Age trends in children's time-sharing performance

To investigate developmental differences in time-sharing performance, 60 boys, 20 in each of three age groups (7-, 10-, and 13-year-olds) performed an auditory matching task and a tracking task alone and concurrently, the latter under two sets of instructions. Decrements produced by concurrent performance were compared for the three age groups. When the time-shared tasks were presented as equally important, time-sharing produced significantly greater proportional decrements in the tracking performance of the younger children and for all age groups tracking task decrements were directly related to matching task difficulty. Subsequently, the children were instructed that one or the other of the tasks was more important and that they were to improve their performance on that task. All three age groups showed a significant improvement on the task emphasized by instructions. The relationship of the results to two models of information processing is discussed.     

A dual task response modality effect: Support for multiprocessor models of attention

In Experiment I two groups of 11 men performed a continuous visual input/manual output task simultaneously with a two-choice tone identification task. One group responded vocally to the tones; one group responded with the hand not involved in the continuous tracking task. In either perceptual or stimulus uncertainty terms the two combinations were identical; the only difference between them was the modality of the two-choice responses. The continuous task was performed significantly worse when the two-choice responses were manual. The probability of response production on the continuous task was affected by the production of manual responses but not by the production of vocal responses. It was concluded that although the two manual responses were produced by a single limited capacity process, the manual and vocal responses were produced by independent processes. In Experiment II the same manual tracking task was combined with a mental arithmetic task at two levels of difficulty. Tracking performance was independent of the difficulty of the arithmetic task. These results support a multi-processor approach to attention as opposed to single channel models. Results of dual task studies which have used only one pair of response modalities are re-examined in the light of the response modality effect found in Experiment I.     

Automaticity and preattentive processing.

The characteristics of automatized performance resemble those of preattentive processing in some respects. In the context of visual search tasks, these include spatially parallel processing, involuntary calling of attention, learning without awareness, and time-sharing with other tasks. However, this article reports some evidence suggesting that extended practice produces its effects through different mechanisms from those that underlie preattentive processing. The dramatic changes in search rate seem to depend not on the formation of new preattentive detectors for the task-relevant stimuli, nor on learned abstracted procedures for responding quickly and efficiently, but rather on changes that are very specific both to the particular stimuli and to the particular task used in practice. We suggest that the improved performance may depend on the accumulation of separate memory traces for each individual experience of a display (see Logan, 1988), and we show that the traces differ for conjunction search in which stimuli must be individuated and for feature search where a global response to the display is sufficient.     

Menstrual cycle effects on task performance examined in the context of stress research

The study examined the effects of degree of paramenstrual distress, signal frequency, task load and time on task on psychomotor performance across the menstrual cycle. Simple reaction time, choice reaction time and pursuit tracking were the tasks employed, and performance was assessed using the metrics of mean level, variability, and errors of omission and commission. The results showed performance as a function of menstrual cycle phase and paramenstrual distress to be highly task and metric specific, a finding typical of stressor variables: pursuit tracking was affected by phase, with mean performance at its worst premenstrually; choice reaction time was dependent on a complex interaction of experimental variables and measurement metrics; simple reaction time showed no significant effects. Patterns of attention allocation in a time-sharing situation combining both pursuit tracking and choice reaction time components were also investigated. Trends here indicated relatively better performance both menstrually and intermenstrually as components increased in signal/response frequency, with a corresponding deterioration premenstrually. Overall performance capacity appeared to be greatest at menstruation, and the degree of attentional selectivity was least. High distress women performed better on low frequency components, whereas asymptomatic women did better at higher signal rates.     

Role of multiple resources in predicting time-sharing efficiency: evaluation of three workload models in a multiple-task setting

