Introduction

The N-Back task goes back more than half a century, developed in the 1950s by Kirchner, as you can read in more detail on wikipedia.

In short, in the N-Back task, participants are presented a sequence of stimuli one-by-one. For each stimulus, they need to decide if the current stimulus is the same as the one presented N trials ago.

The N can be 1 trials, 2 trials, 3 trials, etc. The higher the number, the more difficult the task. The factors that seem to influence the performance are not only the N, but also the speed of presentation and the size of the set of stimuli.

In a typical experiment, you see that letters are presented for 500 ms followed by a 2500 black period. This timing seems to be used in lots of N-back studies (e.g., Kane & Conway, 2007).

In total, people get 3 seconds (500 ms + 2500 ms) to respond if the letter matches the letter N trials ago.

If there is no match, people do not need to respond.

There are different types of response (or lack thereof):

Name of response Type Meaning

Match

Correct

Participant correctly pressed the m key because the letter matches the letter of 2 trials ago

False Alarm

Error

Participant pressed m key wrongly, because the letter 2 trials ago was a different one

Miss

Error

Participant did not press m key, but they should have because the letter 2 trials ago was the same

In the following, a matching trial is one in the letter matches the letter of two trials ago and the participant should press the m key.

About this implementation

Key features of this implementation:

  • This is a 2-back task

  • The total stimulus set is 15 stimuli (letters)

  • Each stimulus is presented for 500 milliseconds

  • People get 3 seconds to respond

  • A new stimulus is presented every 3000 milliseconds

The letters A,B,C,D,E,H,I,K,L,M,O,P,R,S, and T are being used.

There are 3 blocks of each 25 trials.

Detailed feedback is given.

Run the demo

You need to press the m if the stimulus is the same as 2 trials ago. Otherwise withhold. The m key was chosen because the work memory starts with an "m".

Click here to run a demo of the N-back task

Data output file

In PsyToolkit, the data output file is simply a textfile. The save line of the PsyToolkit experiment script determines what is being saved in the data output file. Typically, for each experimental trial, you would have exactly one line in your text file, and each number/word on that line gives you the information you need for your data analysis, such as the condition, response speed, and whether an error was made.

Meaning of the columns in the output datafile. You need this information for your data analysis.

Colum Meaning

1

Blocknumber (the number of the block, there are 3 blocks)

2

Trial number (the number of the trial)

3

Type of trial (1=a matching stimulus ; 0=a non-matching stimulus)

4

Score (1 means correct, 0 means incorrect)

5

Match (1 means participants matched correctly, 0 otherwise; only meaningful on match trials)

6

Miss (1 means participants missed, 0 otherwise; only meaningful on non-matching trials)

7

False Alarm (1 means participants wrongly pressed button, 0 otherwise; only meaningful on non-matching trials)

8

Reaction Time

9

Memory (a variable used internally)

10

Current letter (the current letter, a number between 1 and 15, representing letterA, etc)

11

nback1 (the letter 1 trial ago, a number between 1 and 15, representing with letterA, etc)

12

nback2 (the letter 2 trials ago, a number between 1 and 15, representing with letterA, etc)

Download

If you have a PsyToolkit account, you can upload the zipfile directly to your PsyToolkit account. Watch a video on how to do that. If you want to upload the zipfile into your PsyToolkit account, make sure the file is not automatically uncompressed (some browsers, especially Mac Safari, by default uncompress zip files). Read here how to easily deal with this.

Further reading

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

  • Jaeggi, S.M., Buschkuehl, M., Perrig, W.J., & Meier, B. (2010). The concurrent validity of the N-back task as a working memory measure. Memory, 18, , 394–412.

  • Kane, M.J. & Conway, A. (2007). Working memory, attention control, and the N-back task: A question of construct validity. Journal of Experimental Psychology: Learning, Memory, and Cognition, 33(3), 615-622.