Intentional Inhibition in Memory and Hallucinations: Directed Forgetting and Updating M.F. Soriano, J.F. Jim énez, P. Román, and M.T. Bajo Presented by Ed Harris, Jordan McNeely, and Keith Pelstring
In 2003 Waters et al. performed a study in which control and schizophrenic participants were given the Hayling Sentence Completion Test (HSCT) and the Inhibition of Currently Irrelevant Memories task (ICIM).
HSCT--participants must complete a sentence with a single word unrelated to the rest of the sentence, which requires inhibition of semantic memory
ICIM--a series of pictures are shown to participants, some of which are repeated. Participants are instructed to note which pictures repeat. On subsequent trials, different pictures repeat and the participant is required to forget which pictures were repeated in the preceding trial
In order to reproduce the findings of Waters et al. a Directed Forgetting (DF) task was used
Typically participants are presented items that are cued to be remembered or forgotten, which can lead to confounds
To avoid these confounds the authors presented participants in the forget condition with 2 lists, one of which they were instructed to forget only after having studied it. The remember condition was presented with 2 lists, both of which they were instructed to recall.
For the Forget task, the same procedure was followed, except that between the two lists, participants were told that that the first list was only for practice reasons and instructed to forget the words on it. During the recall phase they were asked to recall as many words from both lists as possible.
The Experiment was carried out in two sessions, with each participant taking part first in a Remember task and later a Forget task.
A period of two weeks passed between the two sessions for each subject.
This was a mixed design study, with Group (patients with and without hallucinations, and controls) as a between-subjects factor, and Instructions (Remember or Forget) and List (First or Second) as within-subjects factors.
An adapted version of the WM task used by Palladino et al. (2001) was used.
The task was presented in Spanish, and shortened from 24 lists of 12 words to 4 lists of 12 words.
Lists of words consisted of both concrete and abstract nouns.
Two types of lists were used, representing two memory load conditions, high-load and low-load
Participants in the high-load condition were asked to recall five words, and Participants in the low-load condition were asked to recall three. Lists differed only in the instruction of how many words to recall.
Each participant was presented with two high and two low-load lists.
Each participant was presented with two practice lists before the actual task.
All lists were presented in random order, and contained two words which would have to be discarded because they were not the smallest on the list.
Participants were told that they would hear a list of words, and at the end they would have to recall a given number of the smallest animals or objects on the list.
The nature of the items on the list (animals or objects) and the number of items to be recalled (5 for high-load lists, 3 for low-load) was told to the participant immediately preceding the presentation of the list.
The words were presented via a tape recorder, and the responses were given orally, then recorded by an experimenter.
The dependent variables were the percentage of words recalled and the number of intrusions.
Given the findings of this study and study done by Soriano on patients with FTD’s the authors suggest further research to try and find more relationships between inhibitory impairments and other positive schizophrenic symptoms