[Show abstract][Hide abstract] ABSTRACT: The aim of the present study was to investigate the modulations in amplitude of H reflexes elicited in a hand muscle, the flexor pollicis brevis, during the performance of a choice reaction time (RT) task in which this muscle was directly involved. Ten subjects were to choose between a left- or a right-thumb key-press according to the lateral location of a flash of light. The stimulus-response mapping was either compatible or incompatible. Hoffman reflexes were elicited at different times during the RT by stimulation of the median nerve. Twenty-five milliseconds before the voluntary response, the amplitude of the H reflex suddenly increased when the muscle was involved in the response and decreased symmetrically when the muscle was not involved in the response. Mapping compatibility exerted no detectable influence on the changes in spinal excitability. The latter result supports the assumptions that are at the core of Sternberg's additive factor method.
[Show abstract][Hide abstract] ABSTRACT: Choice reaction time (RT) is shorter when the stimulus corresponds spatially to the response than when the stimulus does not, even when the stimulus location is irrelevant to the task. We used electromyographic measures to document that this effect is the result of a response conflict. The activity of the prime movers of two alternative responses was recorded during the performance of a visual RT task in which the irrelevant spatial correspondence between the stimuli and the responses was varied. Only the premotor component of RT was affected by the stimulus-response correspondence. Correct trials were distinguished according to whether or not the activation of the prime mover involved in the required response was preceded by an activation of the prime mover involved in the alternative response. Double muscular activation trials were more numerous for noncorresponding than for corresponding stimulus-response associations. Furthermore, these trials yielded longer RTs than the single muscular activation trials.
[Show abstract][Hide abstract] ABSTRACT: Changes in cortico-spinal excitability related to time and event preparation were investigated by transcranial magnetic stimulation (TMS) of the motor cortex during the foreperiod of a movement-precuing task. Subjects performed a four alternative choice reaction time (RT) task involving a button-press with the index or middle finger (FI) of the left or right hand. Advance information about the to-be-signaled response was provided by a precue, which preceded the response signal by a 1 s foreperiod. The precue either indicated the hand (right or left) or FI (index or middle) with which the response would be executed or was uninformative. TMS was delivered to the left or right cortical hand area at one of five possible times during the foreperiod: -1000, -500, -333, -166 or 0 ms prior to the response signal. Surface EMG activity from a prime mover involved in flexion of the response FIs (Flexor digitorum superficialis) was used to measure the magnitude of the motor evoked potential (MEP) elicited by TMS. Cortico-spinal excitability--as assessed by the magnitude of the MEP evoked in the target muscle contralateral to the stimulated hemisphere--progressively decreased during the foreperiod. The identity of the precued responses, however, had no effect on MEP magnitude. These results suggest that preparation to respond at a particular time inhibited excitability of the cortico-spinal tract, while advance preparation to perform specific responses affected more central structures only.
[Show abstract][Hide abstract] ABSTRACT: Previous studies have shown that fluvoxamine, an inhibitor of serotonin reuptake, shortens choice reaction time. The present study, was intended to explore this effect by using two complementary approaches: (i) Sternberg's additive factor method, and (ii) the analysis of the electromyographic activity of a prime mover. Eight healthy subjects who received either a single oral dose of fluvoxamine (100 mg) or a placebo participated in a choice reaction time experiment in which imperative signal intensity, stimulus-response mapping, and response repertoire were manipulated. Previous results were replicated. Moreover, it was shown that fluvoxamine shortens the interval between prime mover activation and overt response. This supports the hypothesis proposed in a previous study that fluvoxamine affects motor processes. A possible mechanism of this effect is discussed.
[Show abstract][Hide abstract] ABSTRACT: In a previous study where reaction-time methods were combined with transcranial magnetic stimulation (TMS) of the motor cortex, cortico-spinal excitability was shown to reflect time preparation. Provided that subjects can accurately estimate time, the amplitude of motor-evoked potentials (MEPs) diminish progressively during the interval separating the warning signal from the response signal (i.e., the foreperiod). On the other hand, several experiments have demonstrated that the amplitude of the Hoffman (H) reflex elicited in prime movers diminishes during the foreperiod of reaction-time tasks. The aim of the present study was to compare the time course of the respective decrements of H-reflex and MEP amplitude during a constant 500-ms foreperiod. The subjects (n=8) participated in two experimental sessions. In one session, H-reflexes were induced in a tonically activated, responding hand muscle, the flexor pollicis brevis, at different times during the foreperiod of a visual-choice reaction-time task. In the other session, motor potentials were evoked in the same muscle by TMS of the motor cortex delivered in the same behavioral conditions and at the same times as in the first session. The results show that both H-reflexes and MEPs diminish in amplitude during the foreperiod, which replicates and extends previous findings. Interestingly, the time constants of the two decrements differed. There was a facilitatory effect of both electrical and magnetic stimulations on the subject's performance: reaction time was shorter for the trials during which a stimulation was delivered than for the no-stimulation trials. This facilitation was maximal when the stimulations were delivered simultaneously with the warning signal and vanished progressively with stimulation time.
