Anders Fridberger

A functional role for common auditory illusions

When two or more tones are sounding simultaneously, normal-hearing people perceive additional tones that are not physically present. These combination tones, or distortion products, are usually regarded a side effect of sensory transduction and although various forms of such distortions are widely used for research and clinical diagnosis, they are not thought to have an important functional role. Here we show, using in vivo recordings of sound-evoked basilar membrane motion and sensory cell receptor potentials, that distortion produced by cochlear sensory cells facilitates the detection of sound envelopes. The envelope, or low-frequency ‘outline’ of an acoustic stimulus, has fundamental importance for communication in humans and animals alike. Hence, far from being mishaps, distortions generated in the cochlea assist in tracking important features in animal vocalizations and in human speech and music.