All of these are examples of how readers use the stability of the symbol system in books to slow their rate of progression or even to regress over text in a way that would seem difficult or impossible to do with audiotape's ever-advancing presentation of information. However, this distinction is likely to be crucial only in certain situations. For example, readers in the Shebilske and Reid study (1979) reduced their rate from 302 words per minute to 286. While statistically significant, this difference may not have practical significance with regard to media use since the typical audiotape presentation rate of 110-120 words per minute would seem to be slow enough to accommodate these comprehension difficulties. Even the apparent inability to regress over speech might be accommodated by the two second duration of information in acoustic memory (Baddeley, 1981) that would allow a listener to "recover" the three or four most recently spoken words and achieve the same affect as regression over text. The clearest advantage to the use of the stability of text to aid comprehension is when the reader must regress over segments of information larger than a phrase.