Multisensory processing of looming signals in primates

The world is full of rapidly approaching danger. In order to survive in such a dynamic and dangerous environment, one must perceive and respond appropriately such events. Looming signals are those sensory cues that indicate the rapid approach of objects. Many animal species possess behavioral biases toward visual and auditory looming signals. However, the ability to integrate looming signals across modalities has not been directly studied and is the subject of the presented work. First, using a preferential looking paradigm, we found that rhesus monkeys naturally integrate auditory-visual looming signals, using simple motion-in-depth cues (dynamic intensity change and visual expansion/contraction). Second, in a psychophysical study in humans, we found that humans also spontaneously integrate auditory-visual motion-in-depth signals. Finally, to investigate the neural correlates of this integration, we recorded local field potential (LFP) activity in the monkey temporal lobe while the subject was presented with auditory, visual and bimodal looming and receding signals. Preliminary analysis of LFP signals shows multisensory effects in auditory cortex, and increased coherence between simultaneously recorded LFP signals in auditory cortex and STS during bimodal stimulation. These results might suggest that the brain integrates information across modalities by synchronizing activity from different sensory areas