I have been looking at research in which the time taken to react to a response in an experiment is compared for two different conditions. The participant is exposed to a stimulus on the computer screen and the time to react by pressing one of two keys on the keyboard (in a classification task) is compared. As the response requires mental processing followed by a musculoskeletal reaction, does this count as non-verbal behaviour? If the stimulus were a presented word (text or speech), would this count as verbal behaviour? Comments plus, if possible, citations of papers where reaction / response time has been explicitly described as either non-verbal or verbal behaviour would be welcome.