Processing of stimulus properties: evidence for dual-task integrality

The conditions under which dual-task integrality can be fostered were assessed in a study in which we manipulated four factors likely to influence the integrality between tasks: intertask redundancy, the spatial proximity of primary and secondary task displays, the degree to which primary and secondary task displays constitute a single object, and the resource demands of the two tasks. The resource allocation policy is inferred from changes in the amplitude of the P300 component of the event-related brain potential. Twelve subjects participated in three experimental sessions in which they performed both single and dual tasks. The primary task was a pursuit step tracking task. The secondary tasks required subjects to discriminate between different intensities or different spatial positions of a stimulus. Task pairs that required the processing of different properties of the same object resulted in better performance than task pairs that required the processing of different objects. Furthermore, these same object task pairs led to a positive relation between primary task difficulty and the resources allocated to secondary task stimuli. Intertask redundancy and the physical proximity of task displays produced similar effects of reduced magnitude.     

Easier tasks can have higher processing loads: task difficulty and cognitive resource limitations in schizophrenia

A differential deficit on the more difficult of 2 cognitive tasks has been found in numerous studies of schizophrenia. Resource limitations, rather than impairments in particular cognitive abilities, can explain these findings. Researchers often match tasks for difficulty level (healthy participant performance) to rule out resource limitations. This assumes processing resource load can be estimated from task difficulty, which is not always the case. A direct measure of resource allocation is needed. In this study, pupillary responses were recorded to index resource allocation (greater dilation indicates greater allocation) during performance of the digit span distractibility task in participants with schizophrenia (n=35) and nonpsychiatric participants (n=35). Nonpsychiatric participants recalled significantly more digits in the distraction, relative to the neutral, condition but also showed significantly greater pupil dilation in the distraction condition. The psychometrically "easier" condition, therefore, had a higher processing load. Participants with schizophrenia showed greater impairment relative to nonpsychiatric participants in the distraction condition. This finding cannot be attributed to a deficit in distractibility, however, because poorer performance was found in the higher-load condition, so resource limitations cannot be ruled out.     

Resource allocation and the attentional demands of letter encoding

The idea that familiar events can be encoded automatically has gained general acceptance in cognitive psychology since Posner and Boies (1971) first reported that reaction times to a secondary probe were not interfered with by letter encoding. More recently, Ogden, Martin, and Paap (1981) used a more valid control for estimating baseline probe performance and found secondary task interference, suggesting that letter encoding does require attentional resources. The present series of experiments began with the aim of evaluating Ogden et al's evidence against automaticity when the first letter was not terminated after a brief exposure, as was done in their study. In the first set of experiments we found evidence of encoding interference when the interval between the two letters was varied (50 to 1,000 msec), but this interference disappeared when there was a constant 1,000-msec interval between the letters. On the basis of these findings, we hypothesized that changes in the primary task (e.g., the exposure duration of the first letter or the interval between the two letters) may influence the momentary allocation of resources between the primary and secondary tasks. More specifically, we hypothesized that any momentary reduction in the resources demanded by the primary tasks results in a reallocation of resources to the secondary task, which in turn reduces the sensitivity of the secondary task to the demands of the primary task, that is, probe performance is moved into the data-limited region of processing (Norman & Bobrow, 1975). This idea was tested by reducing resource allocation to the probe task at the time of encoding by reducing the expectancy (i.e., the probability) of probes in the temporal proximity of the first letter. The results showed that this manipulation produced a large and significant increase in encoding interference. Moreover, when the intensity of the tone (probe) was decreased from 70 to 60 dB, the magnitude of encoding interference was further increased. In regard to the specific issue of automaticity, the findings suggest that encoding familiar events does require resources, which will result in secondary task interference given that the secondary task is in the resource-limited region of processing. More important, the findings suggest that the magnitude of secondary task interference is dependent on within-trial changes in resource allocation between the primary and secondary tasks. This possibility has general implications for dual-task methodology and the measurement of attentional demands.     

