The best fitting of three contemporary observer models reveals how participants' strategy influences the window of subjective synchrony.

When experimenters vary the timing between two intersensory events, and participants judge their simultaneity, an inverse-U-shaped psychometric function is obtained. Typically, this simultaneity function is first fitted with a model for each participant separately, before best-fitting parameters are utilized (e.g., compared across conditions) in the second stage of a two-step inferential procedure. Often, simultaneity-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 judgments, we demonstrate how the width of the simultaneity function is prone to strategic change and thus questionable as a measure of either sensitivity to asynchrony 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 hypothesizes, in particular, Gaussian latency noise and difficulty maintaining the stability of decision criteria across trials, is most plausible for these data. (PsycInfo Database Record (c) 2023 APA, all rights reserved).