The Corsi Block Span (Backward) task is an established measure of visuospatial working memory capacity. Unlike the forward version, which tests passive visuospatial storage, the backward task requires active manipulation: participants must hold the highlighted block sequence in mind and reverse it before responding. This executive demand makes backward Corsi span more sensitive to working memory capacity and frontal lobe function than forward span.

Nine grey blocks are arranged in a fixed irregular pattern on screen. On each trial, the blocks light up one at a time in a sequence. Immediately after the last block fades, the participant clicks the blocks in reverse order — starting from the last block that lit up and working backwards.

The task begins at span 2 and increases through spans 3, 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 correctly recalls the reversed sequence on at least one of two trials — the backward Corsi block span. The task ends automatically after both trials at a given span level are failed.

This implementation uses 2 practice trials (span 2, with feedback) followed by the main task (up to 16 trials: 2 per span level from 2 to 9). Each block is highlighted for 1000 ms, separated by a 400 ms blank inter-stimulus interval.