心理 101 王雅慧 f ollowing the c rowd : b rain s ubstrates of l ong -t erm m emory c onformity
TRANSCRIPT
INTRODUCTION
影片
http://www.youtube.com/watch?v=bDu-2UosnEQ&hd=1
INTRODUCTION
Our memories are often inaccurate.
Memory conformity : Ubiquitous sources of false recollection are social pressure and interpersonal influence.
Although these social influences on memory have been extensively demonstrated , the underlying neurobiology of this process is unknown.
CONFORMITY( 從眾 )
Private Conformity ( 私下從眾 )
an individual’s recollection may genuinely be altered by social influence, resulting in long-lasting, persistent memory errors ( 持久性的記憶錯誤 ).
Public Conformity ( 公開從眾 )
individuals may choose to outwardly comply, providing an account that fits that of others, but inwardly maintain certitude in their own original memory, resulting in transient memory error( 短暫性的記憶錯誤 ).
CONFORMITY( 從眾 )
These processes are probably mediated by distinct
activation in interconnected brain circuits previously found
to be active in mnemonic functions and social cognition
(such as the hippocampal complex, amygdala, and frontal
regions)
METHOD - BEHAVIOR
Participant
Thirty right handed subjects (12F,18M)
Stimuli
40 minute eyewitness styled documentary
Procedure
Encoding phase
Memory Test 1 (day3)
Memory Test 2 : Manipulation phase (day7)
Memory Test 3 (day14)
METHOD - BEHAVIOR
Procedure
Encoding phase
viewed an eyewitness-style documentary movie on a large screen in groups of five.
Memory Test 1 (day3)
a memory test:400 questions, two-forced choice
rated how confidence they were after memory test.
assess the participants’ baseline accuracy and confidence.
METHOD - BEHAVIOR
Procedure
Memory Test 2:Manipulation phase (day7)
performed a memory test while in an fMRI scanner
The questions were identical to those in Test 1.
Before answering the question, participants were presented with answers they were led to believe were given by their four fellow co-observers
co-observer’s photo and answer
METHOD - BEHAVIOR
Procedure
Memory Test 2:Manipulation phase (day7) (cont.)
Three Conditions
Manipulation
the answers provided by the four co-observes were all false.(80 questions)
No- Manipulation
the letter X was presented instead of the co-observers’ answers (25 questions).
Credibility
to prevent the answers from fabricating because of suspicion.
METHOD - BEHAVIOR
Procedure
Memory Test 3 (day14)
were informed that the answers given by the co-observers during the previous fMRI session were in fact determined randomly.
after informing , the participants were then requested to complete the memory test in scanner again.
RESULT-BEHAVIOR
Behavioral data revealed that manipulation induced memory errors.
Participants conformed to the majority opinion.
Not due to forgetting.
Lower error rate in no-manipulation conditions.
RESULT-BEHAVIOR
Social influence was removed (test 3) participants maintained erroneous answers
in 40.8% of the previously conformed trials (persistent errors).
participants reverted to their original correct answer in 59.2 % of the previously conformed trials (transient errors)
RESULT-BEHAVIOR
Confidence ratings
No difference either before or
after the manipulation stage.
(persistent and transient errors)
During the manipulation stage,
confidence ratings in transient
errors were significantly lower
than in persistent errors .
RESULT
Regions of interest (ROIs)
A-priori anatomical ROIs
Memory encoding and maintenance
bilateral anterior hippocampus
bilateral posterior hippocampus
bilateral parahippocampal gyrus
social-emotional processing
bilateral amygdala
RESULT
The BOLD (Blood Oxygenation Level Dependent) signal :
persistent errors > transient errors or nonconformity (In all regions
except for the left posterior hippocampus)
No significant difference was found between transient
error and nonconformity trials
BOLD
RESULT
Whole-brain exploratory analysis
persistent errors > transient errors greater activity in four regions, all in medial temporal lobe.
left amygdala
right hippocampus
right parahippocampal gyrus (PHG)
a region bordering the left PHG and occipital cortex
transient errors > persistent errors
enhanced activation was in the bilateral dorsal anterior cingulate cortex
RESULT
Amygdala
plays a key role in social and emotional processing and modulates memory related hippocampal activity.
rich anatomical connections with the hippocampal complex and with neocortical areas.
A striking activation was found in the left amygdala.
Heightened activation in the amygdala was not due to heightened emotional arousal, seemed specific to socially induced memory change.
RESULT
Psychophysiological interaction(PPI)
A method for finding out whether the correlation in activity between two distant brain areas is different in different psychological contexts.
This analysis showed heightened functional connectivity between the left amygdala and bilateral anterior hippocampus (ROIs), during trials that subsequently resulted in persistent memory errors as opposed to transient errors and nonconformity.
RESULT-BRAIN IMAGE
Information was presented(manipulation relative to no-manipulation conditions)
Frontal regions : bilateral inferior frontal gyrus,dorsal ACC, dorsal medial pre-frontal cortex 。
occipital cortex
Further analysis of brain activity in these regions suggests that they are involved in non-mnemonic processes, such as conflict monitoring in the face of competing memories .
RESULT
Were our findings driven merely by the presentation of additional information regardless of social context?
Control Study : Non-social
information → four different computer algorithms.
Behavior (Conformity): Social manipulation > non-social > no-manipulation
Brain image : Bilateral amygdala: greater activation in the social
manipulation, but not in the nonsocial manipulation.
→enhanced activity in these regions is related specifically to
socially induced persistent memory errors.
RESULT
Brain image(cont.) : Right anterior, posterior hippocampus, left PHG: No difference in any
manipulation type.
→long lasting memory errors irrespective of the medium by which
information was conveyed.
left amygdala, bilateral anterior hippocampus : a significant interaction.
→ a pattern specific to the social manipulation
Heightened amygdala activation and enhanced connectivity with the hippocampus are specific to socially induced memory changes.
Hippocampal complex activation differentiates between persistent and transient errors regardless of the source of influence.
DISSCUSSON-1
Results indicate that memory is highly susceptible to
alteration due to social influence, creating both
transient and persistent errors.
A mechanism by which social influence produces long-
lasting alterations in memory.
The critical role of the amygdala in mediating this
influence.
DISSCUSSON-2
Heightened activation in the hippocampal complex
was seen when false information induced a long-
lasting change in the participants’ memories
regardless of social context.
The hippocampal complex activation may represent a
process of reconsolidation or encoding of new stable
representations