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
Schizophrenic individuals have been known to have difficulty with inhibitory processes (Frith 1979)
Difficulties have been shown in ignoring irrelevant targets and in suppression of dominant responses to stimuli (Park et al. 2002; Weisbrod et al. 2000)
Relatively few studies done on inhibitory processes for memory in schizophrenics
Some similarity between hallucinations and intrusive thoughts (Badcock et al. 2007; Morrison 2001)
An increased amount of intrusive thought has been seen in patients who hallucinate, as compared to those who do not (Morrison, Baker 2000)
It has been proposed that hallucinations might be related to an inhibitory problem which would cause irrelevant memories or mental images to intrude into consciousness (Hemsley 2005).
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
The results of that study showed a schizophrenic participants performed significantly worse than the controls on measure of inhibition.
A correlation was found between the severity of hallucinations and demonstrated inhibitory deficits.
The results suggest that difficulties in mental inhibitions may be an underlying factory in hallucinations, and support the idea that hallucinations are related to intrusive thoughts.
Our authors wanted to explore this relationship between hallucinations and memory inhibition.
Two separate experiments were to be run.
The first was to replicate the findings of Waters et al. with a different but related task
The second was to explore whether the relationship found by Waters extended to working memory as well.
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.
Based on the typical results from this type of DF task we would expect to find a smaller DF effect in schizophrenic participants if inhibition of episodic memory is impaired in said participants.
The authors also expected to see an inverse correlation between the magnitude of the DF effect and the severity of hallucinations
It has been proposed that working memory (WM) deficit is a core dysfunction of schizophrenia (Goldman-Rakic, 1994).
Inhibitory processes are a vital part of a healthy WM, controlling access to it, and suppressing both distracting and irrelevant information.
Lustig et al. (2001) have suggested that differences in this process are responsible for individual differences in WM.
Little research has been done on these inhibitory processes in schizophrenic patients.
To test the inhibition in WM the authors used a task from Palladino et al (2001) in which participants are presented a list of words and asked to recall words that fit a given criterion.
For example in a list of animals, recall the small ones.
Intrusion errors can be considered indications of failure to inhibit.
If inhibition in WM functions similarly to other memory systems the authors expected to find more intrusions in schizophrenic participants than in controls.
37 outpatients from the rehabilitation unit of St. Cecilio Hospital in Granada, Spain.
All participants were diagnosed with Schizophrenia, Schizophreniform, or Schizoaffective Personality Disorders.
Diagnosis by hospital professionals
Also assessed using the Positive and Negative Syndrome Scale Test (PANSS)
All actively taking antipsychotic medications, in addition to neuroleptics (i.e. risperdone, clozapine, haloperidol)
Additionally, 20 healthy subjects were recruited from the families of employees at the hospital as a control group.
Subjects were divided into groups based on the presence and severity of hallucination symptoms (determined by PANSS).
Materials and Procedure
Four lists of words were generated, drawn from a previous study by Alameda and Cuetos (1995). Words were all of medium to high frequency and consisted of two to three syllables.
The experiment consisted of two tasks, a “Remember Task” and a “Forget Task”.
In the Remember task, participants were asked to learn randomly selected 10 word list.
They were then told that they would be shown another list of 10 words and that they would later be asked to recall words from both lists.
Prior to the recall participants were shown a random three digit number and asked to count backward by three for a period of one minute.
They were then presented with a piece of paper and asked to recall as many words as they could.
Materials and Procedure, Contd.
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.
In experiment 1 patients with and without hallucinations did not differ in their general recall, but in their pattern of recall
Patients with hallucinations showed no direct forget (DF) effect
35 outpatients from the Mental Health Day Centre at St. Agustín Hospital in Linares, Spain.
Selected using similar criteria to participants in Experiment 1.
These participants were also divided into two groups using scores from the PANSS test.
22 control participants were recruited from the local community and tested.
Materials and Procedure
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.
Materials and Procedure, Contd.
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.
Again, in experiment 2 patients with and without hallucinations did not differ in their general recall
Both groups showed deficits in WM, but only patients with hallucinations had a significantly higher number of WM intrusions than the control group
This finding suggests an acute inability of hallucinating patients to intentionally inhibit irrelevant or unnecessary memory representations in both episodic and working memories
General Discussion The results of this study supported the hypothesis that there is a relationship between hallucinations and inhibitory deficits in memory
A significant negative correlation was found between the severity of hallucinations and the magnitude of DF effect
Also, a significant positive correlation was found between severity of hallucinations and number of WM intrusions
There were no significant correlations between these inhibitory indexes and any other symptom or cluster of symptoms
The findings of this research supports the hypothesis that:
Hallucinations are uninhibited memories that intrude on a persons consciousness and then get attributed to external sources
Soriano et al. 2008 found inhibitory deficits in semantic memory for patients with formal thought disorders (FTD)
This may be building evidence that the various symptoms of schizophrenia are due to inhibitory deficits in different parts of memory
There were significantly more females in the control group that in either of the test groups
Also the authors admitted that both the test groups were predominantly male and they had no evidence to suggest that these findings would transfer to a primarily female group
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