Ritske de Jong

Multiple bottlenecks in overlapping task performance

A dual-bottleneck model for overlapping-task performance is proposed. A central bottleneck prevents central processes in overlapping tasks from operating in parallel. A response-initiation bottleneck prevents 2 responses from being initiated in close succession. Response requirements of the overlapping tasks were manipulated in order to demonstrate the existence of the latter bottleneck and to assess its role in delimiting overlapping-task performance. In several experiments, elimination of this bottleneck resulted in a strong reduction of underadditive interactions that serve as key indicators of parallel processing in overlapping-task performance. Results indicate that these interactions were caused primarily by the response initiation bottleneck instead of the central bottleneck and suggest that perceptual identification and categorization require the central bottleneck. Language: en

Goal neglect and inhibitory limitations: dissociable causes of interference effects in conflict situations

Interference effects on task performance in conflict situations might reflect real limitations in inhibitory capabilities or failures to fully or consistently utilize such capabilities in executive control of task performance. We propose that useful clues regarding the actual cause of interference effects may be obtained from examination of their robustness within and between experimental conditions. We illustrate this approach for two major types of interference effects that have commonly been attributed to fundamental inhibitory limitations: Stroop-type interference and residual switch costs. We present results that indicate that these effects may not be unavoidable consequences of fundamental inhibitory limitations but may stem from goal neglect, i.e., failures to fully or effectively deploy inhibitory capabilities. These results indicate that, in addition to mean performance levels, variability of task performance may provide a valuable source of evidence regarding the actual cause of performance limitations or deficits in conflict situations.

The Role of Preparation in Overlapping-task Performance

We examined how performance of two overlapping discrete tasks is organized and controlled. Experiment 1 showed that when stimuli were presented in an unexpected order, expectations rather than actual presentation order determined the order in which the two stimuli were processed. In Experiment 2, when task order was unpredictable, performance was facilitated when task order was repeated on consecutive trials. In Experiment 3, performance of the second but not the first task benefited greatly when task order was held constant as compared to regularly alternated between trials; such effects were especially pronounced at short intertrial intervals. These results suggest that sequential performance of overlapping tasks is scheduled in advance and is regulated by initially allocating the central processing channel to one task and subsequently switching this channel to the other task.We examined how performance of two overlapping discrete tasks is organized and controlled. Experiment 1 showed that when stimuli were presented in an unexpected order, expectations rather than actual presentation order determined the order in which the two stimuli were processed. In Experiment 2, when task order was unpredictable, performance was facilitated when task order was repeated on consecutive trials. In Experiment 3, performance of the second but not the first task benefited greatly when task order was held constant as compared to regularly alternated between trials; such effects were especially pronounced at short intertrial intervals. These results suggest that sequential performance of overlapping tasks is scheduled in advance and is regulated by initially allocating the central processing channel to one task and subsequently switching this channel to the other task.

Adult age differences in goal activation and goal maintenance.

According to the goal-neglect hypothesis of age-related decrements in cognitive control advocated in this paper, such decrements can be usefully and parsimoniously attributed to a reduced capacity for goal selection and goal maintenance in working memory. A selective review of research findings on age-related differences in exogenous and endogenous control of visual attention and eye movements and on performance in the task-switching paradigm serves to illustrate and clarify this hypothesis. The relative merits and scope of the hypothesis are examined within a broader theoretical perspective on the organisation of the domain of executive functions.

Strategical determinants of compatibility effects with task uncertainty

Three experiments were conducted to investigate why effects of stimulus-response compatibility (SRC) disappear when the mapping rule is varied randomly and provided only briefly before the imperative stimulus arrives. Three alternative explanations were tested by manipulating automatic response priming, relative probabilities of the mappings, and degree of interference or crosstalk between the mappings. The results indicate that the reduction of SRC effects reflects an active initial suppression of the compatible mapping rule. This suppression appears to be necessary in order to prevent the compatible rule from producing detrimental interference when the incompatible rule is called for instead. These results demonstrate the important role of strategical factors in regulating performance in dynamic task settings.

A goal activation approach to the study of executive function: An application to antisaccade tasks

We argue that a general control process, responsible for the activation and maintenance of task goals, is central to the concept of executive function. Failures of this process can become manifest as goal neglect: disregard of a task requirement even though it has been understood (Duncan, 1995). We discuss the results of several published and new experiments using various versions of the antisaccade task in order to investigate the circumstances under which goal neglect is likely to occur. Potentially conflicting results in the literature on adaptive control of saccadic eye movements are argued to be attributable to the extent to which different task versions elicit goal neglect. The results suggest an increased susceptibility to goal neglect of high-functioning older adults (Experiment 1) and of first-episode schizophrenia patients (Experiment 2), but not of patients with obsessive-compulsive disorder (Experiment 3). However, the degree to which such differences in susceptibility become manifest in task performance, is shown to be strongly influenced by manipulations of the relative saliency of task requirements. Theoretical and methodological implications for the study of executive function are discussed.

