What this measures
Cells light up in a sequence and you tap them back in the same order. This is the Corsi block-tapping task, introduced by Philip Corsi in 1972 and still the standard measure of visuospatial short-term memory.
It is the spatial counterpart to digit span. Digit span uses numbers you can rehearse silently; Corsi uses positions, which you cannot easily convert to words — which is exactly why the two dissociate in patients and why both are used.
Typical spans
Healthy adults usually reach a Corsi span of 5 to 6. That number is strikingly consistent across studies and is a little lower than digit span, where 7 is the familiar figure.
- Span 3–4 — below the usual range for adults; often just distraction
- Span 5–6 — typical
- Span 7+ — strong, and usually means you found a chunking strategy
Note the ceiling: spans above 8 or 9 are rare enough that if you are getting them reliably, you are almost certainly encoding the pattern as a shape rather than a list. Which is a legitimate strategy, and also the point below.
Strategy — and why it is not cheating
- See a shape, not a sequence. Four separate positions is four items. The same four traced as a path is one item. This is chunking, the single most effective memory technique there is.
- Name the pattern. "Down the left, then across" survives a two-second delay far better than a raw list of coordinates.
- Do not stare at each cell as it lights. Keep your eyes near the centre and use peripheral vision — you want the whole path, not five separate snapshots.
- Rehearse in the gap. The moment between the last flash and your first tap is where sequences are lost. Replay it once before you touch anything.
Using strategy raises your score without raising your raw capacity — which is a fair description of most memory improvement. That is not a swindle: chunking is precisely how people with "great memories" actually do it. More on this in how to improve your memory.
Why it drops when you are tired
Spatial span is unusually sensitive to sleep and stress, because maintaining a pattern against decay is effortful in a way that recognising something is not. A single poor night commonly costs a full span level. If you want a stable measure of yourself, test at the same time of day.
Frequently asked
Q. Is a bigger grid harder?
A. Yes, and not only because there are more cells — a larger grid makes paths less
distinctive, so chunking gets harder too.
Q. Why do I fail immediately after a long correct run?
A. Because span is a cliff, not a slope. You hold N items comfortably and N+1 not at all.
That sharp edge is what the task is designed to find.
Q. Does practising raise my span permanently?
A. Your score will rise, mostly through strategy. Underlying capacity is quite stable —
see does brain training actually work?
For the updating version of the same idea, try N-back. For all five areas at once, the full cognitive test.