N-Back Task

Background

The N-back task is a continuous go/nogo performance test used in cognitive psychology and neuroscience to measure and train working memory. It primarily tests executive functions, specifically the ability to monitor, update, and temporarily store information. Participants view a sequence of stimuli (e.g., letters, numbers, or spatial positions) and must indicate if the current item matches the one presented N steps earlier in the series (the go 'targets'). The higher N is, the more difficult the task becomes. For example, for N=1, the task is still pretty easy for most people. Participants are asked to make a response anytime the current stimulus matches the one preceding it (aka 'one position back'). For N=2, the task already gets harder as more working memory activity is required: Participants are asked to make a response anytime the current stimulus matches the one that was presented two positions before it (aka 'two positions back'). It's highly uncommon for untrained participants to perform above chance levels for N-levels above 3. With extensive training, some people may manage to go to level 7 or even beyond.

The n-back paradigm was first published by Wayne Kirchner in 1958, though W.K. Kay used the procedure in an unpublished dissertation even earlier in 1953. These early n-back procedure specifically targeted spatial (location) working memory: Participants watched a row of lights that would turn on one at a time in a completely random order, changing at a fast pace of 1.5-second intervals. Any time an N-target was noticed, participants had to physically press a corresponding telegraph key.

Today's n-back versions usually run on keyboard and touchscreen devices and use a variety of stimuli (e.g. letters, numbers, shapes, images, locations and even emotions) in visual and auditory modality. They can run fixed N-levels or adapt N-levels based on prior block performance. They can even run extremely challenging dual n-back tasks as introduced by Susanne Jaeggi and colleagues in 2008 who asked participants to track a location n-back (visual modality) at the same time as a number n-back (auditory modality), using two different keyboard keys to indicate visual and auditory targets, respectively. Using the dual n-back procedure as a training task, Jaeggi and colleagues reported observing actual increases in fluid intelligence (IQ); which is typically considered to be stable after childhood.

The popularity of the n-back task is based on a combination on facts: for one it's an ideal task for neuroimaging studies of working memory as the actual physical response stays exactly the same while the cognitive load rises. And second, unlike many cognitive tests that have a low ceiling or become useless once a participant figures out the 'trick', the N-back task features infinite difficulty. By simply changing the 'N' variable, a researcher can push anyone—from a patient recovering from a traumatic brain injury to a genius memory champion—to their absolute cognitive limit. This makes the n-back procedure highly valuable for tracking incremental progress or decline in working memory over time.

Task Procedure

A classic non-adaptive letter n-back procedure presents a participant with a sequence of letters, presented one at a time at a fast pace (e.g. every 2.5seconds). Depending on the level of N tested participants are asked to do the following
• 0-back: For a 0-back procedure, participants are given one target stimulus (e.g. the letter 'M') at the beginning of a test blocks and have to press the response button (e.g. key 'A') anytime the letter 'M' is presented (M: go trial; any other letter: nogo).
• 1-back: For a 1-back procedure, participants must press the response key anytime a letter repeats the previous one ('M-M').
• 2-back: For a 2-back procedure, participants must press the response key anytime a letter repeats the letter presented two times back in the sequence (e.g. 'M-L-M').
and so on for higher levels of N.

The Millisecond letter n-back procedure tests N-levels '0','1','2' and '3' with 3 blocks each. The resulting 12 test blocks are run in random order. Each block presents 15 test trials (5 target trials and 10 non-target trials) as well as the N-starter trials that cannot be targets yet. The order of the target (go) and non-target (nogo) trials is randomized in each block. Participants receive performance feedback after each block.

Before the test phase, participants get to practice the various n-back levels.

