The "heart" of categorical speech discrimination in young infants.

Categorical discrimination of place of articulation in the stimuli [dae] and [gae] was investigated in three- to four-month-old infants using a 20/20 cardiac orienting response paradigm. In this procedure infants were presented with 20 tokens of one syllable followed immediately by 20 tokens of a change stimulus. Each infant received a between-category shift, a within-category shift, and a no-shift control condition, with the order of conditions completely counterbalanced across subjects. Discrimination was indexed by an orienting response to the onset of the second 20 stimuli. The data were analyzed for evidence of categorical discrimination both within subjects (each condition pooled across orders of presentation) and between subjects, as is typical of infant-categorical discrimination studies. Both sets of results revealed that infants discriminate the cues for place of articulation categorically. These findings demonstrate the generality of the infant categorical discrimination observed with the nonnutritive operant sucking paradigm and indicate the usefulness of the heart rate paradigm employed in the present study for the collection of within-subject speech discrimination data across a wide-range of subject populations.