Memory, Assessment of

Immediate Memory

Often termed short-term memory, immediate memory refers to the ability to hold information in [Page 687]consciousness. This ability is demonstrated when one remembers a phone number long enough to make a call. Immediate memory is distinct from long-term memory, which is the ability to store information for later use, often over extremely long periods such as weeks, months, or years.

The earliest known assessment of immediate memory is the “memory span test” developed in 1887. In this test, a person is given a sequence of items (such as digits) to report in the order in which they were presented. The sequences begin small (e.g., 3-8-4) and are increased in size until they reach a length that consistently exceeds the person's reporting capacity. The maximum length that a person can consistently report is the person's memory span. A version of this task, the digit span task, is a component of many present-day memory assessment batteries such as the Wechsler scale (described below).

Working Memory

Working memory refers to the ability to actively manipulate information in immediate memory. It is possible to think of immediate memory as a component of working memory. For example, one might hold a digit sequence in immediate memory while performing computations on it. Some psychologists make the distinction between simple memory span tasks (e.g., the digit span task) and complex memory span tasks. Simple memory span tasks are thought to tap a person's immediate holding capacity, while complex memory span tasks are thought to tap a person's higher-order abilities. A complex memory span task involves a simple retention component (e.g., holding a sequence of items in immediate memory) as well as active manipulation (e.g., performing arithmetic on numbers preceding each item in the sequence). Examples of complex span tasks include the reading span, in which people read lists of sentences and are told to remember the last word of each sentence. Later, they are told to repeat all of the “last” words in the right order.

There are verbal and visual forms of simple memory span, each involving different parts of the brain. Verbal memory span involves maintaining verbal information, such as sequences of letters or digits; visual memory span involves maintaining visual information, such as mental pictures. Visual analogs to simple verbal memory span tasks (e.g., the digit span task) include the Corsi Block Test, in which nine small cubes are arranged on a table and an experimenter taps them at the rate of one a second. This is done several times, with different orders and different lengths of sequences. Participants are asked to point to the same blocks in the same order, and this is a measure of their visual memory span. The procedure can have several variations, in which more or fewer blocks are used, or placed in different positions.

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