UC Irvine

In choice reaction time tasks, response latency varies as the subject changes his bias for speed vs accuracy; this is the speed-accuracy tradeoff. Ollman’s Fast Guess model provides a mechanism for this tradeoff by allowing the subject to vary his probability of making a guess response rather than a stimulus controlled response (SCR). It is shown that the mean latency of SCR’s (μs) in two-choice experiments can be estimated from a single session, regardless of how the subject adjusts his guessing probability. Three experiments are reported in which μs apparently remained virtually constant despite tradeoffs in which accuracy varied from chance to near-perfect. From the standpoint of the Fast Guess model, this result is interpreted to mean that the tradeoff here was produced almost entirely by mixing different proportions of fast guesses and constant (mean) latency SCR’s. The final sections of the paper discuss the question of what other models might be compatible with μs invariance. © 1971.