Responses are faster and more accurate when stimulus and response locations correspond

What it is

Stimulus-response compatibility (S-R compatibility) refers to whether there is a natural spatial correspondence between where a stimulus appears and where the required response is located. When the two correspond (a light on the left calls for pressing a key on the left), participants respond faster and make fewer errors; when they don't — or are reversed (a light on the left calls for pressing a key on the right) — responses slow down and errors increase, even when the mapping rule itself has been stated clearly and fully understood.

Why it happens

Spatial correspondence affects response speed because the location of a stimulus automatically activates a response tendency that is spatially aligned with it, whether or not the task calls for that. When the response the task actually requires happens to match this automatically activated tendency, the two reinforce each other and the response can be produced faster. When they don't match, extra time is needed to suppress the automatically activated but incorrect tendency and switch to the response the rule actually calls for — and this suppression-and-switch process shows up directly as the rise in reaction time and error rate.

Studying it

The classic paradigm has participants respond with a left or right key to a stimulus presented on the left or right, under two mapping conditions — "compatible" (left stimulus, left key) and "incompatible" (left stimulus, right key) — comparing the RT and error-rate differences between them; that difference is called the compatibility effect. Researchers also systematically vary combinations of stimulus dimension (visual position, auditory location) and response dimension (keypress, speech, limb orientation) to map out which dimension pairings produce this automatic spatial correspondence.

Where it stops holding

The strength of the compatibility effect depends on the specific stimulus and response dimensions involved — the correspondence between visual spatial position and hand keypress location is typically strong, but pairing a non-spatial stimulus attribute (color) with a spatial response (left/right key) produces almost no such automatic correspondence, so the compatibility effect is weak or absent. Practice also weakens, but usually does not fully eliminate, the cost of an incompatible mapping.

Applying it

When designing an interface that needs a fast response, align a control's spatial position directly with the spatial position of the effect it produces (a left button controls the left object, a top button controls an upward-moving effect); avoid flipping controls that should correspond left-right just to satisfy a visual layout preference. How to check: test the same set of controls under both a corresponding and a non-corresponding layout, measuring RT and mispress rate for each, to confirm the corresponding layout actually delivers a measurable speed and accuracy advantage rather than assuming that a layout that looks tidier is automatically more usable.

Related

• Same group: A8.02.2 Task-irrelevant location information still causes interference · A8.02.3 Population stereotypes determine what counts as "compatible" · A8.02.4 An incompatible mapping requires extra mental recoding time · A8.02.5 Spatial correspondence between a control and what it acts on is the strongest source of compatibility
• Nearby: A8.01 The structure of reaction time
• Search terms: stimulus-response compatibility · spatial compatibility · S-R compatibility