On doing two things at once: III. Confirmation of perfect timesharing when simultaneous tasks are ideomotor compatible.

A. G. Greenwald and H. G. Shulman (see record 1974-10326-001) found that 2 tasks characterized by ideomotor (IM) compatibility could be perfectly timeshared (i.e., performed simultaneously without mutual interference). The 2 tasks were pronouncing "A" or "B" in response to hearing those letter names, and making a manual left or right response to seeing a left- or right-positioned arrow. M.-C. Lien, R. W. Proctor, and P. A. Allen (2002) did not replicate Greenwald and Shulman's result, and concluded that their finding of perfect timesharing of 2 IM-compatible tasks might not be replicable. In the present research, Experiment 1 replicated Greenwald and Shulman's 1973 finding while also supporting the conclusion that Lien et al's nonreplication was due to their not instructing subjects to make 2 responses simultaneously in their timeshared task. Experiment 2 again replicated the perfect timesharing finding, using an alternative control procedure that mixed manual and vocal tasks in the same block. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On Doing Two Things at Once: IV. Necessary and Sufficient Conditions: Rejoinder to Lien, Proctor, and Ruthruff (2003).

Responds to the reply by Lien et al (see case 2003-09958-012) to the author's comments (see record 2003-08747-004) on Lien et al's (see record 2002-02027-010) article about the psychological refractory period. Four publications have demonstrated perfect timesharing of 1 simultaneous decisions. In all of these, (a) subjects were motivated to respond as quickly as possible, and with 1 exception that involved unusually extensive practice (E. Hazeltine, D. Teague, & R. B. Ivry, 2002, Experiment 4), (b) at least 1 of the 2 tasks was characterized by ideomotor (IM) compatibility, meaning that each task stimulus incorporated a component of the sensory feedback from its required response. Conclusions justified by these reports are that (a) the use of speed-stress instructions is necessary for perfect timesharing of 2 simultaneous decision tasks: (b) when both tasks are IM compatible, perfect timesharing requires little or no practice: (c) extensive practice is needed to achieve perfect timesharing when only 1 of the 2 tasks is IM compatible: and (d) very large amounts of practice can yield perfect timesharing of 2 decision tasks when neither is IM compatible. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Confirming and Disconfirming Theories About Ideomotor Compatibility in Dual-Task Performance: A Reply to Greenwald (2005).

Because small dual-task costs with ideomotor-compatible tasks do not necessarily indicate the absence of a bottleneck, M.-C. Lien, R. S. McCann, E. Ruthruff, and R. W. Proctor (see record 2005-01366-010) considered additional sources of evidence regarding bottleneck bypass. This evidence argued against complete bottleneck bypass and, instead, supported an engage-bottleneck-later model in which early bottleneck substages are bypassed but late substages are not. A. G. Greenwald (see record 2005-01366-017), however, contended that M.-C. Lien et al. did not use the procedures needed to produce complete bottleneck bypass and that a complete bottleneck bypass hypothesis, combined with additional assumptions, could explain their data. The authors contend that this disagreement stems from Greenwald's focus on confirming predictions of complete bottleneck bypass (small dual-task costs) without disconfirming predictions of bottleneck presence. In particular, Greenwald neglects to consider the possibility that a latent bottleneck limitation could also produce small dual-task costs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ideomotor compatibility in the psychological refractory period effect: 29 years of oversimplification.

Four experiments examined whether the psychological refractory period (PRP) effect can be eliminated with ideomotor compatible (IM) but not stimulus-response compatible (SR) tasks, as reported by A. G. Greenwald and H. G. Shulman (1973). Their tasks were used: a left or right movement to a left- or right-pointing arrow (IM) or to the word left or right (SR) for Task 1; saying "A" or "B" (IM) or "1" or "2" (SR) to an auditory A or B for Task 2. The stimulus onset asynchronies were 0, 100, 200, 300, 500, and 1,000 ms in Experiment 1, and only 0, 100, 200, and 1,000 ms in Experiments 2-4. The arrow was in the center of the screen in Experiments 1-3 and to the left or right in Experiment 4. As in Greenwald and Shulman's Experiment 2, the instructions stated that most often the 2 stimuli would be presented simultaneously. A PRP effect was obtained in all conditions, most likely because response-selection decisions are required even for IM tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A Reminder About Procedures Needed to Reliably Produce Perfect Timesharing: Comment on Lien, McCann, Ruthruff, and Proctor (2005).

