Abstract
It is well known that choice reaction time decreases logarithmically with increasing probability of the stimulus (Hick's Law). In experiments and modeling we show that sequential dependencies in the response play a major role in eliciting this probability effect and that the implicit short-term memory mechanism of Priming of Pop Out (PoP) can be implicated in the genesis of probability effects on reaction times. By cross-correlating the responses with the stimulus series we characterize the first-order Wiener kernel underlying PoP. Assuming system linearity, we then show that the accumulation of memory traces over trials can induce large shifts in mean response times when the probability of the target is varied. However, this linear characterization of the memory-induced probability effect fails to capture the nonlinearity of Hick's law. We then discuss sources of nonlinearity and propose that an important function of PoP is to provide the basis for unconscious inferences that are essential in associative learning.