The Preyer reflex audiogram of several rodents, and its relation to the "absolute" audiogram in the rat.

Careful examination under a hand lens of the Preyer reflex in 7b mice, 4 voles, and 10 rats established thresholds from 4 up to 60 kc/s using an ionophone loudspeaker. Thresholds wre reliable, and the location of prounced species-specific sensitivity peaks agreed with those establised in the literature by conditioning and by electrophysiologic techniques. It would appear that such peaks coincide with frequency peaks in the vocalizations of these species. In 3 of the rats, conditioned (lever-pressing) audiograms were collected. These exhibited relatively greater sensitivity below 20 kc/s than has previously been reported, declining from 20 to 4 kc/s at only about 3 db/octave. From maximum at 20 kc/s to 40 kc/s sensitivity declined at about 12 db/octave, and from 40-60 kc/s at about 46 db/octave. At 4 and 10 kc/s the difference between the Preyer and the conditioned thresholds was constant (the Preyer about 80 db less sensitive), but at 20 kc/s and above, the reflex threshold appeared relatively and progressively higher. While the Preyer reflex is thus not necessarily a good predictor of the conditioned-response audiogram, it may come to be a useful index of loudness sensitivity.