Serial Position Effect (Glanzer & Cunitz, 1966)

Some of the strongest evidence for the multi-store model (Atkinson & Shiffrin, 1968) comes from serial position effect studies and studies of brain-damaged patients.

The serial position effect is the tendency to remember the first and last items in a series better than those in the middle. It is a form of cognitive bias that is thought to be due to how information is processed and stored in memory.

The tendency to recall earlier words is called the primacy effect; the tendency to recall later words is called the recency effect.

Murdock (1962)

Procedure

Murdock’s experiment involved a total of 103 participants, all of whom were students from an introductory psychology course. The participants were of both sexes and were fulfilling a course requirement by taking part in the study.

Murdock presented participants with lists of 10 to 40 words, one word at a time, at a rate of either one word per second or one word every two seconds.

Independent variables:

1. List length: The number of words in each list, which varied among 10, 15, 20, 30, and 40 words.
2. Presentation rate: The speed at which the words were presented, either 1 word per second or 1 word every 2 seconds.

Dependent variable:

1. Probability of recall: The likelihood that a word would be recalled, based on its serial position in the list. This was measured by the proportion of participants who correctly recalled each word at a given serial position

Detween Subjects Design

The participants were assigned to one of the six groups, each of which had a different combination of list length and presentation rate.

• Group 10-2 (10 words, 2 seconds/word): 18 participants
• Group 20-1 (20 words, 1 second/word): 16 participants
• Group 15-2 (15 words, 2 seconds/word): 19 participants
• Group 30-1 (30 words, 1 second/word): 19 participants
• Group 20-2 (20 words, 2 seconds/word): 15 participants
• Group 40-1 (40 words, 1 second/word): 16 participants

After the list was finished, participants were asked to recall as many words as they could in any order.

Results

Murdock found that the probability of recalling any word depended on its serial position in the list.

Words presented early in the list (primacy effect) and at the end of the list (recency effect) were more often recalled, while words in the middle were more frequently forgotten.

The recency effect extended over the last 8 serial positions and was present even in longer lists of up to 40 words.

Additionally, Murdock observed a flat middle section (asymptote) in the serial position curve, which was less pronounced in shorter lists.

The improved recall of words at the beginning of the list is called the primacy effect; that at the end of the list, the recency effect. This recency effect exists even when the list is lengthened to 40 words.

Conclusion

Separate Memory Stores

According to the multi-store model, when participants recall words from the beginning and end of the list, they are retrieving information from two separate memory stores: long-term memory for the primary information and short-term memory for the recent information.

The primacy effect occurs because participants have time to rehearse the first few words in the list, transferring them from short-term memory to long-term memory.

The recency effect occurs because the last few words in the list are still available in short-term memory, which is thought to have a capacity of around 7 items.

Words in the middle of the list are less likely to be recalled because they have been displaced from short-term memory by subsequent words, but not rehearsed enough to be transferred to long-term memory. This results in the asymptote, or flat middle section of the serial position curve.

Inhibition Effects

Glanzer and Cunitz (1966)

Procedure

The study involved two separate experiments (immediate vs delayed recall).

Participants were Army enlisted men (not randomly assigned). They recalled 20-word lists in Exp I and 15-word lists in Exp II.

Experiment I (Immediate Recall)

In Experiment I, presentation rate (1S/P, 2S, 3S) and repetition of words (1S/P, 2P, 3P) were manipulated to examine effects on long-term storage and the beginning of the serial position curve.

• Army enlisted men were presented with lists of 20 common monosyllabic nouns (e.g. pen, house, car) under different conditions:
  • Presentation rate: 1 sec/word (1S/P), 2 sec/word (2S), or 3 sec/word (3S)
  • Repetition: Each word presented once (1S/P), twice (2P), or thrice (3P)
• After each list, participants had 2 minutes to write down the words they recalled in any order.

Experiment II (Delayed Condition)

In Experiment II, delay between end of list and recall (0, 10, 30 sec) was varied to examine effects on short-term storage and the end of the serial position curve. During the delay, subjects counted out loud.

