Among researchers who are studying memory processes, consensus appears to exist regarding a model of memory which contains three basic components: sensory information storage (SIS); short-term memory (STM) storage; and long-term memory (LTM) storage (Greeno and Bjork, 1973).
The SIS system stores information impinging upon the sensory receptor surfaces in the form of an "image" for very short durations of time (on the order of 300 milliseconds). The information load capacity of the SIS is relatively large; its function is to momentarily represent and store high quantities of the structural information in the environmental display in the form of an analog internal structural information display.
The "image" stored in the SIS decays rapidly, and must be recoded in some different form if the information is to be of longer lasting utility to the person. The extraction of information from SIS is accomplished by certain control processes which operate in STM. These control processes make up the activities we commonly refer to as "attending to" something. Thus, to extract information from SIS, we attend to part of the internal representation or "image" by the initiation of recoding processes. While the nature of all such control processes is not clear, one which is familiar is the transformation of sensory information into language structures; that is, we name certain features of the display. We may also add information from past experiences to part of the information in the "image" and construct a new image in STM which we "recognize" as a familiar thing or event. Thus if the following information is briefly stored in SIS:
| we may recode this as: | |
and label it a "square." Later, if asked what we saw, we would say "a square." The important point, however, is that some active attention to the information in SIS is necessary to extract the information in SIS for further cognitive processing in STM.