COMPARISONS between t e ac hing machines and programmed texts as presentation modes have been made by Eigen and Komoski (3), Holt and Hammock (6), Roe et al (8), and Silverman and Alter (1). In each of these studies, the machine was compared to either a horizontal programmed text orto a vertical programmed text. This study compares the ma chine with both the horizontal and vertical text for mats. A teaching machine presents an ordered sequence of instruction to the learner one frame at a time. After responding to a stimulus frame, the learner's answer is immediately confirmed or corrected. The learner then proceeds to the next frame; he is prevented from changing his previous answers or going back in the program. In a horizontal programmed text, succeeding frames appear on alternate pages. The learner writes his answer to the frame either in the pro gram booklet or on a separate answer sheet. He then turns the page, and the correct response is re vealed along with the next stimulus frame. A hori zontal text is read from the front of the book to the back, across the pages, at one level. After com pleting the top level, the learner reads across the text at the next lower level. This procedure is con tinued until the entire text has been read. Reading a horizontal programmed text involves much page turning. All the frames on any one level are allotted the same amount of space. This space limitation may influence the programmer's con struction of his frames; i. e., he may tend to make all frames of a uniform length. In a sense, these space limitations control the programmer's behav ior. When frame lengths vary, shorter frames will waste space. From the standpoint of printing costs, this is an important consideration. Vertical programmed texts are read from the top of the page to the bottom. The number of frames appearing on one page may vary from one to ten or twelve. A mask or slider is used with this mode of presentation. The learner exposes one frame at a time, together with the answers to the preceding frame, by moving the slider down the page. As each new frame is exposed, the learner writes his answer either in the textbook or on a separate answer sheet. The vertical programmed text does not require as much page turning as does the horizontal text; the problem of space limitation is also avoided. In both the horizontal and vertical formats, however, the programmer's control over the learning se quence may be easily broken by the learner's turn ing ahead or back in the text. Neither of these modes of presentation is cheat-proof; both re quire a maximum of self-control on the part of the learner. The question of control of the learner's behavior has been discussed in the literature for some time. Skinner (9) and Holland (7) have stated that the teaching machine gives more precise control over the behavior of the learner than does the pro grammed text. Evans, Glaser, and Homme (4) have commented that with a well-written program, ma chine control may not be necessary. Eigen (2), basing his stand on previous research, which has failed to demonstrate differential effects between presentation modes, has advocated that the pro grammed-text format be used in initial field trials in school systems. Each of these points of view has merit. The learner using a teaching machine must follow the presented by the programmer. Therefore, with this mode of presentation, the learner's be havior is almost entirely under the control of the programmer. With programmed texts, this control may be diluted. The learner using a programmed text may deviate from the path set down by the pro grammer by looking back in the program or looking ahead. However, this diminution of control maybe