Thomas Kleinsorge

Short-term mobilization of processing resources is revealed in the event-related potential

This study investigates whether an occasional effortful improvement of performance, as asked for by a precue, is reflected in event-related potential (ERP) changes. To estimate the limits of possible effort-induced behavioral and ERP changes, we manipulated the time between precue and imperative stimulus (IS; precue interval, PCI). The subjects could, in fact, improve their performance in the effort trials, with all but the shortest PCI. The postcue ERP revealed a fronto-central contingent negative variation (CNV), which was preceded by a frontal positive/occipital negative wave (P2/N2). Both the P2/N2 and the CNV were larger for effort than for standard trials for all PCIs. For the shortest PCI (300 ms), the CNV increase was seen after the IS. The CNV increase for PCIs 600 and 300 began at about 400 ms postcue. The results suggest that effortful performance improvement is associated with prior increase of a frontocentral CNV and a preceding P2/N2. The CNV increase is thought to reflect the activity of a frontal executive process by which additional processing resources can be mobilized on a trial-to-trial basis within less than 500 ms.

Preparation of bimanual movements with same and different amplitudes : specification interference as revealed by reaction time

Abstract Two experiments are reported that tested the hypothesis of transient coupling during during programming of different movements of the hands in a bimanual reaction-time (RT) task. Subjects performed bimanual movements with same or different amplitudes. Manipulation of the state of preprogramming of the amplitudes was accomplished by precues. In the first experiment the time course of preparation was traced by varying the precuing interval between 0 and 750 ms using words as precues. A clear transient cross-manual effect was found. As the precuing interval increased, the difference between the RTs of bimanual reversal movements with same and different amplitudes decreased. However, preparation of different movements did not converge completely to that of same amplitudes. Therefore, in a second experiment the range of precuing interval was extended to 1000 ms and movement-compatible precues were used, i.e., pairs of horizontal bars with same and different lengths. The expected convergence of RTs of same and different amplitudes at longer precuing intervals was confirmed. The results fit the two-level model of cross-talk that assumes that cross-talk in bimanual tasks occurs during programming and is not restricted to actual execution of the movement.

The time course of cross-talk during the simultaneous specification of bimanual movement amplitudes

Abstractu2002We investigated the time course of the amplitude specification of rapid bimanual reversal movements (lateral displacements on two digitizers). To this end we used the timed-response paradigm in which the response has to be initiated synchronously with an auditory signal. Information about the required amplitudes was presented at various times before the synchronization signal. Consistent with previous results, the progression of amplitude specification was reflected in the dependence of the amplitudes of the reversal movements on the time interval between amplitude information and synchronization signal. Same or different amplitudes for the hands were used to examine cross-talk at the programming level of the two-level model of intermanual interference. The results indicate the existence of cross-talk in particular at short intervals between information about amplitude and movement initiation. This is consistent with the notion that cross-talk between concurrent processes of amplitude specification is transient and vanishes as the time available for motor programming increases.

Response repetition benefits and costs.

In a wide variety of tasks, choice reaction time (RT) is reduced for repetitions of the previous response. However, when the task itself or a relevant physical feature that successive trials have in common changes, costs for response repetitions can be observed. In a series of three experiments it was investigated whether the repetition of a response results in costs if the stimulus category changes. Furthermore, it was asked whether there need to be informative physical task features that successive trials have in common to produce response repetition costs. In alternating runs, participants had to respond to either one of four symbols or one of the letters with a binary choice reaction: Results suggest that a change of stimulus category is a sufficient condition to produce response repetition costs. It is hypothesized that any change of a task feature that is part of the task representation participants adopt leads to a disruption of repetition-based facilitation and tends to facilitate a response alternation.

Static and phasic cross-talk effects in discrete bimanual reversal movements

Abstract The authors examined the hypothesis that the phasic and the static cross-talk effects found in bimanual movements with different target amplitudes originate at different functional levels of motor control, which implies that the effects can be dissociated experimentally. When the difference between the short and the long amplitudes assigned to the 2 hands of 12 participants was decreased, the static effect disappeared. In contrast, the phasic effect, which can be observed only at short preparation intervals, did not disappear; although it became smaller in absolute terms, in relative terms it did not. In addition, the authors compared the time course of amplitude assimilation with the time course of amplitude variability and examined the correlation between left hand and right hand amplitudes. The disappearance of the phasic amplitude assimilation at increasing preparation intervals turned out to be delayed relative to the decline of the correlation between amplitudes. That finding suggests that the assimilation of mean amplitudes and the correlation between left hand and right hand amplitudes are not fully equivalent indicators of intermanual interactions, but may indicate different kinds of inter-limb coupling.

Electrophysiological correlates of residual switch costs.

