An organism is continuously assailed by information. The external bombardment of the senses is only a part of the total set of messages reaching the central nervous system, since to it are added more signals originating within the body and carrying information about its function. The selective mechanism must instead be operating with a more sophisticated code than anatomical site. This suggests that the apparent location of the message is more crucial than its anatomical locus. A number of developments attribute to the memory process a major role in the matter of selection. Working along the lines of the J. A. Deutschs' model, R. M. Shiffrin and his colleagues assert that subjects are quite incapable of directing attention to input channels until these channels have been identified by the nature of the information they carry. A. M. Treisman concluded that the concept of an all-or-none switch of the kind postulated by Broadbent was unduly stretched by these findings.