Inspection time and the additive factors approach

17 practiced subjects were required to discriminate whether a briefly displayed probe digit was a member of a previously memorised set in both a reaction time task and an inspection time task. Subject's reaction time and inspection time were measured as a function of the manipulation of a number of factors based on Sternberg's (1969) additive factors methodology (that is, stimulus quality, size of positive set, and response type required). - All factor effects were found to be additive in the RT task thus replicating Sternberg's (1969) findings. The stimulus quality manipulation was found to affect IT as well as RT, yet the remaining factors did not, thus illustrating a simple experimental demonstration of the separability of processing stages. The present results provide strong empirical support for the proposition that encoding takes place temporally prior to the serial comparison stage. If one remains committed to the serial processing model, the temporal divide between early and late processing can be made prior to the serial comparison stage on the basis of Sternberg's (1969) additive factors methodology. Thus, whatever affects the IT measure includes encoding but does not include the serial comparison stage. This is compatible with the views of both Brand and Nettelbeck who maintain that IT be seen as a measure of initial sensory input.