The brain integrates information from multiple sensory systems for signal enhancement, and the mammalian superior colliculus (SC) is a popular model system in which many of the principles of this phenomenon have been described. Recent observations suggest that multisensory enhancement is not uniform throughout the response, but can speed physiological response latencies and commonly show "superadditive" (greater than the predicted sum) enhancements near response onset ("Initial Response Enhancement"). Closer examination of the temporal profiles of the responses suggests two underlying principles: incoming signals appear to be integrated as soon as they arrive at the target neuron, and most significant multisensory enhancements occur when one or both of the signals are near threshold. This analysis supports a simple neural network model in which time-varying sensory signals interact with each other and other random inputs to produce unisensory and multisensory responses that can account for a great deal of the extant observations. Supported by NIH Grants NS036916 and EY016716 and the Tab Williams Family Foundation.