52 Forgetting and Memory Errors
Learning Objectives
By the end of this section, you will be able to:
- Compare and contrast different types of amnesia
- Discuss factors that affect the reliability of eyewitness testimony
- Discuss encoding failure
- Discuss the various memory errors
- Compare and contrast the different types of interference
“I’ve a grand memory for forgetting,” quipped author Robert Louis Stevenson. Forgetting refers to loss of information from long-term memory. In 1885, German psychologist Hermann Ebbinghaus studied forgetting by memorizing lists of nonsense syllables and measuring how many words he remembered when he attempted to relearn each list. He compared memory performance over different delay periods, from 20 minutes to 30 days later. The result is his famous forgetting curve (Figure M.14) showing that information fades with the passage of time. An average person will lose 50% of the memorized information after 20 minutes and 70% after 24 hours (Ebbinghaus, 1885-1964). Memory for new information decays quickly and then eventually levels out. But why do we forget? To answer this question, we will look at several perspectives on forgetting.
Schacter and the Seven Sins of Memory
There are many theories explaining different types of memory, but there aren’t as many theories about types of forgetting. Memory researcher Daniel Schacter attempted to organize memory errors into a unified framework in his book, The Seven Sins of Memory (2001). Schacter presents these as a list of seven “sins,” falling into one of two categories: errors of omission, involving failures of recall, and errors of commission, where recall is distorted or unwanted (Table M.1).
| Table M.1 Schacter’s Seven Sins of Memory | |||
|---|---|---|---|
| Sin | Type | Description | Example |
| Transience | Forgetting | Accessibility of memory decreases over time | Forget events that occurred long ago |
| absentmindedness | Forgetting | Forgetting caused by lapses in attention | Forget where your phone is |
| Blocking | Forgetting | Accessibility of information is temporarily blocked | Tip of the tongue |
| Misattribution | Distortion | Source of memory is confused | Recalling a dream memory as a waking memory |
| Suggestibility | Distortion | False memories | Result from leading questions |
| Bias | Distortion | Memories distorted by current belief system | Align memories to current beliefs |
| Persistence | Intrusion | Inability to forget undesirable memories | Traumatic events |
Let’s look at the first sin: transience, which means that memories can fade over time, as demonstrated by Ebbinghaus’ forgetting curve for nonsense syllables (Figure M.13). Information that’s stored but not used is vulnerable to this type of forgetting. Consider this real life example: Nathan’s English teacher has assigned students to read the novel To Kill a Mockingbird. He tells his mom he has to read this book for class and she says, “Oh, I loved that book!” Nathan asks her what the