Biomedical subjects

T Hasbroucq

Publications and source records attributed to T Hasbroucq.

29 records · Page 2Linked to original sources

PubMed1997

Preparatory inhibition of cortico-spinal excitability: a transcranial magnetic stimulation study in man.

In order to investigate the preparatory modulations of cortico-spinal excitability, reaction time (RT) methods were combined with transcranial magnetic stimulation (TMS) of the motor cortex. We analyzed the variations in the amplitude of motor potentials evoked in a prime mover (flexor digitorum sublimis) by TMS delivered during the foreperiod of a visual choice RT task. In experiment 1 (n = 10), the TMS was delivered either simultaneously with the warning signal or simultaneously with the response signal in two conditions of foreperiod duration: short (500 ms) and long (2500 ms). The peak amplitude of the motor evoked potentials diminished during the short foreperiod but not during the long foreperiod. Since RT was shorter when the foreperiod lasted 500 ms than when it lasted 2500 ms, this result suggests that the excitability of the cortico-spinal structures is minimal when the subject is optimally ready to react. In experiment 2 (n = 10), the time-course of this decrement was further explored. With this aim, only the short foreperiod was used and the TMS was delivered either 500 ms, 333 ms, 167 ms or 0 ms before the response signal. Cortico-spinal excitability decreased during the first 333 ms and then remained stable until the occurrence of the response signal. In light of previous studies, the present results suggest that the decrement of cortico-spinal excitability during the short foreperiod reflects an adaptative mechanism which increases the sensitivity of the motor structures to the forthcoming voluntary command.

Adult↗

PubMed1997

Why does the single neuron activity change from trial to trial during sensory-motor task?

Single neuron activities from cortical areas of a monkey were recorded while performing a sensory-motor task (a choice reaction time task). Quantitative trial-by-trial analysis revealed that the timing of peak activity exhibited large variation from trial to trial, compared to the variation in the behavioral reaction time of the task. Therefore, we developed a multi-unit dynamic neural network model to investigate the effects of structure of neural connections on the variation of the timing of peak activity. Computer simulation of the model showed that, even though the units are connected in a cascade fashion, a wide variation exists in the timing of peak activity of neurons because of parallel organization of neural network within each unit.

Animals↗

PubMed1995

Stimulus preprocessing and response selection in depression: a reaction time study.

Depressed subjects are slower than normal controls in reaction time (RT) tasks. However, it is not clear whether depression affects all stages of information-processing or only some of them. In the present study, this question was addressed by using the additive factor method. Ten inpatients and ten control subjects performed a two-choice visual RT task. Stimulus intensity and stimulus-response compatibility were manipulated. The effect of intensity was similar in both groups whereas the effect of compatibility was larger for the patients than for the controls. This suggests that stimulus preprocessing is unaffected by depression whilst response selection is impaired.

Adult↗

PubMed1995

Does irrelevant stimulus location affect response selection?

Reaction time (RT) is shorter when the irrelevant location of the stimulus corresponds to the relevant location of the response: When a subject is to perform a left or right keypress according to the colour of a stimulus delivered either to the left or to the right of a fixation, RT is typically shorter when the location of the stimulus corresponds to the location of the response (e.g., left stimulus/left response) than when it does not (e.g., left stimulus/right response). Umiltà and Nicoletti (1990) have suggested that this effect, known as the ¿Simon effect' in the literature, occurred at the response selection stage, a stage whose duration depends on the effectors used to perform the task. In the present study, this effect and that of the finger response repertoire (within- versus between-hand composition) were found to be additive, which does not support the response selection hypothesis of the Simon effect.

Adult↗

PubMed1995

A comparison of tactile, auditory, and visual feedback in a pointing task using a mouse-type device.

A mouse was modified to add tactile feedback via a solenoid-driven pin projecting through a hole in the left mouse button. An experiment is described using a target selection task under five different sensory feedback conditions ('normal', auditory, colour, tactile, and combined). No differences were found in overall response times, error rates, or bandwidths; however, significant differences were found in the final positioning times (from the cursor entering the target to selecting the target). For the latter, tactile feedback was the quickest, normal feedback was the slowest. An examination of the spatial distributions in responses showed a peaked, narrow distribution for the normal condition, and a flat, wide distribution for the tactile (and combined) conditions. It is argued that tactile feedback allows subjects to use a wider area of the target and to select targets more quickly once the cursor is inside the target. Design considerations for human-computer interfaces are discussed.

Attention↗

PubMed1993

Intensity to force translation: a new effect of stimulus-response compatibility revealed by analysis of response time and electromyographic activity of a prime mover.

