How do temporal mechanisms influence numerosity perception?

We have previously shown that adaptation to visual duration affects numerosity perception, which supports the theory of a common magnitude system underlying numerical and temporal processing. We performed two follow-up experiments to elucidate the nature of the interaction between numerosity and duration. The first experiment tested the effect of adaptation to visual duration on numerosity discrimination, whereas the second experiment tested the combined effect of adaptation to visual duration and numerosity on numerosity discrimination. In both experiments, we manipulated the onset/offset duration of the adapter, the adapter’s total presentation time and the total duration of the adaptation trial. We hypothesized that if the effect of duration on numerosity is driven by adapting duration ‘channels’ tuned to specific durations, then what matters is the onset-offset duration of the adapter, whereas if duration reflects the ‘strength’ of adaptation, then what matters is the total duration of the adaptation trial. We found that the effect of adaptation to duration on numerosity perception is driven by adapting specific duration channels. In contrast, the effect of adaptation to numerosity on numerosity perception is driven by the total duration of the adaptation trial, in accordance with the strength of adaptation hypothesis. We propose that different temporal mechanisms affect numerosity perception.