Experimental Brain Research 02/1999; 124(1):33-41. · 2.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fluvoxamine is a specific serotonin reuptake inhibitor. Recent evidence suggests that this antidepressive drug shortens the reaction time (RT) of healthy volunteers. The first objective of the present study was to decipher whether this effect is due to an improvement in information processing per se or to the adoption of an error-prone strategy. The second objective was to locate the effect of fluvoxamine within the series of information processing stages by means of Sternberg's additive factor method. After administration of a single oral dose of fluvoxamine (100 mg) or a placebo (randomized double-blind, cross-over design), eight healthy volunteers performed a choice RT task in which stimulus intensity, stimulus-response compatibility and response repertoire were manipulated. Fluvoxamine shortened RT without decreasing the accuracy of the responses. This demonstrates that fluvoxamine improves information processing per se. The effect of fluvoxamine was additive on RT with the respective effects of stimulus intensity and stimulus-response compatibility. This result suggests that fluvoxamine spares the processing stages of stimulus preprocessing and response selection.
[Show abstract][Hide abstract] ABSTRACT: It has been shown that transcranial magnetic stimulation can delay simple reaction time; this happens when the stimulation is delivered during the reaction time and over the cortical area which commands the prime mover of the required response. Although it is agreed that magnetic stimulation could be a useful tool for studying information processing in man, we argue that, because of the use of simple reaction time, the results reported so far are difficult to interpret within this theoretical framework. In the present paper, three experiments are reported. Six subjects participated in experiment 1 in which magnetic stimulation was delivered, at different times, during choice reaction time. The effects of the magnetic stimulation of the cortical area involved in the response (induced current passing forward over the motor representation of the responding hand), were compared to the effects of an electrical stimulation of the median nerve (H-reflex). In a first control experiment (experiment 2a; 5 subjects), the coil was placed over the ipsilateral motor cortex (induced current passing backward over the motor representation of the non-responding hand) thus minimizing the probability to excite the same neural nets as in the first experiment. In a second control experiment (experiment 2b; 4 subjects), the coil was placed a few centimeters away from the subject's scalp thus ensuring no stimulation of any neural nets. The results show that: (1) the noise and the smarting of the skin associated with the coil discharge produce an intersensory facilitation thereby shortening reaction time (experiment 2a), (2) actually, the noise produced by the stimulation is sufficient to produce such a facilitatory effect (experiment 2b), (3) a stimulation over the area at the origin of the motor command causes a reaction time delay which counteracts this intersensory facilitation effect (experiment 1), (4) in this latter case, the closer the stimulation to the actual overt response, the longer the delay and (5) there is no trace of correlation between the amplitude of the motor evoked potential and the reaction time change.
Brain Research 06/1997; 755(2):181-92. · 2.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Cognitive Brain Research 04/1997; 5(3):185-92. · 3.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Canadian Journal of Experimental Psychology 10/1995; 49(3):349-56. · 1.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: We recall how Hasbroucq and Guiard (1991) defined stimulus (S) congruity, the SS-correspondence factor they demonstrated to account for both the Simon effect and the Hedge and Marsh effect, and how they explained the mechanisms that bring S congruity into play in the verbal and nonverbal versions of the Simon task and in the Hedge and Marsh task. We show that, contrary to O'Leary, Barber, and Simon's claim, Hasbroucq and Guiard used a consistent definition of S congruity across the various tasks of interest. Finally, we recognize that Hasbroucq and Guiard's experiments produced no direct falsification of the display control arrangement correspondence (DCC) hypothesis — the special-purpose hypothesis put forward by Simon and his group as an attempt to reconcile the Hedge and Marsh effect with their interpretation of the Simon effect in terms of irrelevant spatial SR correspondence —, but we argue that the DCC account is unnecessary and implausible.
Psychological Research 01/1994; 56(3):210-212. · 2.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Cognitive Brain Research 11/1993; 1(3):197-201. · 3.77 Impact Factor