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. ((c) 2003 APA, all rights reserved)     

On doing two things at once: Temporal constraints on actions in language comprehension

In two experiments, we investigated how text comprehension is influenced by the interaction between the properties of actions and the temporal relations specified by adverbs. Participants read short narratives describing a protagonist who performed two actions that involved similar sensorimotor systems (e.g., chopping wood and painting a fence) or different ones (e.g., whistling a melody and painting a fence). The actions were described as simultaneous or successive by means of the temporal adverbs while and after, respectively. Comprehension, both in Spanish and in English, was markedly impaired (longer reading times and lower subjective coherence) for sentences including the adverb while and actions involving the same sensorimotor system. However, when one of the same sensorimotor system actions was described as a mental plan (e.g., chopping wood and thinking of painting a fence), comprehension was equally easy with the adverbs while and after. These results are compatible with a revised version of the indexical hypothesis that specifies how comprehension is guided by syntax and embodied constraints within multiple noninteracting mental spaces.     

Doing two things at once: The role of temporal compatibility

Performance in a periodically repeating keypress response was measured as a function of the relation between the response patterns required of the two hands. Compared to identical left- and right-hand responses, performance was degraded when the temporal periods of the left- and right-hand responses were not harmonically related. By contrast, performance was not degraded compared to the identical task control when the left- and right-hand responses had the same or harmonically related periods. These findings suggest a limitation in parallel generation of multiple time frames that is assumed to be associated with a late stage of central processing in which response commands are generated.     

Revealing language deficits following stroke: the cost of doing two things at once

The costs of doing two things were assessed for a group of healthy older adults and older adults who were tested at least 6 months after a stroke. A baseline language sample was compared to language samples collected while the participants were performing concurrent motor tasks or selective ignoring tasks. Whereas the healthy older adults showed few costs due to the concurrent task demands, the language samples from the stroke survivors were disrupted by the demands of doing two things at once. The dual task measures reveal long-lasting effects of strokes that were not evident when stroke survivors were assessed using standard clinical tools.     

Interfering with memory for faces: The cost of doing two things at once

We inferred the processes critical for episodic retrieval of faces by measuring susceptibility to memory interference from different distracting tasks. Experiment 1 examined recognition of studied faces under full attention (FA) or each of two divided attention (DA) conditions requiring concurrent decisions to auditorily presented letters. Memory was disrupted in both DA relative to FA conditions, a result contrary to a material-specific account of interference effects. Experiment 2 investigated whether the magnitude of interference depended on competition between concurrent tasks for common processing resources. Studied faces were presented either upright (configurally processed) or inverted (featurally processed). Recognition was completed under FA, or DA with one of two face-based distracting tasks requiring either featural or configural processing. We found an interaction: memory for upright faces was lower under DA when the distracting task required configural than featural processing, while the reverse was true for memory of inverted faces. Across experiments, the magnitude of memory interference was similar (a 19% or 20% decline from FA) regardless of whether the materials in the distracting task overlapped with the to-be-remembered information. Importantly, interference was significantly larger (42%) when the processing demands of the distracting and target retrieval task overlapped, suggesting a processing-specific account of memory interference.     

On doing two things at once: IV. Necessary and sufficient conditions: Rejoinder to Lien, Proctor, and Ruthruff (2003)

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.     

Qualitative attentional changes with age in doing two tasks at once

Does practice reduce, or even eliminate, aging effects on the attentional limitations responsible for dual-task interference? The studies reviewed in this article show that age differences reliably persist after extensive practice. Strikingly, dual-task interference remains larger among older adults even in training conditions that allow them to achieve single-task performance as fast as younger adults. These findings demonstrate that age deficits in attentional functioning are robust. Advancing age also can be accompanied by improvements in cognitive functioning, such as in the ability to access the lexicon without attention (i.e., automatically), due to lifelong experience with word reading. Future research needs to establish whether age deficits in central attention are due to structural changes that are irreversible or reversible to some extent.     

Searching for two things at once: Establishment of multiple attentional control settings on a trial-by-trial basis

Recent work has demonstrated that attention can be configured to multiple potential targets in spatial search. However, this previous work relied on a fixed set of targets across multiple trials, allowing observers to offload attentional control settings to longer-term representations. In the present experiments, we demonstrate multiple attentional control settings that operate independently of space (Experiments 1 and 2). More important, we show that observers can be cued to different control settings on a trial-by-trial basis (Experiment 3). The latter result suggests that observers were capable of maintaining multiple control settings when the demands of the task required an attentional search for specific feature values. Attention can be configured to extract multiple feature values in a goal-directed manner, and this configuration can be can be dynamically engaged on a trial-by-trial basis. These results support recent findings that reveal the high precision, complexity, and flexibility of attentional control settings.     

The costs of doing two things at once for young and older adults: talking while walking,finger tapping,and ignoring speech or noise

Young and older adults provided language samples in response to questions while walking, finger tapping, and ignoring speech or noise. The language samples were scored on 3 dimensions: fluency, complexity, and content. The hypothesis that working memory limitations affect speech production by older adults was tested by comparing baseline samples with those produced while the participants were performing the concurrent tasks. There were baseline differences: Older adults' speech was less fluent and less complex than young adults' speech. Young adults adopted a different strategy in response to the dual-task demands than older adults: They reduced sentence length and grammatical complexity. In contrast, older adults shifted to a reduced speech rate in the dual-task conditions.     

