New perceptual information quickly writes over (masks) the old, a process sometimes described as "interference." Attended information is not only protected from interference, it is processed by higher-level mechanisms that figure out what it means. For instance, information in the SIS might indicate a bright red object somewhere ahead. Attending to this information might reveal that there it is a stop sign. Once information is processed in this way, it can be encoded into the short-term store (STS). Usually, the STS is described as having a limited storage capacity (seven, plus or minus two items) that "decay" and become inaccessible after a relatively brief interval (estimates range from 12 to 30 seconds). In addition to decay, loss of information from the STS can occur by interference when new information displaces older information. Interference does not always cause information to be lost, but may instead produce memory retrieval errors in which one recalls information that is similar to but not identical with that which is needed. .
Information in short term memory tends to be encoded acoustically, although other codes, such as visual, can be used. Information can be maintained in STM for relatively long periods using maintenance rehearsal (MR), a term describing the act of mentally (subvocally) repeating the information to be maintained. In many cases, the reason one wishes to maintain information in the STS is to allow time for it to be encoded into the long-term store (LTS), and thus become more permanently available. However, maintenance rehearsal does not appear to be very .
efficient way to get the memory into long-term memory. Another memory maintenance technique, elaboration rehearsal (ER- deeper rehearsal involving meaning) seems to work better. .
Long-term memory can store a very large quantity of information and can maintain that information for very long periods of time.