Form perception and visual acuity in a chimpanzee

A 6.5-year-old female chimpanzee learned to distinguish perfectly every letter of the alphabet in a matching-to-sample task with 26 letters as choice alternatives. Confusion of letters during the initial training was used to scale them in a multidimensional similarity space and to associate them in hierarchical clusters. The results resembled those obtained from similarity judgements by humans. Using letters of various sizes, a visual acuity test revealed that the chimpanzee's acuity was about 1.5, comparable to that in normal humans. The chimpanzee also readily learned to use letters as names of individual humans and chimpanzees. A species-typical feature was identified in the perceptual processes associated with complex forms, such as those involved in individual recognition.     

Vocal-auditory functions in the chimpanzee: Vowel perception

The perception of vowels was studied in chimpanzees and humans, using a reaction time task in which reaction times for discrimination of vowels were taken as an index of similarity between vowels. Vowels used were five synthetic and natural Japanese vowels and eight natural French vowels. The chimpanzees required long reaction times for discrimination of synthetic [i] from [u] and [e] from [o], that is, they need long latencies for discrimination between vowels based on differences in frequency of the second formant. A similar tendency was observed for discrimination of natural [i] from [u]. The human subject required long reaction times for discrimination between vowels along the first formant axis. These differences can be explained by differences in auditory sensitivity between the two species and the motor theory of speech perception. A vowel, which is pronounced by different speakers, has different acoustic properties. However, humans can perceive these speech sounds as the same vowel. The phenomenon of perceptual constancy in speech perception was studied in chimpanzees using natural vowels and a synthetic [o]- [a] continuum. The chimpanzees ignored the difference in the sex of the speakers and showed a capacity for vocal tract normalization.     

Vocal-auditory functions of the chimpanzee: consonant perception

The perception of consonants which were followed by the vowel [a] was studied in chimpanzees and humans, using a reaction time task in which reaction times for discrimination of syllables were taken as an index of similarity between consonants. Consonants used were 20 natural French consonants and six natural and synthetic Japanese stop consonants. Cluster and MDSCAL analyses of reaction times for discrimination of the French consonants suggested that the manner of articulation is the major determinant of the structure of the perception of consonants by the chimpanzees. Discrimination of stop consonants suggested that the major grouping in the chimpanzees was by voicing. The place of articulation from the lips to the velum was reproduced only in the perception of the synthetic unvoiced stop consonants in the two dimensional MDSCAL space. The phoneme-boundary effect (categorical perception) for the voicing and place-of-articulation features was also examined by a chimpanzee using synthetic [ga]-[ka] and [ba]-[da] continua, respectively. The chimpanzee showed enhanced discriminability at or near the phonetic boundaries between the velar voiced and unvoiced and also between the voiced bilabial and alveolar stops. These results suggest that the basic mechanism for the identification of consonants in chimpanzees is similar to that in humans, although chimpanzees are less accurate than humans in discrimination of consonants.     

Speech perception: linking comprehension across a cortical network

Listening to speech amidst noise is facilitated by a variety of cues, including the predictable use of certain words in certain contexts. A recent fMRI study of the interaction between noise and semantic predictability has identified a cortical network involved in speech comprehension.     

Inversion effect in perception of human faces in a chimpanzee (Pan troglodytes)

Three experiments investigated the inversion effect in face perception by a chimpanzee (Pantroglodytes) under the matching-to-sample paradigm. The first two experiments addressed the inversion effect in the perception of human faces. In Experiment 1, the subject received identity matching using 104 photographs of faces and houses presented in four different orientations. The chimpanzee showed better accuracy when the faces were presented upright than when they were inverted. The inversion effect was not found for photographs of houses. In Experiment 2, the subject received rotational matching in which the sample and comparisons differed in orientation. The subject showed a clear inversion effect for faces but not for houses. Experiment 3 explored the hemispheric specialization of the face inversion effect with chimeric (artificially composed) faces. The subject showed no visual-field preference when the chimeric faces were presented as samples under nonreinforced probe testing, while the inversion effect was evident when the discrimination was based on the left part of the chimeric sample. The results suggested that the face-inversion was specific to the left visual field (i.e. right hemispheric processing). In general, these results were consistent with those found in humans in similar testing situations.     

Proteomics: the nucleolus weighs in.

Numerous studies have indicated that the nucleolus is involved in a variety of cellular processes besides its well-known function in ribosome biosynthesis. A recent study describing the nucleolar proteome opens the way to new avenues of research on this important nuclear suborganelle.     

Bone weighs in on obesity

Obesity, insulin resistance, and diabetes are related disorders of energy metabolism for which therapies are suboptimal. In this issue of Cell, Lee et al. (2007) demonstrate in mice that bone regulates the insulin/glucose axis and energy metabolism, providing a new framework for approaching common disorders of bioenergetics.     

Functionally referential communication in a chimpanzee

The evolutionary origins of the use of speech signals to refer to events or objects in the world have remained obscure. Although functionally referential calls have been described in some monkey species, studies with our closest living relatives, the great apes, have not generated comparable findings. These negative results have been taken to suggest that ape vocalizations are not the product of their otherwise sophisticated mentality and that ape gestural communication is more informative for theories of language evolution. We tested whether chimpanzee rough grunts, which are produced during feeding contexts, functioned as referential signals. Individuals produced acoustically distinct types of "rough grunts" when encountering different foods. In a naturalistic playback experiment, a focal subject was able to use the information conveyed by these calls produced by several group mates to guide his search for food, demonstrating that the different grunt types were meaningful to him. This study provides experimental evidence that our closest living relatives can produce and understand functionally referential calls as part of their natural communication. We suggest that these findings give support to the vocal rather than gestural theories of language evolution.     

