John D. Newman

Auditory Cortex of Squirrel Monkey: Response Patterns of Single Cells to Species-Specific Vocalizations

Most of the neurons tested in the superior temporal cortex of awake squirrel monkeys responded to recorded species-specific vocalizations. Some cells responded with temporally complex patterns to many vocalizations. Other cells responded with simpler patterns to only one call. Most cells lay between these two extremes. On-line deletion of parts of a vocalization revealed the role of temporal interactions in determining the nature of some responses.

Multiple coding of species-specific vocalizations in the auditory cortex of squirrel monkeys

Abstract Eighty-three cells in the superior temporal gyrus of awake squirrel monkeys were tested with 12 different species-specific vocalizations; 75 (90%) responded to one or more calls. A wide range of selectivity and response probabilities were seen. Eighty-nine percent of the cells responded to more than half of the vocalizations. In only one case did a cell respond to only one call type (‘peep’). This cell also responded to steady tone bursts, but only in a narrow range of frequencies approximating the major band of acoustic energy in peeps. In most cases, no obvious acoustic relationships were seen between calls effective for a given cell. Likewise, in most cases the frequency range over which a cell responded to steady tone bursts did not readily explain responses to vocalizations. More than half of the cells discriminated between one or more pairs of acoustically similar vocalizations. The response patterns of different cells to the same vocalization showed considerable variety. This was especially true for responses to the temporally more complex calls. The variety of responses given by different cells to the same vocalization suggests that no vocalization is coded by one unique discharge pattern. Our results suggest that many neurons in the STG do not select between different classes of vocalizations according to presence or absence of simple acoustic features.

Role of midline frontolimbic cortex in production of the isolation call of squirrel monkeys

Since the separation cry of mammals serves to maintain (1) mother-offspring contact and (2) contact between members of a group, it probably ranks as a basic mammalian vocalization. The present study is part of an investigation concerned with identifying the cerebral representation of the separation call in squirrel monkeys. For this purpose, monkeys are tested for their ability to produce spontaneous calls in isolation before and after ablations of different parts of the brain. Because of the subjects auditory and visual isolation, the call emitted during testing is referred to as the isolation call. In a preceding study, it was shown that lesions at the thalamomidbrain junction and in the ventral central gray interfere with the structure and/or production of the call. The present study focuses on the rostral midline limbic cortex, known to be one of the two cortical areas where stimulation elicits vocalization in monkeys. Evidence derived by the process of elimination indicates that the spontaneous call depends on the concerted action of a continuous band of rostral limbic cortex comprising parts of areas 24, 25, and 12. The midline frontal neocortex peripheral to this limbic zone does not appear to be essential for the call.

Individuality and stability of isolation peeps in squirrel monkeys

Isolation peeps (IPs) made by captive squirrel monkeys (Saimiri sciureus) of both the Gothic and Roman type have been analysed by spectrographic and statistical methods designed to quantify the degree of individuality found in utterances from single individuals. Clustering analysis confirmed that in both groups of monkeys individually distinct combinations of acoustic features characterize the IP and that such unique combinations persist over periods of several years. Differences between the Gothic and Roman form of the IP were found in more aspects of acoustic structure than had previously been known. The evidence suggests that information about the identity of the vocalizer is contained in the the IP.

DEVELOPMENT OF THE ISOLATION PEEP IN LABORATORY-BRED SQUIRREL MONKEYS

The development of Isolation Peeps (IPs) was studied in seven laboratory-reared squirrel monkeys (Saimiri sciureus) over the age range of one day to two years. IPs were identified by specified criteria from the wide range of vocalizations recorded and analysed by descriptive and statistical methods. Despite the presence of substantial maturational changes in IPs, the data reveal individuality or vocal signature at all ages tested. Furthermore, the animals had developed by the end of the study unique and stable IPs comparable to those recorded previously from wild-caught adults.

Effects of separation and novelty on distress vocalizations and cortisol in the common marmoset (Callithrix jacchus).

