用自回归白化滤波器提取脑-机接口信号VEP

利用脑-计算机接口这种新颖的人-机交互模式构建一种脑控拼写装置,其主要问题是实时、准确地从头皮电极记录到的脑电背景信号中提取视觉诱发电位,以决定用户选择按键。由于在一个短时程内可以认为自发脑电是平稳的,利用靶刺激出现前记录到的非靶刺激信号计算自回归模型参数,构造一个白化滤波器,再将实时信号通过白化滤波器滤波,使自发脑电得以白化,然后采用小波分析方法滤除白噪信号。结果表明靶刺激信号更加突出,提高了后续模式分类的正确率。采用模拟自然阅读诱发模式使短时信号的平稳性得到了保障,利用白化滤波器去除自发脑电是可行的。     

Aberrant retinal projections to midbrain targets mediate spared visual orienting function in hamsters with neonatal lesions of superior colliculus

Summary Rodents, cats, and most nonmammalian vertebrates with bilateral tectal deafferentation or ablation in adulthood are extremely deficient at orienting to visual stimuli; yet animals with neonatal lesions of superficial layers of the superior colliculus (SC) show partial sparing of this response, particularly for targets in the central visual field. In this study, we sought to determine whether these spared orienting abilities are mediated by aberrant retinal projections to the remaining intermediate layers of the SC, or whether visual cortex (VC) mechanisms or alternative behavioral strategies are responsible. Neonatal golden hamsters received either bilateral heat lesions of the SC (rlSC), or a heat lesion of the right SC and enucleation of the right eye (rSCrE). This latter procedure causes axons from the left eye to recross the tectal midline and terminate in the wrong (left) SC (Schneider 1973). As adults, both groups of hamsters were extremely deficient in visually guided approach to stationary targets, although rlSC-lesioned hamsters showed some sparing for central field targets and rSCrE-lesioned hamsters often made wrong-direction turns for targets in the left peripheral field. We then subjected both groups of neonatally lesioned hamsters to bilateral aspiration lesions of the VC. Retesting showed no change in visual orienting behavior as a result of the cortical lesions. Labeling of the optic tract with horseradish peroxidase (HRP) revealed abundant aberrant retinal projections to remaining intermediate layers of the SC and thalamic nucleus lateralis posterior (LP), as well as supernormal innervation of pretectal nuclei, the dorsal terminal nucleus of the accessory optic tract, and the ventral nucleus of the lateral geniculate body (LGv). We conclude that the spared visual orienting capabilities of hamsters with rlSC and rSCrE lesions are mediated by the aberrant midbrain projections, and that cortical mechanisms are not involved in spared visual orienting functions following these neonatal lesions.     

The interaction of conflicting retinal motion stimuli in oculomotor control

Summary Oculomotor response has been assessed in humans during the presentation of conflicting retinal motion stimuli. In the majority of experiments a background stimulus was made to move with a constant velocity ramp in one direction followed by rapid resets at regular intervals. In the absence of an adequate fixation target this ramp-reset stimulus induced a nystagmus with a slow-phase velocity and saccadic frequency which remained almost constant as reset frequency was increased from 2 to 5 Hz. Moreover, the induced eye velocity could be considerably increased if the subject attempted active matching of display velocity. During both active and passive responses eye velocity gain reached a peak when display velocity was between 2°/s and 5°/s. The presence of small stationary targets induced a suppression of the passive ramp-reset response which was modified by target eccentricity and by tachistoscopic target illumination. When subjects pursued a sinusoidally oscillating target against a stationary structured background, eye velocity gain was significantly less than for pursuit against a blank background. The degree of interaction between conflicting stimuli was found to be dependent on their relative size, peripheral location and velocity. However, it appears that the human observer is able selectively to enhance feedback gain from one particular source in order to dominate stimuli from other unwanted sources.     

Hand and joint paths during reaching movements with and without vision

 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     

Non-cerebellar visual afferents to the vestibular nuclei involving the prepositus hypoglossal complex: An autoradiographic study in the rat

Summary Radioactive amino-acids were injected into the nucleus reticularis tegmenti pontis (NRTP) and the pretectum (PT) in the rat. Beside the labeling of the several nuclei which are known to receive afferents of either the NRTP and/or the PT, monosynaptic projections from these two structures to the prepositus hypoglossal complex (PHN) were demonstrated. Pretectal visual inputs to the vestibular nuclei (VN) may thus be conveyed not only by the classical PT-inferior olive-cerebellar route, but also by two other non-cerebellar ones involving the strong efferent projections of the PHN onto the VN. These last two pathways are strong candidates to account for the residual visual sensitivity of VN neurons after cerebellectomy or inferior olive lesions.Supported by CNRS (A.T.P. 8115)     

