Coding, Capacity, and duration of memory

• Baddeley investigated coding in STM and LTM. After immediate recall, acoustically similar words did worse - so STM is acoustic. Recall after 20 minutes worse with semantically dissimilar words - LTM is semantic.
• Jacobs studied capacity of STM. Digit span - researcher reads four digits and increases untill the ppts cannot recall the order correctly. Average was 9 numbers and 7 letters.
• Miller also studied the capacity of STM. He noted that everyday things often happpen in sevens, ex. 7 sins, 7 days of the week, etc. The span of STM is roughly 7 plus or minus 2 items. Can be improved by chunking.
• Peterson and Peterson looked into the duration of STM. 24 students given consonant syllable (ex. YCG) and a 3 digit number to count backwards in multiples of 3 seconds. Students recalled roughly 80% of the syllables correctly w a 3 second interval. Recall after 18s fell to 3%. Duration of STM w/out rehearsal is 18-30 seconds.
• Bahrick et al. studied the duration of LTM. He tested 392 Americans aged between 17 and 74.

  1. Recognition test: 50 photos from highschool yearbook
  2. Free recall tests: ppts listed names of graduating class -ppts tested 48 years after graduation were 70% accurate in photo recognition, free recall was less accurate.
• Limitation of Baddeley's study - words used had no personal meaning to participants. when processing meaningful info people may use semantic coding even for STM. Could mean that results of the study have limited application; we should be cautious about generalising the findings to different kinds of memory task.
• Limitation of Jacobs' study on capaticy of STM - early psych research tended to lack control of extraneous variables. Ex. some participants may have been distracted while they were being tested so they didn't perform as well at they might. Would mean that the results found may not be valid as confounding variables weren't controlled. Other research does validate findings.
• Strength of Bahrick et al.'s study on duration of LTM - used meaningful memories. When lab studies with meaningless pictures were remembered, recall rates were lower. But confounding variables were not controlled, for example participants may have looked at their yearbooks prior to the study.