Should multisensory temporal acuity be viewed through the window of perceived simultaneity?

Temporal coincidence provides a powerful cue that events originating from different sensory modalities, such as audition and vision, have a common cause. Multisensory integration is often found across a range of sub-second physical asynchronies, supporting the existence of a temporal binding window. In recent years, it has become de rigueur to measure temporal binding windows using the simultaneity judgement (SJ) task, and interpret differences between groups as indicative of differences in the temporal sensitivity of integration processes. Recently, it was reported that a multisensory deficit (indicated by a widened range of perceived simultaneity) can be observed for audiovisual (but not visuotactile) processing following early visual deprivation. This report is likely of considerable interest to the multisensory community. However, we believe that like similar work it does not include sufficiently explicit caveats about the processes that generate the window of simultaneity, potentially misrepresenting the underlying cause(s) of differences between groups. Here, we advocate more explicit recognition of the fundamentally subjective nature of the ‘window’ derived from SJs. We argue that it has poor face validity to measure the conceptually distinct temporal binding window, and demonstrate that its extent is dependent on how the observer decides to interpret the word “simultaneous.”