Continuous priming effects on discrete response choices

When primed by backward-masked, target-like stimuli, discrete responses (e.g. button presses) to simple visual targets can be slower when prime and target match (compatible) than when they do not (incompatible). The current study investigated the nature of the stimulus–response mapping underlying this negative compatibility effect (NCE). Discrete left–right responses to arrow targets were primed with arrows oriented in one of 16 directions. Responses were either a standard button press or a 10 cm movement on a graphics tablet. Both tasks showed an identical NCE; importantly, reaction times in both tasks decreased smoothly as the angular distance between prime and target increased (i.e. as compatibility decreased), with the largest NCE evident between the extreme cases (prime-target distances of 0° and 180°). Primes exerted an effect on the required response in proportion to the amount of overlap (reflecting population vector coding). The mapping between the priming stimulus and response is continuous, not categorical.