Attentional resources in timing: Interference effects in concurrent temporal and nontemporal working memory tasks

Three experiments examined interference effects in concurrent temporal and nontemporal tasks. The timing task in each experiment required subjects to generate a series of 2- or 5-sec temporal productions. The nontemporal tasks were pursuit rotor tracking (Experiment 1), visual search (Experiment 2), and mental arithmetic (Experiment 3). Each nontemporal task had two levels of difficulty. All tasks were performed under both single- and dual-task conditions. A simple attentional allocation model predicts bidirectional interference between concurrent tasks. The main results showed the classic interference effect in timing. That is, the concurrent nontemporal tasks caused temporal productions to become longer (longer productions represent a shortening of perceived time) and/or more variable than did timing-only conditions. In general, the difficult version of each nontemporal task disrupted timing more than the easier version. The timing data also exhibited a serial lengthening effect, in which temporal productions became longer across trials. Nontemporal task performance showed a mixed pattern. Tracking and visual search were essentially unaffected by the addition of a timing task, whereas mental arithmetic was disrupted by concurrent timing. These results call for a modification of the attentional allocation model to incorporate the idea of specialized processing resources. Two major theoretical frameworks—multiple resource theory and the working memory model—are critically evaluated with respect to the resource demands of timing and temporal/ nontemporal dual-task performance.     

结构限制和作业难度对双重作业绩效的影响

通过对不同双重任务的呈现间隔时间和不同任务难度的双重任务的操作研究,探讨了结构限制与资源竞争对双重任务操作绩效的影响。实验结果表明：(1)两种作业呈现的间隔时间对双重任务操作绩效有明显的影响。间隔时间越大,双重任务的作业绩效越好。(2)作业难度对双重任务的操作有明显的影响。作业难度越大,双重任务的操作绩效越差。(3)两个作业呈现的间隔时间不同并不影响作业难度对双重任务操作绩效的作用。本研究的实验结果进一步证实了双重任务操作的三因素假设：结构限制、信息干扰和资源竞争是影响双重任务操作绩效的三个独立的原因。     

Attentional demands following perceptual skill training

Practicing simple visual tasks induces substantial improvement. We investigated whether increased efficiency is accompanied by automaticity and immunity to across-task interference. We found that although practice speeds orientation feature detection, it does not abolish susceptibility to interference from introduction of concurrent central-letter identification, which takes priority. Yet following training with each task, observers successfully managed to perform the tasks concurrently. The effectiveness of separate training implies that the role of improved intertask coordination in achieving concurrent performance was minor. Indeed, even when initial training was concurrent, improvement on the two tasks was sequential, and the higher-priority (central) task was learned first. However, automatic processing was not accomplished either, because increasing the difficulty of the higher-priority task interfered with performance of both tasks. What appears to be orchestrated posttraining performance is actually mainly an emergent property of speeded initial processes rather than either eliminated bottlenecks or improved central executive management.     

A dynamical framework to understand performance trade-offs and interference in dual tasks.

This study demonstrated that the dynamic pattern approach may reconcile resource and outcome conflict theories to explain performance in dual tasks. Participants performed a bimanual coordination task and a reaction time task with different conditions of attentional priority. Results showed a trade-off between pattern variability and reaction time when priority was given to the coordination task. Such a trade-off was indicative of resource allocation. An analysis of perturbation in the bimanual coordination revealed interference, a reputed sign of outcome conflict. Moreover, interference diminished substantially when priority was given to the bimanual task. The coexistence of performance trade-off and outcome conflict suggests that these two phenomena are not mutually exclusive. Rather, both may follow from modifying the coupling between the limbs through attention.     

Dual-task decrements in driving performance: The impact of task type,working memory,and the frequency of task performance

Driving while carrying out another (secondary) task interferes with performance, though the degree of interference may vary between tasks and individual drivers. In this study, we focused on two potentially interrelated individual difference variables that may play a role in determining dual-task interference: working memory capacity and the driver’s experience with the relevant secondary task. We used a driving simulator to measure interference, comparing single-task performance (driving alone) with driving performance during three secondary tasks: conversing on a handsfree cellphone, texting, and selecting a song on a touchscreen Mp3 player. Drivers also rated the difficulty of driving while carrying out each secondary task. For the individual difference variables, working memory was measured using the Operation Span test (OSPAN), and experience was assessed in terms of self-reported daily driving exposure and exposure to the relevant secondary tasks (frequency, duration). Overall, we found evidence of dual-task interference, though interference varied between tasks; the texting and Mp3 tasks produced significantly more interference than handsfree cellphone conversation. For the texting and Mp3 song selection tasks, interference was apparent in terms of increased steering variability, but for the Mp3 task there was also compensatory slowing, with drivers slowing down while carrying out the task. OSPAN performance and daily driving exposure were both covariates in predicting the amount of dual-task interference. However, our results suggest that in all but two cases, both involving the texting task, the effects of the OSPAN and the driving and secondary task exposure variables were independent rather than interrelated.     

