Can response preparation begin before stimulus recognition finishes?

The present experiments were designed to determine whether information obtained early in the process of recognizing a stimulus can be used to begin preparing keypress responses before recognition of the stimulus has completely finished. This question is relevant to the recent debate between discrete (e.g., Sternberg, 1969a) and continuous (e.g., McClelland, 1979) models of human information processing. Stimulus sets were chosen so that recognition processes could extract incomplete preliminary information about a stimulus much faster than they could extract secondary information needed for unique stimulus identification. Discriminability of the secondary information was manipulated to vary the opportunity for response preparation based on preliminary information, with difficult secondary discriminations providing more time for response preparation than easy ones. Precues were given on some trials to allow response preparation to occur before the stimulus was presented, thereby reducing any difference in response preparation as a function of discriminability. Continuous models predict that precues should facilitate response preparation less when the secondary discrimination is difficult than when it is easy, and discrete models predict equal facilitation regardless of secondary discrimination difficulty. Evidence of response preparation was obtained with some but not all stimulus sets. The results were interpreted as support for the asynchronous discrete coding model (Miller, 1982a), in which response preparation can begin only after recognition processes have completely activated a code used in categorizing the stimulus.