Task-set reconfiguration with binary and three-valued task dimensions.

Recently, we [Kleinsorge & Heuer (1999) Psychological Research, 62, 300-312] introduced the notion of generalizing switching operations to account for a characteristic pattern of shift costs that can be observed when participants have to shift between four tasks that result from an orthogonal combination of the two binary task dimensions kind of judgment (numerical vs spatial) and judgment-to-response mapping (compatible vs incompatible). Specifically, while a change of the kind of judgment always results in costs, a change of mapping results in costs only when the kind of judgment is repeated, but results in benefits when the kind of judgment changes as well. In Experiment 1, we replicated and extended this finding with a combination of two spatial kinds of judgment that were more similar to each other and were more unlikely to result in build-in dependencies of the two task dimensions. In Experiment 2, we extended this design to a combination of nine tasks that resulted from a factorial combination of two three-valued task dimensions. In this experiment, shift costs grew monotonically with the number of task dimensions on which a change took place. This outcome is consistent with the assumption that a generalizing switching operation is a forward-acting process that requires a specific target value to switch to.

The time course of effort mobilization and strategic adjustments of response criteria.

In two-choice reaction time experiments, participants were instructed within a variable precueing interval to speed up responding in 20% of trials and to maintain their basic level of performance in the remaining trials. The achievement of this goal was rewarded by a monetary bonus. The requirement to speed up was signaled at varying intervals before the onset of the imperative stimulus. The main questions to be answered were whether participants would be able to dynamically adjust their response speed, and if so, whether a speed up would be due to enhanced effort with a genuine improvement of performance or due to an adjusted response criterion, accompanied by a speed-accuracy trade-off. The data of both experiments suggest that participants were able to invest some extra effort, the amount of which varied as a function of the length of the precueing interval. This speed-up was evident already in the fastest bins of the reaction time distribution, indicating a continuous modulation of processing efficiency. Only in the first experiment was there clear evidence for a speed-accuracy trade-off in addition to effort mobilization.

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.

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

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 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.

Switching attention--additional aspects for the analysis.

Problems related to attentional functions have often been reported within the neurotoxicology of long-term exposure to solvents, but knowledge about neuroanatomical sites involved in this degenerative process is still rare. However, some studies have emphasized the frontal cortex as a region of structural or functional changes in long-term exposed patients or accidental intoxications. Neurobehavioral tests using active switching tasks are widely used to detect frontal lobe dysfunction. Test batteries used in neurotoxicology provide such tasks but standard test interpretations often neglect these aspects. Rotogravure printing workers exclusively exposed to toluene were investigated in a longitudinal study with cross-sectional design. Data from two examination periods are presented. In the first sample 333 male workers were investigated. In the second examination period 278 workers could be retested. The workers differed with respect to level and duration of lifetime exposure to toluene. All subjects completed a neurobehavioral test battery including the task switching attention (EURONES). Different parameters were computed for consecutive trials with constant vs. shifted tasks and repetitions vs. changes of the response direction. In general the expected interaction between the two sequence factors could not be observed. In both examination periods the alternative strategy revealed no marked differences between task/response shifts. Considering the result of previous studies on task/response shifts, the results were highly unexpected. One explanation might be the strong deviations from equality for the relative frequencies of the four sequence conditions, resulting in biased expectancies. These may have superimposed on the basic effects of task shifts. However, in both examination periods weak effects of task shift could be revealed in the subgroup of the long-term exposed workers. In further studies it is necessary to balance conditions more carefully in order to exploit the sensitivity that the measurement of shift costs promises to provide. The exposure-related results of this study support this aspect.

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.

[Parametric coupling in sequences of bimanual reversal movements with identical and different amplitudes]. / Parametrische Kopplung bei Folgen beidhändiger Umkehrbewegungen mit gleichen und unterschiedlichen Weiten.

In sequences of bimanual movements, the voluntary modulation of the amplitude of the one hand (inducing hand) induces an involuntary modulation of the amplitude of the other hand (dependent hand), the strength of which increases with increasing tempo. By means of a task in which subjects perform sequences of two short and two long reversal movements in alternation with the inducing hand, but constant short or long reversal movements with the dependent hand, we addressed two questions. The first question was concerned with differences in the effects of tempo on the involuntary amplitude modulation of short and long movements; the second question was whether the involuntary amplitude change fades away or is propagated when bimanual movements with certain target amplitudes are repeated. At low tempo the contralateral effect of voluntary amplitude changes on short-amplitude movements was stronger than the effect on long-amplitude movements, but at high tempo this difference was reversed. This result is not consistent with the assumption that contralateral amplitude modulation results from an overflow of efferent commands, which increases with the force of the movement; however, it is consistent with other findings on a transient coupling during amplitude specification (parametric coupling). The involuntary amplitude change was essentially propagated to the next movement in the sequence and did not fade away. This finding suggests that the assimilation of amplitudes that can be observed in bimanual sequences of movements with different, but for each hand constant, amplitudes could result from an effect of transient parametric coupling during the initial specification of amplitudes and need not necessarily be attributed to cross-talk at the level of motor commands or efferent innervation.

Bimanual coupling during the specification of isometric forces.

The 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.

[Coding specificity of orthogonal S-R compatibility]. / Die Kodierungsabhängigkeit orthogonaler Reiz-Reaktions-Kompatibilität.

According to Weeks and Proctor (1990), stimulus-response compatibility effects with vertically oriented stimuli and horizontally oriented responses are a result of coding stimuli and responses with respect to their salient features. The corresponding asymmetries in salience are assumed to hold for both verbal and spatial codes. In contrast, Umiltá (1991) argued that these effects are restricted to verbal coding. Experiment 1 tested the coding specificity of the orthogonal compatibility effect by instructing the S-R mapping either verbally or pictorially, varying the stimulus-response mapping unpredictably within experimental blocks. In Experiment 2, the sequences of trials with changed and unchanged mappings were controlled more extensively. Experiment 3 employed incomplete instructions by explicitly denoting the mapping of one stimulus to one response only. The results of Experiments 1 and 2 are consistent with the assumption of a verbal mediation of the orthogonal compatibility effect under investigation, whereas Experiment 3 shows that it is not verbal coding as such that is responsible for the occurrence of the effect.

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.

Period duration of physical and imaginary movement sequences affects contralateral amplitude modulation.

The hypothesis was tested that the strength of cross-manual effects of voluntary amplitude modulations in bimanual tasks increases when less preparation time is available during the execution of a sequence of movements. By means of the continuation procedure, various period durations (600, 800, 1200, and 1800 msec) of movement sequences were imposed. Subjects performed bimanual periodic arm movements on two digitizers: constant-amplitude movements (short or long) with the one hand, and movements of constant short or constant long amplitudes and movements of alternating short and long amplitudes with the other hand. Period-duration-dependent modulations of the amplitude were observed in movements of instructed constant amplitudes when the other hand performed alternating-amplitude movements, but not when the other hand performed constant-amplitude movements. Not only physical performance, but also the imaginary production of alternating-amplitude movements resulted in period-duration-dependent cross-manual effects, though reduced in size. The pattern of results is in agreement with a recently proposed two-level model of cross-manual effects according to which cross-talk can occur at the programming level as well as at the execution level.

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

We 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.