Searching for two things at once: Evidence of exclusivity in semantic and autobiographical memory retrieval

We examined whether retrieval from semantic memory (Experiment 1) and autobiographical memory (Experiment 2) is exclusive, or whether people can search for two things at once. In Experiment 1, participants retrieved items as quickly as possible over 4 ruin from single categories (e.g., foods, countries) and from disjunctive categories (e.g., foods or countries). In Experiment 2, participants retrieved autobiographical episodes associated with single cue words (e.g., flower, ticket) or with disjunctive cue words (e.g., flower or ticket). In both experiments, retrieval of items from the disjunctive category did not exceed predictions based on optimal sequencing of retrieval from the corresponding two single categories. That is, exclusivity was observed to occur in retrieval from among multiple nonoverlapping categories in both semantic and autobiographical memory.     

Verbal-manual time sharing in children as a function of task priority

Eighty-three normal, right-handed children performed (a) unimanual finger tapping, (b) recitation of a tongue twister, and (c) both tasks concurrently. Tradeoffs in dual-task performance were measured as the priority assigned to each task was manipulated. Irrespective of task priority, speaking interfered to a greater degree with right-hand tapping than with left-hand tapping, but the effect of tapping upon verbal production and speech errors was not lateralized. The asymmetric effect of speech upon tapping, which was seen in 85.5% of the children, cannot be attributed to the disparity between hands in baseline tapping rate. The findings suggest that time-sharing asymmetry reflects cerebral lateralization of speech, but only some of the results would be predicted on the basis of a functional distance principle of cerebral organization.     

Planning sentences while doing other things at the same time: effects of concurrent verbal and visuospatial working memory load

This study investigated to what extent advance planning during sentence production is affected by a concurrent cognitive load. In two picture–word interference experiments in which participants produced subject–verb–object sentences while ignoring auditory distractor words, we assessed advance planning at a phonological (lexeme) and at an abstract–lexical (lemma) level under visuospatial or verbal working memory (WM) load. At the phonological level, subject and object nouns were found to be activated before speech onset with concurrent visuospatial WM load, but only subject nouns were found to be activated with concurrent verbal WM load, indicating a reduced planning scope as a function of type of WM load (Experiment 1). By contrast, at the abstract–lexical level, subject and object nouns were found to be activated regardless of type of concurrent load (Experiment 2). In both experiments, sentence planning had a more detrimental effect on concurrent verbal WM task performance than on concurrent visuospatial WM task performance. Overall, our results suggest that advance planning at the phonological level is more affected by a concurrently performed verbal WM task than advance planning at the abstract–lexical level. Also, they indicate an overlap of resources allocated to phonological planning in speech production and verbal WM.     

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 (2005) 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 (2005), 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.     

The relation of perception and motor action: ideomotor compatibility and interference in divided attention

Ideomotor theory is one variation of the general position that perception and motor action are related. According to this theory, a perceptual representation of the goal of a response must be generated prior to response initiation. Ideomotor theory can be extended by assuming that generation of this representation, which usually is required prior to motor action, is not needed if the stimulus itself corresponds to the response goal, that is, if the stimulus and response are ideomotor compatible. Because processing to generate the response representation is not needed with ideomotor compatibility, it should be possible to control two responses simultaneously without mutual interference if at least one stimulus-response relation is ideomotor compatible. Although supported in previous work involving discrete responses, this prediction of perfect time-sharing was found not to hold in the experiments reported here. These experiments, unlike those showing perfect time-sharing, involved continuous responses. We propose an alternative version of ideomotor compatibility, in which perfect time-sharing can occur if an integrated stimulus is provided to match the continuous and integrated response.     

Error-detection and correction latencies as a function of S-R compatibility

In choice-response tasks employing correction-procedure, error-correcting responses are typically found to be faster than equivalent correct responses. An experiment was made to compare error-correction RT under conditions of good and poor S-R compatibility in a two-choice task. After practice, variations in S-R compatibility producing significant variations in mean correct RT nevertheless have no effect on error-correction time. The contrast between this result, and one previously reported (Burns, 1965) leads to a re-discussion of the processes of error detection and correction.     

Anticipated compatibility as a function of attitude or status similarity1

Two experiments explored the effects of self-other discrepancies in attitude or status on judgments of another's desirability as a companion It was found that increasing discrepancy in status or attitudes led to lower judgments of compatibility and liking In one experiment, similarity of attitudes of another was found to correlate with liking him, desire to befriend him, do favors for him, and possibly conform to him. The contribution of some personality measures to the relationship between similarity and anticipated compatibility was a major focus of the study The inhibitory effect of a target's status discrepancy was more pronounced for subjects who were more sensitive to rejection Also, between targets of equally discrepant status, there was a general preference to affiliate with the one whose status was higher than the one whose status was lower–an effect which was even more pronounced for subjects who were sensitive to rejection More anxious subjects judged themselves as generally less acceptable to others, particularly to others of higher status. When predicting attitudes on the basis of limited information, females showed a greater tendency than males to see others as similar to themselves Finally, persons holding different attitudes from one's own were judged as more harmful socially, a bias which was more pronounced in females than in males.