Relative unisensory strength and timing predict their multisensory product.

Understanding the principles by which the brain combines information from different senses provides us with insight into the computational strategies used to maximize their utility. Prior studies of the superior colliculus (SC) neuron as a model suggest that the relative timing with which sensory cues appear is an important factor in this context. Cross-modal cues that are near-simultaneous are likely to be derived from the same event, and the neural inputs they generate are integrated more strongly than those from cues that are temporally displaced from one another. However, the present results from studies of cat SC neurons show that this "temporal principle" of multisensory integration is more nuanced than previously thought and reveal that the integration of temporally displaced sensory responses is also highly dependent on the relative efficacies with which they drive their common target neuron. Larger multisensory responses were achieved when stronger responses were advanced in time relative to weaker responses. This new temporal principle of integration suggests an inhibitory mechanism that better accounts for the sensitivity of the multisensory product to differences in the timing of cross-modal cues than do earlier mechanistic hypotheses based on response onset alignment or response overlap.