Project A3 – New methods to study visual influences on auditory processing
Processing of sensory information in the auditory pathway has almost exclusively been studied under purely acoustical stimulation. However, recent studies suggest direct influences of the visual system on early auditory processing. In humans, prism-induced lateral shifts of visual space produce a corresponding shift in sound localization . Visual stimulation and eye position have been reported to modulate midbrain responses to auditory sti muli [2,3]. Where along the auditory pathway  and exactly how spatial visual information influences neuronal representation of auditory space remain open questions. An ideal tool to study and evaluate such multi-modal integration is the iso-response technique . We will test this new approach with recordings from neurons in the avian tectum  and the mammalian superior colliculus. Both nuclei are well-known for being responsive to both visual and auditory spatial cues.
Objectives and description of work
The Bernstein Virtual Reality setup will allow us to present coherent as well as incoherent 3D audio-visual cues to study the influence of static and dynamic visual cues at several stages of the binaural auditory pathway (figure 1). Recordings in the gerbil superior colliculus and chicken tectum, where such interactions are to be expected, will be used to investigate the relative contributions of visual and auditory inputs using advanced iso-response techniques. In a second set of experiments, we will wor k our way down the auditory system via the inferior colliculus (IC) and the dorsal nucleus of the lateral lemniscus (DNLL) to the superior olivary complex (SOC), the initial stage of binaural processing. First, we will record from single neurons in anesthetized Mongolian gerbils (which have exquisite vision and audition) to identify visual influences on early auditory processing of spatial cues. In a second step, we will record in the IC of freely behaving gerbils to reveal how the population representation of spatial cues is influenced by orientation and navigation.
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