Brigham and Women's Hospital and Harvard Medical School, Cambridge, MA 02139, USA.
J Cogn Neurosci. 2012 Feb;24(2):440-50. doi: 10.1162/jocn_a_00107. Epub 2011 Aug 3.
In everyday life, we often need to track several objects simultaneously, a task modeled in the laboratory using the multiple-object tracking (MOT) task [Pylyshyn, Z., & Storm, R. W. Tracking multiple independent targets: Evidence for a parallel tracking mechanism. Spatial Vision, 3, 179-197, 1988]. Unlike MOT, however, in life, the set of relevant targets tends to be fluid and change over time. Humans are quite adept at "juggling" targets in and out of the target set [Wolfe, J. M., Place, S. S., & Horowitz, T. S. Multiple object juggling: Changing what is tracked during extended MOT. Psychonomic Bulletin & Review, 14, 344-349, 2007]. Here, we measured the neural underpinnings of this process using electrophysiological methods. Vogel and colleagues [McCollough, A. W., Machizawa, M. G., & Vogel, E. K. Electrophysiological measures of maintaining representations in visual working memory. Cortex, 43, 77-94, 2007; Vogel, E. K., McCollough, A. W., & Machizawa, M. G. Neural measures reveal individual differences in controlling access to working memory. Nature, 438, 500-503, 2005; Vogel, E. K., & Machizawa, M. G. Neural activity predicts individual differences in visual working memory capacity. Nature, 428, 748-751, 2004] have shown that the amplitude of a sustained lateralized negativity, contralateral delay activity (CDA) indexes the number of items held in visual working memory. Drew and Vogel [Drew, T., & Vogel, E. K. Neural measures of individual differences in selecting and tracking multiple moving objects. Journal of Neuroscience, 28, 4183-4191, 2008] showed that the CDA also indexes the number of items being tracking a standard MOT task. In the current study, we set out to determine whether the CDA is a signal that merely represents the number of objects that are attended during a trial or a dynamic signal capable of reflecting on-line changes in tracking load during a single trial. By measuring the response to add or drop cues, we were able to observe dynamic changes in CDA amplitude. The CDA appears to rapidly represent the current number of objects being tracked. In addition, we were able to generate some initial estimates of the time course of this dynamic process.
在日常生活中，我们经常需要同时跟踪多个目标，这一任务在实验室中通过多目标跟踪（MOT）任务进行建模[Pylyshyn, Z., & Storm, R. W. Tracking multiple independent targets: Evidence for a parallel tracking mechanism. Spatial Vision, 3, 179-197, 1988]。然而，与 MOT 不同的是，在现实生活中，相关目标的集合往往是流动的，并随时间变化。人类非常擅长在目标集合中“抛接”目标[Wolfe, J. M., Place, S. S., & Horowitz, T. S. Multiple object juggling: Changing what is tracked during extended MOT. Psychonomic Bulletin & Review, 14, 344-349, 2007]。在这里，我们使用电生理方法测量了这个过程的神经基础。Vogel 及其同事[McCollough, A. W., Machizawa, M. G., & Vogel, E. K. Electrophysiological measures of maintaining representations in visual working memory. Cortex, 43, 77-94, 2007; Vogel, E. K., McCollough, A. W., & Machizawa, M. G. Neural measures reveal individual differences in controlling access to working memory. Nature, 438, 500-503, 2005; Vogel, E. K., & Machizawa, M. G. Neural activity predicts individual differences in visual working memory capacity. Nature, 428, 748-751, 2004]表明，持续的侧化负向波（contralateral delay activity，CDA）的幅度可以反映视觉工作记忆中存储的项目数量。Drew 和 Vogel[Drew, T., & Vogel, E. K. Neural measures of individual differences in selecting and tracking multiple moving objects. Journal of Neuroscience, 28, 4183-4191, 2008]表明，CDA 还可以反映在标准 MOT 任务中跟踪的项目数量。在本研究中，我们旨在确定 CDA 是仅仅代表试验期间被注意的目标数量的信号，还是能够反映单个试验期间跟踪负载变化的动态信号。通过测量添加或删除线索的反应，我们能够观察到 CDA 幅度的动态变化。CDA 似乎可以快速表示当前正在跟踪的目标数量。此外，我们还能够生成这个动态过程的时间过程的一些初步估计。
