His work has focused on how language emerges in the social context of interaction between infants, children and caregivers, how speech and language disorders can shed light on the normal developmental process and vice versa, how brain and cognitive science can help illuminate language capability and learning, and on how the special life history of humans offers perspectives on why humans are so much more intensely social and vocally communicative than their primate relatives.

In recent time he has authored widely accessible volumes designed for the general public on the nature of human communication and its origins.

He was a founding editor of the journal Applied Psycholinguistics, and has served on numerous other editorial boards.

[9][10] He has recently authored two additional volumes directing attention to the significance of speech communication in the modern world,[11] (reviewed by, among others, The New York Times and the Washington Times) and to eavesdropping and gender differences in understanding of human communication and the human condition.

[12] Key articles among the more than 100 that he has published include fundamental contributions to: a) the understanding of infant babbling and how it lays foundations for speech,[13][14] b) various aspects of communication disorders and how they illuminate the language faculty and neurolinguistics,[15][16] c) a groundbreaking contribution to the understanding of how language evolved in humanity based on a theory of parental selection,[17] and d) the role of human life history (with Barry Bogin) in language evolution, based on the argument that the prolonged developmental period of humanity includes a childhood and an adolescence, phases that are absent in non-human primates, and both of which provide extensive and long-term opportunities for learning that lay groundwork for human language and culture.