In reaction time studies of stimulus-response compatibility, emphasis has been placed on the influence of spatial stimulus-response relationships, but what seems to be essential for the emergence of an effect of stimulus-response compatibility is the existence of a conceptual match between stimulus and response variables. This notion was at the origin of the present study to assess the compatibility relationship between the intensity of a visual stimulus and the force of a voluntary muscle contraction. A stimulus-response compatibility effect was demonstrated. This effect was entirely due to premotoric processes.

Adult↗

PubMed1992

The effects of intensity and irrelevant location of a tactile stimulation in a choice reaction time task.

Simon and his colleagues have demonstrated that the location of a stimulus in the sensory field, even if it is irrelevant for the task, may critically affect reaction time. This so-called 'Simon effect' is a general phenomenon that encompasses all sensory modalities. The experiment reported here showed that the tactile version of the Simon effect was additive on reaction time with the respective effects of stimulus intensity and of the within-hand/between-hand composition of the repertoire of fingers devoted to the task. In light of recent theoretical developments, the present data suggest that the locus of the Simon effect is stimulus identification, a perceptual stage which follows stimulus encoding and precedes stimulus-response translation.

Adult↗

PubMed1991

Stimulus-response compatibility and the Simon effect: toward a conceptual clarification.

The current view that the Simon effect (Simon & Small, 1969) reflects stimulus-response compatibility (SRC) is questioned. Previous accounts of the Simon effect have overlooked stimulus congruity (SC), the correspondence relation borne by the two simultaneous aspects of the stimulus, a factor inevitably confounded in the Simon paradigm with irrelevant spatial S-R correspondence. The Hedge and Marsh (1975) reversal effect, replicated in Experiment 1, is reinterpreted as decisive evidence that the Simon effect is entirely accounted for by SC. Furthermore, in Experiment 2 irrelevant S-R correspondence was manipulated in the absence of any variation of SC, and the Simon effect vanished. It is concluded that the Simon effect, contrary to current opinion, represents a spatial variant of the Stroop effect and is irrelevant to the SRC issue. The view that mental operations proceed automatically at the stage of response determination loses one of its strongest empirical arguments.

Adult↗

PubMed1990

Dimensional overlap: cognitive basis for stimulus-response compatibility--a model and taxonomy.

The classic problem of stimulus-response (S-R) compatibility (SRC) is addressed. A cognitive model is proposed that views the stimulus and response sets in S-R ensembles as categories with dimensions that may or may not overlap. If they do overlap, the task may be compatible or incompatible, depending on the assigned S-R mapping. If they do not overlap, the task is noncompatible regardless of the assigned mapping. The overlapping dimensions may be relevant or not. The model provides a systematic account of SRC effects, a taxonomy of simple performance tasks that were hitherto thought to be unrelated, and suggestive parallels between these tasks and the experimental paradigms that have traditionally been used to study attentional, controlled, and automatic processes.

Arousal↗

PubMed1987

Preliminary evidence for body-centered coding of tactile motor events.

A number of experimental studies have consistently shown that on reaction time tasks with visual or auditory stimuli, the subjects code their responses in environmental rather than body-centered terms. The aim of the present study was to determine which of these two frames of reference subjects spontaneously adopt to code tactile motor events. Eight subjects were requested to respond with key-presses to mechanical stimulations delivered under the finger tips. Reaction time was analysed as a function of device- and body-centered S-R relationships. Subjects displayed a strong S-R compatibility effect that suggested their body-centered coding of tactile motor events.

Functional Laterality↗

PubMedDate not supplied

Levodopa-induced drowsiness in healthy volunteers: results of a choice reaction time test combined with a subjective evaluation of sedation.

The aim of the present study was to assess levodopa (L-Dopa)-induced drowsiness in healthy volunteers using two parameters: choice reaction time and a subjective rating of sedation. Sixteen subjects participated in a randomized, double-blinded, crossover study. A single dose of 200 mg L-Dopa or placebo was administered at 9:00 AM. To limit peripheral side effects connected with L-Dopa, subjects were treated with 20 mg domperidone three times daily. Subjective rating of sedation consisted of visual analogue scale. Reaction time was measured by means of responses to two light-emitting diodes. The illumination of one of these diodes constituted the imperative signal. Manual responses were performed on two buttons located under the right and left index fingers. Results demonstrated a positive correlation between sedation level and reaction time (r = 0.70, p = 0.0026). Adverse events of L-Dopa were nausea (four cases) and excitation (one case). Subjects who did not develop adverse events were faster under L-Dopa than under placebo (p = 0.02), whereas subjects who had nausea or excitation were slower. A single dose of L-Dopa either deteriorated or improved choice reaction time in healthy volunteers according to whether it was sedative and whether it generated disruptive adverse events.

Adult↗