TEMPORAL SELECTIVITY FOR COMPLEX SIGNALS BY SINGLE NEURONS IN THE TORUS SEMICIRCULARIS OF PLEURODEMA THAUL (AMPHIBIA, LEPTODACTYLIDAE)

Responses of auditory neurons in the torus semicircularis (TS) of Pleu rodema thaul, a leptodactylid from Chile, to synthetic stimuli having diverse temporal patterns and to digitized advertisement calls of P. t haul and three sympatric species, were recorded to investigate their t emporal response selectivities. The advertisement call of this species consists of a long sequence of sound pulses (a pulse-amplitude-modula ted, or PAM, signal) having a dominant frequency of about 2000 Hz. Eac h of the sound pulses contains intra-pulse sinusoidal-amplitude-modula tions (SAMs). Synthetic stimuli consisted of six series in which the f ollowing acoustic parameters were systematically modified, one at a ti me: PAM rate, pulse duration, number of pulses, and intra-pulse SAM ra te. The carrier frequency of these stimuli was set at the characterist ic frequency (CF) of the isolated units (n = 47). Response patterns of TS units to synthetic call variants reveal different degrees of selec tivities for each of the temporal variables, with populations of neuro ns responding maximally to specific values found in the advertisement call of this species. These selectivities are mainly shaped by neurona l responsiveness to the overall sound energy of the stimulus and by th e inability of neurons to discharge to short inter-pulse gaps.