First words begin to appear at 12 months. Then there is a naming explosion and by the age of 5 children know around 13,000 words. Fast mapping is the term used to describe the phenomena whereby young children can learn a word just after a few observations. Baby talk or motherese is characterized by a high pitched intonation and exaggerated prosodic contours. Research using the preferential looking procedure has shown that babies prefer listening to motherese over standard speech. One of the problems that babies face is the segmentation problem. This refers to the issue of how we can identify the spaces in between, and thus segment, the words in a sentence. Saffran conducted a study where she made up non-words that were english sounding in the sense that they adhered to our laws of syllabic sequences and prosody. She played these words on a tape recorder to babies in a sentence like fashion.