Automaticity in fast lexical decision sequential effects: much like telling left from right

Successive lexical decisions have shown sequential effects where faster word responses and slower nonword responses follow the same versus different prior response. To date, explanations of these effects have been based on processes specific to discriminating words from nonwords. However, a more parsimonious explanation is possible, based on generic choice processes that apply even to left/right discriminations. Under conditions that promote automaticity, this explanation distinctly predicts equal facilitation by response repetition for words and nonwords. This hypothesis was here tested in an experiment involving 82 participants completing 850-trial blocks of lexical decision with a 100 ms response-stimulus interval-a much faster rate of choice succession than previously used-and including a factor of word/nonword discriminability so as to further test the applicability of choice-specific processes. Distinct from earlier findings, sequential effects were found to be identical in sign and substance for words and nonwords. This reliably occurred as facilitation by repetition across the decile distribution of response-times, across high and low levels of word/nonword discriminability, within each block of the run, and in interaction with higher-order sequential effects involving up to four prior trials. The main effect of facilitation by repetition at the second-order was particularly strong, being equal in effect-size to the interactive effect of the word/nonword factor and word/nonword discriminability (η (2) = 0.61). Hence, generic choice processes appeared to be sufficient to produce lexical decision sequential effects, independently of choice-specific processes. The findings particularly suggested a primary role for automatic response-facilitation, with accuracy-monitoring and expectancy contributing to higher-order effects. The further role of choice-specific processes in these and other findings, and the utility of lexical decision in studying generic choice processes, are discussed.