Set-shifting as a component process of goal-directed problem-solving

In two experiments, we compared secondary task interference on Tower of London performance resulting from three different secondary tasks. The secondary tasks were designed to tap three different executive functions, namely set-shifting, memory monitoring and updating, and response inhibition. Previous work using individual differences methodology suggests that, all other things being equal, the response inhibition or memory tasks should result in the greatest interference. However, this was not found to be the case. Rather, in both experiments the set-shifting task resulted in significantly more interference on Tower of London performance than either of the other secondary tasks. Subsequent analyses suggest that the degree of interference could not be attributed to differences in secondary task difficulty. Results are interpreted in the light of related work which suggests that solving problems with non-transparent goal/subgoal structure requires flexible shifting between subgoals—a process that is held to be impaired by concurrent performance of a set-shifting task.     

Simplest tasks have greatest dual task interference with balance in brain injured adults

Attention difficulties and poor balance are both common sequel following a brain injury. This study aimed to determine whether brain injured adults had greater difficulty than controls in performing a basic balance task while concurrently completing several different cognitive tasks varying in visuo-spatial attentional load and complexity. Twenty brain injured adults and 20 age-, sex- and education level-matched controls performed a balance-only task (step stance held for 30 s), five cognitive-only tasks (simple and complex non-spatial, visuo-spatial, and a control articulation task), and both together (dual tasks). Brain injured adults showed a greater centre of pressure (COP) excursion and velocity in all conditions than controls. Brain injured adults also demonstrated greater interference with balance when concurrently performing two cognitive tasks than control subjects. These were the control articulation and the simple non-spatial task. It is likely that distractibility during these simple tasks contributed to an increase in COP motion and interference with postural stability in stance. Performing visuo-spatial tasks concurrently with the balance task did not result in any change in COP motion. Dual task interference in this group is thus unlikely to be due to structural interference. Similarly, as the more complex tasks did not uniformly result in increased interference, a reduction in attentional capacity in the brain injured population is unlikely to be the primary cause of dual task interference in this group.     

Resources, confusions, and compatibility in dual-axis tracking: displays, controls, and dynamics

Why do people often find that performing two tasks at once is harder than performing one task at a time? Three mechanisms of task interference that might answer that question were investigated: resource competition, confusions, and incompatible task proximity between processing stages. The subjects performed dual-axis compensatory tracking with error displays that were either integrated or separated, with axis controls that either were integrated into one stick or remained separate, and with control dynamics on the two axes that were either the same or different. Tracking error increased and control activity decreased as a function of the combined difficulty of the two control dynamics. Integrated displays and integrated controls both led to increased confusions between tracking axes although error was not reliably affected. Significantly, performance was also affected by whether the integrality of displays matched that of controls. These results suggest that resource competition, confusions, and compatibility of proximity play distinct roles in dual-axis tracking performance.     

A methodological assessment and evaluation of dual-task paradigms

This article outlines three major assumptions often implicitly made in dual-task experiments conducted to assess attentional capacity requirements of memorial processes. These assumptions are shown to be incorrect. Three criteria which should be met in dual-task experiments that draw inferences from secondary task decrements are proposed: (1) there should be resource trade-off with the secondary task sensitive to the resource demands of the primary task; (2) there should be equivalence of single and dual primary task performance; and (3) the secondary task must remain resource sensitive throughout the experiment. An experiment was carried out in which the primary and secondary tasks were designed according to these criteria. The results demonstrate that when the criteria are met then secondary task performance can be predictive of primary task difficulty: however, the experiment also highlights the fact that a simple assessment of capacity will not predict total task performance.     

Vocal-manual trade-offs in hemispheric sharing of human performance control

Experiment 1 established the linear ordering of performance and rated difficulty of three finger-sequencing tasks. Experiment 2 embedded these tasks within a dual-task paradigm employing vocalization of words and nonwords as concurrent activities. Concurrent vocal activity interfered with right-more than with left handed performance, and this lateralized interference effect increased monotonically with increased sequence difficulty. Results are discussed in terms of hemispheric sharing of dual task performance control.     

结构限制和信息干扰对双重作业绩效的影响

研究通过改变双重任务呈现的间隔时间来探讨结构限制与信息干扰对双重任务操作绩效的影响。实验结果表明：(1)两种作业呈现的间隔时间对双重任务操作绩效有明显的影响。间隔时间越大,双重任务的作业绩效越高。(2)信息干扰对双重任务的操作有明显的影响。信息干扰越大,双重任务的操作绩效越差。(3)两个作业呈现的间隔时间不同并不影响信息干扰对双重任务操作绩效的作用。根据实验结果,该研究提出了三因素假设：结构限制、信息干扰和资源竞争是影响双重任务操作绩效的三个主要因素。     

Gradual training reduces practice difficulty while preserving motor learning of a novel locomotor task

