Social stimuli are often multi-sensory. Animals recognize a con specific often through visual, auditory and olfactory sensory cues. Human face recognition has also audio-visual interaction, for example, McGurk effects. Using morphing stimuli consisting of human and monkey faces, we found that presentation of human or monkey voice affected judgment of visually ambiguous face stimuli (Experiment 1). Human ERP study using the morphing stimuli and two voices showed facilitative effect of human voice on visual ERP (Experiment 2). Pigeons were trained on discrimination between human and monkey faces then tested with morphing images of the human and the monkey faces (Experiment 3). Then, the morphing images were presented with auditory stimuli, namely, vocalization of human or monkey. Facilitative effect of human voice on human face discrimination was demonstrated but that of the monkey voice was not. The subjects had been exposed to the human voice in the living cages but not to the monkey face or monkey vocalization. This difference in experience should result in difference in effects of auditory stimuli on visual discrimination. Anatomical study (Experiment 4) provided evidence that visual and auditory pathways were independent at the level of primary sensory area in the telencephalon (entopallium and field L). Thus, the visual and auditory systems should integrated in higher associative area, such as neopallium caudo-lateralis (NCL). These results agreed to human ERP study, which suggested integration of two sensory systems in later stage of sensory processing.

Part 1: Brain and Evolution