What it Measures

N-back tasks measure working memory

Psychological domains

• Working Memory: Storing and updating short term memory
• Inhibition: Suppressing responses to familiar items that do not match the n-back rule
• Cognitive Flexibility: Continuously adjusting mental sets as the stream of stimuli and levels changes rapidly
• Sustained Attention: Maintaining focus over a repetitive series of trials without 'drifting'

Main Performance Metrics

• d prime (Signal Detection Paradigm): Estimated discriminability index to distinguish targets from non-targets overall and/or for each level of N, measure of accuracy
• hit rate: Percentage of correct go-trials
• false alarm rate: Percentage of error nogo trials
• hit response time: Mean response time to respond to a target; measure of processing speed

Psychiatric Conditions

Researchers use the n-back task to evaluate cognitive deficits, track neuroimaging biomarkers, and measure the impact of interventions across several major patient populations:

• Schizophrenia
• Major Depressive Disorder
• Bipolar Disorder
• Post-Traumatic Stress Disorder (PTSD)
• Attention Deficit Hyperactivity Disorder (ADHD)
• Autism Spectrum Disorder (ASD)
• Parkinson’s Disease (PD)
• Traumatic Brain Injury (TBI)

Test Variations

References

Search Google Scholar for peer-reviewed, published research using the Inquisit N-Back Task.

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Kirchner, W. K. (1958), Age differences in short-term retention of rapidly changing information. Journal of Experimental Psychology, 55(4), 352-358

Vanderplas, J.M., Garvin, E.A., 1959. The association value of random shapes. Journal of Experimental Psychology, 3, 147-154.

Gevins AS, Cutillo BC (1993): Neuroelectric evidence for distributed processing in human working memory. Electroencephalographic Clinical Neurophysiology, 87, 128-143

Ragland, J.D., Turetsky, B.I., Gur, R.C, Gunning-Dixon, F., Turner, T, Schroeder, L., Chan, R., & Gur, R.E. (2002). Working Memory for Complex Figures: An fMRI Comparison of Letter and Fractal n-Back Tasks. Neuropsychology, 16, 370-379.

Jaeggi, S. M., Seewer, R., Nirkko, A. C., Eckstein, D., Schroth, G., Groner, R., et al., (2003). Does excessive memory load attenuate activation in the prefrontal cortex? Load-dependent processing in single and dual tasks: functional magnetic resonance imaging study, Neuroimage 19(2) 210-225.

Owen, A. M., McMillan, K. M., Laird, A. R., & Bullmore, E. (2005). N-back working memory paradigm: a meta-analysis of normative functional neuroimaging studies. Hum Brain Mapp, 25(1), 46-59.

Ladouceur, C. D., Silk, J. S., Dahl, R. E., Ostapenko, L., Kronhaus, D. M., & Phillips, M. L. (2009). Fearful faces influence attentional control processes in anxious youth and adults. Emotion, 9(6), 855-864.

Maruff P, Thomas E, Cysique L, Brew B, Collie A, Snyder P, Pietrzak RH. Validity of the CogState brief battery: relationship to standardized tests and sensitivity to cognitive impairment in mild traumatic brain injury, schizophrenia, and AIDS dementia complex. Arch Clin Neuropsychol. 2009 Mar;24(2):165-78. doi: 10.1093/arclin/acp010. Epub 2009 Mar 25. PMID: 19395350.

Jaeggi, Susanne M.; Studer-Luethi, Barbara; Buschkuehl, Martin; Su, Yi-Fen; Jonides, John; Perrig, Walter J. (2010). "The relationship between n-back performance and matrix reasoning -- implications for training and transfer". Intelligence 38 (6): 625–635

Bertocci, M., Bebko, G., Mullin, B., Langenecker, S., Ladouceur, C., Almeida, J., & Phillips, M. (2012). Abnormal anterior cingulate cortical activity during emotional n -back task performance distinguishes bipolar from unipolar depressed females. Psychological Medicine, 42(7), 1417-1428.

Pe, M.L., Koval, P. & Kuppens, P. (2013). Executive well-being: Updating of positive stimuli in working memory is associated with subjective well-being. Cognition, 126, 335-340. https://doi.org/10.1016/j.cognition.2012.10.002.

Pelegrina, S. et al (2015). Normative data on the n-back task for children and young adolescents. Frontiers in Psychology, 6.

Villemonteix, Marx, Septier, Berger, Hacker, Bahadori, . . . Massat. (2017). Attentional control of emotional interference in children with ADHD and typically developing children: An emotional N-back study. Psychiatry Research, 254, 1-7.

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