What Needs to be Known in Order to Perform a Meaningful Scientific Comparison Between Animal Communications and Human Spoken Language

Human spoken language has long been the subject of scientific investigation, particularly with regard to the mechanisms underpinning speech production. Likewise, the study of animal communications has a substantial literature, with many studies focusing on vocalisation. More recently, there has been growing interest in comparing animal communications and human speech. However, it is proposed here that such a comparison necessitates the appraisal of a minimum set of critical phenomena: i) the number of degrees-of-freedom of the vocal apparatus, ii) the ability to control those degrees-of-freedom independently, iii) the properties of the acoustic environment in which communication takes place, iv) the perceptual salience of the generated sounds, v) the degree to which sounds are contrastive, vi) the presence/absence of compositionality, and vii) the information rate(s) of the resulting communications.