Assessing response times and force of responses to the size and brightness of visual stimuli.

Together with response time the force of responses to stimuli can provide important clues about cognitive and affective processes. However, while there has been much discussion of factors involved in the accurate measurement of response time (RT), key issues and assumptions in assessment of response force (RF) have been far less studied. Here, hierarchical Bayesian analysis is used to examine the extent to which changes in RTs and peak RFs to visual stimuli of increasing brightness and size arise as a result of the subjective control of force parameters. The findings show RTs to decrease with increased stimulus magnitude, but no corresponding increase in peak RFs. Yet, peak RFs were affected by instructions informing participants that the force of their responses was being measured and by auditory feedback when RF crossed a minimum criterion sufficient for RT registration. Implications of these findings for measuring RF in RT research are discussed.