M.-C. Lien, R. S. McCann, E. Ruthruff, and R. W. Proctor (see record 2005-01366-010) argued that simultaneous ideomotor-compatible choice tasks cannot be perfectly timeshared. Their conclusion is limited in generalizability for 2 reasons: (a) Their experiments did not include procedures that previous research has shown to be necessary for obtaining perfect timesharing (motivating subjects to perform the 2 tasks rapidly and simultaneously; homogeneous blocks of simultaneous stimuli for the 2 tasks), and (b) their experiments included a procedure that previous research has shown to interfere with perfect timesharing of simultaneous tasks (within-block variation of task interstimulus intervals). Also discussed here are problems in M.-C. Lien et al.'s (2005) analysis of slopes relating Task 2 latency to Task 1 latency and their advocacy of a central bottleneck theory that may not be disconfirmable. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous Cognitive Operations in Working Memory After Dual-Task Practice.

The authors tested the hypothesis that with adequate practice, people can execute 2 cognitive operations in working memory simultaneously. In Experiment 1, 6 students practiced updating 2 items in working memory through 2 sequences of operations (1 numerical, 1 spatial). In different blocks, imperative stimuli for the 2 sequences of operations were presented either simultaneously or sequentially. Initially, most participants experienced substantial dual-task costs. After 24 sessions of practice, operation latencies for simultaneous presentation were equal to the maximum of times for the 2 operations in the sequential condition, suggesting perfect timesharing. Experiment 2 showed that a reduction of dual-task costs requires practice on the combination of the 2 updating tasks, not just practice on each individual task. Hence, the reduction of dual-task costs cannot be explained by shortening or automatization of individual operations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response activation in overlapping tasks and the response-selection bottleneck.

The authors investigated the impact of response activation on dual-task performance by presenting a subliminal prime before the stimulus in Task 2 (S2) of a psychological refractory period (PRP) task. Congruence between prime and S2 modulated the reaction times in Task 2 at short stimulus onset asynchrony despite a PRP effect. This Task 2 congruence effect was paralleled by a Task 1 congruence effect and emerged exclusively under conditions of cross talk, whereas it did not occur under dual-task conditions preventing cross talk between tasks. This suggests that response activation operates during the PRP in dual tasks and affects the response times in Task 2 via cross talk between common processing elements at prebottleneck stages but not by directly affecting the postbottleneck stages. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aging and the psychological refractory period: Task-coordination strategies in young and old adults.

The apparently deleterious effect of aging on dual-task performance is well established, but there is little agreement about the source of this effect. Studies of the psychological refractory period (PRP) indicate that young adults can flexibly control dual-task performance through task-coordination strategies. Thus, the performance of older adults might differ from young adults because older adults use different task-coordination strategies. To test this hypothesis, the executive-process interactive control (EPIC) architecture was applied to quantify the reaction time data from two PRP experiments conducted with young (age 18–26) and older (age 60–70) adults. The results show that participants' ability to coordinate the processing of two tasks did not decline with age. However, dual-task time costs were greater in the older adults. Three sources for this increase were found: generalized slowing, process-specific slowing, and the use of more cautious task-coordination strategies by the older adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dual-task crosstalk between saccades and manual responses.

Between-task crosstalk has been discussed as an important source for dual-task costs. In this study, the authors examine concurrently performed saccades and manual responses as a means of studying the role of response-code conflict between 2 tasks. In Experiment 1, participants responded to an imperative auditory stimulus with a left or a right key press (manual task), a left or a right saccade (saccade task), or both. In Experiments 2 and 3, participants crossed their hands, and a modest (Experiment 2) or substantial (Experiment 3) degree of between-task response-code conflict through specific instructions was introduced. In Experiment 4, response codes across tasks were compatible, and stimulus–response mappings in both tasks were incompatible. Overall, the results indicate that performance not only in manual responses but also in saccades suffers from dual-task conditions, even though saccades were typically performed first and are usually assumed to be controlled quite independently. Moreover, the systematic introduction of response-code conflict between tasks modulated the pattern of dual-task performance. The authors propose confusability of response codes as an underlying mechanism of the observed effects of between-task crosstalk. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dual-Task Performance With Ideomotor-Compatible Tasks: Is the Central Processing Bottleneck Intact, Bypassed, or Shifted in Locus?

