Psychological research has shown that memory is not a unitary construct. Instead, memory consists of a coordinated collection of processes and abilities that work together to enable individuals’ day-to-day functioning. Furthermore, one aspect of memory can be impaired while another remains intact. For that reason, psychologists do not rely on a single procedure for assessing memory. Many assessment measures exist, and commonly used assessment procedures contain multiple subcomponents, each aimed at assessing a particular type of memory. This entry reviews several types of memory and explains the different ways that they are assessed. At the end, it describes several full-length memory assessment measures.
Types of Memory
Often termed short-term memory, immediate memory refers to the ability to hold information in 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 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.
Long-Term Episodic Memory
The Ability to Form New Memories.
Long-term episodic memory refers to the ability to store particular pieces of information in memory for access at a later time, and to retrieve that information after hours, days, months, or even years have passed. Long-term and immediate memory represent two different types of abilities. Some neuropsychological patients have impaired long-term memory but normal immediate memory span, while others show the opposite pattern.
Disruption to the ability to form lasting memories is associated with damage to the hippocampal, medial temporal, and diencephalic regions of the brain. It can also be associated with frontal lobe damage. Patients with such damage tend to show anterograde amnesia (a marked deficit in the ability to form new long-term memories). Anterograde amnesia can be revealed on memory tests that involve a delay between the encoding and retrieval of information (so that the person cannot rely on simple memory span). An example is a list-learning situation in which there is a delay between the study list and the memory test. Therefore, many memory assessment tests contain delayed list-learning tasks.
The Ability to Access Established Memories.
Retrograde amnesia, a disruption of the ability to access already-formed long-term memories, can result from head injury. Memories that had been acquired during a short window of time prior to the head injury are commonly affected. However, access to more distant memories can be disrupted when a network of neurons that played a role in a well-established set of memories is damaged. Damage to this neural network can result in disruption of the ability to retrieve portions of one’s past. Tests for assessing retrograde amnesia often assess memory for commonly known information, such as memory for famous faces, famous events, or television shows from a particular era. An alternative assessment procedure involves obtaining personal information from friends and relatives and then interviewing the amnesic to see what information is still retained.
Long-Term Semantic Memory
Semantic memory refers to one’s general knowledge base, such as that an apple is a fruit or a hammer is a tool. Whereas episodic memories are linked to particular events in time, semantic memories appear to have been abstracted away from the particular episodes that led to their formation. For example, many people know state capitals, but few remember the act of learning them. The relation of general knowledge to specific experiences remains a controversial topic, because it is not always easy to make the distinction between semantic and episodic memory.
Disorders of semantic memory, commonly termed semantic dementia, are often category specific. For example, there are documented cases of patients having impaired knowledge of plants and animals, but intact knowledge of objects. In other instances individuals’ knowledge of objects is impaired, but their knowledge of plants and animals remains intact.
Whereas the aforementioned types of memory involve the ability to access information from the past, prospective memory refers to the ability to remember to do things in the future. Time-based prospective memory involves remembering to perform a task at a particular time in the future (e.g., remembering to make a phone call at 3:00 p.m.). In contrast, event-based prospective memory involves remembering to do something in response to a particular event (e.g., remembering to say “happy birthday” to a colleague when encountering her at work). This distinction has been incorporated into some assessment tests. For example, the Cambridge Behaviour Prospective Memory Test (CBPMT) contains four time-based and four event-based tasks.
Skill Learning and Implicit Memory
Implicit memory refers to memory performance on tasks that do not require awareness or conscious remembering. That is to say, people can demonstrate memory for an event without knowing it. An example would be if people received a list of words and later saw the stems of those words (such as drain and dr_), then were asked to complete the word stems. People often complete the stems to make words they saw earlier, instead of new words (such as drop to complete dr_). This demonstrates memory for the word list, even through participants may not be aware of what guided the word choice. People with anterograde amnesia (the inability to form new memories) can typically still form implicit memories, or learn new skills without being aware of it. There have been examples of anterograde amnesics even learning to play chess after acquiring the disorder.
