The goal of this basic experimental clinical trial is to understand the effect of multitasking practice on the structure of neural representations of tasks in the human lateral prefrontal cortex and control brain regions. The main question it aims to answer is: What changes in neural representational structure predict improvements in multitasking behavior due to multitasking practice? Healthy human participants will learn two independent tasks, each mapping a set of stimuli to motor responses based on different rules. Participants will be randomized to one of two interventions. Participants assigned to the multitask practice intervention (MPI) will practice multitasking the two tasks over multiple days. Those assigned to the single-task practice intervention (SPI) will instead practice each task separately while controlling for the total number of practice opportunities associated with each task across the interventions. Both before and after the practice, the ability of all participants to perform both tasks simultaneously will be behaviorally measured using a well-established psychological refractory period (PRP) paradigm, and their neural representations will be measured using functional MRI while they perform the two tasks. Researchers will then compare improvements in multitasking behavior across the two groups, as well as changes in neural representational geometry of the tasks in the lateral prefrontal cortex and control brain regions, and test whether multitasking training is associated with specific changes in neural representations in the lateral prefrontal cortex.
Normal or corrected to normal vision.
Left handedness
Presence or history of neurological or psychiatric disorders
Usage of brain related medications
Previous head injury and time spent unconscious
Parallel
Multitask Practice Intervention (MPI)
BehavioralMultitask practice intervention (MPI) includes multiple behavioral testing sessions during which participants receive practice with multitasking two tasks using the psychological refractory period procedure.
Single-task Practice Intervention (SPI)
BehavioralSingle task practice intervention (SPI) includes multiple behavioral testing sessions during which participants receive separate practice on two tasks.
Effect of the practice intervention on change in overall and task-relevant neural separability in lateral prefrontal cortex
Overall neural separability (also referred to as shattering dimensionality) will be measured by employing cross-validated neural decoding of lateral PFC fMRI BOLD multi-voxel patterns, averaging decoding accuracies across all balanced dichotomies of the task inputs. Task-relevant neural separability will be measured by averaging decoding accuracies across all task-relevant variables.
Effect of multitasking practice on behavioral multitasking cost
Behavioral multitasking cost will be estimated by computing the difference in mean response time on task 2 on long SOAs and short SOAs in the Psychological Refractory Period paradigm. The effect of multitasking practice on behavioral multitasking will be estimated using linear mixed-effects regression, and is defined as the regression weight associated with the interaction effect of time point and intervention on multitasking cost.
Contribution of overall and task-relevant neural separability in lateral prefrontal cortex to the effect of multitasking practice on behavioral multitasking cost
The contribution of prefrontal neural separability change to the effect of multitasking practice on behavioral multitasking will be estimated using linear mixed-effects regression, and is defined as the regression weight associated with the interaction effect of time point, intervention and separability on multitasking cost.
Cross-classification generalization performance of task-relevant variables in lateral prefrontal cortex
Cross-classification generalization performance will be estimated by averaging decoding accuracies from cross-classification of individual task variables across subsets of task inputs in the lateral prefrontal cortex.
Coding axis angles between stimulus feature representations in two tasks in lateral prefrontal cortex
Coding axis angles will be estimated by computing the angle between the weight vectors of linear classifiers trained to decode stimulus features in each task context.
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Brown University
Lead sponsor
National Institute of Mental Health (NIMH)
Collaborator
