Study Notes on Murdock's Research on Serial Position Effect

Serial Position Effect in Free Recall

Murdock (1962) PSYC 3451

Overview of the Serial Position Effect

  • The serial position effect is a psychological phenomenon that describes how the position of an item in a list affects its recall in memory tasks.

  • Murdock (1960) observed a linear relationship between presentation time (t) and the total amount of words recalled in a list, indicating significant findings about memory recall patterns.

Key Findings

  • Linear Relationship: Both presentation time and the total number of words recalled demonstrated a linear relationship, challenging the expectation of a non-linear serial position curve.

  • Goal of Study: Provide a quantitative description and an explanation for the serial position curve observed in free recall tasks.

Methodology

  • Procedure: Conducted a repeated study and free recall with a set duration of 1.5 minutes for subject recall involving 20 lists over 4 sessions.

  • Groups: Divided subjects into six groups based on different combinations of total length and presentation rates:

    • Group 1: 10 words at 2 seconds per word (10-2)

    • Group 2: 20 words at 1 second per word (20-1)

    • Group 3: 15 words at 2 seconds per word (15-2)

    • Group 4: 30 words at 1 second per word (30-1)

    • Group 5: 20 words at 2 seconds per word (20-2)

    • Group 6: 40 words at 1 second per word (40-1)

  • Presentation Time Matching:

    • Groups 10-2 and 20-1 both had a total presentation time of 20 seconds.

    • Groups 15-2 and 30-1 both had a total presentation time of 30 seconds.

    • Groups 20-2 and 40-1 both had a total presentation time of 40 seconds.

Inconsistencies in Past Research

  • Bousfield et al. (1958) found greater primacy effects; however, their study used longer presentation rates (2.5 seconds per word) and longer recall periods.

  • Bonus Experiment of 20-2.5:

    • Conducted a recall with a 4-minute period; results did not replicate Bousfield et al. (1958).

    • Possible reason for the discrepancy could be differences in instructions provided: “…in the order in which they occur in your memory.”

Theoretical Explanation

  • Interference in Memory:

    • Short-term proactive inhibition (PI) and retroactive inhibition (RI) can be observed in recall tasks.

    • Currently, PI and RI are understood as forms of interference, as they do not strictly imply inhibition.

  • Proactive Interference (PI):

    • More words presented before a target word lead to greater PI.

    • This effect is prominent after the first 3-4 serial positions and eventually levels off (asymptote).

    • This behavior correlates with the middle section of the serial position curve.

  • Retroactive Interference (RI):

    • The greater the number of words following a target word, the greater the RI.

    • RI effects can suggest an S-curve, aligning with recency effects observed in memorization tasks.

Conclusion

  • The research conducted by Murdock brings to light significant evidence pertaining to the sequential positioning effect in memory recall. Findings challenge previous assumptions about non-linear relationships and highlight the complexity of memory interference that influences recall ability.