PUB - Publikationen an der Universität Bielefeld

Recent studies have investigated adaptation to temporal discrepancies between different sensory modalities by first exposing participants to asynchronous multisensory signals, and subsequently assessing the magnitude of the adaptation effect (the size of the shift in subjective simultaneity). Although never reported, there is reason to assume that the strength of the adaptation effect declines during this measurement period. Usually, short re-exposures are interleaved with testing to prevent such declining. In the present study, we show that a decrease in the strength of adaptation still can take place, even when a common re-exposure procedure is used. In a second experiment, we investigated whether the observed decline is due to: (1) a dissipation of adaptation with the passage of time or, (2) a new adaptation induced by the test stimuli. We find that temporal adaptation does not dissipate with time but is stored until new sensory information, i.e., stimuli that differ from those used during the adaptation procedure, is presented. An alternative explanation, namely that adaptation decays over time but is re-established before the first test trial due to the experimental procedure we chose, is addressed in a control experiment. This finding is discussed in terms of Helson's adaptation level (AL) theory [1947, Adaptation-level as frame of reference for prediction of psychophysical data. The American Journal of Psychology, 60, 1–29], according to which the null point of any perceptual dimension, in our case the perception of simultaneity on the dimension of temporal order, is a summarizing statistic of all stimuli presented in the past. Any single stimulus pulls the AL toward its own value, and any single stimulus is judged as though it was being compared with the current AL.