Pre-stimulus EEG effects related to response speed, task switching and upcoming response hand

The task-switching paradigm provides an opportunity to study whether oscillatory relations in neuronal activity are involved in switching between and maintaining task sets. The EEG of subjects performing an alternating runs [Rogers, R.D., Monsell, S., 1995. Costs of a predictable switch between simple cognitive tasks. Journal of Experimental Psychology: General 124, 207-231] task-switching task was analyzed using event-related potentials, the lateralized readiness potential, instantaneous amplitude and the phase-locking value [Lachaux, J.P., Rodriguez, E., Martinirie, J., Varela, F.J., 1999. Measuring phase synchrony in brain signals. Human Brain Mapping 8, 194-208]. The two tasks differed in the relevant modality (visual versus auditory) and the hand with which responses were to be given. The mixture model [de Jong, R., 2000. An intention driven account of residual switch costs. In: Monsell, S., Driver, J. (Eds.), Attention and Performance XVII: Cognitive Control. MIT Press, Cambridge] was used to assign pre-stimulus switch probabilities to switch trials based on reaction time; these probabilities were used to create a fast-slow distinction between trials on both switch and hold trials. Results showed both time- and time-frequency-domain effects, during the intervals preceding stimuli, of switching versus maintenance, response speed of the upcoming stimulus, and response hand. Of potential importance for task-switching theory were interactions between reaction time by switch-hold trial type that were found for a frontal slow negative potential and the lateralized readiness potential during the response-stimulus interval, indicating that effective preparation for switch trials involves different anticipatory activity than for hold trials. Theta-band oscillatory activity during the pre-stimulus period was found to be higher when subsequent reaction times were shorter, but this response speed effect did not interact with trial type. The response hand of the upcoming task was associated with lateralization of pre-stimulus mu- and beta-band amplitude and, specifically for switch trials, beta-band phase locking.

EEG coherence obtained from an auditory oddball task increases with age

Summary: Changes in coherence with aging during cognitive tasks have, until now, not been investigated. However, several fMRI and positron emission tomography studies of cognitive tasks have found increased bilateral activity in elderly subjects. Changes in coherence with aging during a cognitive task were investigated to see if EEG coherence was present in older adults. An auditory oddball task, which is a widely used test for cognitive function, was used. Eleven young adults (27.8 ± 4.8 years, six females) and 10 older adults (61.3 ± 4.6 years, six females) were studied, and both interhemispheric and long- and short-range intrahemispheric coherence were considered. Higher interhemispheric coherence was found in the older subjects in the delta band. Short intrahemispheric coherence was also increased in the theta, delta, and alpha bands. Higher coherence, although not significantly different, was also found for all other coherence types and bands, except for long intrahemispheric coherence in the low gamma band. The results presented here provide the first evidence that aging is associated with increased EEG coherence during a relatively easy cognitive task.

Age-related changes in event-related prospective memory performance: A comparison of four prospective memory tasks

The primary purpose of the study was to identify event-based prospective-memory tasks that provide sensitive and reliable tools for assessing effects of normal aging in prospective-memory performance. Four prospective-memory tasks were selected from the literature or were newly developed, with the tasks differing on various dimensions that, for theoretical reasons or based on previous evidence, might determine task sensitivity to age effects on prospective-memory performance: perceptual saliency of prospective target events, frequency of occurrence of prospective target events, complexity of prospective-memory instructions, and provision of feedback after prospective-memory errors. Two of the four tasks yielded large and robust age effects on prospective-memory performance. Correlational analyses suggested that these age effects on prospective-memory performance were mediated, at least in part, by a reduced ability of older adults to maintain prospective intentions in a highly activated state and not by age effects on basic mental speed alone.

Dissociable mechanisms underlying individual differences in visual working memory capacity

Individuals scoring relatively high on measures of working memory tend to be more proficient at controlling attention to minimize the effect of distracting information. It is currently unknown whether such superior attention control abilities are mediated by stronger suppression of irrelevant information, enhancement of relevant information, or both. Here we used steady-state visual evoked potentials (SSVEPs) with the Eriksen flanker task to track simultaneously the attention to relevant and irrelevant information by tagging target and distractors with different frequencies. This design allowed us to dissociate attentional biasing of perceptual processing (via SSVEPs) and stimulus processing in the frontal cognitive control network (via time-frequency analyses of EEG data). We show that while preparing for the upcoming stimulus, high- and low-WMC individuals use different strategies: High-WMC individuals show attentional suppression of the irrelevant stimuli, whereas low-WMC individuals demonstrate attentional enhancement of the relevant stimuli. Moreover, behavioral performance was predicted by trial-to-trial fluctuations in strength of distractor-suppression for high-WMC participants. We found no evidence for WMC-related differences in cognitive control network functioning, as measured by midfrontal theta-band power. Taken together, these findings suggest that early suppression of irrelevant information is a key underlying neural mechanism by which superior attention control abilities are implemented.