| Popis: |
When experimenters vary the timing between two intersensory events, and participants judge their simultaneity, a non-standard (i.e. non-sigmoidal, non-monotonic) psychometric function is obtained. Typically, this function is first characterised (i.e. fitted with a model) for each participant separately, before best-fitting parameters are utilised (e.g. compared across conditions) in the second stage of a two-step inferential procedure. Often, psychometric-function width is interpreted as representing sensitivity to asynchrony, and/or ascribed theoretical equivalence to a window of multisensory temporal binding. Here, we instead fit a single (principled) multilevel model to data from the entire group and across several conditions at once. By asking 20 participants to sometimes be more conservative in their judgements, we demonstrate how the width of the simultaneity function is prone to strategic change and thus questionable as a measure of either sensitivity or multisensory binding. By repeating our analysis with three different models (two implying a decision based directly on subjective asynchrony, and a third deriving this decision from the correlation between filtered responses to sensory inputs) we find that the first model, which hypothesises, in particular, Gaussian latency noise and difficulty maintaining the stability of decision criteria across trials, is most plausible for these data. |
