopamine and the origins of human intelligence.

A general theory is proposed that attributes the origins of human intelligence to an expansion of dopaminergic systems in human cognition. Dopamine is postulated to be the key neurotransmitter regulating six predominantly left-hemispheric cognitive skills critical to human language and thought: motor planning, working memory, cognitive flexibility, abstract reasoning, temporal analysis/sequencing, and generativity. A dopaminergic expansion during early hominid evolution could have enabled successful chase-hunting in the savannas of sub-Saharan Africa, given the critical role of dopamine in counteracting hyperthermia during endurance activity. In turn, changes in physical activity and diet may have further increased cortical dopamine levels by augmenting tyrosine and its conversion to dopamine in the central nervous system (CNS). By means of the regulatory action of dopamine and other substances, the physiological and dietary changes may have contributed to the vertical elongation of the body, increased brain size, and increased cortical convolutedness that occurred during human evolution. Finally, emphasizing the role of dopamine in human intelligence may offer a new perspective on the advanced cognitive reasoning skills in nonprimate lineages such as cetaceans and avians, whose cortical anatomy differs radically from that of primates.

Animals↗

PubMed1998

The neuropsychology of 3-D space.

The neuropsychological literature on 3-D spatial interactions is integrated using a model of 4 major behavioral realms: (a) peripersonal (visuomotor operations in near-body space), (b) focal extrapersonal (visual search and object recognition), (c) action extrapersonal (orienting in topographically defined space), and (d) ambient extrapersonal (orienting in earth-fixed space). Each is associated with a distinct cortical network: dorsolateral peripersonal, predominantly ventrolateral focal-extrapersonal, predominantly ventromedial action-extrapersonal, and predominantly dorsomedial ambient-extrapersonal systems. Interactions in 3-D space are also regulated neurochemically with dopaminergic and cholinergic excitation associated with extrapersonal activation and noradrenergic and serotonergic excitation associated with peripersonal activation. This model can help explain the 3-D imbalances in prominant neuropsychological disorders.

Humans↗

PubMed1997

Vertical biases in scene memory.

In a recent theoretical paper (Behavioral and Brain Sciences, 1990, 13, 519-542), Previc argued that vertical asymmetries in perception may largely result from the biases of the lower and upper visual fields toward proximal and distal space, respectively. The present study examined whether this same relationship may exist for visual scene memory, by re-analyzing data from Intraub and Richardson (Journal of Experimental Psychology: Learning, Memory, and Cognition, 1989, 15, 179-187). In that study, subjects remembered photographs of scenes as being farther away than was actually the case and extended the boundaries of the scenes accordingly; in some cases, the remembered scenes were also shifted vertically. This study formally examined whether prominent landmarks in Intraub and Richardson's close-up and wide-angle photographs were displaced vertically in subjects' reproductions of them from memory. A total of 475 measurements in 210 drawings by 41 subjects were made. The results were that 64% of the original landmark points were shifted downward in the drawings made from memory, whereas only 36% were shifted upward. Although most of the original points were located in the upper-field and would have been expected to be shifted downward as the original image contracted in memory, a chi-square analysis showed that more upper-field points were shifted downward than were lower-field points shifted upward in the remembered scenes. The downward shift could reflect an expansion of the upper-field in memory, consistent with the scene being placed farther away, or it could reflect an elevation of the assumed viewing (head) position in memory.

Adult↗

PubMed1997

Effects of vestibular and oculomotor stimulation on responsiveness of the carotid-cardiac baroreflex.

Twelve healthy men underwent measurement of their carotid-cardiac baroreflex response during varying conditions of vestibulo-oculomotor stimulation to test the hypothesis that vestibular and/or oculomotor stimulation associated with head movements in the yaw plane inhibit baroreflex control of heart rate. We assessed the carotid-cardiac baroreflex response by plotting R-R intervals (in milliseconds) at each of eight neck pressure steps with their respective carotid distending pressures (in millimeters mercury). Baroreflex sensitivity was measured under four experimental conditions: 1) sinusoidal whole body yaw rotation of the subject in the dark without visual fixation (combined vestibular-oculomotor stimulation); 2) yaw oscillation of the subject while tracking a small head-fixed light moving with the subject (vestibular stimulation without eye movements); 3) subject stationary while fixating on a small light oscillating in yaw at the same frequency, peak acceleration, and velocity as the chair (eye movements without vestibular stimulation); and 4) subject stationary in the dark (no eye or head motion). Head motion alone reduced baseline baroreflex responsiveness by 30% from 3.8 +/- 0.5 to 2.6 +/- 0.5 ms/mmHg. Eye motion alone also reduced the baroreflex response by 13% (0.5 ms/mmHg) to 3.3 +/- 0.5 ms/mmHg. During head motion, the effect of eye motion was negligible (2.7 +/- 0.4 ms/mmHg). These results suggest that vestibular stimulation associated with head movements in yaw inhibits vagally mediated baroreflex control of heart rate, whereas oculomotor stimulation is less of a factor and only in the absence of vestibular stimulation.

Adult↗

PubMed1997

Vertical eye movements during mental tasks: a re-examination and hypothesis.

Previous research has shown that both vertical and lateral eye movements occur during mental tasks, although the neuropsychological basis for such movements remains unclear. Vertical and lateral eye movements were recorded from 24 right-dominant subjects as they performed three different mental tasks: a mental arithmetic task, a visuospatial imagery task, and a proverb interpretation task. Significant upward biases in the direction of the initial eye movement were observed as subjects answered a series of arithmetic and visuospatial questions along with a nonsignificant upward bias following a series of proverbs that subjects had to interpret. By contrast, no consistent lateral eye movement biases were found during any task. The results are interpreted according to Previc's recent theory linking processing in the upper and lower visual fields to ventral versus dorsal posterior cortical activation, respectively.

