When people are asked to memorize a long list of words or numbers, they often find that they have an easier time remembering some items in the sequence than other items in the same sequence. For example, let’s say that you are asked to memorize the following word list:

hive   ice   lake   oar   year   care   yarn   air   axe   rod   bear   week   door

Let's say that someone reads the list out loud to you and, as soon as he's done, you quickly write down all the words you can remember. It is likely that the position of an item in the list will affect your memory for that item — a phenomenon known as the serial-position effect (Murdock, 1962).

In general, people tend to remember best the first few items in a list as well as the last item or two; but they forget most of the items in the middle of the list. In other words, there are two serial-position effects (see Figure 1):

• the primacy effect, which is the tendency to remember well the first items in a list;
• the recency effect, which is the tendency to remember well the last items in a list.

Figure 1. The two seerial-position effects (the graph can be found here)

Can you think of a good explanation for each of the serial-position effects? Cognitive psychologists have explained them by suggesting that they represent the workings of two memory subsystems (Glanzer & Cunitz, 1966): one dedicated to remembering information over a very short period of time (short-term memory) and another for remembering onformation over longer periods of time (long-term memory). This interpretation led to efforts to develop models of how the mind remembers and forgets information.

The most popular model of memory was developed by Atkinson and Shiffrin (1968). They developed what has been called the standard (or modal) model of memory (SMM). The SMM conceives of memory as consisting of a system subdivided into three interacting subsystems: sensory memory, short-term memory, and long-term memory:

• Sensory memory is a subsystem that maintains a copy of a perception in mind for a very brief period of time — a fraction of a second for visual sensations and up to about two seconds for auditory sensations.
• Short-term memory is a subsystem that maintains a very limited amount of encoded information in mind for up to about fifteen seconds.
• Long-term memory is a subsystem that maintains an unlimited amount of information in mind for minutes, hours, days, weeks, months, or years.

According to the SMM, when a word list is read aloud, the sounds of the words are held briefly in sensory memory, which comprises five sensory "registers" — one for each of the five major senses. A sensory memory moves into short-term memory if it is attended to, and the information is further encoded there. A short-term memory may move into long-term memory if it is encoded in certain ways (for example, by repeating a word over and over). Once in long-term memory, a memorized word may be held anywhere from minutes to years (this depends on many factors, some of which will be described later in Section 6).

The SMM can explain the two serial-position effects in the following way. The first few items in a word list are well remembered (the primacy effect) because these are the items most likely to become long-term memories: individuals have time to repeat them over and over (or to use some other strategy for memorizing words), which causes them to be transferred to the long-term subsystem. The last couple of items in the word list are well remembered (the recency effect) because they are still in short-term memory. The words in the middle of the list are not remembered well because they no longer are in short-term memory and also are less likely to have been transferred to long-term memory.

The flow of information through the three memory subsystems of the SMM is illustrated in Figure 2.

Figure 2. A sketch of the standard model of memory

Study Questions for Section 6-5

1. What are the two serial-position effects?
2. How would you define the primacy effect in your own words?
3. How would you define the recency effect in your own words?
4. What is the standard model of memory (SMM)?
5. How are the three subsystems making up the SSM similar to and different from each other?

Go to Quiz 6-5 questions

Go to Readings Section 6-6