Biomedical subjects

M Nawrot

Publications and source records attributed to M Nawrot.

8 recordsLinked to original sources

PubMed1992

A human visual disorder resembling area V4 dysfunction in the monkey.

We surveyed a broad range of visual functions in a man who complained of abnormal color experience and inability to recognize faces following bilateral damage in the visual cortex. A lesion in his right visual cortex caused complete left visual field loss. A lesion in his left visual cortex, located entirely below the calcarine fissure, affected the vision in his remaining hemifield, the right one. Psychophysical testing showed severely defective color vision and pattern processing, but relatively normal luminance contrast detection thresholds. The finding of normal spatial contrast sensitivity and static stereopsis did not resemble a parvocellular defect of the type described in the monkey. The abilities to detect global coherent motion among noise, structure from motion and dynamic stereopsis, and to pursue moving targets showed normal motion processing at several levels. Together with normal flicker perception, these results excluded magnocellular or MT-like defects. Altogether, the findings mimic area V4 dysfunction.

Adult↗

PubMed1991

A neural network model of kinetic depth.

We propose a network model that accounts for the kinetic depth in structure from motion phenomena. Using plausible neural mechanisms, the model accounts for (1) fluctuations in perception when viewing a simple kinetic depth stimulus, (2) disambiguation of this stimulus with stereoscopic information, and (3) subsequent bias of the percept of this stimulus following stereoscopic adaptation. The model comprises two levels: a layer of monocular directionally selective motion detectors that provide input to a second layer of disparity-selective and direction-selective binocular mechanisms. The network of facilitatory and inhibitory connections between binocular mechanisms gives rise to fluctuations in network activity that mimic the fluctuations in perception of kinetic depth in the absence of disparity information. The results of a psychophysical experiment are consistent with the nature of the proposed interactions.

Adaptation, Ocular↗

PubMed1991

The interplay between stereopsis and structure from motion.

In a series of psychophysical experiments, an adaptation paradigm was employed to study the influence of stereopsis on perception of rotation in an ambiguous kinetic depth (KD) display. Without prior adaptation or stereopsis, a rotating globe undergoes spontaneous reversals in perceived direction of rotation, with successive durations of perceived rotation being random variables. Following 90 sec of viewing a stereoscopic globe undergoing unambiguous rotation, the KD globe appeared to rotate in a direction opposite that experienced during the stereoscopic adaptation period. This adaptation aftereffect was short-lived, and it occurred only when the adaptation and test figures stimulated the same retinal areas, and only when the adaptation and test figures rotated about the same axis. The aftereffect was just as strong when the test and adaptation figures had different shapes, as long as the adaptation figure contained multiple directions of motion imaged at different retinal disparities. Nonstereoscopic adaptation figures had no effect on the perceived direction of rotation of the ambiguous KD figure. These results imply that stereopsis and motion strongly interact in the specification of structure from motion, a result that complements earlier work on this problem.

Adaptation, Ocular↗

PubMed1990

Assimilation and contrast in motion perception: explorations in cooperativity.

Motions within one region of the field influence motion seen elsewhere. To explore this phenomenon we used cinematograms comprised of alternating strips within which dots (i) tended to move in one direction, or (ii) moved in random directions (dynamic noise). When alternating strips were narrow, motion in one direction induced a similar direction of illusory motion in the adjoining dynamic noise (assimilation); when alternating strips were wide, motion tended to induce an illusory opposed motion in the dynamic noise (contrast). Since this illusory motion exhibits hysteresis, it probably results from spatially distributed, cooperative processes. The shift from assimilation to contrast, as the cinematogram's strips increase in size, suggests that facilitatory and inhibitory influences of the network extend over different distances.

Contrast Sensitivity↗

PubMed1989

Neural integration of information specifying structure from stereopsis and motion.

When one views a two-dimensional parallel projection of dots on the surface of a rotating globe, the direction of rotation is ambiguous, and the perceived direction of rotation of the two-dimensional figure is unstable over time. Stability can be temporarily induced by adaptation to a three-dimensional globe with a direction of rotation unambiguously specified by stereo disparity; adaptation causes the two-dimensional figure to appear to rotate in the direction opposite that experienced during stereoscopic adaptation. This adaptation effect is selective for axis of rotation but is not shape-specific. It does depend on simultaneous stimulation by multiple depth planes defined by elements moving in different directions. Evidently information about stereopsis and information about structure from motion are integrated within a common neural site in the brain.

Adaptation, Ocular↗

PubMed1989

Evidence for in vivo upregulation of 1,25(OH)2 vitamin D3 receptor in human monocytes.

Mammalian cells increase net expression of 1,25(OH) 2D3 receptors after exposure to physiological concentrations of 1,25(OH) 2D3 in vitro. We examined specific binding of 1,25(OH) 2D3 by human monocytes before and after daily administration of 1.5-2 micrograms 1,25(OH) 2D3 p.o. for 3 days in 5 healthy normal D-replete probands. Median specific binding (Nmax) at baseline was 793 molecules/cell and 2052 or 2828 at 24h and 72h of 1,25(OH) 2D3 treatment respectively. The results suggest (a) upregulation of 1,25(OH) 2D3 receptors occurs in man and (b) monocyte preparations can be used to assess receptor regulation in vivo.

Adult↗

PubMed1987

Localization of signals in images.

We have observed the ability of observers to locate signals embedded in white noise and other nonwhite and nonstationary images. Performance was found to be consistent with that predicted by a cross correlator that takes into account the variability of the background image (normalization) and that assumes a degree of uncertainty as to the precise location of the signal.

Form Perception↗

PubMed1973

Methaqualone.

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Adult↗