Shaping of rule-governed behaviour.

Over an experimental session of 80 trials, subjects counted brief auditory stimuli ("clicks") in stimulus presentation periods and indicated the number counted by pressing a key the corresponding number of times in subsequent response periods. "Correct" answers resulted in feedback. Unknown to the subjects, the feedback criterion was based on speed of pressing rather than on the correct number of presses. Speed of pressing was modified by response consequences when feedback was made dependent on pressing faster or slower than baseline speed. Modification of speed occurred independently of rules and without the subjects' ability to describe contingency or response requirements. The results suggest that non-verbal contingencies may have a shaping effect on non-salient and non-described attributes of rule-governed behaviour, and it is argued that this may be an important control mechanism of low-level behavioural attributes that are unlikely to be guided by verbal discriminative stimuli.