Hearing in primitive primates: Slow loris (Nycticebus coucang) and potto (Perodicticus potto).

The behavioral audiograms of slow loris and potto were determined by the technique of conditioned suppression, and the auditory characteristics of Prosimians then estimated by combining the data with that of bushbaby. It is concluded that high-frequency hearing, low-frequency sensitivity, and total area of the audible field are well correlated with phyletic level, while lowest threshold and best frequency are not. Furthermore, the rela-tion of high-frequency hearing to ecological demands for accurate sound localization is supported. For almost a century it has been known that human hearing differs markedly from that of many other animals (e.g., Galton, 1883). But until recently, the nature and extent of this difference and the evolutionary transformation that brought it about have been mostly a matter of conjecture (cf.