• Army enlisted men were shown fifteen 15-word lists. Each word was shown for 1 sec with 2 sec between words.
• After the last word of each list, a number from 0-9 was shown. If 0, participants immediately recalled the words. If another number, they counted aloud from that number for either 10 or 30 sec before recalling.
• Each delay condition (0, 10, 30 sec) was used for 5 lists per participant, in random order.

Results

Primacy Effect (Experiment I)

• In the first experiment, people were better at remembering words from the beginning of a list compared to words in the middle. This is called the primacy effect.
• When the words were shown for a longer time (2 or 3 seconds instead of 1 second), people remembered the words at the beginning and middle of the list better, but it didn’t help much for the last few words.
• Showing the words more than once didn’t really help people remember the words at the beginning of the list better than just showing them for a longer time.
• The researchers think that the primacy effect happens because people have time to store the first few words in their long-term memory, which is like a big mental library.

Recency Effect (Experiment II)

• In the second experiment, people initially remembered words from the end of the list better than words from the middle. This is called the recency effect.
• When people had to count numbers for 10 or 30 seconds before trying to remember the words, they had a harder time remembering the words at the end of the list. Counting for 30 seconds made the recency effect completely go away.
• Counting didn’t really affect how well people remembered words from the beginning or middle of the list.
• The researchers think the recency effect happens because the last few words are still in people’s short-term memory, which is like a small mental notepad that gets erased quickly unless you keep repeating the words to yourself or move them to your long-term memory.

Conclusion

• Dual storage mechanisms: The study provides evidence for the involvement of both long-term and short-term storage mechanisms in free recall tasks.
• Primacy effect and long-term storage: The primacy effect (better recall of early list items) is attributed to long-term storage. This is supported by Experiment I, which showed that increasing presentation rate, a variable thought to affect long-term storage, improved recall of early list positions.
• Recency effect and short-term storage: The recency effect (better recall of last list items) is attributed to short-term storage. Experiment II demonstrated that introducing a delay filled with a distracting task (counting) before recall diminished or eliminated the recency effect, suggesting that the last few words were held in a short-term store that decayed rapidly.
• Implications for memory strategies: The findings suggest that to improve memory for a list of items, one should: a. Repeat or spend more time on the items at the beginning of the list to facilitate long-term storage. b. If there is a delay between learning and recall, rehearse the items during the delay to prevent decay from short-term memory.

Strengths

1. The monosyllabic nouns (e.g. cat, ball, hat) used would have been chosen to be familiar to the participants and consistently easy to pronounce and recall. Using simple, high-frequency nouns helps isolate the effects of the independent variables (presentation rate, repetition, delay) on recall performance in different list positions.
2. The experiments systematically manipulated variables thought to affect long-term and short-term memory (presentation rate, repetition, and delay) and measured their impact on recall performance at different list positions.

Weaknesses

1. The double dissociation between variables affecting primacy (presentation rate) and recency (delay) provides strong evidence for distinct memory stores or processes underlying these effects, advancing our understanding of human memory.
2. Limited generalizability: The experiments used a specific population (Army enlisted men) and simple verbal materials (lists of common nouns), so the findings may not generalize to other populations, materials, or real-world memory situations.
3. The study did not examine how individual differences in cognitive abilities, strategies, or prior knowledge might influence the primacy and recency effects.
4. The use of only verbal materials (words) limits the generalizability of the findings to other types of information, such as visual or spatial memories.

References

Atkinson, R. C., & Shiffrin, R. M. (1968). Chapter: Human memory: A proposed system and its control processes. In Spence, K. W., & Spence, J. T. The psychology of learning and motivation (Volume 2). New York: Academic Press. pp. 89–195.

Glanzer, M., & Cunitz, A. R. (1966). Two storage mechanisms in free recall. Journal of Verbal Learning and Verbal behavior, 5(4), 351-360.

Murdock, B. B. (1962). The serial position effect of free recall. Journal of Experimental Psychology, 64(5), 482–488.