Motor Preparation Tracks Decision Boundary Crossing Rather Than Accumulated Evidence in Temporal Decision-Making.

Interval timing, the ability of animals to estimate the passage of time, is thought to involve diverse neural processes rather than a single central "clock" (Paton and Buonomano, 2018). Each of the different processes engaged in interval timing follows a different dynamic path, according to its specific function. For example, attention tracks anticipated events, such as offsets of intervals (Rohenkohl and Nobre, 2011), while motor processes control the timing of the behavioral output (De Lafuente et al., 2024). However, which processes are involved and how they are orchestrated over time to produce a temporal decision remains unknown. Here, we study motor preparation in the temporal bisection task, in which human (female and male) participants categorized intervals as "long" or "short." In contrast to typical perceptual decisions, where motor plans for all response alternatives are prepared simultaneously (Shadlen and Kiani, 2013), we find that temporal bisection decisions develop sequentially. While preparation for "long" responses was already underway before interval offset, no preparation was found for "short" responses. Furthermore, within intervals categorized as "long," motor preparation was stronger at interval offset for faster responses. Our findings support the two-stage model of temporal decisions, where "long" decisions are considered during the interval itself, while "short" decisions are only considered after the interval is over. Viewed from a wider perspective, our study offers methods to study the neural mechanisms of temporal decisions, by studying the multiple processes that produce them.