When does response duration track performance?

A founding insight of psychophysics was to link internal mental processes to the timing of the behaviors they produce. Perhaps the most obvious and well-characterized example is the relationship between performance and response time, as when salient targets are found faster in visual search or when more confident perceptual decisions are made more quickly. But what is “response time”? Whereas nearly all psychophysical studies that measure the timing of behavior focus on the time taken to initiate a response, another potentially relevant magnitude is the duration of the response itself — e.g., not just how long it takes between the appearance of a stimulus and the onset of a keypress, but also how long one holds down the key before letting it go. Recent work makes a theoretical case that response duration may be a neglected source of data about visual processing (Pfister et al., 2023); here, 4 experiments provide empirical support for this proposal. Subjects completed a detection task in which a field of white noise either contained or didn’t contain a face, with difficulty manipulated by varying the face’s opacity. Subjects responded with a keypress (with both keyUp and keyDown events recorded separately). Remarkably, on more difficult trials, subjects not only took longer to initiate a response but also held down the response key for longer, as if answering in a tentative fashion. Response duration also tracked accuracy, with subjects holding down the response key for longer on incorrect as opposed to correct trials. These effects emerged again in a direct replication, but not in follow-up experiments using easier tasks. Overall, our results suggest that response duration may be an untapped source of information about performance — especially in tasks with high uncertainty — raising a wealth of avenues for future investigation.