In this paper we demonstrate categorical perception of an intraspecific communication call in the frequency domain by female house mice (Mus rnusculus, strain NMRI). As far as we know, it has not been shown before, except in studies of human speech perception, that mammals can perceive intra-specific vocalizations categorically. The criteria for categorical perception have been well described [1]: a) A subject has to label (or to identify) stimuli from an acoustic continuum as members of discrete classes; b) these classes are named categories if the subject is able to discriminate between stimuli drawn from different classes (inter-categorical discrimination) and not between stimuli drawn from the same class (intra-categorical non-discrimination).

Mouse pups in discomfort produce highly communicative ultrasonic whistles which release searching and retrieving behavior in their mothers [2, 3]. We show that lactating females respond (in a two-alternative choice test) not only to natural calls but also to model calls consisting of bandpassed noise of variable bandwidth with noise energy in the frequency range of the natural calls (about 40-80 kHz). Data were collected under dim red light in a soundproof and anechoic room (procedures and equipment are described elsewhere [4, 5]). A female together with her litter was placed in a nest depression in the middle