Digit Span Test Explained: Miller's Law, Working Memory, and Training Guide [2026]

What is the Digit Span Test?

The Digit Span Test is one of the oldest and most established cognitive assessments for measuring short-term memory and working memory. You listen to a sequence of numbers and recall them in the same order (forward span) or reverse order (backward span).

First systematized by Joseph Jacobs in 1887, this test remains a core subtest of the Wechsler Memory Scale (WMS) and Wechsler Adult Intelligence Scale (WAIS), used worldwide in clinical and research settings.

Scientific Background

Miller's Law: The Magical Number 7±2

In 1956, Harvard psychologist George A. Miller published "The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information." This paper became one of the most cited works in psychological history.

Miller's key findings:

• Human short-term memory capacity is approximately 7 items (ranging from 5-9)
• This limit applies not just to numbers, but to words, sounds, and visual objects
• "Chunking" can effectively expand this capacity

For example, "FBICIAUS​A" is 9 letters, but when chunked into three familiar acronyms (FBI, CIA, USA), it becomes just 3 memory units and is much easier to remember.

Modern Research

Contemporary researcher Nelson Cowan suggests that pure working memory capacity may be even smaller—around 4 items (ranging from 3-5). The number 7 may include the effects of strategies like chunking and rehearsal.

Forward vs. Backward Span: The Cognitive Difference

Neuroscience research has revealed that forward and backward span engage different cognitive processes:

Use in Wechsler Memory Scale

The Digit Span Test is a core subtest of the Wechsler Memory Scale (WMS), developed by David Wechsler in 1945. In the current WAIS-IV, it is a key component of the Working Memory Index.

How to Play

1. Select Mode

   Choose Forward or Backward mode. Beginners should start with Forward mode.

2. Memorize the Numbers

   Numbers appear one at a time on screen (0.8 seconds each). Remember all the numbers in order.

3. Enter the Numbers

   In Forward mode, enter numbers in the order you saw them. In Backward mode, enter them in reverse order. Use the number pad or keyboard.

4. Level Up

   Correct answers advance you to the next level with one more digit. Three mistakes end the game. The game starts at 4 digits.

Score Guide

Note: Backward span is typically 1-2 digits lower than forward span. A backward span of 6+ digits is excellent.

Training Benefits

Regular Digit Span Test practice may provide the following benefits:

• Improved Working Memory Capacity: Enhanced ability to temporarily hold and manipulate information
• Strengthened Auditory Attention: Improved focus on sequential information
• Better Mental Arithmetic: Develops the ability to hold numbers in mind while processing them

Note: Results vary between individuals. Not everyone will experience the same effects.

Tips and Strategies

1. Use Rhythm - Repeat the numbers mentally in rhythm with their display to improve retention.

2. Apply Chunking - Group long sequences into sets of 2-3 digits. For example, remember "3-7-2-9-4" as "37," "29," "4."

3. Visualize - Create a visual image of the numbers in your mind for stronger memory encoding.

4. Backward Span Tip - Imagine "rewinding" from the last number to the first.

5. Maintain Pace - Enter numbers at a steady rhythm without rushing to reduce errors.

Combining with Dual N-Back

The Digit Span Test and Dual N-Back both train working memory but have different characteristics.

Combining both allows you to comprehensively strengthen different aspects of working memory.

Related Articles:

• What is Working Memory?
• How to Start Dual N-Back
• Benefits of Dual N-Back

FAQ

Conclusion

The Digit Span Test is a reliable cognitive assessment with over 130 years of history. From measuring short-term memory capacity as described by Miller's "7±2" law, it continues to be widely used in clinical psychology and neuroscience research.

Forward mode measures short-term memory, while backward mode assesses working memory manipulation. It's quick and easy to play—consider adding it to your daily brain training routine.