The law of inverse effectiveness in neurons and behaviour: multisensory integration versus normal variability

Multisensory research is often interpreted according to three rules: the spatial rule, the temporal rule, and the law of inverse effectiveness. The spatial and temporal rules state that multisensory stimuli are integrated when their environmental sources occur at similar locations and times, respectively. The law of inverse effectiveness states that multisensory stimuli are integrated inversely proportional to the effectiveness of the best unisensory response. Neurally, these rules are grounded in anatomical and physiological mechanisms. By contrast, behavioural evidence often contradicts these rules, and direct links between multisensory neurons and multisensory behaviour remain unclear. This note discusses evidence supporting the law of inverse effectiveness, and reports a simulation of a behavioural experiment recently published in Neuropsychologia. The simulation reveals an alternative, statistical, explanation for the data. I conclude that the law of inverse effectiveness only sometimes applies, and that the choice of statistical analysis can have profound effects on whether the data abides the law.