A chimpanzee recognizes varied acoustical versions of sine-wave and noise-vocoded speech.

Previous research demonstrated that a language-trained chimpanzee recognized familiar English words in sine-wave and noise-vocoded forms (Heimbauer et al. Curr Biol 21:1210-1214, 2011). However, those results did not provide information regarding processing strategies of the specific acoustic cues to which the chimpanzee may have attended.

Visual artificial grammar learning by rhesus macaques (Macaca mulatta): exploring the role of grammar complexity and sequence length.

Humans and nonhuman primates can learn about the organization of stimuli in the environment using implicit sequential pattern learning capabilities. However, most previous artificial grammar learning studies with nonhuman primates have involved relatively simple grammars and short input sequences. The goal in the current experiments was to assess the learning capabilities of monkeys on an artificial grammar-learning task that was more complex than most others previously used with nonhumans.

Vocal acoustics in the endangered proboscis monkey (Nasalis larvatus).

The endangered proboscis monkey (Nasalis larvatus) is a sexually highly dimorphic Old World primate endemic to the island of Borneo. Previous studies focused mainly on its ecology and behavior, but knowledge of its vocalizations is limited. The present study provides quantified information on vocal rate and on the vocal acoustics of the prominent calls of this species.

Silky sifaka (Propithecus candidus) "zzuss" vocalizations: sexual dimorphism, individuality, and function in the alarm call of a monomorphic lemur.

Vocalizations of Madagascar's lemurs have generally been less investigated than those of other primate groups, with virtually no information available about calling in the silky sifaka (Propithecus candidus), a large rainforest species. Current work examined the "zzuss" vocalization, one of the most common and loudest sounds produced by this monomorphic species, and included 160 calls from nine adults (five males, four females) in three groups. Analyses focused on overall acoustic features, individual and sex differences, call usage, and likely function.

A Serial Reaction Time (SRT) task with symmetrical joystick responding for nonhuman primates.

The serial reaction time (SRT) task is a simple procedure in which participants produce differentiated responses to each of a series of stimuli presented at varying locations. Learning about stimulus order is revealed through decreased latencies for structured versus randomized sequences. Although widely used with humans and well suited to nonhumans, this paradigm is little used in comparative research.

A chimpanzee recognizes synthetic speech with significantly reduced acoustic cues to phonetic content.

A long-standing debate concerns whether humans are specialized for speech perception, which some researchers argue is demonstrated by the ability to understand synthetic speech with significantly reduced acoustic cues to phonetic content. We tested a chimpanzee (Pan troglodytes) that recognizes 128 spoken words, asking whether she could understand such speech. Three experiments presented 48 individual words, with the animal selecting a corresponding visuographic symbol from among four alternatives.

Capuchin monkeys (Cebus apella) use positive, but not negative, auditory cues to infer food location.

Nonhuman primates appear to capitalize more effectively on visual cues than corresponding auditory versions. For example, studies of inferential reasoning have shown that monkeys and apes readily respond to seeing that food is present ("positive" cuing) or absent ("negative" cuing). Performance is markedly less effective with auditory cues, with many subjects failing to use this input.

Two organizing principles of vocal production: Implications for nonhuman and human primates.

Vocal communication in nonhuman primates receives considerable research attention, with many investigators arguing for similarities between this calling and speech in humans. Data from development and neural organization show a central role of affect in monkey and ape sounds, however, suggesting that their calls are homologous to spontaneous human emotional vocalizations while having little relation to spoken language. Based on this evidence, we propose two principles that can be useful in evaluating the many and disparate empirical findings that bear on the nature of vocal production in nonhuman and human primates.

The evolution of laughter in great apes and humans.

It has long been claimed that human emotional expressions, such as laughter, have evolved from nonhuman displays. The aim of the current study was to test this prediction by conducting acoustic and phylogenetic analyses based on the acoustics of tickle-induced vocalizations of orangutans, gorillas, chimpanzees, bonobos and humans. Results revealed both important similarities and differences among the various species' vocalizations, with the phylogenetic tree reconstructed based on these acoustic data matching the well-established genetic relationships of great apes and humans.

I Like the Sound of Your Voice: Affective Learning about Vocal Signals.

This paper provides the first demonstration that the content of what a talker says is sufficient to imbue the acoustics of his voice with affective meaning. In two studies, participants listened to male talkers utter positive, negative, or neutral words. Next, participants completed a sequential evaluative priming task where a neutral word spoken by one of the same talkers was presented before each target word to be evaluated.

Reconstructing the evolution of laughter in great apes and humans.

Human emotional expressions, such as laughter, are argued to have their origins in ancestral nonhuman primate displays. To test this hypothesis, the current work examined the acoustics of tickle-induced vocalizations from infant and juvenile orangutans, gorillas, chimpanzees, and bonobos, as well as tickle-induced laughter produced by human infants. Resulting acoustic data were then coded as character states and submitted to quantitative phylogenetic analysis.

Asymmetries in the individual distinctiveness and maternal recognition of infant contact calls and distress screams in baboons.

A key component of nonhuman primate vocal communication is the production and recognition of clear cues to social identity that function in the management of these species' individualistic social relationships. However, it remains unclear how ubiquitous such identity cues are across call types and age-sex classes and what the underlying vocal production mechanisms responsible might be. This study focused on two structurally distinct call types produced by infant baboons in contexts that place a similar functional premium on communicating clear cues to caller identity: (1) contact calls produced when physically separated from, and attempting to relocate, mothers and (2) distress screams produced when aggressively attacked by other group members.

