Derived guinea pig compound VIIIth nerve action potentials to continuous pure tones.

A technique is described which verifies neural activity to a very faint continuous sine wave through subtraction of two different far-field whole nerve action potentials from one another. A brief transient is presented to an animal in order to elicit a supra-threshold action potential. The technique is then repeated, but on the second trial a near-threshold sine wave is mixed with the transient and another action potential is collected. The resultant evoked is then subtracted from the evoked potential generated by the transient alone and a small but persistent difference potential is acquired that presumably represents the unit activity occupied by the continuous sine wave. Four experiments are presented to show the validity of this technique, along with a surprising stability of the derived-response latency despite a 30 dB range of the probes. The technique may have promise in predicting behavioral responses to sinusoids acquired from individual animals.

Objective auditory threshold estimation using sine-wave derived responses.

A derived response method of acquiring frequency specific auditory evoked potentials that utilizes a pure tone in combination with a toneburst is applied to the measurement of hearing sensitivity in guinea pigs, chinchillas and pocket gophers. Two experiments which demonstrate that thresholds acquired via tone-derived responses are 10 to 15 dB more sensitive than thresholds to solitary tonebursts are described. The derived potentials approximate behaviorally acquired thresholds at frequencies of 0.5 kHz and above. This technique may provide a more rapid means of assessing hearing sensitivity in laboratory animals than by behavioral means.