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.”

英国研究人员发现，短期视觉记忆比科学家想象的更加灵活。这种记忆并不像人们原来以为的那样，只局限于有限数目的物体，而是能够在整体景象中进行“分配”。让人感兴趣的物体会分配到更多的记忆，背景因素则分配到较少的记忆。

保罗?贝斯(Paul Bays)和马苏德?侯赛因(Masud Husain)要求伦敦大学学院(University College London)的志愿者观看一个电脑屏幕，屏幕上先是显示一些物体，几秒后变成空白，然后一个物体重新出现，但位置略有些变动。志愿者须说出这个物体向左还是向右移了。

随着屏幕上的物体增多，人们回忆物体原始位置的准确性出现递减。但在物体只有四、五件时，记忆的准确性并未大幅下降，这与普遍的观点不同。此项研究结果登载在8月8日的《科学》(Science)杂志上。

譬如，在观看奥运会接力赛跑时，我们可能将更多的记忆分配给我们所支持的那一队，场中关键物体——接力棒也会占据较大一部分记忆。虽然对于次要的细节，如运动员的服装和其他队的成员，记忆会比较不清晰，但在视觉上容易引起注意的细节，如运动员粉红色的头发，会吸引我们的注意。

“这涉及到将工作记忆分配给那些最重要的事物。”贝斯表示。“当某样东西吸引我们的注意时，我们将部分工作记忆转移到它上面，以备这件东西最终变得很重要。换句话说，它得到很大份额的记忆资源。”