Speech perception at the interface of neurobiology and linguistics

Speech perception consists of a set of computations that take continuously varying acoustic waveforms as input and generate discrete representations that make contact with the lexical representations stored in long-term memory as output. Because the perceptual objects that are recognized by the speech perception enter into subsequent linguistic computation, the format that is used for lexical representation and processing fundamentally constrains the speech perceptual processes. Consequently, theories of speech perception must, at some level, be tightly linked to theories of lexical representation. Minimally, speech perception must yield representations that smoothly and rapidly interface with stored lexical items. Adopting the perspective of Marr, we argue and provide neurobiological and psychophysical evidence for the following research programme. First, at the implementational level, speech perception is a multi-time resolution process, with perceptual analyses occurring concurrently on at least two time scales (approx. 20-80 ms, approx. 150-300 ms), commensurate with (sub)segmental and syllabic analyses, respectively. Second, at the algorithmic level, we suggest that perception proceeds on the basis of internal forward models, or uses an 'analysis-by-synthesis' approach. Third, at the computational level (in the sense of Marr), the theory of lexical representation that we adopt is principally informed by phonological research and assumes that words are represented in the mental lexicon in terms of sequences of discrete segments composed of distinctive features. One important goal of the research programme is to develop linking hypotheses between putative neurobiological primitives (e.g. temporal primitives) and those primitives derived from linguistic inquiry, to arrive ultimately at a biologically sensible and theoretically satisfying model of representation and computation in speech.     

Use of exclusion by a chimpanzee (Pan troglodytes) during speech perception and auditory-visual matching-to-sample

An adult female chimpanzee showed responding through use of exclusion in an auditory to visual matching-to-sample procedure. The chimpanzee had previously learned to associate specific visuographic symbols called lexigrams with real world referents and the spoken English words and photographs for those referents. On some trials, an unknown spoken English word was presented as the sample, and the match choices could consist of photographs or lexigrams that already were associated with known English words as well as unknown lexigrams or photos of objects without associated lexigrams. The chimpanzee reliably avoided choosing known comparisons for these unknown samples, instead relying on exclusion to choose comparisons that were of unknown lexigrams or photographs of items without associated lexigram symbols.     

Third-party grooming in a captive chimpanzee group

Social grooming is ubiquitous among the captive chimpanzees at Chester Zoo. Seven individuals were chosen here for a study of third-party social dynamics. The grooming decisions of five adult males were analysed, but only insofar as they directed attention to a mother–daughter pair. Uniquely, the daughter was an unpopular and physically disabled subadult whose congenital motor impairments prevented her from grooming others effectively. The impetus for this study was the observation that some males increased their grooming towards the disabled daughter during days when the mother had a tumescent anogenital swelling (sexually attractive to males) compared to days when the mother was not tumescent (less attractive). Apparently, males were grooming the daughter with no possibility of payback (because the daughter could never “return the favour”). A “grooming rate” (avg. grooming time/hour) was calculated that showed the grooming efforts of all five males towards both mother and daughter. These rates were compared on days when (1) the mother’s anogenital swelling was tumescent, and (2) days when the swelling was not tumescent. Each male showed a different pattern of behaviour. Two males groomed the daughter significantly more when the mother was tumescent. Results for all males were graphed against the quality of the social relationship between each male and the mother. Apparently, only males that had a weaker relationship to the mother groomed the daughter more when the mother was tumescent. This pattern did not exist for males with a stronger relationship to the mother. Possibly, the insecure males were using the disabled daughter as a way to curry favour with the attractive mother. If this is confirmed, then this type of triadic situation is a possible setting for indirect reciprocity to occur.     

Leaf-grooming by a wild chimpanzee in Mahale

During the course of systematic observations of the leaf-grooming behavior by the chimpanzees (Pan troglodytes) of the Mahale Mountains National Park, Tanzania, I recovered a louse from a leaf “groomed” by an adult male chimpanzee after a typical leaf-grooming session. During the leaf-grooming session I observed a small object on his lower lip. He picked up a leaf, transferred the small object from his lip to the leaf, folded the leaf and crushed the folded side of the leaf with his thumb. I present this observation as further evidence of the “squashing ectoparasites” hypothesis for leaf-grooming.     

Fatal acute Chagas disease in a chimpanzee

Background  Chagas disease (CD) or American trypanosomiasis is caused by a hemoflagellate protozoan, Trypanosoma cruzi . This organism has been isolated from more than 100 mammalian species and several insect vectors demonstrating a wide host distribution and low host specificity.
Methods  A 23-year-old male chimpanzee died acutely and a complete necropsy was performed to evaluate gross and microscopic pathologic changes. After observation of trypanosomal amastigotes in the myocardium, PCR and immunohistochemistry was employed to confirm the diagnosis of T. cruzi .
Results  Gross findings were consistent with mild congestive heart failure. Microscopic findings included multifocal myocardial necrosis associated with severe lymphocytic to mixed inflammatory infiltrates, edema, and mild chronic interstitial fibrosis. Multifocal intracytoplasmic amastigotes morphologically consistent with T. cruzi were observed in cardiac myofibers. Trypanosoma cruzi was confirmed by PCR and immunohistochemistry .
Conclusion  We report, to the best of our knowledge, the first fatal spontaneous case of T. cruzi infection in a chimpanzee.