Tactile flash lag effect: Taps with changing intensities lead briefly flashed taps

A brief flash, presented in spatial alignment with a moving object, appears to lag behind the moving object. This illusion has been known as the visual flash lag effect. Sheth et al. (2000) demonstrated that when observers compared the colors of a linear array of flashing circular disks with that of a concurrently-flashed disk of the same color, the former was perceived to lead the latter. An analogous tactile flash-lag illusion is reported here. A sequence of tactile taps with increasing (or decreasing) intensity was presented on one finger. The temporally-middle tap in the sequence was perceived to be weaker in both cases than a synchronous single tap on another finger. This illusion could be accounted by a mechanism of temporal compensation and tactile masking.