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This paper deals with two questions: what are the main characteristics of timing performance, and how do current timing models account for them? An outline of the most significant behavioural and neural indices of time processing is presented, with particular emphasis on the effects of activation and attention, and on data drawn from an important electrophysiological indice, the Contingent Negative Variation (CNV). A sample of influent timing models is then considered, ranged in two categories depending on whether they provide a representation of the time elapsing online between the limits of a target interval or a representation of the interval limits. The authors support the concept of online "pulse accumulation" as various types of cumulative mechanisms have been described at both neural and behavioural levels. [ABSTRACT FROM AUTHOR]

Abstract From electroencephalographic recordings, we estimated the surface Laplacian over motor areas in a Stroop-like between-hand choice reaction time task in humans. Response-locked averages showed a (negative) “motor potential” over the primary motor areas contralateral to the response. At the same time, a positive wave was observed over the primary motor areas ipsilateral to the response. These data suggest that, when a between-hand choice is required, an inhibition of the primary motor cortex ipsilateral to the nonresponding hand is implemented. This observation is relevant to the interpretation of the lateralized readiness potential (LRP) because the LRP is blind to the respective contribution of the contralateral and ipsilateral motor cortices. In addition, a negative wave beginning about 200 ms before EMG onset and peaking about 50 ms before it occurred over the supplementary motor areas (FCz). This wave preceded the motor potential, which supports the view that the supplementary motor areas are upstream in a hierarchy of the motor command. [ABSTRACT FROM AUTHOR]

In between-hand choice-RT-tasks, small incorrect EMG activations occurring before the correct response (“partial errors”) are assumed to reflect the detection, inhibition and correction of erroneous hand selection, revealing the existence of an action monitoring system, acting “on-line”. Now, EMG activations of the correctly selected hand muscles, too small to reach the response threshold, may also occur before these hand muscles produce an overt correct response (“partial corrects”). We hypothesized that partial corrects reflect incorrect execution of correctly selected responses. We found 1) that response force was smaller on trials preceding a partial correct trial and 2) that the Error Negativity, a performance sensitive ERP, assumed to reveal “on-line” action monitoring, was larger for partial corrects than for correct trials. This also suggests that the competence of the action monitoring system is not restricted to selection errors but also extends to execution errors. [ABSTRACT FROM AUTHOR]

Typing is a pervasive phenomenon, yet the underlying neural processes have hardly been studied. Here, the mechanisms of keystroke preparation were studied with a typed picture-naming task performed by expert typists. Electroencephalographic activities recorded over sensorimotor areas prior to first-keystroke onset were examined with time-frequency and event-related potential ( ERP) analyses. In the time-frequency domain, a beta event-related desynchronization was present bilaterally. In the ERP analyses, the activity was asymmetric, with negativity and positivity patterns developing over, respectively, contra- and ipsilateral recording sites. This pattern is similar to that observed in choice reaction time tasks, and thus can be interpreted as evidence of contralateral motor cortex activation accompanied by inhibition of the ipsilateral motor cortex. These data constitute the first electrophysiological demonstration of inhibitory activity in typing and pave the way to a thorough study of typing. [ABSTRACT FROM AUTHOR]

Abstract: A frontocentral electrophysiological wave occurring before the response, the N-40, has been reported in response choice situations compared to no-choice situations. This was interpreted as reflecting response selection. The gradual sensitivity of the N-40 to the demands put on response choice was tested by manipulating stimulus–response (S–R) congruence so as to influence response selection processes. After Laplacian transformation, an N-40 clearly emerged and was larger for incongruent (more demanding) than for congruent (less demanding) S–R associations. The N-40, which possibly reflects SMA activation, thus provides information about the implementation of response selection in the brain. [Copyright &y& Elsevier]