Trajectory control in targeted force impulses

Summary This study was undertaken in order to determine the time course of the process by which information derived from a visual target is used to accurately set the amplitude of a simple motor response. We refer to this process as response specification. Separate auditory and visual cues were given to the subjects in order to independently control the moment of response initiation and the time available for processing amplitude information from the target. Six subjects initiated impulses of isometric force in synchrony with the last of predictable series of regular tones. Response amplitudes were to match one of three visual target steps occurring at random times between 0 and 400 ms before the response-synchronizing tone. Using these separate auditory and visual cues, we were able to systematically vary the time interval between target presentation and response onset, termed here Stimulus-Response or S-R interval. Target steps were presented in blocks of either predictable (simple condition) or unpredictable (choice condition) amplitudes. The peak forces and the peaks of their time derivatives were analyzed to determine how subjects achieved accuracy under the different conditions and at different S-R intervals. The trajectories of responses produced in the simple condition were independent of the S-R interval. In contrast, when targets were presented in unpredictable order, the distribution of the peak forces of the subjects' responses depended on the S-R interval. At short S-R intervals (<125 ms), subjects made responses whose peak forces were distributed around the center of the range of target steps. These responses formed a unimodal, but broad distribution which was independent of actual target amplitude. With increasing S-R interval (>125 ms), the distributions of peak forces gradually shifted toward the correct target amplitudes, with the means reaching the appropriate amplitudes at S-R intervals of 250–400 ms. At S-R intervals comparable to a reaction time, the range of peak forces was constricted to a similar extent as previously observed in a reaction time task (Hening et al. 1988). We found that the gradual improvement of accuracy was not achieved through changes in trajectory control: at all S-R intervals, subjects utilized a pulse-height control policy (Gordon and Ghez 1987a). Different peak forces were achieved by varying the rate of rise of force, while force rise time was held relatively invariant. We did find, however, that within the constraints imposed by rise time regulation, compensatory adjustments to the force trajectories (Gordon and Ghez 1987b) were greatest during the period of specification. We conclude that (1) subjects can initiate their responses independent of the degree of specification achieved and that the normal process of specification of amplitude begins earlier and continues longer than the latency of responses in a reaction time task; (2) before target presentation, subjects prepare a default response whose amplitude is biased by prior experience with the targets presented in the task. We hypothesize that the central mechanisms that specify response amplitude do so by a progressive adjustment of the default parameters.     

Bilateral receptive field neurons in the hindlimb region of the postcentral somatosensory cortex in awake macaque monkeys

Single-neuron activities were recorded in the hindlimb region of the primary somatosensory cortex and part of area 5 in awake Japanese monkeys. A total of 1050 units were isolated from five hemispheres of four animals. Receptive fields (RFs) and submodalities were identified for 90% of isolated neurons in areas 3a and 3b. The percentage decreased as the recoding site moved to the more caudal areas. Deep or skin submodality neurons were dominant in area 3a or area 3b, respectively. Deep submodality neurons increased in more caudal areas and were the majority in areas 2 and 5. These observations were consistent with those in the hand and/or digit or arm and/or trunk region. The identified neurons were classified by their RF positions into four types: the foot, leg, foot and leg, or hindlimb and other body parts type. Among 831 identified neurons, 33 neurons had bilateral RFs, 14 had ipsilateral RFs, and the rest (N=784) had contralateral RFs. The relative incidence of neurons with bilateral or ipsilateral RFs among identified neurons was less than 1% in areas 3a, 3b, and 1, and 16% or 25% in areas 2 or 5, respectively. Within areas 2 and 5, the percentage of neurons with bilateral or ipsilateral RFs was significantly smaller in the foot type (5%) than in other RF types (24-57%). RFs of the foot type were on the sole or single toe but never on multiple toes. These observations contrasted with the previous findings that neurons with bilateral RFs were more frequently seen in the hand and/or digit region and that RFs on multiple digit tips were dominant there. The present study thus demonstrated that neurons with bilateral RFs do exist in the hindlimb region. Similarly to the forelimb region, they were found mostly in areas 2 and 5, the caudalmost areas of the postcentral gyrus and hierarchically higher stages in information processing. The relative paucity of neurons with bilateral RFs on the foot, especially those with RFs on multiple toes, may reflect functional differences between the foot and the hand.     

Freshly isolated mouse 4F7+ splenic dendritic cells process and present exogenous antigens to T cells

The antibody 4F7 was reported to recognize an epitope expressed on dendritic cells (DC) from various tissues. To study the ability of splenic 4F7⁺ dendritic cells to process antigen for presentation to CD4⁺ T cells, DC were enriched using a separation procedure avoiding overnight culture which could lead to an altered phenotype. These DC were used as antigen-presenting cells (APC) in stimulation cultures of major histocompatibility complex class II-restricted T cells. It was found that they induce antigen-dependent lymphokine production by T cells and therefore could present exogenous antigens. These processing takes place intracellularly, because fixation abrogates presentation to T cells. Moreover, antigen presentation needs intracellular processing within endo- or lysosomes as chloroquine-treatment prevents T cell activation. Titration of APC numbers revealed that contaminating APC most likely did not account for antigen-specific T cell activation by DC. No evidence was found for release of antigenic peptides or for partial antigen processing possibly done by cell surface located enzymes on DC. In conclusion, these results indicate that freshly enriched DC are able to process antigens similarly to other APC.     

