Digit Span (Backward)

The Digit Span Backward task is a well-established measure of verbal working memory capacity. Unlike the forward version, which tests simple rehearsal, the backward task requires active mental manipulation: participants must hold the presented sequence in mind and reverse it before responding. This additional processing demand makes backward span more sensitive to working memory capacity and executive function than forward span.

On each trial, a sequence of digits is presented one at a time in the centre of the screen. Immediately after the last digit disappears, the participant types the sequence in reverse order and presses Enter. For example, if the sequence 3, 1, 8 is shown, the correct response is 813.

The task begins with spans of 3 digits and increases through 4, 5, 6, 7, 8, and 9. Two trials are presented at each span level. Performance is assessed as the longest span at which the participant recalls correctly in reverse on at least one of two trials — the backward digit span score. The task ends automatically after both trials at a given span level are failed.

This implementation uses 2 practice trials (span 3, with feedback showing the correct backward sequence) followed by the main task (14 trials: 2 per span level from 3 to 9). Each digit is displayed for 1000 ms, separated by a 500 ms blank inter-stimulus interval.