Number Letter Task
AKA: Category Switch Task
Background
The Number-Letter Task is is a cognitive-behavioral measure of executive functioning and specifically addresses the 'set shifting' subcomponent of executive control under predictable switching conditions (see Category Switch Task for an unpredictable shift task). The task was originally developed by Robert D. Rogers and Stephen Monsell at the University of Cambridge in 1995 to study the influence of endogenous ('internal') and exogenous ('external') factors on switch costs. Akira Miyake and colleagues simplified the task in 2000 as part of a broader study of executive functioning tests.
In the Number-Letter Task participants are shown a stimulus pair consisting of a letter and a number (e.g., 2U or M5) in one of four matrix quadrants. The task they must solve depends on where the pair appears: if the stimulus appears in the upper quadrants, participant must decide if the letter is a consonant or a vowel. If the stimulus appears in the lower quadrants, participants must decide if the number is odd or even. Once participants have decided and pushed a corresponding response key, the stimuli 'wander' clockwise to the next matrix position, where a new stimulus pair is presented. Due to the predictable stimuli rotations, each switch trial is followed by a repeat trial and participants can thus mentally prepare for the next categorization task.
Rogers & Monsell (1995) found that by increasing the preparation time in-between stimuli presentations, switch costs decreased, supporting that task switching requires time-consuming, endogenously prepared mental operations. Nevertheless, even at relatively long preparation times, a 'residual' switch cost could be observed, suggesting that part of the overall switch costs are driven by the stimuli themselves (exogenous control).
Miyake et al (2000) investigated the relationship of several executive functioning tests (set shifting, updating, inhibition) and showed that the 'Shifting' factor was distinct yet correlated with updating and inhibition functions, thus supporting that the different measures indeed tap distinct components ('diversity') of a common underlying function ('unity').
Task Procedure
After a blocked practice of the two categorization tasks (consonant-vowel and odd-even categorizations) and a combined practice of the two tasks, participants work on 128 test trials. Half the trials (64) are Repeat and half the trials are Switch trials. Response keys are the "E" and "I" key on the keyboard. Key assignment to the different tasks is counterbalanced across participants. Half the Repeat/Switch trials run congruent keys (the correct response key for the consonant-vowel and odd-even task are the same), the other half run incongruent ones. Stimuli pairs are presented until a response is given. Errorfeedback is provided during practice. The intertrial interval is 500ms for correct and 1500ms for incorrect responses, as errors require a longer recovery to avoid losing track of which task to perform next (Rogers & Monsell, 1995).
What it Measures
The Number-Letter Task is a cognitive-behavioral test of executive control, particularly set-shifting abilities under predictable shifting conditions.
Psychological domains
- Executive Control: Collection of "top-down" mental processes used to manage and regulate thoughts and actions
- Cognitive Flexibility: Shift to a new rule when the previous rule no longer applies
- Working Memory: storing and selecting the respective response button assignments for the different categorization tasks
- Sustained Attention: Maintaining focus over a repetitive series of trials without 'drifting'
Main Performance Metrics
- Switch Cost: the difference in response times (accuracy) to 'shift' and 'repeat' trials; measure of cognitive flexibility
Psychiatric Conditions
The Number-Letter performance has been found to be impaired in the following patient groups
- Traumatic Brain Injury (TBI)
- Parkinson’s Disease
- Attention Deficit Hyperactivity Disorder (ADHD)
- Autism Spectrum Disorder
- Schizophrenia
- Mild Cognitive Impairment (MCI)
A task switching paradigm in which participants must switch in a predictable fashion between categorizing letters or numbers as described by Miyake et al (2000).
References
Search Google Scholar for peer-reviewed, published research using the Inquisit Number Letter Task.
Rogers, R. D., & Monsell, S. (1995). The costs of a predictable switch between simple cognitive tasks. Journal of Experimental Psychology: General, 124, 207–231.
Miyake, A., Friedman, N. P., Emerson, M. J., Witzki, A. H., Howerter, A., & Wager, T. D. (2000). The unity and diversity of executive functions and their contributions to complex “frontal lobe” tasks: A latent variable analysis. Cognitive Psychology, 41, 49–100.