Several studies have found that adult caretakers usually hyperarticulate to infants by modifying their voice in ways that promote and sustain infants' attention. This articulation when engaging in infant directed speech (IDS) can result in "clear speech" by the expansion of the vowel space area. The degree of speech clarity produced by caregivers appears to provide advantages for young language learners to promote lexical perception and learning. However few studies have ever examined whether infants are able to perceive the difference between hyperarticulation and normal speech. In this study, 7-to 12-month-olds' (n=17) speech discrimination when hearing hyperarticulated and non-hyperarticulated words in mothers' natural speech production was examined. The degree of speech clarity was determined by the relations of the first (F1) and second formant frequencies (F2) of the vowel. The result showed that there was no discrimination between listening to hyperarticulated and non-hyperarticulated words, indicating that the benefit accrued by exposure to clear speech may require no selective attention on the part of the infant. Thus the advantages of hyperarticulation might be related to other characteristics. / Master of Science