Motor learning strategies that increase practice difficulty and the size of movement errors are thought to facilitate motor learning. In contrast to this, gradual training minimizes movement errors and reduces practice difficulty by incrementally introducing task requirements, yet remains as effective as sudden training and its large movement errors for learning novel reaching tasks. While attractive as a locomotor rehabilitation strategy, it remains unknown whether the efficacy of gradual training extends to learning locomotor tasks and their unique requirements. The influence of gradual vs. sudden training on learning a locomotor task, asymmetric split belt treadmill walking, was examined by assessing whole body sagittal plane kinematics during 24 hour retention and transfer performance following either gradual or sudden training. Despite less difficult and less specific practice for the gradual cohort on day 1, gradual training resulted in equivalent motor learning of the novel locomotor task as sudden training when assessed by retention and transfer a day later. This suggests that large movement errors and increased practice difficulty may not be necessary for learning novel locomotor tasks. Further, gradual training may present a viable locomotor rehabilitation strategy avoiding large movement errors that could limit or impair improvements in locomotor performance.     

Effects of aging and task difficulty on divided attention performance

We report two experiments that compare the performance of young and older adults on perceptual-motor tasks involving division of attention. Previous studies have shown older people to be especially penalized by divided attention situations, but the generality of this finding was recently challenged by Somberg and Salthouse (1982). The present study was conducted to investigate the possibility that age differences in dual-task performance are amplified by an increase in the difficulty of the constituent tasks, where difficulty was manipulated by varying the central, cognitive nature of the tasks (Experiment 1) or the degree of choice involved (Experiment 2). With the present tasks, strong evidence was found for an age-related decrement in divided attention performance. Contrary to our original expectations, however, it does not seem that division of attention presents some especial difficulty to older people. Rather, division of attention is one of several equivalent ways to increase overall task complexity. In turn, age differences are exaggerated as tasks are made more complex.     

Goal Setting Effects on Implicit and Explicit Learning of Complex Tasks

The robust finding that setting difficult, specific goals leads to increased performance on simple tasks has not generalized to complex task performance. The results of the present research suggest that the moderating effect of task complexity on the goal–performance relationship is due to confounding goal difficulty with explicit and implicit learning. Two multiple cue probability learning studies were performed keeping the learning mode constant while varying goal difficulty. Study 1 examined goal setting effects on performance when task processing was implicit. Consistent with previous research on complex tasks, setting difficult, specific goals did not result in performance gains. Study 2 demonstrated that when complex task processing is explicit, goal setting results in gradual but steady improvements in complex task performance. Protocol analysis of strategies used by participants indicate that goal setting resulted in increased performance through the development of better strategies.     

Developmental changes in attention-deployment skills

The ability to efficiently allocate attention between two tasks differing in payoff was investigated developmentally. Ten subjects from each of three grade levels (second, fourth, and college) performed an auditory and a visual memory task simultaneously. Modality of the primary task, difficulty of the primary task, and difficulty of the secondary task were varied factorially within subjects. The difference between primary and secondary performances increased with age: All college students, about half of the fourth graders, and none of the second graders showed a meaningful degree of differentiation between primary and secondary tasks.     

The locus of the benefits of repetition-lag memory training

The repetition-lag training procedure developed by Jennings and Jacoby (2003 , Neuropsychological Rehabilitation, 14, 417) has been shown to improve older adults' performance in the recognition memory task used for training, and to improve performance in a variety of other memory and executive function tasks ( Jennings, Webster, Kleykamp, & Dagenbach, 2005 , Aging, Neuropsychology, and Cognition, 12, 278). The present study examined the effects of concurrent interference tasks during the study or test phases of training to localize the source of gains. Overall, the results suggest that training is resilient and resistant to interference, but also that the processes used during the test phases of training are more important to the gains seen in the primary task and in the transfer tasks than those used in the study phases.     

Resources and dual-task performance; resource allocation versus task integration

This study aims at contributing to the explanation of dual-task performance in terms of either resource allocation or of task interference and integration. Twenty-four subjects carried out, single and in combination, a motor interval production task and a perceptual target detection task on the basis of combined memory and display search. The demands of the target detection task were varied by increasing or decreasing the presentation rate of successive search displays. Furthermore, the presentation rate was either constant or variable. The dual-task condition had a negative effect on interval production, the extent of which was unaffected by either rate or variability of display presentation. This means that there was no evidence for synchronizing interval production with display presentation, so that the major opportunity for task integration did not substantiate. It is suggested that the two tasks use different resource pools in addition to a common mechanism, the limited capacity of which causes a general interference in dual-task conditions.