Thierry Hasbroucq

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.

Is the ‘error negativity’ specific to errors?

When subjects make an erroneous response in a choice reaction time task, an error negativity, or error-related negativity (N(E)/ERN), peaking at about 100 ms after EMG onset, has been described. This wave is often considered to be absent on correct response trials. We report a small N(E)/ERN wave on correct response trials during a choice reaction time task in which surface Laplacians were estimated by the source derivation method. This wave is well focused at FCz, and its time course is the same for correct responses trials, incorrect sub-threshold EMG activation trials, and error trials. Current source density maps, also indicate a focus at FCz. A second experiment showed the existence of a N(E) at FCz on correct trials during a simple RT task. Rather than an error detection process per se, we propose that the N(E)/ERN reflects either a comparison process leading secondarily to error detection, or an emotional reaction.

Physiological evidence for response inhibition in choice reaction time tasks

Inhibition is a widely used notion proposed to account for data obtained in choice reaction time (RT) tasks. However, this concept is weakly supported by empirical facts. In this paper, we review a series of experiments using Hoffman reflex, transcranial magnetic stimulation and electroencephalography to study inhibition in choice RT tasks. We provide empirical support for the idea that inhibition does occur during choice RT, and the implications of those findings for various classes of choice RT models are discussed.

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.

Error negativity on correct trials: a reexamination of available data

The error negativity, an EEG wave observed when subjects commit an error in a choice reaction time (RT) task, is often considered as a sign of error detection. Recently, reports of Ne-like waves on correct responses did challenge this interpretation. It has been proposed, however, that these Ne-like waves result either from an artifactual contamination of response-locked activities by stimulus-locked ones, or from an implicit monitoring of the time elapsing during the RT. Our aim was to reprocess published data: (1) to compare the shape and amplitude of EMG-locked and stimulus-locked ERPs on correct trials, and (2) to compare the size of the EMG-locked Ne-like waves obtained on fast and slow trials. The results neither support the artifact hypothesis nor the RT monitoring one. Therefore, it seems that the Ne-like waves observed on correct trials do correspond to a Ne, which suggests that the Ne has a broader significance than just error detection.

To Head or to Heed? Beyond the Surface of Selective Action Inhibition: A Review

To head rather than heed to temptations is easier said than done. Since tempting actions are often contextually inappropriate, selective suppression is invoked to inhibit such actions. Thus far, laboratory tasks have not been very successful in highlighting these processes. We suggest that this is for three reasons. First, it is important to dissociate between an early susceptibility to making stimulus-driven impulsive but erroneous actions, and the subsequent selective suppression of these impulses that facilitates the selection of the correct action. Second, studies have focused on mean or median reaction times (RT), which conceals the temporal dynamics of action control. Third, studies have focused on group means, while considering individual differences as a source of error variance. Here, we present an overview of recent behavioral and imaging studies that overcame these limitations by analyzing RT distributions. As will become clear, this approach has revealed variations in inhibitory control over impulsive actions as a function of task instructions, conflict probability, and between-trial adjustments (following conflict or following an error trial) that are hidden if mean RTs are analyzed. Next, we discuss a selection of behavioral as well as imaging studies to illustrate that individual differences are meaningful and help understand selective suppression during action selection within samples of young and healthy individuals, but also within clinical samples of patients diagnosed with attention deficit/hyperactivity disorder or Parkinsons disease.

Error negativity does not reflect conflict: A reappraisal of conflict monitoring and anterior cingulate cortex activity

Our ability to detect and correct errors is essential for our adaptive behavior. The conflict-loop theory states that the anterior cingulate cortex (ACC) plays a key role in detecting the need to increase control through conflict monitoring. Such monitoring is assumed to manifest itself in an electroencephalographic (EEG) component, the error negativity (Ne or error-related negativity [ERN]). We have directly tested the hypothesis that the ACC monitors conflict through simulation and experimental studies. Both the simulated and EEG traces were sorted, on a trial-by-trial basis, as a function of the degree of conflict, measured as the temporal overlap between incorrect and correct response activations. The simulations clearly show that conflict increases as temporal overlap between response activation increases, whereas the experimental results demonstrate that the amplitude of the Ne decreases as temporal overlap increases, suggesting that the ACC does not monitor conflict. At a functional level, the results show that the duration of the Ne depends on the time needed to correct (partial) errors, revealing an on-line modulation of control on a very short time scale.

The dual nature of time preparation: neural activation and suppression revealed by transcranial magnetic stimulation of the motor cortex

Single‐pulse transcranial magnetic stimulations (TMSs) of the motor cortex (M1) were performed in order to decipher the neural mechanisms of time preparation. We varied the degree to which it was possible to prepare for the response signal in a choice reaction time (RT) task by employing either a short (500 ms) or a long (2500 ms) foreperiod in separate blocks of trials. Transcranial magnetic stimulations were delivered during these foreperiods in order to study modulations in both the size of the motor evoked potential (MEP) and the duration of the silent period (SP) in tonically activated response agonists. Motor evoked potential area and silent period duration were assumed to reflect, respectively, the excitability of the cortico‐spinal pathway and the recruitment of inhibitory cortical interneurons. Shorter reaction times were observed with the shorter foreperiod, indicating that a better level of preparation was attained for the short foreperiod. Silent period duration decreased as time elapsed during the foreperiod and this decrement was more pronounced for the short foreperiod. This result suggests that time preparation is accompanied by a removal of intracortical inhibition, resulting in an activation. Motor evoked potential area decreased over the course of the short foreperiod, but not over the long foreperiod, revealing that time preparation involves the inhibition of the cortico‐spinal pathway. We propose that cortico‐spinal inhibition secures the development of cortical activation, preventing erroneous premature responding.

Information processing during physical exercise: a chronometric and electromyographic study

Choice reaction time (RT) is shorter when participants perform a choice task at the same time as a sub-maximal exercise than when they are at rest. The purpose of the present study was to determine whether such an exercise affects response execution or whether it alters processes located upstream from the neuro-muscular level. To this end, the electromyographic (EMG) activity of the response agonists was analysed in a between-hand choice RT task performed either concurrently with a pedalling task or at rest. Visual stimulus intensity was also manipulated so as to determine whether exercise further affects early sensory processes. Results shows that exercise affected the time interval elapsing from the onset of the contraction of the response agonists to the mechanical response, thereby indicating that this variable modifies the peripheral motor processes involved in response execution. EMG signal analyses further revealed that the cortico-spinal command is more efficient during exercise than at rest. In addition, exercise was shown to interact with visual stimulus intensity on the time between stimulus and voluntary EMG onset and to increase the critical flicker fusion frequency threshold, thereby indicating that exercise modifies the peripheral sensory processes involved in early sensory operations. The decomposition of RT, with respect to the EMG activity of response agonists, sheds light on the processes affected by exercise and suggests that exercise affects both sensory processes and late motor processes.

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.