Biomedical subjects

G R Wylie

Publications and source records attributed to G R Wylie.

5 recordsLinked to original sources

PubMed2005

Jumping the gun: is effective preparation contingent upon anticipatory activation in task-relevant neural circuitry?

Subjects switched between tasks that rely on separable "low-level" neural circuits, a motion and a color task. Using functional magnetic resonance imaging, we assessed anticipatory processes within these circuits during preparation to switch between tasks. Once the switch was made, we could then compare activation levels within the circuit associated with the newly relevant task to continuing activity in the circuit associated with the irrelevant task, allowing us to assess both the effectiveness of anticipatory switching mechanisms and the subsequent competition between alternative stimulus-response contingencies. Subjects prepared effectively for the color task, being equally fast and accurate on switch trials as on repeat trials, and this successful preparation was associated with robust preparatory activity within well-known color-processing regions. In contrast, subjects showed considerable behavioral costs when switching to the motion task, evincing a lack of effective preparation, borne out by the fact that motion circuits were silent during the preparatory period.

Adaptation, Physiological↗

PubMed2004

The role of response requirements in task switching: dissolving the residue.

Task-switching paradigms, which are regularly used to assay 'executive control' processes in humans, almost invariably reveal a decrement in subjects' performance on the first trial following a switch of task. That is, subjects are slower to respond and more error prone on the switch trial, a difference in performance that has been termed the 'switch-cost'. This switch cost has then been taken to reflect the time taken by neural control processes. Previous studies have shown that while performance improves as more time is provided to prepare for the switch, switch costs persist, even over very long intervals. In the present study, however, we find that changing the response regimen (choice reaction time vs go-no-go) has profound effects on the switch cost. A task switching paradigm was used in which subjects randomly switched between two tasks, based on a cue that was presented at varying intervals prior to the presentation of the imperative stimulus. While switch costs were found in all conditions in the choice reaction time blocks, they were completely abolished in the go-no-go blocks when sufficient preparation time was provided (500 or 800 ms). This is important because the only difference between the choice reaction time and go-no-go conditions was the response requirement: these conditions did not differ in the stimuli used, in the tasks performed or in the preparation time provided. These data call into question models of executive control that interpret switch costs as reflecting the time taken by neural processes to switch the system from a readiness to perform one task to a readiness to perform another.

Adult↗

PubMed2004

A topography of executive functions and their interactions revealed by functional magnetic resonance imaging.

We used fMRI to study the brain processes involved in the executive control of behavior. The Sustained Attention to Response Task (SART), which allows unpredictable and predictable NOGO events to be contrasted, was imaged using a mixed (block and event-related) fMRI design to examine tonic and phasic processes involved in response inhibition, error detection, conflict monitoring and sustained attention. A network of regions, including right ventral prefrontal cortex (PFC), left dorsolateral PFC (DLPFC) and right inferior parietal cortex, was activated for successful unpredictable inhibitions, while rostral anterior cingulate was implicated in error processing and the pre-SMA in conflict monitoring. Furthermore, the pattern of correlations between left dorsolateral PFC, implicated in task-set maintenance, and the pre-SMA were indicative of a tight coupling between prefrontally mediated control and conflict levels monitored more posteriorly. The results reveal that the executive control of behavior can be separated into distinct functions performed by discrete cortical regions.

Adult↗

PubMed2003

Task switching: a high-density electrical mapping study.

Flexibly switching between tasks is one of the paradigmatic functions of so-called "executive control" processes. Neuroimaging studies have implicated both prefrontal and parietal cortical regions in the processing necessary to effectively switch task. Beyond their general involvement in this critical function, however, little is known about the dynamics of processing across frontal and parietal regions. For instance, it remains to be determined to what extent these areas play a role in preparing to switch task before arrival of the stimulus to be acted upon and to what extent they play a role in any switching processes that occur after the stimulus is presented. Here, we used the excellent temporal resolution afforded by high-density mapping of brain potentials to explore the time course of the processes underlying (1) the performance of and (2) the preparation for a switch of task. We detail the contributions of both frontal and parietal processes to these two aspects of the task-switching process. Our data revealed a complex pattern of effects. Most striking was a period of sustained activity over bilateral parietal regions preceding the switch trial. Over frontal regions, activity actually decreased during this same period. Strongest sustained frontal activity was in fact seen for trials on which no switch was required. Further, we find that the first differential activity associated with switching task was over posterior parietal areas (220 ms), whereas over frontal scalp, the first differential activity is found more than 200 ms later. These and other effects are interpreted in terms of a "competition" model in which preparing to switch task is understood as the beginning of a competition between the potentially relevant tasks that is resolved during the switch trial. Our findings are difficult to account for with models that posit a strong role for frontal cortical regions in "reconfiguring" the system during switches of task.

Adolescent↗

PubMed2003

Cognitive control processes during an anticipated switch of task.

For successful negotiation of our environment, humans must be readily able to switch from one task to another. This ability relies on 'executive control' processes and despite extensive efforts to detail the nature of these processes, there is little consensus as to how the brain achieves this critical function. Behavioural studies show that as subjects are given more time to prepare to switch task, performance improves; yet even with the longest preparation intervals, there remains an ineradicable performance cost on switch trials. As such, some elements of the switching process must wait until the stimulus to be acted upon has actually been presented. Here, using the methods of high-density mapping of brain potentials, we show that early visual processes are substantially different on switch trials than on later trials. Our data show that while there is clearly a degree of preparatory processing that occurs prior to a predictable switch of task, some elements of switching are only achieved after the switch stimulus has been presented. Our findings are discussed in the context of a new model of executive control processes that suggests that preparing to switch task may not be a separate (control) process per se, but rather, the beginning of a competition between the potentially relevant tasks, a competition that is ultimately resolved during the switch trial.

Adolescent↗