Common Assessment Measures
The development of memory assessment measures has been driven not only by basic memory research but also by practical considerations. Tests cannot be too long, or patients may become fatigued or impatient. In addition, the abilities that the assessment measures should resemble those memory abilities that are relevant to a person’s day-to-day functioning. Memory assessments generally contain normative data in their manuals for use in evaluation. However, scores on memory assessments should be interpreted in light of such considerations as the person’s age, intelligence, and level of education. Also, depression can be a significant factor in reported memory problems. An important thing to keep in mind when interpreting scores on a memory assessment is that a wide range of responses can be considered normal, and a large number of variables can affect any one of the different types of memory. This section describes some commonly used memory assessment methods.
Questionnaires provide a simple means of assessing a person’s memory. A number of questionnaires have been developed for this purpose, many of which are aimed at assessing whether a person has memory problems that interfere with day-to-day functioning. Some examples are the Inventory of Memory Experiences, the Everyday Memory Questionnaire, and the Comprehensive Assessment of Prospective Memory (CAPM).
Memory Assessment Batteries
Individuals with memory impairment are not always aware of their impairments and subjective reports by patients and their families are subject to biases. For those reasons, it may be preferable to assess memory by testing memory performance itself.
The Wechsler Memory Scale—Third Edition (WMS-III).
The WMS-III is one of the most widely used memory assessment procedures. The WMS-III consists of eight primary indexes that describe immediate memory, general memory, and working memory in visual and auditory forms. Each index comprises several subtests. Including the optional subtests, there are 11 subtests in total. They are logical memory, verbal paired associates, letter-number sequencing, faces, family pictures, spatial span, information and orientation, word lists, mental control, digit span, and visual reproducing. It takes around 30 minutes to administer, with an extra 20 minutes for the optional subtests. The WMS-III is the third edition, with the original version first appearing in 1945. It is considered by many to be the best memory assessment available.
Rivermead Behavioural Memory Test (RBMT).
This test was developed to assess the types of memory that are most relevant to day-to-day functioning. It includes sub-tests that assess name recall, remembering the locations of hidden objects, prospective memory, picture recognition, recall of a story (immediate and delayed), recognition of unfamiliar faces, recall of a route (immediate and delayed), and remembering a passage. The test requires approximately 25 minutes to administer, and scores on the test correlate well with the number of patient memory lapses observed in clinical settings. The RBMT has four alternative forms for use in longitudinal testing.
Other Memory Assessment Measures.
Other commonly used memory assessment measures include the Recognition Memory Test (RMT) and the Memory Assessment Scale (MAS). The RMT takes approximately 15 minutes to administer and contains two subtests that assess recognition of words and recognition of faces. Each subtest involves presentation of a study list followed by a recognition test that requires the discrimination of studied and nonstudied items. The MAS contains 12 subtests: list learning, prose memory, list recall, verbal span, visual span, visual recognition, visual reproduction, names-faces, delayed recall, delayed prose memory, delayed visual recognition, and delayed names-faces recall. The MAS requires approximately an hour to administer.
The memory assessment procedures described here, like all memory assessment procedures, require graduate-level or professional training to administer and interpret. Most assessments come with manuals that contain extensive instructions on how to administer the test, as well as normative data for the interpretation of performance. Selecting the appropriate test for a given situation is a matter of the examiner’s experience and personal preference.
Factors Influencing Assessment
Memory research has influenced the development of present-day memory assessment techniques, but not all forms of memory are assessed in the commonly used batteries. For example, it is common to assess short-term memory span and delayed episodic memory ability. It is less common to assess implicit memory. Two factors drive such priorities. First, time is of the essence when administering tests. Second, therapists are most concerned with assessing the forms of memory that, when damaged, interfere most with the person’s ability to continue in a career or resume daily living. When a person’s memory skills have been impaired, psychologists consider how the person might capitalize on spared forms of memory for rehabilitation. For example, psychologists have been successful in training people with anterograde amnesia to use skills that draw upon implicit memory.
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