The level of processing at which different modalities interact to either facilitate or interfere with detection has been a matter of debate for more than half a century. This question has been mainly addressed by means of statistical models (Green 1958), or by biologically plausible models (Schnupp et al. 2005). One of the most widely accepted statistical frameworks is the signal detection theory (SDT; Green & Swets, 1966) because it provides a straightforward way to assess whether two sensory stimuli are judged independently of one another, that is when the detectability (d’) of the compound stimulus exceeds the Pythagorean sum of the d' of the components. Here, we question this logic, and propose a different baseline to evaluate integrative effects in multi-stimuli detection tasks based on the probabilistic summation. To this aim, we show how a simple theoretical hypothesis based on probabilistic summation can explain putative multisensory enhancement in an audio-tactile detection task. In addition, we illustrate how to measure integrative effects from multiple stimuli in two experiments, one using a multisensory audio-tactile detection task (Experiment 1) and another with a unimodal double-stimulus auditory detection task (Experiment 2). Results from Experiment 1 replicate extant multisensory detection data, and also refuse the hypothesis that auditory and tactile stimuli integrated into a single percept, leading to any enhancement. In experiment 2, we further support the probabilistic summation model using a unimodal integration detection task.