Continuous vowel discrimination in normal and at risk infants.

The present study investigated vowel discrimination in 2-week-old infants using a nonnutritive, high-amplitude sucking measure in a habituation-dishabituation paradigm. Infants were presented with pairs of vowel stimuli differing in equal logarithmic steps along the /i/ to /I/ continuum. Stimulus pairs of equal acoustic differences were selected to be either within or between the adult phonetic categories. Infants were divided into 3 experimental stimulus shift conditions: within category, between category, and control. Using a scoring system to asses perinatal events, half the infants in each condition were categorized as being at "higher risk" for developmental (p less than .05) were found between the control and both the within and between phonetic category conditions. No effects due to risk score population differences proved to be significant. These results indicate that 8-week-old infants discriminate the vowels /i/ and /I/ in a continuous as opposed to a categorical manner. Some differences were noted in response patterns between high- and low-risk score infants.