In socially‐bonding species, separation from familiar attachment figures is widely known to stimulate a physiological and behavioral stress response. This study investigated the hormonal and vocal responses of adult common marmosets to separation from familiar group members and to 24 hr of cohabitation with an unfamiliar opposite‐sex conspecific. All subjects were removed from their home cages and placed into a novel environment for 20 min. In one group, marmosets were exposed to an unfamiliar, opposite‐sex partner in the novel environment and remained paired with this partner for the 24 hr test period. In three other groups, marmosets experienced the novel environment alone and subsequently were returned to their original social‐ or single‐housing condition, or kept separate from their social groups for a 24 h period. Blood samples were collected the day before, and at 30 min, 90 min, and at 24 h after separation. Cortisol responses were differentially affected by the length of separation and the presence of unfamiliar conspecifics. Brief separation followed by the return to the social group had minimal effect on plasma cortisol levels. All marmosets produced high levels of separation calls in the novel environment, but there was no apparent relationship between calling and cortisol levels. The lack of a temporal relationship between the production of distress vocalizations and serum cortisol has previously been noted in squirrel monkey and rhesus monkey infant separation studies; the behavioral and physiological responses to separation appear to be similarly dissociated in the marmoset. Further, the characteristics of a separation environment can differentially affect the hormonal response by adult marmosets without differentially affecting their behavioral response. Am. J. Primatol. 47:209–222, 1999. Published 1999 Wiley‐Liss, Inc.

Squirrel Monkey Communication

Communication in the squirrel monkey, Saimiri sciureus has been the subject of numerous analyses over the past two decades. One of the interesting aspects of having participated in some of these studies has been the realization that, even in this well-studied species, there are significant gaps in understanding the functional significance, ontogeny, and intraspecific variability of many common communication patterns. The causal mechanisms and evolutionary history of Saimiri communication are also areas of study for which there is a wealth of opportunity for further investigation.

Stress and Emotion Classification using Jitter and Shimmer Features

In this paper, we evaluate the use of appended jitter and shimmer speech features for the classification of human speaking styles and of animal vocalization arousal levels. Jitter and shimmer features are extracted from the fundamental frequency contour and added to baseline spectral features, specifically Mel-frequency cepstral coefficients (MFCCs) for human speech and Greenwood function cepstral coefficients (GFCCs) for animal vocalizations. Hidden Markov models (HMMs) with Gaussian mixture models (GMMs) state distributions are used for classification. The appended jitter and shimmer features result in an increase in classification accuracy for several illustrative datasets, including the SUSAS dataset for human speaking styles as well as vocalizations labeled by arousal level for African elephant and Rhesus monkey species.

Statistical Discrimination among Vocalizations of Individual Squirrel Monkeys (Saimiri sciureus)

Discriminant analysis was used to distinguish statistically between the chuck vocalizations of individual squirrel monkeys. A unique combination of values of six structural parameters characterized the chucks of each of 5 individuals, permitting reliable identification of sources of chuck vocalizations on the basis of chuck structures alone. Certain parameters were found to be nearly invariant within individual monkeys, while others were quite variable within and between individuals. We propose that this technique be used in retrospective classification of vocalizations by source, when observational identification of the sources of all vocalizations in a rapid sequence is not possible.

Effects of tegmental lesions on the isolation call of squirrel monkeys

The present study is concerned with identifying brain mechanisms underlying a basic mammalian vocalization known as the isolation call. The call serves to reestablish contact of separated individuals. Adult squirrel monkeys were used as experimental subjects because the isolation call in these animals has been shown to be stable, well-defined, and readily elicited under experimental conditions. Bilateral, symmetrical electrocoagulations in certain parts of the tegmentum and core gray matter of the thalamus and midbrain variously altered the character and production of isolation calls, but had no apparent effect on other vocalizations. In respective cases the changes were characterized by: (1) reduction in number of calls; (2) calls with abnormal structure; and (3) calls of infantile character. As opposed to earlier investigations on mammals, the present study has shown that damage to certain brain structures may not only affect the production of a vocalization but also its physical characteristics.