Statistical facilitation and the redundant signals effect: What are race and coactivation models?

As a supplement to Gondan and Minakata's (2015) tutorial on methods for testing the race model inequality, this theoretical note attempts to clarify further (a) the types of models that obey and violate the inequality and (b) the conclusions that can be drawn when the inequality is violated. In particular, the idea that individual racers proceed at the same speed in the single and redundant conditions (also known as "context independence") is shown to be better understood as an inherent part of Raab's (1962) original race model than as a separate, additional assumption. Thus, evidence that individual racers proceeded at different speeds in the single and redundant conditions, if available, should be viewed as supporting one type of coactivation model rather than an alternative model. In addition, it is shown that a class of race-like models without the assumption of context independence is so broad that it can never be falsified.