What problem does it solve?
Visuospatial short-term memory is the part of working memory that holds where things are — not just verbal lists. It's the same one you use to remember where you parked, navigate a familiar route, or remember the layout of icons on your desktop. The Corsi task (originally a 1971 wooden-block experiment by Philip Corsi) is the standard measure.
Adding a reverse-recall variant doubles the load: you have to hold the sequence and mentally reverse it before responding. Most adults drop 1–2 levels in reverse vs. forward; the gap is itself a signal.