Research in stuttering can be divided into two broad categories. The focus of attention has either been on the way the stutterer speaks or on the sort of person he is. In the first case, investigators have sought to isolate those conditions under which the stutterer's blocks, repetitions, or prolongations can be modified. For instance, there are studies on the effects of varying the size of the audience (e.g. Siegel and Haugen, 1964; Shulman, 1955), of providing delayed auditory feedback (e.g. Lee, 1951; Neeley, 1961) or various levels of noise (e.g. Mariast and Hutton, 1957; Sutton and Chase, 1961), and on the relationship between number of stutters and rhythmic speech (e.g. Barber, 1940; Fransella and Beech, 1965).