Studies on multisensory interaction repeatedly demonstrated that reaction times [RT] to a stimulus from one sensory modality are altered when accompanied by a stimulus of a second modality in close spatial and/or temporal vicinity (intersensory facilitation effect, e.g., Hershenson, 1962, J Exp Psychol.).

In order to quantify the observed changes in reaction time, different measures have been introduced and utilized in comparing different experimental conditions. Common to all these measures is that they relate RTs on unimodal stimulation to those on crossmodal stimulation on the level of mean RTs (e.g., difference between bimodal and unimodal RT [Bernstein et al., 1970, J.Exp.Psychol.], multisensory response enhancement [Diederich & Colonius, 2004, Percept.Psychophys.], multichannel diffusion model [Diederich, 1995, J. Math. Psych.]). However, as soon as stimuli with intensities near to detection threshold are employed it becomes obvious that not only RT can be influenced by multisensory interaction effects but also detection rate [DR] (e.g., Bolognini et al., 2005, Exp. Brain Res.).

We introduce multisensory indices that combine RT and DR and thereby allow for a more accurate quantification of multisensory interaction effects for near-threshold stimuli. We report simulation results utilizing diffusion models to examine properties of these indices.