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31.
在这篇论文中,我们提出了用于选择视觉的数据和智能控制的动态网络系统的神经实现过程。模型由数个相互作用的子系统构成,用于不同的处理。所有的神经子系统与信息和控制流程的倒序和顺序紧密相关。 相似文献
32.
本文通过用Flash 5.0制作《医学电子学》中PN结的形成过程的介绍,在熟悉Flash 5.0制作方法的同时.完成相应的多媒体教学。 相似文献
33.
The Topography of Non-Linear Cortical Dynamics at Rest, in Mental Calculation and Moving Shape Perception 总被引:3,自引:0,他引:3
Andreas Meyer-Lindenberg Ulrike Bauer Stefan Krieger Stefanie Lis Kinga Vehmeyer Georg Schüler Bernd Gallhofer 《Brain topography》1998,10(4):291-299
Differential cortical activation by cognitive processing was studied using dimensional complexity, a measure derived from nonlinear dynamics that indicates the degrees of freedom (complexity) of a dynamic system. We examined the EEG of 32 healthy subjects at rest, during a visually presented calculation task, and during a moving shape perception task. As a nonlinear measure of connectivity, the mutual dimension of selected electrode pairs was used. The first Lyapunov coefficient was also calculated. Data were tested for non-linearity using a surrogate data method and compared to spectral EEG measures (power, coherence). Surrogate data testing confirmed the presence of nonlinear structure in the data. Cognitive activation led to a highly significant rise in dimensional complexity. While both tasks activated central, parietal and temporal areas, mental arithmetic showed frontal activation and an activity maximum at T3, while the moving shape task led to occipital activation and a right parietal activity maximum. Analysis of mutual dimension showed activation of a bilateral temporal-right frontal network in calculation. The Lyapunov coefficent showed clear topographic variation, but was not significantly changed by mental tasks (p<.09). While dimensional complexity was almost unrelated to power values, nonlinear (mutual dimension) and linear (coherence) measures of connectivity shared up to 37% of variance. Data are interpreted in terms of increased cortical complexity as a result of recruitment of asynchronously active, distributed neuronal assemblies in cognition. The topography of nonlinear dynamics are related to neuropsychological and neuroimaging findings on mental calculation and moving shape perception. 相似文献
34.
Zuidhoek S Visser A Bredero ME Postma A 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2004,157(2):265-268
It has been argued that representations of peripersonal space based on haptic input are systematically distorted by egocentric reference frames. Interestingly, a recent study has shown that noninformative vision (i.e., freely viewing the region above the haptic workspace) improves performance on the so-called haptic parallel-setting task, in which participants are instructed to rotate a test bar until it is parallel to a reference bar. In the present study, we made a start at identifying the different sensory integration mechanisms involved in haptic space perception by distinguishing the possible effects of orienting mechanisms from those of noninformative vision. We found that both the orienting direction of head and eyes and the availability of noninformative vision affect parallel-setting performance and that they do so independently: orienting towards a reference bar facilitated the parallel-setting of a test bar in both no-vision and noninformative vision conditions, and noninformative vision improved performance irrespective of orienting direction. These results suggest the effects of orienting and noninformative vision on haptic space perception to depend on distinct neurocognitive mechanisms, likely to be expressed in different modulations of neural activation in the multimodal parietofrontal network, thought to be concerned with multimodal representations of peripersonal space. 相似文献
35.
Effects of the presentation of false heart-rate feedback on the performance of two common heartbeat-detection tasks. 总被引:3,自引:0,他引:3
Research has indicated that performance on heartbeat counting tasks may be influenced by beliefs about heart rate. Sixty male subjects were administered the Schandry heartbeat counting task after viewing fast, slow, or no heart rate feedback. Subjects were also administered the Whitehead signal-detection type task. Results indicated that subjects who received fast or no heartbeat feedback performed better on the Schandry task than subjects who received slow feedback. Feedback presentation did not affect performance on the Whitehead task. These results suggest that the Schandry task is influenced by external variables (expectations, beliefs) beyond pure awareness of "discrete" visceral sensations and, thus, may not be as powerful a method for determining awareness of individual heartbeats as some other paradigms. 相似文献
36.
