Digit Span
Background
The Digit Span Test (DST) is a classic psychometric assessment tool for short term memory and verbal working memory capacity. Its first publication goes back to 1887 by John Jacobs, a London school teacher, who was interested in the memory capacity of his students. Jacobs read lists of digits to his students and noted how many digits his students could recall in the exact order presented. The DST was later adopted by Binet and Simon for their original intelligence scales (1905) and is still to this day an integral part of the Wechsler Adult Intelligence Scale (WAIS) and the Wechsler Intelligence Scale for Children (WISC).
It's been widely accepted that the average digit span of healthy adults is between 5 and 9, making '7' the 'magical number', a term coined by George Miller in a highly influential paper in 1956.
Today's DST task are usually administered in two formats, the 'Digit Span Forward' ('repeat the digit sequence in the same order as presented') and the the 'Digit Span Backward' ('repeat the digit sequence in the REVERSED order') one. The latter administration is considered more difficult as it not only requires the passive storage of items in short term memory but in addition requires the manipulation and processing of the information.
Most DST procedures use an adaptive testing procedure. They start at small digit sequences (e.g. 3 digits) and increase the sequence length if participants correctly recall the sequence. Traditionally each digit span level provides two chances to get the correct answer. Testing is over when a participant does not recall the correct sequence after two attempts and the final 'Digit Span' is set at the last span that a participant was able to master.
The Millisecond Digit Span test is based on the published procedure by David Woods and colleagues in 2011 whose procedure not only provides the classic DS measure (last span mastered before double failure) but also a maximum DS (highest span mastered during the entire procedure) as well as a new measure they coined the 'MeanSpan' (MS), which represents the digit span that a participant is supposed to get correct 50% of the time.
The Woods et al (2011) procedure can be administered in the 'Forward' or 'Backward' format and can be run with spoken digits or visual ones.
Task Procedure
Participants work through a short practice session before they start with the actual assessment. For each trial, the digit sequence is signalled to start by the appearance of a red dot on the screen. A new digit then appears every 1s until the red dot signals the end of the current sequence. Participants are then asked to recall the sequence by selecting with the mouse or fingers from 9 circular response buttons the sequence of digits presented (either in the forward or backward format depending on instructions). Corrections are possible. Once the 'submit' button is pressed, the next trial is started.
Forward testing starts with 3 digits; Backward testing starts with 2 digits. Each participant works through a total of 14 trials, and digit length is constantly adjusted up (after a correct response) or down (after two failures).
What it Measures
The DST is a measure of (verbal) short term memory and working memory capacity.
Psychological domains
- Verbal Short-Term Memory (Forward): Passive holding of information in working memory
- Verbal Working Memory (Backward): Processing of information in working memory
- Inhibition (Backward): Suppressing the dominant (easier) Forward sequence
Main Performance Metrics
- TEML: Two-error maximum length, the traditional measure of a participant's digit span
- ML: Maximal digit span that a participant recalled correctly during the entire procedure
- MS: The digit span that a participant is expected to get correct 50% of all times based on overall performance during all 14 trials
Psychiatric Conditions
DST performance tends to be impaired in patients with the following psychiatric and neuropsychological conditions:
- Dementia
- Mild Cognitive Impairment (MCI)
- Parkinson’s Disease (PD)
- Schizophrenia
- Major Depressive Disorder
- Attention Deficit Hyperactivity Disorder (ADHD)
- Traumatic Brain Injury (TBI)
Test Variations
The Auditory Digit Span (both forward and backward recall).
The Auditory Digit Span (backward recall).
The Auditory Digit Span (forward recall).
The Visual Digit Span (both forward and backward recall).
The Visual Digit Span (backward recall).
The Visual Digit Span (forward recall).
References
Search Google Scholar for peer-reviewed, published research using the Inquisit Digit Span.
Lumiley, F. H., and Calhoon, S. W.(1934). Memory Span for Words Presented Auditorially. Applied Psychology, 18, 773-784.
Blankenship, A.B. (1938). Memory span: A review of the literature. Psychological Bulletin, 35, 1-25.
Daneman, M., & Carpenter, P. A. (1980). Individual differences in working memory and reading. Journal of Verbal Learning and Verbal Behavior, 19, 450-466.
Drewnowski, A., Murdock, B. B. (1980). The role of auditory features in memory span for words. Journal of Experimental Psychology: Human Learning and Memory, 6, 319 – 332.
Conway, A. R. A., Kane, M. J., Bunting, M. F., Hambrick, D. Z., Wilhelm, O., & Engle, R. W. (2005). Working memory span tasks: A methodological review and user’s guide. Psychonomic Bulletin & Review, 12, 769-786.