Emergent perceptual features in the benefit of consistent stimulus-response mappings on dual-task performance

Duncan (1979) examined all combinations of compatible and incompatible stimulus-response mappings for two spatial three-choice tasks in the psychological refractory period paradigm. Performance was better when the mappings for the tasks were consistent than when they were not, even when both mappings were incompatible. He attributed the benefit for the consistent incompatible mapping to an emergent choice between mappings when they are inconsistent that slows performance. Consistent incompatible mappings also may benefit from emergent perceptual features. The present study examined the role of emergent perceptual and mapping-choice features in two experiments that used pairs of two-choice tasks. Results similar to Duncan’s were obtained with visual stimuli mapped to keypresses at short (stimulus onset asynchrony) SOAs. However, the benefit of the consistent incompatible mapping condition over the inconsistent mapping conditions was eliminated at an SOA of 1,000 ms. Furthermore, this benefit was not evident when the stimuli were auditory for Task 1 and visual for Task 2. With two-choice tasks, the benefit for consistent mappings apparently is due primarily to an emergent perceptual feature.     

Determinants of the benefit for consistent stimulus-response mappings in dual-task performance of four-choice tasks

Reaction times are shorter when the stimulus-response mappings for pairs of three-choice tasks are consistent (both corresponding or both mirrored) than when they are inconsistent. The benefit for consistent mirrored mappings is evident at the side positions for each task, for which the responses are crossed, but not at the middle position, for which the response is corresponding. In the present study, we report experiments in which we tested implications of an emergent mapping-choice account of the consistency benefit using pairs of four-choice tasks. This procedure allows crossed responses for all positions when the mapping is mirrored and use of mixed mappings for which one pair of stimuli and responses within a task has a corresponding assignment and the other a crossed assignment. Results showed that when a pure corresponding or pure mirrored mapping was used, there was a consistency benefit for both the middle and side positions. However, when the mixed mapping was introduced, the consistency benefit for that mapping depended on the overall complexity of the set of individual stimulus-response pairings for the combined tasks. A mapping choice between Tasks 1 and 2 is only one of several emergent processes that contribute to response-selection efficiency in dual-task contexts.     

The neural effect of stimulus-response modality compatibility on dual-task performance: an fMRI study

Recent fMRI studies suggest that the inferior frontal sulcus (IFS) is involved in the coordination of interfering processes in dual-task situations. The present study aims to further specify this assumption by investigating whether the compatibility between stimulus and response modalities modulates dual-task-related activity along the IFS. It has been shown behaviorally that the degree of interference, as measured by dual-task costs, increases in modality-incompatible conditions (e.g. visual–vocal tasks combined with auditory–manual tasks) as compared to modality-compatible conditions (e.g. visual–manual tasks combined with auditory–vocal tasks). Using fMRI, we measured IFS activity when participants performed modality-compatible and modality-incompatible single and dual tasks. Behaviorally, we replicated the finding of higher dual-task costs for modality-incompatible tasks compared to modality-compatible tasks. The fMRI data revealed higher activity along the IFS in modality-incompatible dual tasks compared with modality-compatible dual tasks when inter-individual variability in functional brain organization is taken into account. We argue that in addition to temporal order coordination (Szameitat et al., 2002), the IFS is involved in the coordination of cognitive processes associated with the concurrent mapping of sensory information onto corresponding motor responses in dual-task situations.     

Localizing practice effects in dual-task performance

Practice effects on dual-task processing are of interest in current research because they may reveal the scope and limits of parallel task processing. Here we used onsets of the lateralized readiness potential (LRP), a time marker for the termination of response selection, to assess processing changes after five consecutive dual-task sessions with three stimulus onset asynchronies (SOAs) and priority on Task 1. Practice reduced reaction times in both tasks and the interference between tasks. As indicated by the LRP, the reduction of dual-task costs can be explained most parsimoniously by a shortening of the temporal demands of central bottleneck stages, without assuming parallel processing. However, the LRP also revealed a hitherto unreported early activation over the parietal scalp after practice in the short SOA condition, possibly indicating the isolation of stimulus–response translation from other central processing stages. In addition, further evidence was obtained from the LRP for a late motoric bottleneck, which is robust against practice.     

Localizing practice effects in dual-task performance

Practice effects on dual-task processing are of interest in current research because they may reveal the scope and limits of parallel task processing. Here we used onsets of the lateralized readiness potential (LRP), a time marker for the termination of response selection, to assess processing changes after five consecutive dual-task sessions with three stimulus onset asynchronies (SOAs) and priority on Task 1. Practice reduced reaction times in both tasks and the interference between tasks. As indicated by the LRP, the reduction of dual-task costs can be explained most parsimoniously by a shortening of the temporal demands of central bottleneck stages, without assuming parallel processing. However, the LRP also revealed a hitherto unreported early activation over the parietal scalp after practice in the short SOA condition, possibly indicating the isolation of stimulus-response translation from other central processing stages. In addition, further evidence was obtained from the LRP for a late motoric bottleneck, which is robust against practice.     

