2012年11月19日 星期一

研究:記憶非一成不變 易受情緒環境扭曲

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研究:記憶非一成不變 易受情緒環境扭曲
YOUR MEMORY IS LIKE THE TELEPHONE GAME
Each time you recall an event, your brain distorts it

http://www.northwestern.edu/newscenter/stories/2012/09/your-memory-is-like-the-telephone-game.html


美國西北大學一項最新研究,首次發現了人類記憶的秘密。他們表示,記憶總是經過一次又一次改編,這是回憶失真的原因。記憶並不是一成不變的,環境和時間改變,或者甚至當事人心情不同,就會整合出新的記憶內涵。

大部分人在小時候玩過電話遊戲 (telephone game),從首位開始傳出一句話,並依次小聲傳給下一位,直至所有的人都傳完,回到最後一位接聽的人,大聲說出聽到的內容。通常結果和原本開始傳話的內容,大相逕庭。其實,在每一個複述轉傳的過程,內容已大不同。

據美國醫學新聞網站 MedicalXpress.com 最新報導,根據一項美國西北大學醫學院最新研究,人腦記憶的開啟和電話遊戲非常相似。每次回憶過去的事件,大腦神經網絡運作都會改變,而本次的改變將影響下次回想同一事件的內容。

換言之,下一次回想時,所記得的內容,已不是原本的事件,而是上次回想所記得的內容。西北大學費因伯格醫學院博士後研究員唐娜 ˙ 布里奇 (Donna Bridge) 表示,記憶並不像單純的圖像,通過時光機器回放,便能重現原事件。而是由於先前多次的回憶,事件的圖像變得有些扭曲。布里奇是論文的主要作者,該研究最近 發表在《神經科學期刊》(Journal of Neuroscience) 上。

布里奇強調說:「事件的回想內容會變得不太精確,甚至部分內容,是完全錯誤的。該研究的結果對於刑事案件中,證人作證的有效性產生了影響。也許證人第 1 次回想的內容非常準確,因為這些記憶尚未被歪曲過。在那之後,所記憶的內容便值得商榷。」

研究方法與結果

在此研究中,試驗參與者連續 3 天,1 天 1 次,回想不同物品放置在格子中的原來位置。在第 1 天 2 小時的試驗裡,參與者看了電腦螢幕上一系列 180 個獨特物品的影像所放的位置。第 2 天第 2 次回憶試驗,參與者必須將一些物品由中央的位置移回至第 1 天看到的位置。第 3 天試驗,重複第 2 天的動作。試驗結果表明,第 2 天有經過測試移回物品的參與者,比當天沒有測試的對照組,回憶位置的正確率較高。不過,參與者從未找出物品完全正確的位置。重點是,第 3 天測試中,他們往往將物品放置在第 2 天放錯位置的附近,而不是放在第 1 天看到的正確位置。

布里奇解釋研究結果說,第 2 天不正確的位置記憶,影響了第 3 天回憶物品的位置。縱使有了第 2 天幫助回憶的檢索,第 2 天也無法強化原本正確位置的關聯性,反倒是改變了記憶內容,加強了第 2 天錯誤位置的記憶。

腦波活動證實實驗結果

布里奇的研究結果也符合了參與者腦神經所呈現的信號,也就是第 2 天的腦波活動。她觀察了第 2 天的腦神經信號,藉以預測參與者第 3 天物品的移回位置。

測量結果顯示,當參與者第 2 天回憶起物品的位置,一種特定的腦神經信號出現。當第 3 天物品被放置在靠近第 2 天回想時所放的位置,這個信號呈現更強反應。當信號顯現較弱,代表回憶物品的位置扭曲得較少。

布里奇最後說:「強烈的腦神經信號,代表新的記憶被置入。新形成的記憶內容遭扭曲,下次又再犯前次同樣的錯誤。

這項研究表明,人腦記憶的內容如何隨著時間的推移而改變,有時甚至會被扭曲。當回想發生很久以前的事件,比如小時候第 1 次上學的情景,實際上卻是回顧該事件一段時間之後的檢索內容,而不是原本事件本身了。


YOUR MEMORY IS LIKE THE TELEPHONE GAME
Each time you recall an event, your brain distorts it

September 19, 2012 | by Marla Paul

CHICAGO --- Remember the telephone game where people take turns whispering a message into the ear of the next person in line? By the time the last person speaks it out loud, the message has radically changed. It’s been altered with each retelling.
Turns out your memory is a lot like the telephone game, according to a new Northwestern Medicine study.
Every time you remember an event from the past, your brain networks change in ways that can alter the later recall of the event. Thus, the next time you remember it, you might recall not the original event but what you remembered the previous time. The Northwestern study is the first to show this.
“A memory is not simply an image produced by time traveling back to the original event -- it can be an image that is somewhat distorted because of the prior times you remembered it,” said Donna Bridge, a postdoctoral fellow at Northwestern University Feinberg School of Medicine and lead author of the paper on the study recently published in the Journal of Neuroscience. “Your memory of an event can grow less precise even to the point of being totally false with each retrieval.”
Bridge did the research while she was a doctoral student in lab of Ken Paller, a professor of psychology at Northwestern in the Weinberg College of Arts and Sciences.  
The findings have implications for witnesses giving testimony in criminal trials, Bridge noted.
“Maybe a witness remembers something fairly accurately the first time because his memories aren’t that distorted,” she said. “After that it keeps going downhill.”
The published study reports on Bridge’s work with 12 participants, but she has run several variations of the study with a total of 70 people. “Every single person has shown this effect,” she said. “It’s really huge.”
“When someone tells me they are sure they remember exactly the way something happened, I just laugh,” Bridge said.
The reason for the distortion, Bridge said, is the fact that human memories are always adapting.
“Memories aren’t static,” she noted. “If you remember something in the context of a new environment and time, or if you are even in a different mood, your memories might integrate the new information.”
For the study, people were asked to recall the location of objects on a grid in three sessions over three consecutive days. On the first day during a two-hour session, participants learned a series of 180 unique object-location associations on a computer screen. The next day in session two, participants were given a recall test in which they viewed a subset of those objects individually in a central location on the grid and were asked to move them to their original location. Then the following day in session three, participants returned for a final recall test.
The results showed improved recall accuracy on the final test for objects that were tested on day two compared to those not tested on day two. However, people never recalled exactly the right location. Most importantly, in session three they tended to place the object closer to the incorrect location they recalled during day two rather than the correct location from day one.
“Our findings show that incorrect recollection of the object’s location on day two influenced how people remembered the object’s location on day three,” Bridge explained. “Retrieving the memory didn’t simply reinforce the original association. Rather, it altered memory storage to reinforce the location that was recalled at session two.”
Bridge’s findings also were supported when she measured participants’ neural signals --the electrical activity of the brain -- during session two. She wanted to see if the neural signals during session two predicted anything about how people remembered the object’s location during session three.
The results revealed a particular electrical signal when people were recalling an object location during session two. This signal was greater when -- the next day -- the object was placed close to that location recalled during session two. When the electrical signal was weaker, recall of the object location was likely to be less distorted.
“The strong signal seems to indicate that a new memory was being laid down,” Bridge said, “and the new memory caused a bias to make the same mistake again.”
“This study shows how memories normally change over time, sometimes becoming distorted,” Paller noted. “When you think back to an event that happened to you long ago -- say your first day at school -- you actually may be recalling information you retrieved about that event at some later time, not the original event.”
The research was supported by National Science Foundation grant BCS1025697 and National Institute of Neurological Disorders and Stroke of the National Institutes of Health grant T32 NS047987.