Electrodermal Lability and Visual Information Processing

Individual differences in electrodermal lability have been related to performance in vigilance and reaction time tasks. The goal of the present study was to employ an "additive factors" approach to identify the stages of information processing that might underlie these effects. Nineteen labile and 17 stabile subjects performed a choice reaction time task in which a visual imperative stimulus was presented under two conditions of intensity (presumed to affect the speed of pre-processing operations) X three conditions of degradation (which influences later encoding processes related to feature extraction). Measures of both reaction time and movement time were obtained. The major findings were: (a) labile subjects had faster reaction times than stabiles, and (b) lability interacted significantly with stimulus degradation. Labiles also tended (p less than .10) to have faster movement times. This pattern indicates that labiles and stabiles differ in the performance of later encoding operations, and possibly in the speed of motor processes as well. However, they do not appear to differ in the early pre-processing of the simple physical attributes of a stimulus.     

股骨CT图像轮廓跟踪方法

目的 为重建和测量股骨的解剖结构，需要大量地读取CT图像的信息，以获得股骨轮廓的坐标值。方法本研究采用直方图阈值图像分割、Kirsh边缘提取法获得股骨的二值化轮廓图像。结果轮廓坐标的提取应用了“迷宫”边缘跟踪算法。结论本方法可大量、快捷、正确地提取图像轮廓信息。     

New algorithmic-based digital filter processing system for real-time continuous blood pressure measurement and analysis in conscious rats

A new algorithmic-based digital filter processing system for real-time continuous blood pressure (BP) measurement and analysis in freely-moving conscious rats has been developed. Real-time recognition of BP waveforms, real-time noise rejection and determination of representative waveform indexes (WIs) at indicated time points using digital filters and Smirnov's rejection test were realized with this system. Digital filters were applied for two different purposes: waveform segmentation and smoothing the calculations of representative WIs. Smirnov's rejection test was used for real-time noise rejection and yielded an accurate rejection rate of 99.99%. The result was that the digital filter processing and Smirnov's rejection test realized accurate real-time BP measurement and analysis in freely-moving conscious rats using a personal computer.     

Computerised analysis of auscultatory sounds associated with vascular patency of haemodialysis access

Vascular access for renal dialysis is a lifeline for about 120 000 individuals in the United States. Stethoscope auscultation of vascular sounds has some utility in the assessment of access patency, yet can be highly skill-dependent. The objective of the study was to identify acoustic parameters that are related to changes in vascular access patency. The underlying hypothesis is that stenoses of haemodialysis access vessels or grafts cause vascular sound changes that are detectable using computerised data acquisition and analysis. Eleven patients participated in the study. Their vascular sounds were recorded before and after angiography, which was accompanied by angioplasty in most patients. The sounds were acquired using two electronic stethoscopes and then digitised and analysed on a personal computer. Vessel stenosis changes were found to be associated with changes in acoustic amplitude and/or spectral energy distribution. Certain acoustic parameters correlated well (correlation coefficient=0.98, p<0.0001) with the change in the degree of stenosis, suggesting that stenosis severity may be predictable from these parameters. Parameters also appeared to be sensitive to modest diameter changes (>20%), (p<0.005, Wilcoxon rank sum test). These results suggest that computerised analysis of vascular sounds may be useful in vessel patency surveillance. Further testing using longitudinal studies may be warranted.     

How to Optimize Radiological Images Captured from Digital Cameras, Using the Adobe Photoshop 6.0 Program

Over the past decade, the technology that permits images to be digitized and the reduction in the cost of digital equipment allows quick digital transfer of any conventional radiological film. Images then can be transferred to a personal computer, and several software programs are available that can manipulate their digital appearance. In this article, the fundamentals of digital imaging are discussed, as well as the wide variety of optional adjustments that the Adobe Photoshop 6.0 (Adobe Systems, San Jose, CA) program can offer to present radiological images with satisfactory digital imaging quality.     

Electronic data processing in the Danish Cytogenetic Central Register and EDP problems of registers in general

A brief introduction to the Danish Cytogenetic Central Register (DCCR) is given, and possibilities, principles and problems concerning the establishment and maintenance of a national cytogenetic register are presented.
Various data carrier media for registers in general are discussed, of which the magnetic disc is considered most appropriate. General principles for programs capable of performing insertions, deletions and other modifications in the data base are outlined as well as the principles for the programs in the DCCR.
The individual records should preferably be identified by aid of a central person registration number (CPR) rather than by name. The data should be stored and sorted by this identification in order to facilitate retrieval of a desired record. The structure of the records is discussed with regard to prevention of the occurrence of certain errors as well as the optimization of processing.
Flexibility and economy of space are achieved by using programs able to handle records of unequal length, and problems occurring in connection with this are discussed. The question of how to protect sensitive data is dealt with, and two different methods used in the DCCR are outlined. Programs capable of analyzing karyotypes with the purpose of recognizing various cytogenetic syndromes have been developed for use in the DCCR. Various examples of computing times of typical program runs are presented.