The role of visual feedback of hand position in the control of manual prehension

 Although it is obvious that vision plays a primary role in reaching and grasping objects, the sources of the visual information used in programming and controlling various aspects of these movements is still being investigated. One source of visual information is feedback relating to the characteristics of the reach itself – for example, the speed and trajectory of the moving limb and the change in the posture of the hand and fingers. The present study selectively eliminated this source of visual information by blocking the subject’s view of the reaching limb with an opaque barrier while still enabling subjects to view the goal object. Thus, a direct comparison was made between standard (closed-loop) and object-only (open-loop) visual-feedback conditions in a situation in which the light levels and contrast between an object and its surroundings were equivalent in both viewing conditions. Reach duration was longer with proportionate increases in both the acceleration and deceleration phases when visual feedback of the reaching limb was prevented. Maximum grip aperture and the proportion of movement time at which it occurred were the same in both conditions. Thus, in contrast to previous studies that did not employ constant light levels across closed- and open-loop reaching conditions, a dissociation was found between the spatial and temporal dimensions of grip formation. It appears that the posture of the hand can be programmed without visual feedback of the hand – presumably via a combination of visual information about the goal object and proprioceptive feedback (and/or efference copy). Nevertheless, maximum grip aperture (like the kinematic markers examined in the transport component) was also delayed when visual feedback of the reaching limb was selectively prevented. In other words, the relative timing of kinematic events was essentially unchanged, reflecting perhaps a tight coupling between the transport and grip components. Received: 3 July 1998 / Accepted: 18 November 1998     

Functional magnetic resonance imaging evidence for binocular interactions in human visual cortex

Using functional magnetic resonance imaging (fMRI), we explored the binocular interactions occurring when subjects viewed dichoptically presented checkerboard stimuli. A flickering radial checkerboard was presented to each eye of the subject, while T2*-weighted images were acquired over the visual cortex with gradient-echo, echoplanar sequences. We compared responses in striate and extrastriate visual cortex under four conditions: both eyes were stimulated at the same time (binocular condition), each eye was stimulated in alternation (monocular condition) or first the one eye then the other eye was stimulated (left eye first - right eye trailing, or vice versa). The results indicate that only the striate area, in and near the calcarine fissure, shows significant differences for these stimulation conditions. These differences are not evident in more remote extrastriate or associational visual areas, although the BOLD response in the stimulation-rest comparison was robust. These results suggest that the effect could be related to inhibitory interactions across ocular dominance columns in striate visual cortex.     

Pretectal jerk neuron activity during saccadic eye movements and visual stimulations in the cat

Summary The activity of jerk neurons was recorded extracellularly in the pretectum of the awake cat. The characteristic response of jerk neurons was a short, high-frequency burst that occurred after fast movements (jerks) of a large, structured visual stimulus, during saccadic eye movements in the light, and after on or off visual stimulation. Mean burst latency to pure visual jerks was 50 ms, whereas it was 30 ms to saccadic eye movements. Bursts were found to be stereotyped; the highest discharge rate was always at burst onset. Jerk neurons were not selective for stimulus parameters (such as movement amplitude or direction) except that in some neurons a weak correlation between stimulus velocity and discharge frequency was found. During saccades in the dark, clear bursts were only rarely found. In about half of the neurons, however, there was a slight but significant increase in the number of spikes above spontaneous frequency. Visual receptive fields were very large (46° horizontal and 35° vertical extent, on average). Nevertheless, the pretectal jerk neurons showed a rough retinotopic order, which was in accordance with the published retinotopy of the pretectum. Jerk neurons were found throughout the whole superficial pretectum, but preferentially in an area that corresponds to the nucleus of the optic tract (NOT) and the nucleus pretectalis posterior (NPP). Saccades were elicited by electrical stimulations at the sites where jerk neurons were recorded. The direction of the elicited saccades depended strongly on the pretectal stimulation site. A possible role of the jerk neurons as a visuomotor relay to elicit saccades or to modulate perception and attention is discussed.     

Visual acuity and foveal cone density in the retina of the aged rhesus monkey

The specific aims of this study were to examine age differences in visual acuity among young adult (5 years), middle aged (12 years) and aged (22 years) rhesus monkeys in relation to foveal cone density in the diurnal duplex retina. Classically, acuity has been defined as the reciprocal of the least resolvable detail measured in minutes of visual angle. The minimum separable binocular acuity mean of the young adult group was 0.83 ± 0.11, middle age acuity mean was 0.86 ± 0.12, and the acuity mean of the aged monkeys was 2.0 – 0.70 minutes of visual angle. According to analysis of variance and multiple range tests for specific group means, the 0.83' acuity m mean of the young, and the 0.86' acuity mean of the middle age group did not differ significantly, whereas the 2.0' acuity mean of the old group differed significantly from the 2 younger age groups. Foveal cone density was determined morphometrically by assesmeent of cone inner segment width, and absolute cone inner segment number per 100 Am along the horizontal meridian of the pure cone, rod free 1° × 1° foveola. Foveal cone density decreased significantly from 44.16 per 100 Am in the middle age group to 39.00 per 100 Am in the old macaque group. Since the diurnal macaque is of the same taxonomic order as man, and the visual systems of the two species are directly comparable in terms of ac acuity and the central receptive field organization of the retino-geniculo-striate system, it may be concluded that the macaque may represent an attractive and valid model for studies of aging in photopic and scotopic vision of diurnal primates, including man.     

Polydipsia in the monkey generated by visual display schedules.

Discussions of adjunctive behavior still largely refer to polydipsia induced by food delivery schedules to food deprived animals. In the present experiment polydipsia was induced when socially isolated monkeys housed in barren home cages were exposed to scheduled deliveries of film and scheduled viewing of other monkeys. These data suggest the greater generality and complexity of adjunctive behaviors and show that schedule-induced polydipsia cannot be regarded as an artifact of food associated drinking.