The goal of our study was to assess the validity of the assumptions underlying three prominent workload models: the Time-Line Analysis and Prediction workload model (Parks & Boucek, 1989), the VACP workload model (Aldrich, Szabo, & Bierbaum, 1989), and the W/INDEX model (North & Riley, 1989). Sixteen subjects flew a low-fidelity flight simulation. Subjects were required to perform a two-axis tracking task, a concurrent visual-monitoring task, and a discrete decision task. The decision task had 16 variations defined by two levels on each of the following dimensions: input modality (visual vs. auditory), processing code (spatial vs. verbal), difficulty (easy vs. hard), and response modality (manual vs. voice). Dual-task costs were found only for the tracking task. The tracking data were then analyzed using two approaches: a traditional analysis of variance (ANOVA) and a correlational analysis of tracking performance versus model predictions. The ANOVA revealed that performance on the tracking task was better when the concurrent decision task was responded to vocally and was easy. Input modality and processing code of the concurrent decision task had no significant effect on tracking performance. The correlational analysis was used to evaluate each of the three models, to determine what features were responsible for improving the models' fit, and to compare their performance with a pure time-line model that makes no multiple-resource assumptions. All three models did a good job of predicting variance between experimental conditions, accounting for between 56% and 84% of the variance in our data and between 10% and 40% of an earlier data set. Different features of each model that affect the fit are then discussed. We conclude that it is important for models to retain a multiple-resource coding, although the best features of that coding remain to be determined. Coding tasks by their demand level appears to be less critical.     

Aging, exercise, and attention.

The authors investigated the relationship among aging, attentional processes, and exercise in 2 experiments. First they examined age differences on 2 attentional tasks, a time-sharing task and an attentional flexibility task. Young adults alternated attention between 2 sequenced tasks more rapidly and time-shared the processing of 2 tasks more efficiently than older adults. They then investigated the effects of aerobic exercise on the same 2 attentional tasks in older adults. Following the 10-week exercise program, older exercisers showed substantially more improvement in alternation speed and time-sharing efficiency than older controls. Interestingly, this exercise effect was specific to dual-task processing. Both groups of subjects showed equivalent effects on single-task performance. These results indicate that aerobic exercise can exert a beneficial influence on the efficiency of at least 2 different attentional processes in older adults.     

Attention alters the appearance of motion coherence

Selective attention enhances visual information processing, as measured by behavioral performance and neural activity. However, little is known about its effects on subjective experience. Here, we investigated the effect of transient (exogenous) attention on the appearance of visual motion, using a psychophysical procedure that directly measures appearance and controls for response bias. Observers viewed pairs of moving dot patterns and reported the motion direction of the more coherent pattern. Directing attention (via a peripheral precue) to a stimulus location increased its perceived coherence level and improved performance on a direction discrimination task. In a control experiment, we ruled out response bias by lengthening the time interval between the cue and the stimuli, so that the effect of transient attention could no longer be exerted. Our results are consistent with those of neurophysiological studies showing that attention modulates motion processing and provide evidence of a subjective perceptual correlate of attention, with a concomitant effect on performance.     

Study of the single channel hypothesis and input regulation within a continuous, simultaneous task situation

Subjects performed simultaneously on an auditory tracking and an auditory discrimination task, with each, task presented to a separate ear. Information transmitted on the tasks was measured as a function of ability to predict task characteristics, input information-rate, and input discriminability. Based on comparison of single-versus simultaneous-task performance, support was found for a single, central decision-type channel in information processing, having as one primary limit the rate at which information can be accepted. Discriminability of inputs also was found to be a limit on information processing rate. Although ability to predict a task's characteristics facilitated performance on that task, in this experiment it did not result in facilitation of performance on the second task. Relevance of these findings to certain aspects of Broadbent's information-processing model is discussed.     

Visual load and variability of muscle activation: Effects on reactive driving of older adults

BackgroundThe functional significance of the increase in motor output variability with increased visual information processing in older adults remains unclear. Here, we test the hypothesis that increased visual information processing increases muscle activation variability in older adults and impairs their ability to react as fast and as precisely as young adults during a simulated reactive driving task.MethodsFourteen young and sixteen older adults performed a reactive driving simulation task that required responding to unexpected brake lights of the car ahead during a simple reaction time task (low visual information processing condition) and a choice reaction time task with “no go” trials condition (high visual information processing condition). We quantified the following: 1) reactive driving performance – combination of premotor response time, motor response time, and brake force error; 2) motor output variability – brake impulse variability; 3) muscle activation variability – variability in the tibialis anterior (TA) muscle activity.ResultsThe increase in information processing exacerbated the impaired reactive driving performance in older adults. The best predictor of this impairment was the increase in brake force error. The impaired reactive driving performance was related to brake impulse variability and variability in the TA activity.ConclusionsThis study provides novel evidence that increased information processing increases muscle activation variability in older adults with detrimental consequences to their ability to perform a simulated reactive driving task.     

