We argue that during evolution, social communication engaged different perceptual and cognitive systems face, facial expression, gesture, vocalization, sound, and oral language that emerged at different times.
During evolution, our social communication used different perceptual and cognitive systems face, facial expression, gesture, vocalization, sound, and oral language that emerged at different times.
Infants heard seven auditory conditions during natural sleep: adult-directed speech, infant-directed speech, human communicative non-speech vocalizations, human non-communicative vocalizations, human non-vocal sounds, rhesus macaque vocalizations, and sounds of water.
During natural sleep, 24 1- to 4-month-old infants heard speech (adult-directed speech and infant-directed speech) and biological non-speech sounds produced by a human (communicative non-speech vocalizations, non-communicative vocalizations, human non-vocal sounds) or non-human (rhesus vocalizations) source.
Finally, although no previous study has investigated infant ERP responses to neutral non-speech human vocalizations compared to non-vocalization sounds, extant evidence on infant ERP correlates of voice processing suggests specific activation at fronto-central and temporal locations within both hemispheres (Cheng et al., 2012; Grossmann et al., 2005).
The present study compared 7-month-old infants' ERP responses to living versus non-living categories of sound, including human action sounds, human non-speech vocalizations, sounds produced by the environment, and sounds produced by automated mechanical devices.
For instance, speech is a signal produced by a human source (as are human non-speech vocalizations and human non-vocal sounds) and is produced by the vocal tract (as are human non-speech vocalizations and rhesus macaque vocalizations).
Calls may be missed in our selection procedure because they overlap in time with other vocalizations or with non-vocal sounds like wing fluttering.
While human communicative vocal non-speech, human non-communicative vocal non-speech, rhesus macaque vocalizations, and human non-vocal sounds are all biological non-speech signals, we recognize that these non-speech sounds vary in the extent to which they share other key properties with speech.
Vocal sounds consist of brief segments of speech (e.g., syllables, words, and sentences in foreign languages) and non-speech (e.g., laughs, sighs, coughs) vocalizations.
