RESPONSES OF INFERIOR COLLICULUS NEURONS IN C57BL 6J MICE WITH AND WITHOUT SENSORINEURAL HEARING-LOSS - EFFECTS OF CHANGING THE AZIMUTHAL LOCATION OF A CONTINUOUS NOISE MASKER ON RESPONSES TO CONTRALATERAL TONES/

Extracellular recordings were obtained from inferior colliculus neuron s of young adult (2-month-old) C57 mice with normal hearing and middle -aged (6-month-old) C57 mice with sensorineural hearing loss as they r esponded to best frequency (BF) tones (signal) in the presence of a co ntinuous background noise (masker). Rate/level functions were obtained for the signal alone, noise bursts alone, and the signal in continuou s noise as a function of masker location. For both groups of mice, thr esholds for BF tones were significantly elevated in the presence of no ise at all three noise locations. Separating the signal and masker sou rces significantly improved masked tone thresholds of 2-month-old mice but not hearing-impaired mice. The decreased ability of middle-aged m ice to benefit from separation of the signal and masker sources may re flect alterations in binaural processing as a result of sensorineural hearing loss.