Time and numerosity estimation are independent: Behavioral evidence for two different systems using a conflict paradigm.

Walsh ( 2003 ) proposed that time and numerical estimation are processed by one generalized magnitude system located mainly in the parietal cortex. According to this perspective, if the time and numerosity share the same mechanism, then interference effects should be observed when the two dimensions are put in conflict. In this study, 16 volunteers were required to listen to 25 audio files, differing in duration and number of tones, in two tasks: One required estimating the duration of the stimulus; the other required estimating the number of tones. For example, the same duration may contain 11, 13, 15, 17 or 19 tones, and 11 tones could last for 5, 7, 9, 11 or 13 s. Results show that estimates of duration were unaffected by the number of tones, and estimates of numerosity were unaffected by duration: This is incompatible with time and numerosity being processed by the same mechanism. Theoretical implications are discussed.