Adolescent↗

PubMed1996

Handedness as a predictor of increased risk of knee, elbow, or shoulder injury, fractures and broken bones.

Several recent studies suggest that left-handers have higher susceptibility to accidental injury. Two studies investigated the suggested link between sinistrality and accidental injury by assessing the prevalence of joint problems, bone breaks, and fractures, which may be the sequelae of such mishaps. Study 1 used retrospective responses on medical history checklists completed by 1064 males on active duty with the United States Air Force. It found that left-handers were at significantly higher risk for knee problems (RR = 2.74), elbow and shoulder problems (RR = 3.03), and also swollen and painful joints (RR = 1.87), although there was no difference in the incidence of broken bones. Study 2 used an expanded handedness scale and retrospective reports of both bone breaks and fractures in a predominantly university sample of 1716 (975 women, 741 men) with median age of 20 years, and demonstrated that non-right-handers were at greater risk for bone breaks and fractures (RR = 1.24). As joint problems, as well as bone breaks and fractures, are often the aftermath of accidents that result in falls or collisions with unyielding objects, the fact that left-handers are more likely to suffer from these problems is consistent with the suggestion that sinistrals are more susceptible to accident-related injuries.

Journal Article↗

PubMed1996

Direction and reliability of head tilt in humans.

It has been proposed that asymmetry in the inner ear underlies various manifestations of brain-behaviour asymmetry in the human. Specifically, Previc (1991) argued that an otolith imbalance manifests itself in an asymmetrical head posture, and later (1994) suggested that head tilt may be consonant with other measures of human laterality. The present study tested the reliability of head tilt across days and assessed its relationship with handedness, footedness, and eyedness. As in Previc's earlier studies, a majority of our subjects tilted rightward. Head tilt proved to be highly stable across days but was not correlated with the other laterality measures. These findings suggest that head tilt may reflect an underlying asymmetric substrate that appears not to be directly related to other measures of cerebral hemispheric dominance.

Journal Article↗

PubMed1995

Discriminability of random-dot stereograms in three-dimensional space.

The discriminability of crossed-disparity (near) and uncrossed-disparity as a function of their location in the upper-left, upper-right, lower-left, and lower-right quadrants of the visual field. Discriminability was assessed using choice reaction-time (RT) and accuracy measures. While near targets were recognized equally well in the upper and lower fields, far targets were perceived more easily in the upper visual field. The discriminability of far targets was particularly poor in the lower left quadrant. These results point to the existence of fundamental asymmetries in perceiving crossed and uncrossed disparities along the vertical and lateral axes.

Anisotropy↗

PubMed1995

In defense of traditional views of spatial disorientation and loss of situation awareness: a reply to Navathe and Singh's "An operational definition of spatial disorientation".

In a recent article in Aviation, Space, and Environmental Medicine, Navathe and Singh proposed new "operational" definitions for spatial disorientation (SD) and loss of situation(al) awareness (LSA). The major feature of their new scheme was to treat the two phenomena as distinct, with SD attributable to physiologically based (peripheral) illusions and LSA to psychological (central) factors. The present commentary argues in favor of traditional views of SD that consider spatial orientation to be a subset of overall situation awareness.

Awareness↗

PubMed1994

Assessing the legacy of the GBG model.

A critique of the article by Bryden, McManus, and Bulman-Fleming ("Evaluating the empirical support for the Geschwind-Behan-Galaburda model of cerebral lateralization") is presented. Bryden et al. expose some of the principal weaknesses of the cerebral lateralization model put forth by Geschwind and colleagues and contribute an important meta-analysis of findings concerning the model's predicted relationship between immune disorders and handedness. Nonetheless, the theory put forth by Geschwind and colleagues retains an important legacy despite a multitude of faulty assumptions and predictive failures. Also offered is a brief synopsis of a new model that explains the many positive relationships found among various neurodevelopmental disorders and medical conditions, as well as why abnormal handedness distributions occur in some but not other neurodevelopmental disorders.

Child↗

PubMed1994

The relationship between eye dominance and head tilt in humans.

Previous data suggest that vertical imbalances between the eyes produced by lateral head tilt are linked to ocular dominance, but no studies have heretofore objectively measured head tilt in addressing this relationship. Photographic measurements of the head tilt of 70 subjects were made, along with measures of sighting dominance and vertical misalignment during sighting. The analyses revealed that photographically measured head tilt is significantly associated with vertical imbalances during sighting and with sighting dominance. These data support the theory that motoric dominance in humans is partly related to mechanisms underlying postural asymmetry.

Adolescent↗

PubMed1993

Visual search asymmetries in three-dimensional space.

Feature-conjunction search performance was investigated as a function of the target's location in three-dimensional (3-D) space. Ten subjects viewed a display that contained 36 shapes, one of which was the target. The targets were presented in one of four quadrants, three depths, and three eccentricities. On a given trial, nontarget distractor shapes were presented at the other 35 locations. The ability to find a target shape was best when it was presented in the upper and right visual fields and was closest to the fixation point in both its depth and eccentricity. These nonuniformities may be partly derived from the link between visual search and an extrapersonal attentional mechanism.

Adolescent↗