No Evidence for an Effect of the Distance Between the Hands on Tactile Temporal Order Judgments

Localizing somatosensory stimuli is an important process, as it allows us to spatially guide our actions toward the object entering in contact with the body. Accordingly, the positions of tactile inputs are coded according to both somatotopic and spatiotopic representations, the latter one considering the position of the stimulated limbs in external space. The spatiotopic representation has often been evidenced by means of temporal order judgment (TOJ) tasks. Participants’ judgments about the order of appearance of two successive somatosensory stimuli are less accurate when the hands are crossed over the body midline than uncrossed but also when participants’ hands are placed close together when compared with farther away. Moreover, these postural effects might depend on the vision of the stimulated limbs. The aim of this study was to test the influence of seeing the hands, on the modulation of tactile TOJ by the spatial distance between the stimulated limbs. The results showed no influence of the distance between the stimulated hands on TOJ performance and prevent us from concluding whether vision of the hands affects TOJ performance, or whether these variables interact. The reliability of such distance effect to investigate the spatial representations of tactile inputs is questioned.

Postural effects on arm movement variability are idiosyncratic and feedback-dependent

Reaching movements are subject to noise arising during the sensing, planning and execution phases of movement production, which contributes to movement variability. When vision of the moving hand is available, reaching variability appears to be strongly influenced by noise occurring during the specification and/or online updating of movement plans in visual coordinates. In contrast, when vision of the hand is unavailable, variability appears more dependent upon hand movement direction, suggesting a greater influence of execution noise. Given that execution noise acts in part at the muscular level, we hypothesized that reaching variability should depend not only on movement direction but initial arm posture as well. Moreover, given that the effects of execution noise are more apparent when movements are performed without vision of the hand, we reasoned that postural effects would be more evident when visual feedback was withheld. To test these hypotheses, subjects planned memory-guided reaching movements to three frontal plane targets, using either an “adducted” or “abducted” initial arm posture. Movements were then executed with and without hand vision. We found that the effects of initial arm posture on movement variability were idiosyncratic in both visual feedback conditions. In addition, without visual feedback, posture-dependent differences in variability varied with movement extent, growing abruptly larger in magnitude during the terminal phases of movement, and were moderately correlated with differences in mean endpoint positions. The results emphasize the role of factors other than noise (i.e. biomechanics and suboptimal sensorimotor integration) in constraining patterns of movement variability in 3D space.

MASS-SPECTROMETRIC STUDIES OF THE DYNAMICS OF EXHALED AIR COMPOSITION DURING DYNAMIC POSTURAL EFFECTS

The paper studies the possibility of using a quadrupole gas mass spectrometer as part of a diagnostic complex based on a rotary (mechanorgical) table to assess the effectiveness of the dynamic postural effects on patients. Analysis of the obtained mass spectrograms indicates that the response of patients is individual and can vary significantly. Taking into account the mass spectrometric parameters of exhaled air allows the patient to be assigned to a specific group. Information on the concentration of oxygen and carbon dioxide in the patient's exhalation, as well as the analysis of the envelope shape of the measured dynamic mass spectrograms can be used for comprehensive diagnostics of the patient's condition in addition to the data of the main sensors in the complex.