STIMULUS BIASING - A COMPARISON BETWEEN COCHLEAR HAIR CELL AND ORGAN OF CORTI RESPONSE PATTERNS

Responses from the organ of Corti (OC) fluid space and from individual hair cells are collected for short duration tone pips measured alone and in the presence of a 20 Hz bias tone. Because of the relatively lo ng period of the acoustic bias signal, a probe can be selectively plac ed at precise locations within a single response period. Since bias ef fects produced during maximum basilar membrane velocity are negligible , this report documents changes associated with basilar membrane displ acements to scala vestibuli and scala tympani. Hair cell response patt erns are compared with those measured nearby in the OC to determine th e degree to which inner (IHC) and outer hair cells (OHC) contribute to the gross cochlear potentials. It is shown that intracellular OHC and OC de responses are strongly influenced by the bias while intracellul ar IHC de responses are minimally affected. Although an association ha s been established between the cochlear microphonic and outer hair cel l ac receptor potentials, the well correlated changes in the outer hai r cell de receptor potential and the organ of Corti summating potentia l suggest that gross cochlear potentials reflect de as well as ac cont ributions from nearby OHCs. Since IHC responses are not influenced by the bias, they appear to contribute less than OHCs to extracellular po tentials. These conclusions, however, are restricted to the moderately high input levels required to produce these effects (Durrant and Dall os, 1974) and to the central region of the cochlea where the recording s are made. Finally, the degree to which bias effects are contaminated by two-tone suppression is discussed.