Intermedia synchronisation in network design: using an adaptive psychophysical method to specify the perceivable audio-visual delay

Network reliability in multimedia telecommunication can be studied under two points of view, that of a designer and that of a user. Choosing to study the users’ point of view, we examined the parameter intermedia synchronisation. This parameter describes the delay between audio and video channels in a multimodal telecommunication system. Aiming to offer design recommendations for audio-visual delay, we carried out an empirical study with sixteen subjects presented with visual and auditory stimuli. Using a compare-and-select task, delay was independent and user selection dependent variable. Focussing on the perception threshold, we achieved significant results for delays formed by audio before visual and the opposite order. Our experiment followed the forced-choice paradigm and applied the so-called best-PEST procedure. The best-PEST procedure is a powerful adaptive method to estimate thresholds of perception. For different delays, we visualize the user’s perception performance, and the progression of the threshold convergence. These plots can help network designers in assuring the best trade-off between user perception and network optimisation. In a future study, we will examine the user acceptance for different delay impairments.