Strategic control in word reading: evidence from speeded responding in the tempo-naming task

To investigate strategic control over response initiation in word reading, the authors introduce the tempo-naming task. Relative to baseline performance in the standard-naming task, participants were induced to respond with faster latencies, shorter durations, and lower levels of accuracy by instructing them to time response initiation with an experimentally controlled tempo. The tempo response cue attenuated stimulus effects, and as faster tempos reduced latencies, the number of spelling-sound errors remained constant, whereas the number of word, nonword, and articulatory errors increased. To explain these results, the authors propose input gain as a mechanism of control over processing speed. The experimenters sketch how input gain could account for the current results as well as for the results from stimulus-blocking experiments testing the route emphasis and time criterion hypotheses of strategic control.     

When causality does not imply correlation: more spadework at the foundations of scientific psychology

Experimental research in psychology is based on an open-loop causal model which assumes that sensory input causes behavioral output. This model was tested in a tracking experiment where participants were asked to control a cursor, keeping it aligned with a target by moving a mouse to compensate for disturbances of differing difficulty. Since cursor movements (inputs) are the only observable cause of mouse movements (outputs), the open-loop model predicts that there will be a correlation between input and output that increases as tracking performance improves. In fact, the correlation between sensory input and motor output is very low regardless of the quality of tracking performance; causality, in terms of the effect of input on output, does not seem to imply correlation in this situation. This surprising result can be explained by a closed-loop model which assumes that input is causing output while output is causing input.     

Aging and time-sharing aspects of executive control

A particularly important aspect of executive functioning involves the ability to coordinate two simultaneous activities. The role of this aspect of executive functioning in adult-age differences in cognitive performance was examined in a study involving 150 adults between 20 and 91 years of age who performed the same visual-motor tracking task with three different primary tasks. The participants also performed several additional cognitive tasks that allowed examination of the relation of time-sharing efficiency to other types of cognitive functioning The results were consistent with the existence of a distinct time-sharing ability because the time-sharing costs in the three dual-task combinations were significantly correlated with one another but only weakly correlated with other cognitive variables. Increased age was associated with reductions in time-sharing ability, and greater efficiency in performing two tasks at once was associated with better performance on tasks assessing spatial, reasoning, and memory abilities. Although this pattern is what one would expect if executive processes contribute to age differences in cognitive functioning, the effects were smaller than those associated with a perceptual speed construct.     

Testing the limits of cognitive plasticity in older adults: application to attentional control

Laboratory based training studies suggest that older adults can benefit from training in tasks that tap control aspects of attention. This was further explored in the present study in which older and younger adults completed an adaptive and individualized dual-task training program. The testing-the-limits approach was used [Lindenberger, U., & Baltes, P. B. (1995). Testing-the-limits and experimental simulation: Two methods to explicate the role of learning in development. Human Development, 38, 349-360.] in order to gain insight into how attentional control can be improved in older adults. Results indicated substantial improvement in overlapping task performance in both younger and older participants suggesting the availability of cognitive plasticity in both age groups. Improvement was equivalent among age groups in response speed and performance variability but larger in response accuracy for older adults. The results suggest that time-sharing skills can be substantially improved in older adults.     

Regarding time-sharing with convergent operations

This study contrasts the structural bottleneck and the resource view of attentional limits in time-sharing performance. The research incorporated features of the psychological refractory period (PRP) and the relative priority paradigm designed to maximize joint performance. A main distinction between the two attention views was their prediction on the extent that graded performance tradeoff was possible with graded priority changes. Detailed analysis of the performance and time-sharing strategies called into question the conclusions based exclusively on the PRP paradigm.     

Task-hemispheric integrity in dual task performance

A condition of task hemispheric integrity is predicted to result in a dual task situation when the central processing and response components of each task are associated exclusively with a given cerebral hemisphere. The prediction that this condition will generate more efficient time-sharing is tested in a series of four experiments. In experiment 1 the prediction is confirmed when a spatial (tracking) and verbal (letter memory search) task are time-shared, and the hand assignment to task responses is manipulated. In experiment 2 a spatial variant of the memory search is used instead of the verbal letter search, and hand assignment effects are not obtained, since when two spatial tasks are time-shared an integrity assignment is impossible. Experiment 3 validates the hemispheric lateralization of the two single task variants of the memory search task, while experiment 4 establishes the separate “spatial’ and “verbal” resource demands of the two variants by observing their differential interference with concurrent spatial and verbal tasks.     

