The effects of morphine and buprenorphine on auditory perceptual discrimina
tions and response latency ("reaction time") in baboons are compared. The t
ask employed synthetic human vowel sounds that art: readily generated in th
e laboratory, and closely approximate natural baboon "grunt" vocalizations
[J. Acoust. Sec. Am. 101 (1997) 2951]. Baboons pressed a lever to produce o
ne repeating "standard" vowel, and released the lever only when one of four
other "comparison" vowels occasionally occurred in place of the standard v
owel. The percentage of correct detections and median reaction time for eac
h comparison were measured following intramuscular drug administrations of
morphine (0.01-1.8 mg/kg) and buprenorphine (0.00032-0.032 mg/kg). Both mor
phine and buprenorphine impaired vowel discriminability, and greater impair
ments occurred for those comparison vowels that were mon similar in formant
structure to the standard vowel. Morphine increased reaction time in all b
aboons, and buprenorphine increased reaction time in two of three baboons.
Morphine's perceptual effects occurred within 20-30 min following drug admi
nistration; buprenorphine's perceptual effects occurred 50-100 min followin
g drug administration. Morphine and buprenorphine did not differ in the tim
e course of their maximal reaction time effects. The results demonstrate th
at both morphine and buprenorphine can impair auditory discriminations invo
lving human vowel sounds in baboons, as well as lengthen reaction times to
the stimuli. (C) 2001 Elsevier Science Inc. All rights reserved.