Selective amnesia is a type of amnesia in which the sufferer loses only certain parts of their memory. Common elements that may be forgotten are relationships, where they live, and certain special abilities and talents (e.g., juggling, whistling, instrumental talents, etc.).
Factors
Emotional connotations
People may be more susceptible to hypnotic amnesia if the words they are asked to forget (or remember) have significant emotional connotations. Clemes (1964) was able to identify participants’ critical words—words that are linked with inner conflict—and neutral words—words that are not linked with inner conflict. He then placed the participants under hypnosis and listed nine critical words and nine neutral words. Participants were then instructed, under the influence of hypnosis, to forget half of the words they were given. They found that participants are more likely to forget critical words than neutral words. However, a replication study conducted by Stam and colleagues (1980) failed to replicate these results, suggesting that these conclusions may be invalid.
Familiarity
One's familiarity with a task influences how selective amnesia affects the subject's memories. To study this phenomenon, Lewis and colleagues (1969) taught rats a simple passive avoidance task, a fear-aggravated test used to evaluate learning and memory in rodent models. Some rats were allowed to familiarize themselves with the task while others were only allowed to experience the task once. After the rats had completed their task a pre-determined number of times, the experimenters administered an electroconvulsive shock to the rats meant to induce selective amnesia. These shocks varied in duration, lasting from zero to five seconds. The results of this study showed that only the rats unfamiliar with the task demonstrated selective amnesia 24 hours later. The rats that were familiar with the task seemed to display normal memory for the task. Thus, there might be a particular stage in the memory process that is vulnerable to selective amnesia. The current hypothesis is that this vulnerable stage is located during the transition from active memory to short term memory.
Types of memory
In an experiment investigating the functional role of the entorhinal cortex entorhinal cortex pars medialis in memory formation, Hölscher and Schmidt (1994) found that they could produce selective amnesia for specific types of memories by creating lesions that is painful in the brains of rats. In this experiment, both lesioned and non-lesioned rats were placed in an eight-armed maze with food in one of the arms. The rats had to orientate themselves to their surroundings to find the food. Rats with lesions showed significant memory problems, including memory failure and increased memory retrieval times, during trials in which they had to orient themselves using distal cues, the most distant cues. The researcher labeled these memory problems as selective amnesia. They also found that lesion-ed rats had a more difficult time finding the food when it was moved to a different arm. When the lesion-ed rats had to orient themselves in an egocentric egocentric test using proprioceptive proprioceptive cue, there were no detectable memory defects. This finding suggests that the type of memory a subject is trying to remember may influence the subject's susceptibility to selective amnesia.
Serial position
Watanabe and Yanagisawa (2000) found that the serial position effect may determine the task's susceptibility to selective amnesia. In their study, the researchers put mice through a maze with six ‘gates’. Each of these ‘gates’ had three doors, two of them locked and the third unlocked. They found that the mice were better at remembering the position of the unlocked gate if the gate's position was taught at the beginning or end of the trial. These findings provide support for the primacy effect and recency effect of serial positioning. Watanabe and Yanagisawa then took this a step further and injected some of the mice with high and low doses of scopolamine. At low doses, scopolamine intensified the primacy effect of serial positioning, and at high doses, scopolamine created major defects in general learning abilities. Their findings suggest that scopolamine may contain a property which plays a role in selective amnesia, specifically as it relates to serial positioning.