L. E. Sergio Stephen H. Scott 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,122(2):157-164
This study examines whether the kinematics of pointing movements are altered by the sensory systems used to select spatial
targets and to guide movement. Hand and joint paths of visually guided reaching movements of human subjects were compared
with two non-visual conditions where only proprioception was available: (1) movements of the same subjects with blindfolds,
and (2) movements by congenitally blind subjects. While hand-path curvatures were overall quite small, sighted subjects wearing
a blindfold showed a statistical increase in hand-path curvature compared with their visually guided movements. Blindfolded
subjects also showed greater hand-path curvature than blind subjects. These increases in hand-path curvature for blindfolded
subjects did not always lead to a decrease in joint-path curvature. While there were differences between blind subjects and
sighted subjects using vision for some movement directions, there was no systematic difference between these two groups. The
magnitude of joint-path curvature showed much greater variation than hand-path curvature across the movement directions. We
found variation in joint-path curvature to be correlated to two factors, one spatial and one geometrical. For all subject
groups, joint-path curvature tended to be smaller for sagittal-plane movements than for transverse or diagonal movements.
As well, we found that the magnitude of joint-path curvature was also related to the relative motion at each joint. Joint-path
curvature tended to increase when movements predominantly involved changes in shoulder angle and was minimal when movements
predominantly involved elbow motion. The consistently small curvatures of hand trajectory across blind and sighted subjects
emphasize the powerful tendency of the motor system to generate goal-directed reaching movements with relatively straight
hand trajectories, even when deprived of visual feedback from very early in life.
Received: 16 July 1997 / Accepted: 20 May 1998 相似文献
37.
F. Richer M. Martinez H. Cohen J. -M. Saint-Hilaire 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1991,87(3):649-652
Summary Visual phenomena evoked by direct electrical stimulation of extrastriate cortex were observed in 30 epileptic patients as part of a presurgical investigation. An incremental sequence of low-level bipolar stimulation trains was delivered at medial and lateral pairs of contacts of stereotaxically-implanted multilead intracerebral electrodes in parietal, occipital and posterior temporal regions. Diffusion of stimulus afterdischarges was monitored by electrodes in temporal and frontal lobes and by the non-stimulated contacts of the stimulated electrode. Localized stimulations evoked few visual phenomena. The strongest anatomo-perceptual correlation was found for stimulation in the medial parieto-occipital fissure which evoked visual motion phenomena in all three patients stimulated in that region. The evoked motion perceptions were not associated with eye movements or any particular localization of the epileptic focus. These perceptions were only evoked once outside of the medial PO region at the 61 sites examined. The results suggest that the medial parieto-occipital region is closely linked to the human visual motion processing system. 相似文献
38.
Twelve females were tested at four times during the menstrual cycle with a visual detection task and a visual pattern discrimination task. Mood levels and confidence ratings were evaluated for each session. In addition to the behavioral testing, plasma samples were collected and radioimmunoassayed for estradiol, progesterone, luteinizing hormone, and follicle stimulating hormone levels. Visual detection fluctuated significantly during the menstrual cycle with impaired performance occurring at the premenstrual session. In contrast to previous reports, the impaired performance was not related to lowered confidence ratings or to mood levels. 相似文献
39.
V. S. Gurfinkel Yu. S. Levik 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1993,95(2):359-364
Horizontal eye movements were recorded in eight healthy subjects during super-slow trunk rotation with respect to the space-stationary head. In some trials, subjects simultaneously indicated their perception of selfmotion by means of a joystick. Over the frequency range employed (0.007–0.05 cycles per second, ±20°), all subjects perceived the relative motion of head and trunk as a head rotation with respect to the stationary trunk. Eye movements were observed which were in phase with imaginary head rotation; their amplitude exceeded the amplitude of actual body rotation. The grasping of a rigid ground-based handle (1) produced a sensation of trunk rotation in space, (2) suppressed the sensation of imaginary head rotation in space and (3) gave rise to a significant decrease in amplitude of eye movements. The grasping of a stiff rod with non-zero compliance did not produce these effects. It is concluded that eye movements in response to body rotation with respect to the fixed head are not purely reflex reactions, but are influenced by the internal representation of body motion. 相似文献
40.
Mon-Williams M McIntosh RD Milner AD 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2001,139(2):137-142
It has been shown that a patient with visual form agnosia (DF) relies predominantly on vergence information when gauging
target distance in an open-loop pointing task. This finding suggested that the programming of prehension might be severely
disrupted if DF viewed target objects through ophthalmic prisms. An initial experiment showed that this prediction was not
upheld; DF was able to programme reasonably accurate movements to objects located on a tabletop despite large changes in vergence
angle. A second experiment, however, showed that placing the target objects at eye height whilst manipulating vergence angle
caused gross disruption to prehension, with DF mis-programming the reach component in a predictable manner. Notably, the evidence
for DF's reliance on vergence distance information was obtained in a task where the targets were viewed at eye height. These
experiments indicate that DF uses vertical gaze angle to gauge target distance in normal prehension and suggest that this
extra-retinal cue may be a useful source of distance information for the human nervous system, especially where pictorial
cues are impoverished.
Electronic Publication 相似文献