Robert D. Hienz

Sex differences in the acoustic structure of vowel-like grunt vocalizations in baboons and their perceptual discrimination by baboon listeners

This study quantifies sex differences in the acoustic structure of vowel-like grunt vocalizations in baboons (Papio spp.) and tests the basic perceptual discriminability of these differences to baboon listeners. Acoustic analyses were performed on 1028 grunts recorded from 27 adult baboons (11 males and 16 females) in southern Africa, focusing specifically on the fundamental frequency (F0) and formant frequencies. The mean F0 and the mean frequencies of the first three formants were all significantly lower in males than they were in females, more dramatically so for F0. Experiments using standard psychophysical procedures subsequently tested the discriminability of adult male and adult female grunts. After learning to discriminate the grunt of one male from that of one female, five baboon subjects subsequently generalized this discrimination both to new call tokens from the same individuals and to grunts from novel males and females. These results are discussed in the context of both the possible vocal anatomical basis for sex differences in call structure and the potential perceptual mechanisms involved in their processing by listeners, particularly as these relate to analogous issues in human speech production and perception.

Discrimination of steady‐state vowels by blackbirds and pigeons

Redwing blackbirds, brown‐headed cowbirds, and pigeons were trained with operant conditioning techniques to discriminate the steady‐state vowels /e/, /ae/, /a/, and /sa/ from each other. A pulsed train of one of these vowels comprised the background stimulus. Birds were trained to peck on one response key to produce occasional alternations from this standard vowel to one of the three remaining comparison vowels, and to peck on a second response key during these alternations to produce a grain reward. All birds discriminated all combinations of vowel pairs employed when only one comparison vowel occurred during a session. Differences in discriminability emerged when three comparison vowels occurred within each session. For pigeons, increased discriminability (indicated by shorter response latencies and higher rates of correct detections) was directly related to the size of the first or second formant frequency shifts between standard and comparison vowels. For blackbirds, this was only true if the first or...

Effects of bilateral olivocochlear lesions on vowel formant discrimination in cats

Operant conditioning procedures were used to measure the effects of bilateral olivocochlear lesions on the cats discrimination thresholds for changes in the second formant frequency (deltaF2) of the vowel /epsilon/. Three cats were tested with the formant discrimination task under quiet conditions and in the presence of continuous broadband noise at signal-to-noise ratios (S/Ns) of 23, 13, and 3 dB. In quiet, vowel levels of 50 and 70 dB produced average deltaF2s of 42 and 47 Hz, respectively, and these thresholds did not change significantly in low levels of background noise (S/Ns = 23 and 13 dB). Average deltaF2s increased to 94 and 97 Hz for vowel levels of 50 and 70 dB in the loudest level of background noise (S/N = 3 dB). Average deltaF2 thresholds in quiet and in lower noise levels were only slightly affected when the olivocochlear bundle was lesioned by making bilateral cuts into the floor of the IVth ventricle. In contrast, post-lesion deltaF2 thresholds in the highest noise level were significantly larger than pre-lesion values; the most severely affected subject showed post-lesion discrimination thresholds well over 200 Hz for both 50 and 70 dB vowels. These results suggest that olivocochlear feedback may enhance speech processing in high levels of ambient noise.

Novel long-term cardiovascular effects of industrial noise.

Baboon subjects were instrumented with indwelling arterial catheters for continuous measurement of blood pressure and heart rate before, during, and after exposure to industrial noise eight hours daily. Initial exposure to noise produced transient, acute elevations of systolic and diastolic blood pressures and heart rates at noise onset, which habituated over the course of noise exposure. Chronic exposure to noise lowered blood pressure and heart rate not only during noise, but particularly after daily noise offset. Blood pressures returned toward baseline after noise exposure was terminated. Plasma catecholamines were also decreased during noise exposure. A control animal which received only masking noise did not demonstrate decreases in cardiovascular parameters. The possibility of classically conditioned associations of noise onset with feeding was discussed.

Central nervous system correlates of behavioral deficits following simian immunodeficiency virus infection

Despite the high incidence of cognitive and motor impairment in acquired immunodeficiency syndrome (AIDS) patients, the mechanisms of AIDS-related central nervous system (CNS) pathology are not completely understood. Infection with simian immunodeficiency virus (SIV) in macaques provides an excellent model of AIDS, including human immunodeficiency virus (HIV)-induced CNS pathology and cognitive/behavioral impairment. Co-inoculation with two SIV strains, SIV/17E-Fr and SIV/DeltaB670, accelerates SIV CNS disease, producing SIV encephalitis in over 90% of pig-tailed macaques within 3 months. In the present study, this SIV model was employed to identify cellular and viral correlates of behavioral impairment following SIV infection. Measures of psychomotor speed (simple reaction time), fine motor control (bimanual motor task), and general motor activity (home cage movement) were all adversely affected by SIV disease. Prior to euthanasia, performance was significantly impaired in both a simple reaction time task in 6 of 12 monkeys and a bimanual motor task in 5 of 6 monkeys. All monkeys evaluated (11 of 11) showed significant reductions in spontaneous motor activity. Significant correlations were found between impaired performance on the bimanual motor test and axonal damage (accumulation of β-amyloid precursor protein in the corpus callosum) as well as increased microglial activation and macrophage infiltration (levels of CD68 and Ham56 immunostaining). These results suggest that axonal damage is related to the behavioral impairment induced by infection with SIV. The axonal damage may result from neuroimmune responses, including microglial and macrophage activation. Therefore, axonal damage may be a morphologic manifestation of neuronal dysfunction that underlies development of behavioral impairment in HIV/SIV CNS infection.