Increased locus coeruleus tonic activity causes disengagement from a patch-foraging task

High levels of locus coeruleus (LC) tonic activity are associated with distraction and poor performance within a task. Adaptive gain theory (AGT; Aston-Jones & Cohen, 2005) suggests that this may reflect an adaptive function of the LC, encouraging search for more remunerative opportunities in times of low utility. Here, we examine whether stimulating LC tonic activity using designer receptors (DREADDs) promotes searching for better opportunities in a patch-foraging task as the value of a patch diminishes. The task required rats to decide repeatedly whether to exploit an immediate but depleting reward within a patch or to incur the cost of a time delay to travel to a new, fuller patch. Similar to behavior associated with high LC tonic activity in other tasks, we found that stimulating LC tonic activity impaired task performance, resulting in reduced task participation and increased response times and omission rates. However, this was accompanied by a more specific, predicted effect: a significant tendency to leave patches earlier, which was best explained by an increase in decision noise rather than a systematic bias to leave earlier (i.e., at higher values). This effect is consistent with the hypothesis that high LC tonic activity favors disengagement from current behavior, and the pursuit of alternatives, by augmenting processing noise. These results provide direct causal evidence for the relationship between LC tonic activity and flexible task switching proposed by AGT.     

Baseline differences,attention, and age differences in time-sharing performance

The purpose of this experiment was to determine whether age differences noted when two tasks are performed concurrently can be accounted for in terms of age differences in single task baseline performance. Two groups of 12 8-year-olds and one group of 12 13-year-olds performed a compensatory tracking task and an auditory matching task, first alone and then time shared. The 8- and 13-year-old baseline groups performed baseline trials on each task prior to time-sharing trials. Each training group 8-year-old was randomly paired with a 13-year-old and given sufficient single task practice before time sharing to equate the 8- and 13-year-old pair members' baselines on both tasks. Results showed trained 8-year-olds to be indistinguishable from 13-year-olds in time sharing, whereas the 8-year-old baseline group showed significantly greater decrements in time-sharing and higher baseline scores on both tasks. These data provide support for the hypothesis that time-shared performance is directly related to level of baseline performance.     

Hydrocortisone infusion exerts dose- and sex-dependent effects on attention to emotional stimuli

Glucocorticoid administration has been shown to exert complex effects on cognitive and emotional processing. In the current study we investigated the effects of glucocorticoid administration on attention towards emotional words, using an Affective Go/No-go task on which healthy humans have shown an attentional bias towards positive as compared to negative words. Healthy volunteers received placebo and either low-dose (0.15 mg/kg) or high-dose (0.45 mg/kg) hydrocortisone intravenously during two separate visits in a double-blind, randomized design. Seventy-five minutes post-infusion, the subjects performed tests of attention (Rapid Visual Information Processing [RVIP]), spatial working memory (Spatial Span) and emotional processing (Affective Go/No-go task [AGNG]). On the attention task, performance was impaired under both hydrocortisone doses relative to placebo, though the effect on error rate was not significant after controlling for age; Spatial Span performance was unaffected by hydrocortisone administration. On the AGNG task, relative to the placebo condition the low-dose hydrocortisone infusion decreased response time to emotional words while high-dose hydrocortisone increased response time. In the females specifically, both high and low dose hydrocortisone administration attenuated the normal attentional bias toward positively valenced words. These data suggest that, in healthy women, the modulation of attention by the emotional salience of stimuli is influenced by glucocorticoid hormone concentrations.     

Top-down influences mediate hand bias in spatial attention

Spatial attention can be biased to locations near the hand. Some studies have found facilitated processing of targets appearing within hand-grasping space. In this study, we investigated how changing top-down task priorities alters hand bias during visual processing. In Experiment 1, we used a covert orienting paradigm with nonpredictive cues and emphasized the location of the hand relative to the target. Hands or visual anchors (boards) were placed next to potential target locations, and responses were made with the contralateral hand. Results indicated a hand-specific processing bias: Hand location, but not board location, speeded responses to targets near the hand. This pattern of results replicated previous studies using covert orienting paradigms with highly predictive cues. In Experiment 2, we used the same basic paradigm but emphasized the location of the response hand. Results now showed speeded responses to targets near response locations. Together these experiments demonstrated that top-down instructional sets (i.e., what is considered to be most relevant to task performance) can change the processing priority of hand location by influencing the strength of top-down, as compared with bottom-up, inputs competing for attention resources.