Biomedical subjects

Paul Nagelkerke

Publications and source records attributed to Paul Nagelkerke.

5 recordsLinked to original sources

PubMed2006

Use of visual information in the correction of interceptive actions.

Use of visual information in interceptive actions requiring large-scale changes to movement timing was investigated. The task consisted of intercepting a moving target on a monitor screen through an angular arm movement. In half of the trials, the initial target velocity of 8 cm/s was unexpectedly decreased to 4 cm/s or increased to 12 cm/s, leaving 800 ms to target arrival after velocity change. Visual information about target displacement was manipulated by interpolating full vision with occlusion of the last 200, 400, or 600 ms before the due time of interception. The results revealed that reduction of visual exposure of target displacement affected movement variability, but not arm velocity or directional trend of temporal errors. This finding supports the concept that motor control in interception is based on an internal representation of target displacement, formed during the initial portion of visual exposure following velocity change, which is updated by further visual information of target displacement.

Adult↗

PubMed2006

Compatibility effects in stopping and response initiation in a continuous tracking task.

Two experiments explored stopping performance using a new stimulus-response compatibility effect spanning action initiation and stopping. Participants tracked a sometimes-moving, sometimes-stationary target by controlling the speed of a response marker via a force sensor. In the compatible condition, participants pressed the sensor in response to the target moving and stopped pressing in response to the target stopping. In the incompatible condition, participants stopped pressing in response to the target moving and initiated pressing in response to the target stopping. Response initiation and stopping were found to be faster under compatible than under incompatible conditions, regardless of whether compatible and incompatible trials were blocked or mixed. These findings indicate that stopping, like response initiation, is influenced by stimulus-response properties such as compatibility. This in turn suggests that stopping is governed by constraints similar to those of other behaviours.

Adolescent↗

PubMed2006

Reprogramming of interceptive actions: time course of temporal corrections for unexpected target velocity change.

The authors investigated the time course of reprogramming of the temporal dimension of motor acts in a task requiring interception of a moving target. The target moved at a constant velocity on a monitor screen; in part of the trials, target velocity was unexpectedly increased or decreased. Those modifications were produced at different moments during target displacement, leaving periods of time from 100 to 800 ms for movement timing correction. The authors assessed the effects of probability of target velocity change (25% vs. 50%), uncertainty about direction of velocity change (unidirectional vs. bidirectional), and direction of velocity change (increase vs. decrease). Analysis of 24 participants' arm acceleration showed that fast adjustments took place between 100 and 200 ms after target velocity change similarly for all uncertainty conditions. Analysis of temporal error indicated that the combination of high probability of target velocity change and certainty on direction of target velocity change led to the most successful movement timing reprogramming. For the other experimental conditions, temporal accuracy was still poor when a period of 800 ms was available for correction. Movement reprogramming was a continuous process that was more efficient for target velocity increase than for target velocity decrease.

Adult↗

PubMed2005

Identifying visual-vestibular contributions during target-directed locomotion.

The purpose of this experiment was to examine the potential interaction between visual and vestibular inputs as participants walked towards 1 of 3 targets located on a barrier 5m away. Visual and vestibular inputs were perturbed with displacing prisms and galvanic vestibular stimulation (GVS), respectively. For each target there were three vision conditions (no prisms, prisms left, and prisms right), and three GVS conditions (no GVS, anode left, and anode right). Participants were instructed to start with eyes closed, and to open the eyes at heel contact of the first step. GVS and target illumination were triggered by the first heel contact. This ensured that the upcoming visual condition and target were unknown and that both sensory perturbations occurred simultaneously. Lateral displacement was determined every 40 cm. Irrespective of target or direction, GVS or prism perturbation alone resulted in similar lateral deviations. When combined, the GVS and prism perturbations that had similar singular effects led to significantly larger deviations in the direction of the perturbations. The deviations were approximately equal to the sum of the single deviations indicating that the combined effects were additive. Conflicting GVS and prism perturbations led to significantly smaller deviations that were close to zero, indicating that opposite perturbations cancelled each other. These results show that when both visual and vestibular information remain important during task performance, the nervous system integrates the inputs equally.

Adult↗

PubMed2004

Inhibiting prepared and ongoing responses: is there more than one kind of stopping?

Inhibiting movements has been investigated widely using the countermanding (stop signal) paradigm. Although it has been assumed that response inhibition, as measured by the countermanding task, generalizes to all forms of stopping, this has never been tested. In the present study, stopping performance in the countermanding paradigm was compared with stopping performance in a new paradigm in which a continuous-tracking task was used. Although stimulus presentations were matched across paradigms, the two tasks differed in the type of stopping required. In the countermanding paradigm, response inhibition latency was measured prior to response execution-this is, it was inferred from the successful withholding of a go response. In the new paradigm, response inhibition was carried out after response execution-that is, it was measured as the time to begin stopping a continuous tracking response. Results indicated that stopping latencies between the two paradigms were highly correlated, providing strong evidence that stopping an unexecuted response engages the same mechanisms as stopping an ongoing response.

Adult↗