Assessing Drugs for Abuse Liability and Dependence Potential in Laboratory Primates

Distinctions between abuse liability and dependence potential are developed within the context of an assessment approach focusing upon the reinforcing, discriminative, and eliciting properties of drugs as the basis for an effective technology to evaluate a broad range of pharmacological agents. Procedures and outcomes from extensive studies with primates assessing drug self-administration, drug discrimination, physiological dependence, and behavioral toxicity are described and discussed.

Individual Differences in Attentional Deficits and Dopaminergic Protein Levels following Exposure to Proton Radiation

To assess the possible neurobehavioral performance risks to astronauts from living in a space radiation environment during long-duration exploration missions, the effects of head-only proton irradiation (150 MeV/n) at low levels (25–50 cGy, approximating an astronauts exposure during a 2-year planetary mission) were examined in adult male Long-Evans rats performing an analog of the human psychomotor vigilance test (PVT). The rodent version of PVT or rPVT tracks performance variables analogous to the human PVT, including selective attention/inattention, inhibitory control (“impulsivity”) and psychomotor speed. Exposure to head-only proton radiation (25, 50, 100 or 200 cGy) disrupted rPVT performance (i.e., decreased accuracy, increased premature responding, elevated lapses in attention and slowed reaction times) over the 250 day testing period. However, the performance decrements only occurred in a subgroup of animals at each exposure level, that is, the severity of the rPVT performance deficit was unrelated to proton exposure level. Analysis of brain tissue from irradiated and control rats indicated that only rats with rPVT performance deficits displayed changes in the levels of the dopamine transporter and, to a lesser extent, the D2 receptor. Additional animals trained to perform a line discrimination task measuring basic and reversal learning showed no behavioral effects over the same exposure levels, suggesting a specificity of the proton exposure effects to attentional deficits and supporting the rPVT as a sensitive neurobehavioral assay.

Pure tone thresholds in the yellow baboon (Papio cynocephalus)

Abstract Using a reaction-time procedure, pure tone thresholds were measured behaviorally in four baboons at 12 frequencies, ranging from 62 Hz to 40 kHz. Lowest mean individual thresholds were in the range of 3 to -8 dB SPL between 1.0 and 16.0 kHz, and rose to 48 dB at 62 Hz, and 59 dB at 40.0 kHz. These threshold functions closely match those of other Old World monkeys.

Vowel discrimination in cats: Acquisition, effects of stimulus level, and performance in noise

The ability of cats to discriminate accurately among different synthetic, steady-state vowels was examined across a range of stimulus levels and in background noise. Cats were trained to press and hold down a lever to produce a pulsed train of a standard vowel stimulus, and to release the lever only when a different vowel sound occurred. Five synthetic vowels were tested (/e/, /ae/, /a/, /o/, and /u/) at levels of 30, 50, 70, and 90 dB SPL. In separate experiments, each of these vowels served in turn as the standard vowel. All cats discriminated among the vowels accurately, and in general performed at least as well at high stimulus levels as at low levels. Where differences in vowel discriminability occurred, they were correlated with the relative changes in first and second formant peaks. Cats appear to predominantly utilize upward frequency changes in either the first or second formants of the vowels to make the discriminations; downward formant changes produced considerably lower discrimination performances. In background noise, high vowel discriminability was still maintained at an average signal/noise ratio of -12.3 dB. Thus cats can discriminate among vowels at high signal levels and in background noise, despite the fact that the neural representations of vowels based on rate responses in the auditory nerve can be severely degraded under these conditions.

The effects of pentobarbital upon auditory and visual thresholds in the baboon

Adult male baboons were trained to perform a reaction time procedure, which required holding a lever depressed for varying time intervals and releasing it during a 1.5 sec test stimulus to receive food. The test stimulus was a 16 kHz tone for auditory threshold testing, and a white light for visual threshold testing. Stimulus intensities were randomly varied to determine detection thresholds, and the latency of each correct lever release was recorded as a measure of reaction time. Acute, IM injections of pentobarbital (1.0 to 17.0 mg/kg) were given at the beginning of 2-hr experimental sessions. Pentobarbital elevated the absolute visual threshold and increased both auditory and visual reaction times in a dose-related manner. Two of three baboons showed reaction time and visual threshold decrements at pentobarbital doses which produced no change in absolute auditory thresholds.