Parallel response selection in dual-task situations via automatic category-to-response translation

In contrast to the response selection bottleneck theory of dual-task performance, recent studies have demonstrated compatibility effects between secondary and primary responses on Task 1, suggesting that response information for two tasks may be generated in parallel. In two experiments, we examined the nature of Task 2 response activation in parallel with Task 1, using a psychological refractory period paradigm. Evidence of Task 2 to Task 1 response priming when each Task 2 stimulus was unique indicated that automatic parallel generation of response information occurred for Task 2 via abstract semantic category-to-response translation processes, independent of any direct stimulus-response influences. These findings are discussed in terms of their implications for the traditional response selection bottleneck theory of dual-task performance.     

Age differences in dual-task performance after practice

This study investigated whether older adults could acquire the ability to perform 2 cognitive operations in parallel in a paradigm in which young adults had been shown to be able to do so (K. Oberauer & R. Kliegl, 2004). Twelve young and 12 older adults practiced a numerical and a visuospatial continuous memory updating task in single-task and dual-task conditions for 16 to 24 sessions. After practice, 9 young adults were able to process the 2 tasks without dual-task costs, but none of the older adults had reached the criterion of parallel processing. The results suggest a qualitative difference between young and older adults in how they approach dual-task situations.     

Selective impairment of masked priming in dual-task performance

This study investigated the impact of divided attention on masked priming. In a dual-task setting, two tasks had to be carried out in close temporal succession: a tone discrimination task and a masked priming task. The order of the tasks was varied between experiments, and attention was always allocated to the first task—that is, the first task was prioritized. The priming task was the second (nonprioritized) task in Experiment 1 and the first (prioritized) task in Experiment 2. In both experiments, “novel” prime stimuli associated with semantic processing were essentially ineffective. However, there was intact priming by another type of prime stimuli associated with response priming. Experiment 3 showed that all these prime stimuli can reveal significant priming effects during a task-switching paradigm in which both tasks were performed consecutively. We conclude that dual-task specific interference processes (e.g., the simultaneous coordination of multiple stimulus–response rules) selectively impair priming that is assumed to rely on semantic processing.     

A psychophysiological study of the use of partial information in stimulus-response translation.

Ss performed a hybrid go/no-go reaction task in which colored letters were assigned in various ways to 4 finger responses, 2 on each hand. In addition to reaction time, psychophysiological measures were used to assess the duration of stimulus identification and the onset of central and peripheral motor activity. The results suggest that response selection can begin on the basis of 1 stimulus dimension (e.g., color), while the other dimension (e.g., letter form) has not yet been identified. Other results are discussed with regard to "selection for action" (Allport, 1987) and the importance of stimulus-response translation strategies in the use of partial information.     

Multiple spatial correspondence effects on dual-task performance

Three dual-task experiments were conducted to examine whether the underadditive interaction of the Simon effect and stimulus onset asynchrony (SOA) on Task 2 performance is due to decay. The experiments tested whether the reverse Simon effect obtained with an incompatible stimulus-response (S-R) mapping would show an overadditive interaction with SOA, as predicted by R. De Jong, C.-C. Liang, and E. Lauber's (1994) dual-process model. Tone or letter identification tasks with vocal or keypress responses were used as Task 1. Task 2 was keypresses to arrow direction (or letter identity in Experiment 1). For all experiments, the normal Simon effect showed an underadditive interaction with SOA, but the reverse Simon effect did not show an overadditive interaction. The results imply that the dual-process model is not applicable to the dual-task context. Multiple correspondence effects across tasks implicate an explanation in terms of automatic S-R translation.     

Effect of preparation on dual-task performance in postural control

The authors applied an overlapping-task design to study the interaction between postural control and cognitive task processes in young (n = 10) and older (n = 10) adults. A rapid destabilizing floor translation was followed at specific time intervals by a simple auditory reaction time (RT) task. The translations were preceded by either an informational cue or no cue. Interference between postural task demands and the RT task was found only in the first 50 ms. Cueing also had an effect on both the onset of the postural recovery response and RT performance. The results suggest (a) only a brief interference between postural and cognitive processing demands in relatively easy tasks, (b) competition for a common central mechanism, possibly a response-selection mechanism, and (c) no differential impact of aging on that interaction.     

Aging and dual-task performance: a meta-analysis

The relations between dual-task effects and aging were examined through a meta-analysis of 33 studies (with 48 independent participant groups) using latency as the dependent measure and 30 studies (with 40 independent participant groups) focusing on accuracy. Brinley plots and state traces were derived, and a model to explicate different types of complexity (additive and multiplicative) was developed. The effects of dual-task processing on latency were additive, and this additive cost was larger in older adults than in younger adults and larger than predicted from general slowing. This cost was small and independent of task complexity. The effects of dual-task processing on logit-transformed accuracy were likewise additive, but no specific age deficit was associated with this dual-task cost.     

