Cocaine's effects on the perception of socially significant vocalizations in baboons

The effects of cocaine on the ability of baboons to discriminate among their natural affiliative 'grunt' vocalizations were examined to determine whether cocaine would produce discrimination impairments similar to those observed previously with acoustically-similar human vowel sounds [Hienz, R.D. Spear, D.J. Pyle, D.A. Brady, J.V. 1995. Cocaine's effects on speech sound discriminations and reaction times in baboons. Psychopharmacology, 122 (2) 147-157], or whether differences in cocaine's effects might occur associated with the social significance of the calls. The task employed digitized calls of actual vocalizations recorded in the wild [Rendall, D. Owren, M.J. Weerts, E.M. Heinz, R.D. 2004. Sex differences in the acoustic structure of vowel like grunt vocalizations in baboons and their perceptual discrimination by baboon listeners. Journal of the Acoustical Society of America, 115 (1) 411-421]. Baboons pressed a lever to produce a repeating 'standard' grunt, and released the lever only when one of four other 'target' grunts was selected to occur in place of the standard grunt. Cocaine (0.01-.56 mg/kg, i.m.) impaired call perception, and these impairments were more pronounced than those observed previously for acoustically-similar human vowel sounds. Cocaine also elevated reaction times as a function of dose. The results demonstrate that cocaine impairs perceptual discriminations of the natural grunt vocalizations of baboons, and suggest that cocaine may have more pronounced effects on the perception of biologically-relevant as opposed to non-relevant communication signals.