Biomedical subjects

J Sangals

Publications and source records attributed to J Sangals.

3 recordsLinked to original sources

PubMed2000

Impairments of manual tracking performance during spaceflight: more converging evidence from a 20-day space mission.

Studies of human performance during spaceflight have consistently revealed degradations of manual tracking performance in space. The present investigation analysed these performance decrements in more detail by applying frequency-response analyses of tracking performance. It was hypothesized that tracking impairments result from two factors: at an early adaptation phase in space they primarily reflect effects of microgravity on human visuo-motor processes, whereas later into the mission they are also caused by impairments of attentional processes induced by cumulative workload and fatigue. In order to investigate this hypothesis, performance of one cosmonaut in a first-order unstable tracking task was repeatedly assessed before, during and after a 20-day space mission. Single-case statistical analyses revealed the following effects: tracking performance declined at the first assessment in space and in two later inflight sessions compared to pre-flight baseline. Whereas the early tracking decrement was mainly due to an increase of the effective time-delay during tracking and accompanied by only minor changes of mood or workload, one of the later inflight impairments was due to an increase of effective time-delay, a decreased tracking gain, and an increase of tracking remnant, and both were associated with considerably higher workload ratings. This pattern of effects supports the two-factor hypothesis.

Adult↗

PubMed1999

Changed visuomotor transformations during and after prolonged microgravity.

A series of step-tracking experiments was conducted before, during, and after a 3-week space mission to assess the effects of prolonged microgravity on a non-postural motor-control task. In- and post-flight accuracy was affected only marginally. However, kinematic analyses revealed a considerable change in the underlying movement dynamics: too-small force and, thus, too-low velocity in the first part of the movements was mainly compensated by lengthening the deceleration phase of the primary movement, so that accuracy was regained at its end. The observed in-flight decrements in peak velocity and peak acceleration point to an underestimation of mass, in agreement with the re-interpretation hypothesis of Bock et. al. Post-flight no reversals of the in-flight changes (negative aftereffects) were found. Instead, there was a general slowing down, which could be due to post-flight physical exhaustion.

Adult↗

PubMed1998

Task-dependent mixtures of coordinate systems in visuomotor transformations.

In two experiments the involvement of relative and fixed coordinate systems in visuomotor transformations was examined. The experimental task required the successive performance of two movements in each trial, which had to "correspond" to different visual stimuli. One kind of visual display indicated target positions by way of different horizontal positions of a vertical line on a monitor (position mode), while the other indicated movement amplitudes by way of different lengths of a horizontal line (amplitude mode). Formal analysis of variances and covariances of successive individual movements led to the conclusion that in the position mode visuomotor transformations were based on a mixture of relative and fixed coordinate systems, while in the amplitude mode only a relative coordinate system was involved. Thus, visuomotor transformations can be characterized as mixtures of different coordinate systems, and their respective weights in the mixtures are task-dependent.

Adolescent↗