The present study examined whether the central bottleneck, assumed to be primarily responsible for the psychological refractory period (PRP) effect, is intact, bypassed, or shifted in locus with ideomotor (IM)-compatible tasks. In 4 experiments, factorial combinations of IM- and non-IM-compatible tasks were used for Task 1 and Task 2. All experiments showed substantial PRP effects, with a strong dependency between Task 1 and Task 2 response times. These findings, along with model-based simulations, indicate that the processing bottleneck was not bypassed, even with two IM-compatible tasks. Nevertheless, systematic changes in the PRP and correspondence effects across experiments suggest that IM compatibility shifted the locus of the bottleneck. The findings favor an engage-bottleneck-later hypothesis, whereby parallelism between tasks occurs deeper into the processing stream for IM- than for non-IM-compatible tasks, without the bottleneck being actually eliminated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Is dual-task slowing instruction dependent?

When 2 tasks must be performed concurrently, each requiring a choice of response, dual-task slowing is typically found. However, E. H. Schumacher et al. (1997) reported that dual-task slowing can be eliminated when equal priority is assigned to each task. Experiment 1 largely confirmed this with the same tasks as Schumacher et al. (tasks using stimulus–response combinations of visual–manual and auditory–vocal pairings). Experiment 2 retained the equal-priority instructions but switched the task pairings (to visual–vocal and auditory–manual); substantial dual-task slowing occurred. Experiment 3 used the same two response sets but only a single stimulus; slowing was again obtained despite equal priority instructions. Equalizing task priority was not sufficient to eliminate interference; relatively unusual cases in which dual-task interference is eliminated seem to depend on task-specific features. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Why practice reduces dual-task interference.

M. A. Van Selst, E. Ruthruff, and J. C. Johnston (1999) found that practice dramatically reduced dual-task interference in a Psychological Refractory Period (PRP) paradigm with 1 vocal response and 1 manual response. Results from 3 further experiments using the highly trained participants of M. A. Van Selst et al. (1999) support 4 main conclusions: (a) A processing bottleneck exists even after extensive practice; (b) the principal cause of the reduction in PRP interference with practice is shortening of Task 1 bottleneck stages; (c) a secondary cause is that 1 or more, but not all, of the Task 2 substages that are postponed before practice are not postponed after practice (i.e., become automatized); and (d) the extent of PRP reduction with practice depends on the modalities of the 2 responses. A control experiment with 2 manual response tasks showed less PRP reduction with practice than that found by Van Selst et al. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous dual-task performance reveals parallel response selection after practice.

E. H. Schumacher, T. L. Seymour, J. A Glass, D. E. Kieras, and D. E. Meyer (2001) reported that dual-task costs are minimal when participants are practiced and give the 2 tasks equal emphasis. The present research examined whether such findings are compatible with the operation of an efficient response selection bottleneck. Participants trained until they were able to perform both tasks simultaneously without interference. Novel stimulus pairs produced no reaction time costs, arguing against the development of compound stimulus-response associations (Experiment 1). Manipulating the relative onsets (Experiments 2 and 4) and durations (Experiments 3 and 4) of response selection processes did not lead to dual-task costs. The results indicate that the 2 tasks did not share a bottleneck after practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The psychological refractory period effect following callosotomy: Uncoupling of lateralized response codes.

A callosotomy patient was tested in 2 dual-task experiments requiring successive speeded responses to lateralized stimuli. The patient showed a robust psychological refractory period (PRP) effect. Three aspects of the data indicate that, unlike for the control participants, the PRP effect for the split-brain patient should not be attributed to a response selection bottleneck. First, the patient did not show an increase in reaction time (RT) when the 2 tasks required responses from a common output system compared with when different output systems were used. Second, inconsistent stimulus-response mappings for the 2 tasks increased RTs for the control participants but had minimal effect on the performance of the split-brain patient. Third, the consistency manipulation was underadditive with stimulus onset asynchrony but was additive or overadditive for the normal participants. These results suggest that the persistent PRP effect following callosotomy should be attributed to a bottleneck associated with response initiation, a strategy adopted to comply with the task demands, or a combination of these factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Validity of the salience asymmetry account of the Implicit Association Test: Reply to Greenwald, Nosek, Banaji, and Klauer (2005).

In their comment on K. Rothermund and D. Wentura (see record 2004-14313-001), A. G. Greenwald, B. A. Nosek, M. R. Banaji, and K. C. Klauer (see record 2005-09704-008) agreed that salience asymmetries can be a source of Implicit Association Test (IAT) effects. The authors applaud this conclusion but point to problems with the other points that Greenwald et al. made. The authors have difficulties understanding the nominal feature account that Greenwald et al. put forward and have doubts about the usefulness of their broad conception of the concept association. The authors also argue that existing evidence concerning the construct validity of the IAT does not allow one to discriminate between the association and the salience accounts. In addition, the new studies that were presented by Greenwald et al. do not provide insights into what the IAT measures because they are either irrelevant for a decision between the different accounts or contain methodological problems that prevent a meaningful interpretation in terms of the models. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attentional limits in memory retrieval—Revisited.

