Fred H. Previc

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.

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

Abstract. 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°) roll motion; (2) coherent counterclockwise (CCW) wide-FOV roll motion; (3) wide-FOV incoherent motion; (4) CCW motion confined to the central visual field (~55°); 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.

Areas of the human brain activated by ambient visual motion, indicating three kinds of self-movement.

In a positron emission tomography (PET) study, a very large visual display was used to simulate continuous observer roll, yaw, and linear movement in depth. A global analysis based on all three experiments identified brain areas that responded to the three conditions’ shared characteristic of coherent, wide-field motion versus incoherent motion. Several areas were identified, in the posterior-inferior temporal cortex (Brodmann area 37), paralimbic cortex, pulvinar, and midbrain tegmentum. In addition, occipital region KO was sensitive to roll and expansion but not yaw (i.e., coherent displays containing differential flow). Continuous ambient motion did not activate V5/MT selectively. The network of sites responding specifically to coherent motion contrasted with the extensive, contiguous activation that both coherent and incoherent motion elicited in visual areas V1, V2, and V3. The coherent motion mechanisms, furthermore, extended beyond the traditional dorsal pathway proposed to account for visual motion processing, and included subcortical and limbic structures, which are implicated in polysensory processing, posture regulation, and arousal.

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 controlf andselfmotion 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 tbafrequency 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.

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.

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 subjects 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° and 115°) 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.