Abstract
Perceptual decisions are heavily influenced by previous stimuli and decisions. This serial dependence has been the subject of extensive study but a mechanistic understanding of this phenomenon is yet to emerge. One difficulty with understanding the nature of serial dependence is that it is unclear what factors modulate its strength. Here we examined whether serial dependence is affected by speed-accuracy tradeoff (SAT). We created five different SAT conditions by designing a payoff structure that increasingly punished long reaction times (RTs). This design allowed us to study serial dependence across a wider range of SAT conditions than what is normally done. Subjects (N = 20) came for five separate sessions, completing a total of 5,000 trials each of a Gabor orientation discrimination task. We analyzed whether the SAT condition modulated several different types of serial dependence. First, we performed regression analyses to understand how RT and accuracy on the current trial are influence by RT and accuracy on the previous trial. We found that serial dependence in RT increased with higher speed stress (F(4,60) = 3.2, p = 0.019). A similar effect was obtained for RT on the previous trial predicting accuracy on the current trial. Second, we computed the lag-1 and lag-2 autocorrelation in subjects’ choices and found that both increased with increasing speed stress (lag-1: F(4,60) = 10.95, p < 0.0001; lag-2: F(4,60) = 22.27, p < 0.0001). In addition, these results were modulated by accuracy such that previous corrected responses tended to lead to more response repetitions, especially for high speed stress conditions (F(4,60) = 4.22, p < 0.0044). These results demonstrate that greater speed stress almost universally increases serial dependence and suggest that serial dependence may be the result of automatic processes that can be partly suppressed by increased deliberation.