GSU Praat Tools: scripts for modifying and analyzing sounds using Praat acoustics software.

The Praat acoustics program (Boersma, 2001) is powerful freeware that is widely used bybehavioral scientists working with digital sound. This article describes GSU Praat Tools, a script package that helps simplify and automate such work. The routines use Praat's scripting language to create new menus and commands within the existing interface, and can operate either on individual files or in batch mode.

An acoustic analysis of laughter produced by congenitally deaf and normally hearing college students.

Relatively few empirical data are available concerning the role of auditory experience in nonverbal human vocal behavior, such as laughter production. This study compared the acoustic properties of laughter in 19 congenitally, bilaterally, and profoundly deaf college students and in 23 normally hearing control participants. Analyses focused on degree of voicing, mouth position, air-flow direction, temporal features, relative amplitude, fundamental frequency, and formant frequencies.

Listeners judge talker sex more efficiently from male than from female vowels.

Speech routinely provides cues as to the sex of the talker, in voiced sounds, these cues mainly reflect dimorphism in vocal anatomy. This dimorphism is not symmetrical, however, since during adolescent development, males specifically diverge from a previously shared trajectory with females. We therefore predicted that listeners would show a corresponding perceptual advantage for male sounds in talker-sex discrimination, a hypothesis tested using very brief, one- to eight-cycle vowel segments.

Nonlinear acoustics in the pant hoots of common chimpanzees (Pan troglodytes): vocalizing at the edge.

Common chimpanzee (Pan troglodytes) "pant hoots" are multi-call events that build from quiet, consistently harmonic introductory sounds to loud, screamlike "climax" calls with acoustic irregularities known as "nonlinear phenomena" (NLP). Two possible functions of NLP in climax calls are to increase direct auditory impact on listeners and to signal physical condition. These possibilities were addressed by comparing climax calls from 12 wild chimpanzee males with "screams" and pant hoot "introduction" calls from the same individuals.

Acoustics and behavioral contexts of "gecker" vocalizations in young rhesus macaques (Macaca mulatta).

Loud, pulsed "gecker" vocalizations are commonly produced by young rhesus macaques in distressful circumstances. The acoustics, usage, and responses associated with these calls were examined using audio recordings and observational data from captive, socially living rhesus up to 24 months old. One-hundred-eleven gecker bouts were recorded from ten individuals (six males, four females), with most geckers produced during the first 6 months of age.

The relative roles of vowels and consonants in discriminating talker identity versus word meaning.

Three experiments tested the hypothesis that vowels play a disproportionate role in hearing talker identity, while consonants are more important in perceiving word meaning. In each study, listeners heard 128 stimuli consisting of two different words. Stimuli were balanced for same/different meaning, same/different talker, and male/female talker.

Characterizing noise in nonhuman vocalizations: Acoustic analysis and human perception of barks by coyotes and dogs.

Measuring noise as a component of mammalian vocalizations is of interest because of its potential relevance to the communicative function. However, methods for characterizing and quantifying noise are less well established than methods applicable to harmonically structured aspects of signals. Using barks of coyotes and domestic dogs, we compared six acoustic measures and studied how they are related to human perception of noisiness.

Nonlinear acoustics in pant hoots of common chimpanzees (Pan troglodytes): frequency jumps, subharmonics, biphonation, and deterministic chaos.

The pant hoot calls produced by common chimpanzees (Pan troglodytes) are multi-call vocalizations that have figured prominently in investigations of acoustic communication in this species. Although pant hoots are predominantly harmonically structured, they can exhibit an acoustic complexity that has recently been linked to nonlinearity in the vocal-fold dynamics underlying typical mammalian sound production. We examined the occurrence of these sorts of nonlinear phenomena in pant hoot vocalizations, contrasting quieter and lower-pitched "introduction" components with loud and high-pitched "climax" calls in the same bouts.

Sounds of emotion: production and perception of affect-related vocal acoustics.

In his writing Darwin emphasized direct veridical links between vocal acoustics and vocalizer emotional state. Yet he also recognized that acoustics influence the emotional state of listeners. This duality-that particular vocal expressions are likely linked to particular internal states, yet may specifically function to influence others-lies at the heart of contemporary efforts aimed at understanding affect-related vocal acoustics.

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.

Salience of caller identity in rhesus monkey (Macaca mulatta) coos and screams: perceptual experiments with human (Homo sapiens) listeners.

Recent evidence from acoustic analysis and playback experiments indicates that adult female rhesus monkey (Macaca mulatta) coos are individually distinctive but their screams are not. In this study, the authors compared discrimination of individual identity in these sounds by naive human listeners who judged whether 2 sounds had been produced by the same monkey or 2 monkeys. Each of 3 experiments using this same-different design showed significantly better discrimination of vocalizer identity from coos than from screams.

Classification of domestic cat (Felis catus) vocalizations by naive and experienced human listeners.

To test for possible functional referentiality in a common domestic cat (Felis catus) vocalization, the authors conducted 2 experiments to examine whether human participants could classify meow sounds recorded from 12 different cats in 5 behavioral contexts. In Experiment 1, participants heard singlecalls, whereas in Experiment 2, bouts of calls were presented. In both cases, classification accuracy was significantly above chance, but modestly so.