Automaticity versus timesharing in timing and tracking dual-task performance

Two experiments investigated the interfering effects of a manual tracking task on timing performance. Subjects generated a series of 5-s temporal productions under control (timing only) and experimental (timing + pursuit rotor tracking) conditions. Timing was more variable under experimental conditions, a finding consistent with attentional models which argue that timing tasks compete with concurrent distractor tasks for limited processing resources. A pretest-posttest paradigm was employed to evaluate the hypothesis that practice on the tracking task would lessen its attentional demands and thereby attenuate the interference effect. Experiment 1 involved single-task practice (tracking alone). Single-task practice leads to automaticity, the ability to perform a skilled task using fewer processing resources. Pretest-posttest comparisons showed that such practice reduced interference in timing. Experiment 2 involved dual-task practice (timing + tracking). Dual-task practice promotes the development of timesharing, the ability to efficiently switch attention between multiple tasks. In this case, practice failed to reduce the interference effect in timing. The results suggest that effective strategies for timing in dual-task situations must allow one to closely monitor the ongoing flow of temporal events. Received: 11 November 1996 / Accepted: 6 May 1997     

A central capacity sharing model of dual-task performance

The authors present the central capacity sharing (CCS) model and derive equations describing its behaviors to explain results from dual-task situations. The predictions of the CCS model are contrasted with those of the central bottleneck model. The CCS model predicts all of the hallmark effects of the psychological refractory period (PRP) pardigm: -1 slope of the PRP effect at short stimulus onset asynchronies (SOAs), underadditivity of precentral Task 2 manipulations, additivity of central or postcentral Task 2 manipulations with SOA, and carry forward to Task 2 of Task 1 precentral or central manipulations at short SOAs. The CCS model also predicts that Task 1 response times increase with decreasing SOA. The model is a viable alternative to the central bottleneck model.     

Effects of explicit sway-minimization on postural--suprapostural dual-task performance

Participants performed a visual search task under immersive visualization conditions while standing in open or closed stance. In the combined instruction condition, participants were asked to minimize their sway while they performed the search task, and in the search-only condition, they were advised that sway was not of interest, and they were asked to focus their efforts on performing the search task. Regardless of instructions, participants swayed more and made more errors as search load increased. Participants also succeeded in reducing their sway when asked to do so. While search in closed stance tended to be faster than in open stance under search-only instructions, this pattern reversed significantly under combined instructions. We suggest that neither the facilitatory control hypothesis nor any resource-competition model of postural--suprapostural dual-tasking can fully account for the observed interplay of task-facilitation and task-interference effects. We offer adaptive resource-sharing as an alternative to these theories.     

Strategic adaptation to performance objectives in a dual-task setting

How do people interleave attention when multitasking? One dominant account is that the completion of a subtask serves as a cue to switch tasks. But what happens if switching solely at subtask boundaries led to poor performance? We report a study in which participants manually dialed a UK‐style telephone number while driving a simulated vehicle. If the driver were to exclusively return his or her attention to driving after completing a subtask (i.e., using the single break in the xxxxx‐xxxxxx representational structure of the number), then we would expect to see a relatively poor driving performance. In contrast, our results show that drivers choose to return attention to steering control before the natural subtask boundary. A computational modeling analysis shows that drivers had to adopt this strategy to meet the required performance objective of maintaining an acceptable lateral position in the road while dialing. Taken together these results support the idea that people can strategically control the allocation of attention in multitask settings to meet specific performance criteria.     

Effect of age on dual-task performance in children and adults

Age effects on dual-task costs were examined in healthy adults (Exp. 1) and in typically developing children (Exp. 2). In both experiments, individual differences in performance on the single-task components were titrated so that any age differences in dual-task costs could not be attributed to differences in single-task performance. Dual-task costs were found, but there were no age-related differences in these costs in older relative to younger adults, in 7-year-old relative to 9-year-old children, or across all four age groups. The results from these experiments suggest that previously reported age differences in dual-task costs, in both healthy ageing and child development, may be due to a failure to adequately equate single-task difficulty.     

Age- and practice-related influences on dual-task costs and compensation mechanisms under optimal conditions of dual-task performance

Impaired dual-task performance in younger and older adults can be improved with practice. Optimal conditions even allow for a (near) elimination of this impairment in younger adults. However, practice effects under these conditions in older adults are unknown. Further, it is open, how changed task scheduling and/ or the acquisition of task coordination skills affect the temporal overlap of two tasks in different age groups; this overlap indicate the involvement of these practice-related mechanisms to compensate for impaired dual-task performance. In a dual-task situation of Schumacher et al. (2001 , Psychological Science, 12, 230) including optimal conditions for dual-task performance, both younger and older adults were able to achieve an improvement in dual-task performance with 8 practice sessions to the same degree. The temporal task overlap changed similarly in both age groups during these sessions demonstrating a similar degree of the involvement of compensation mechanisms in younger and older adults. At the end of practice, however, we showed that older adults do not achieve the same optimized dual-task performance level of younger adults.