Ten unanswered questions in multimodal communication.

The study of multimodal communication has become an active and vibrant field. This special issue of Behavioral Ecology and Sociobiology brings together new developments in this rapidly expanding area. In this final contribution to the special issue, I look to the future and discuss ten questions in need of further work, touching on issues ranging from theoretical modeling and the evolution of behavior to molecular mechanisms and the development of behavior.

Testosterone may increase selective attention to threat in young male macaques.

Animal studies indicate that sex hormones have widespread effects on the brain, cognition and emotion, but findings in humans are inconsistent. Well-controlled studies in nonhuman primates are crucial to resolve these discrepancies. In this study, we examined the effects of testosterone (T) on emotion in male rhesus monkeys.

The neural basis of perceiving emotional bodily expressions in monkeys.

Higher animals invest considerable time and brain resources in monitoring each others' body language. A network of dedicated brain structures is presumably involved in social perception. We hypothesized that functional magnetic resonance imaging may reveal portions of inferior temporal cortex participating in processing social signals.

Neuronal oscillations and visual amplification of speech.

It is widely recognized that viewing a speaker's face enhances vocal communication, although the neural substrates of this phenomenon remain unknown. We propose that the enhancement effect uses the ongoing oscillatory activity of local neuronal ensembles in the primary auditory cortex. Neuronal oscillations reflect rhythmic shifting of neuronal ensembles between high and low excitability states.

Issues in the classification of multimodal communication signals.

Communication involves complex behavior in multiple sensory channels, or "modalities." We provide an overview of multimodal communication and its costs and benefits, place examples of signals and displays from an array of taxa, sensory systems, and functions into our signal classification system, and consider issues surrounding the categorization of multimodal signals. The broadest level of classification is between signals with redundant and nonredundant components, with finer distinctions in each category.

The Umwelt and its relevance to animal communication: introduction to special issue.

This introduction applies J. von Uexküll's (1934/1957) concept of the Umwelt to the study of animal communication, particularly as it pertains to studies presented at a recent workshop on animal communication in the context of the environment. The environment is conceived broadly in the articles that follow, including the many physical and social environments in which an animal may find itself.