Switching among cognitive tasks results in switch costs which are only partly reduced even after sufficient task preparation. These residual switch costs are frequently explained in terms of interference of simultaneously active task representations that delays selection of a correct response. Recent studies showed that the benefit of a task- and response-set repetition can also explain residual costs. We aimed to extend the findings by clarifying the mechanisms underlying task- and response-mode repetition benefit as well as costs arising by switch of one or both dimensions. To this end we used a combination of task-switching and go/no-go paradigm during an electrophysiological recording. Particularly, we focused on the frontocentral N2, which has been usually related to conflict, but also to response selection. The behavioral results replicate previous findings of lack of residual switch costs due to slower responses in task repetitions (TRs) following no-go relative to go trials. This indicates elimination of TR benefit when in a previous trial no response was selected and prepared. In other words, task sets clearly benefits from repetition of response mode whereas interference seems to occur whenever the task-set, the response mode or both were switched. Trial incongruity increased reaction times. The event-related potentials (ERPs) revealed a frontocentral N2 in all conditions which followed the same pattern as the reaction times (RTs), showing smaller amplitude and peaking earlier when both the task and response mode were repeated relative to the three switching conditions. Similar to the behavioral data, the N2 increased as a function of incongruity. Finally, both the N2 amplitude and latency correspond closely to the residual switch costs. This finding suggests that task-set or response mode switching intensify and delay response selection, relative to the repetition of both dimensions.

Implicit learning of sequences of tasks.

Task sets can be configured in advance of performing a new task. However, the degree to which advance information is actually used for advance configuration depends on the nature of the available information. The role of implicit learning was explored in 2 experiments by means of a modified serial reaction time task with repeated sequences of 4 dimensionally organized tasks. Although there was clear evidence for implicit learning of the sequence (of length 8), the learning was not associated with a reduction of shift costs, either with a short (200 ms) or with a long (1,200 ms) response-stimulus interval. In contrast, a reduction of shift costs was observed when external precues were introduced in a 3rd experiment. According to these results, the sequences of stimulus features that serve as cues for the tasks to perform on the stimuli are learned, but the representation of the features is void of their task-associated meanings.

Specification of movement amplitudes for the left and right hands: evidence for transient parametric coupling from overlapping-task performance.

Bimanual coordination tasks suggest transient cross-talk between concurrent specification processes for movements of the left and right hand that vanishes as the time for specification increases. In 2 experiments with overlapping and successive unimanual tasks, the hypothesis of transient coupling was examined for a psychological-refractory-period paradigm. Time for specification was manipulated by varying the delay between first and second signal (Experiment 1) and by precuing the first response (Experiment 2). Participants performed rapid reversal movements of same or different amplitudes with the left and right hands. With different amplitudes, reaction times (RTs) of the second responses were longer than with same amplitudes at short delays, and this disappeared at longer delays in Experiment 1. In Experiment 2, precuing also reduced the difference between RTs of second responses in same-amplitude and different-amplitude trials. These findings are consistent with the hypothesis of transient coupling during amplitude specification obtained with bimanual tasks.

Bimanual coupling during the specification of isometric forces.

Abstractu2002The present study investigated the generalizability of the hypothesis of transient coupling during the preparation of bimanual movements (Spijkers and Heuer 1995) to the specification of isometric forces. In the first experiment we used the timed response paradigm (TRP) to examine the time course of the specification process. Subjects had to generate bimanual isometric force pulses while preparation time was controlled by the TRP. Target forces were weak (20% of maximal voluntary force, MVF) or strong (40% MVF) and assigned randomly to each hand. The first experiment revealed the predicted pattern of correlations between the peak forces but, because the subjects tended to delay responding when time for preparation was very brief, the time course of the specification process did not fully match expectations. In the second experiment we improved force–trajectory feedback and presented two initial cues that were expected to induce better preparation of the default force (30% MVF). Both changes were successful and the results further corroborate the transient-coupling hypothesis.

Effects of monetary incentives on task switching.

In two experiments, effects of incentives on task switching were investigated. Incentives were provided as a monetary bonus. In both experiments, the availability of a bonus varied on a trial-to-trial basis. The main difference between the experiments relates to the association of incentives to individual tasks. In Experiment 1, the association of incentives to individual tasks was fixed. Under these conditions, the effect of incentives was largely due to reward expectancy. Switch costs were reduced to statistical insignificance. This was true even with the task that was not associated with a bonus. In Experiment 2, there was a variable association of incentives to individual tasks. Under these conditions, the reward expectancy effect was bound to conditions with a well-established bonus-task association. In conditions in which the bonus-task association was not established in advance, enhanced performance of the bonus task was accompanied by performance decrements with the task that was not associated with a bonus. Reward expectancy affected mainly the general level of performance. The outcome of this study may also inform recently suggested neurobiological accounts about the temporal dynamics of reward processing.