Race to accumulate evidence for few and many saccade alternatives: an exception to speed-accuracy trade-off.

Hick's law states that increasing the number of response alternatives increases reaction time. Lawrence and colleagues report an exception to the law, whereby more alternatives lead to shorter saccadic reaction times (SRTs). Usher and McClelland (Psychol Rev 108(3):550-592. doi: 10.1037/0033-295X.108.3.550 , 2001) predict such an anti-Hick's effect when accuracy is not prioritized in a task, which should result in higher error rates with more response alternatives, and in turn to a shorter right tail of the SRT distribution. In the current study, we aim to replicate the original controversial findings and we compare them to these predictions by examining error rates and SRT distributions. Two experiments were conducted where participants made rapid eye movements to one of few or many alternatives. In Experiment 1, the saccade target was an onset and participants started either with few or many possible target locations and then alternated between conditions. An anti-Hick's effect emerged only when participants had started with a small set-size block. In Experiment 2, placeholders were displayed at the possible target locations and independent groups were used. A reliable anti-Hick's effect in SRTs was observed. However, results did not meet the stated predictions: anticipations and false direction errors were never more frequent when the set size was larger and SRT differences between the two set-size conditions were not more pronounced at the slower end of the distributions. In line with Lawrence and colleagues, we speculate that initial motor preparation, and the subsequent inhibition to counteract a premature response, may induce the anti-Hick's effect.