Cocaine's effects on speech sound discriminations and reaction times in baboons

Abstract

Three adult baboons were trained using a psychophysical procedure to discriminate between different synthetic vowel sounds [symbol: see text]. Baboons pressed and held a lever down to produce a pulsed train of a single reference vowel that served as the standard stimulus. Animals were trained to release the lever only when this standard vowel sound changed to one of the four remaining comparison vowels. A lever release within 1.5 s of this change in vowel sounds was defined as a correct detection of the change from the standard vowel to one of the comparison vowels, and was reinforced. All baboons readily learned the vowel discriminations and detected vowel changes at the 90-100% correct performance level. Acute IM administration of cocaine prior to test sessions (0.00032-3.2 mg/kg) produced dose-dependent decrements in vowel discriminability. At the same time, cocaine shortened lever release latencies (reaction times) to the vowel stimuli in two of three baboons. The cocaine-induced decrements in vowel discriminability were correlated with the degree to which frequency differences occurred among the different vowels in that lower vowel discriminability scores were found for those vowels with smaller spectral differences from the standard vowel. Further, false alarm rates were not systematically affected by cocaine, indicating that the cocaine-induced decrements in vowel discrimination accuracy occurred in the absence of systematic changes in the reliability of the baboons' discrimination performances.

Cocaine's effects on speech sound identification and reaction times in baboons

“…The vowel-identification procedure used in the present experiment was a modification of a previously-employed vowel-discrimination procedure Brady 1988, 1989;Hienz et al 1995). The major difference between the vowel-identification procedure and the vowel-discrimination procedure was the lack of a reference stimulus during the lever-holding period for the identification procedure.…”

“…Therefore d" scores were averaged across all vowel stimuli for each baboon. Figure 6 shows these average d' scores in the present study and also for data from the vowel-discrimination procedure of Hienz et al (1995) as a function of dose of cocaine. Baseline d' scores were lower for the baboons exposed to the vowel-identification procedure, indicating slightly increased difficulty in performing the vowel-identification procedure.…”

“…These similarities between baboons and humans led to the examination of the effects of drugs on the perception of speech sounds in baboons Brady 1988, 1989;Hienz et al 1995). In these studies the discriminability of speech sounds was measured by requiring subjects to release a lever when a different speech sound occurred within a series of pulses of a standard speech sound (Hienz et al 1995). Cocaine was found to decrease reaction times to the speech sounds, an effect demonstrated previously for the detection of simple tones (Hienz et al 1993(Hienz et al , 1994.…”

“…This in turn suggests that cocaine could have both positive and negative consequences on different aspects of a single performance. Recent data from this laboratory have demonstrated such effects in baboons trained to discriminate among different human speech sounds (Hienz et al 1995) in that cocaine reduced speech sound discriminability and at the same time shortened, or "improved" reaction times to the speech sounds. Previous studies have suggested that cocaine might adversely affect some aspects of auditory perception.…”

“…These studies along with others in the literature (Sinnott 1989;Sinnott and Kreiter 1991;Sommers et al 1992) have demonstrated that, like humans, nonhuman primates rely on the complex spectral information within speech sounds to distinguish among vowel sounds; and that both humans and nonhuman primates appear to employ similar mechanisms for the neural encoding of complex speech sounds in the brain. These similarities between baboons and humans led to the examination of the effects of drugs on the perception of speech sounds in baboons Brady 1988, 1989;Hienz et al 1995). In these studies the discriminability of speech sounds was measured by requiring subjects to release a lever when a different speech sound occurred within a series of pulses of a standard speech sound (Hienz et al 1995).…”