Carrier and Pashler (1995) concluded—based on locus-of-slack dual-task methodology—that memory retrieval was subject to a central bottleneck. However, this conclusion conflicts with evidence from other lines of research suggesting that memory retrieval proceeds autonomously, in parallel with many other mental processes. In the present experiments we explored the possibility that Carrier and Pashler's conclusions were distorted by use of an experimental method unfavorable to parallel memory retrieval. New locus-of-slack experiments were performed that encouraged parallel memory retrieval strategies with instructions and feedback, along with the use of “preferred” stimulus-response modality mappings. Results from two psychological refractory period experiments showed that the effect of Task 2 recognition difficulty was consistently absorbed into cognitive slack, with both word and picture recognition. We conclude that the memory retrieval stage of recognition tasks can proceed in parallel with central operations of another task, at least under favorable conditions. Our new findings bring results from dual-task locus-of-slack methodology into agreement with other evidence that memory retrieval is not subject to severe, generic central resource limitations. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A demonstration of dual-task performance without interference in some older adults.

Highly efficient dual-task processing is demonstrated when reaction time to each of two tasks does not differ between the dual-task situation and the single-task situation. This has been demonstrated reliably in younger adults; nevertheless, the two extant studies of extensive dual-task training did not find evidence for it in any elderly adult. The origins of age-related differences after training were explored in a study in which the stimuli for the two tasks were perfectly redundant although two distinct responses were required. The dual-task situation thus greatly reduced the demands of stimulus categorization while still requiring two response selections and two response executions. After only limited training 8 of 8 younger adults and 5 of 8 older adults showed performance consistent with highly efficient processing. Three older adults failed to show this even after 12 training sessions. The results implicate stimulus categorization more than response selection as an important locus of inefficient dual-task processing, particularly for older adults. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Correcting for measurement error in detecting unconscious cognition: Comment on Draine and Greenwald (1998).

A. G. Greenwald, M. R. Klinger, and E. S. Schuh (1995) have proposed a regression method for detecting unconscious cognition in experiments that obtain measures of indirect and direct effects of stimuli with suspected unconscious effects. Their indirect-on-direct-measure regression approach can produce misleading evidence for indirect effects in the absence of direct effects when the direct-effect measure has typical measurement error. This article describes an errors-in-variables variant of the regression method that corrects for error in the direct-effect measure. Applied to the uses of the regression method by S. C. Draine and A. G. Greenwald (see record 1999-10824-004), the errors-in-variables method affirms substantial evidence for indirect effects in the absence of direct effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Method-Specific Variance in the Implicit Association Test.

The Implicit Association Test (IAT; A. G. Greenwald, D. E. McGhee, & J. L. K. Schwartz, 1998) can be used to assess interindividual differences in the strength of associative links between representational structures such as attitude objects and evaluations. Four experiments are reported that explore the extent of method-specific variance in the IAT. The most important findings are that conventionally scored IAT effects contain reliable interindividual differences that are method specific but independent of the measures' content, and that IAT effects can be obtained in the absence of a preexisting association between the response categories. Several techniques to decrease the impact of method-specific variance are evaluated. The best results were obtained with the D measures recently proposed by A. G. Greenwald, B. A. Nosek, and M. R. Banaji (2003). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Training effects on dual-task performance: Are there age-related differences in plasticity of attentional control?

A number of studies have suggested that attentional control skills required to perform 2 tasks concurrently become impaired with age (A. A. Hartley, 1992; J. M. McDowd & R. J. Shaw, 2000). A. A. Hartley (2001) recently observed that the age-related differences in dual-task performance were larger when the 2 tasks required similar motor responses. The present study examined the extent to which age-related deficits in dual-task performance or time sharing--in particular, dual-task performance of 2 discrimination tasks with similar motor requirements--can be moderated by training. The results indicate that, even when the 2 tasks required similar motor responses, both older and younger adults could learn to perform the tasks faster and more accurately. Moreover, the improvement in performance generalized to new task combinations involving new stimuli. Therefore, it appears that training can substantially improve dual-task processing skills in older adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)