Our short-term visual memory is more flexible than scientists had imagined, UK researchers have discovered. It is not restricted to a limited number of objects, as previously thought, but can be “shared out” across a whole image, with more memory allocated to objects of interest and less to background detail.

Paul Bays and Masud Husain asked volunteers at University College London to look at a computer screen featuring a number of objects. After a few seconds it went blank and one object reappeared in a slightly different place. The volunteer then had to say whether it had moved to the right or left.

The accuracy with which people could recall the object's original position decreased gradually as the scene became more crowded, but there was no sharp drop in performance at a limit of four or five objects as prevailing wisdom would suggest. The study appears on the 8 Aug in Science.

When watching an Olympic relay race, for example, we might allocate more memory to the faces of the team we are supporting but also allocate a significant proportion to the baton, a key object in the scene. While less important details, such as the athletes' clothes and members of the other teams, will be recalled less clearly, visually arresting details – such as a runner's pink hair – will catch our attention and will be allocated more memory, too.

“It's all about allocating working memory to the things that are most important,” says Dr Bays. “When something grabs our attention, we divert some of our working memory to it in case it turns out to be important. In other words, it gets the lion's share of memory resources.”

英國研究人員發現，短期視覺記憶比科學家想象的更加靈活。這種記憶并不像人們原來以為的那樣，只局限于有限數目的物體，而是能夠在整體景象中進行“分配”。讓人感興趣的物體會分配到更多的記憶，背景因素則分配到較少的記憶。

保羅•貝斯(Paul Bays)和馬蘇德•侯賽因(Masud Husain)要求倫敦大學學院(University College London)的志愿者觀看一個電腦屏幕，屏幕上先是顯示一些物體，幾秒后變成空白，然后一個物體重新出現，但位置略有些變動。志愿者須說出這個物體向左還是向右移了。

隨著屏幕上的物體增多，人們回憶物體原始位置的準確性出現遞減。但在物體只有四、五件時，記憶的準確性并未大幅下降，這與普遍的觀點不同。此項研究結果登載在8月8日的《科學》(Science)雜志上。

譬如，在觀看奧運會接力賽跑時，我們可能將更多的記憶分配給我們所支持的那一隊，場中關鍵物體——接力棒也會占據較大一部分記憶。雖然對于次要的細節，如運動員的服裝和其他隊的成員，記憶會比較不清晰，但在視覺上容易引起注意的細節，如運動員粉紅色的頭發，會吸引我們的注意。

“這涉及到將工作記憶分配給那些最重要的事物。”貝斯表示。“當某樣東西吸引我們的注意時，我們將部分工作記憶轉移到它上面，以備這件東西最終變得很重要。換句話說，它得到很大份額的記憶資源。”