Johns Hopkins University, Department of Psychological and Brain Sciences, 3400 N Charles St., Baltimore, MD 21218, United States.
Cogn Psychol. 2013 Jun;66(4):380-404. doi: 10.1016/j.cogpsych.2013.05.001. Epub 2013 Jun 12.
Infants have a bandwidth-limited object working memory (WM) that can both individuate and identify objects in a scene, (answering 'how many?' or 'what?', respectively). Studies of infants' WM for objects have typically looked for limits on either 'how many' or 'what', yielding different estimates of infant capacity. Infants can keep track of about three individuals (regardless of identity), but appear to be much more limited in the number of specific identities they can recall. Why are the limits on 'how many' and 'what' different? Are the limits entirely separate, do they interact, or are they simply two different aspects of the same underlying limit? We sought to unravel these limits in a series of experiments which tested 9- and 12-month-olds' WM for object identities under varying degrees of difficulty. In a violation-of-expectation looking-time task, we hid objects one at a time behind separate screens, and then probed infants' WM for the shape identity of the penultimate object in the sequence. We manipulated the difficulty of the task by varying both the number of objects in hiding locations and the number of means by which infants could detect a shape change to the probed object. We found that 9-month-olds' WM for identities was limited by the number of hiding locations: when the probed object was one of two objects hidden (one in each of two locations), 9-month-olds succeeded, and they did so even though they were given only one means to detect the change. However, when the probed object was one of three objects hidden (one in each of three locations), they failed, even when they were given two means to detect the shape change. Twelve-month-olds, by contrast, succeeded at the most difficult task level. Results show that WM for 'how many' and for 'what' are not entirely separate. Individuated objects are tracked relatively cheaply. Maintaining bindings between indexed objects and identifying featural information incurs a greater attentional/memory cost. This cost reduces with development. We conclude that infant WM supports a small number of featureless object representations that index the current locations of objects. These can have featural information bound to them, but only at substantial cost.
婴儿的工作记忆（WM）带宽有限，可以在场景中分别识别和识别物体（分别回答“有多少个？”或“是什么？”）。对婴儿 WM 进行物体研究的典型方法是分别限制“多少个”或“什么”，从而对婴儿的能力做出不同的估计。婴儿可以跟踪大约三个个体（无论身份如何），但在他们可以回忆的特定身份数量上似乎受到很大限制。为什么“多少个”和“什么”的限制不同？限制是完全分开的，它们相互作用，还是它们只是同一潜在限制的两个不同方面？我们试图在一系列实验中解开这些限制，这些实验在不同难度级别下测试了 9 个月和 12 个月大的婴儿对物体身份的 WM。在违反预期的注视时间任务中，我们一次将一个物体藏在单独的屏幕后面，然后探测婴儿对序列中倒数第二个物体形状身份的 WM。我们通过改变隐藏位置的物体数量和婴儿检测探测物体形状变化的方式数量来改变任务的难度。我们发现，9 个月大的婴儿的身份 WM 受到隐藏位置数量的限制：当探测物体是隐藏在两个物体之一（两个位置中的一个）时，9 个月大的婴儿成功了，即使他们只有一种方法来检测到变化。然而，当探测物体是隐藏在三个物体之一（三个位置中的一个）时，他们失败了，即使他们有两种方法来检测形状变化。相比之下，12 个月大的婴儿在最困难的任务水平上取得了成功。结果表明，“多少个”和“什么”的 WM 并非完全分开。个体化的物体相对便宜地被跟踪。维护索引对象之间的绑定并识别特征信息会产生更大的注意力/记忆成本。这种成本随着发展而降低。我们得出的结论是，婴儿 WM 支持少量无特征的对象表示，这些表示索引对象的当前位置。这些可以具有绑定的特征信息，但代价很高。
