Chakravarthi Ramakrishna, VanRullen Rufin
Université de Toulouse, CerCo, UPS, France.
J Vis. 2011 Apr 20;11(4):12. doi: 10.1167/11.4.12.
Analyzing a scene requires shifting attention from object to object. Although several studies have attempted to determine the speed of these attentional shifts, there are large discrepancies in their estimates. Here, we adapt a method pioneered by T. A. Carlson, H. Hogendoorn, and F. A. J. Verstraten (2006) that directly measures pure attentional shift times. We also test if attentional shifts can be handled in parallel by the independent resources available in the two cortical hemispheres. We present 10 "clocks," with single revolving hands, in a ring around fixation. Observers are asked to report the hand position on one of the clocks at the onset of a transient cue. The delay between the reported time and the veridical time at cue onset can be used to infer processing and attentional shift times. With this setup, we use a novel subtraction method that utilizes different combinations of exogenous and endogenous cues to determine shift times for both types of attention. In one experiment, subjects shift attention to an exogenously cued clock (baseline condition) in one block, and in other blocks, subjects perform one further endogenous shift to a nearby clock (test condition). In another experiment, attention is endogenously cued to one clock (baseline condition), and on other trials, an exogenous cue further shifts attention to a nearby clock (test condition). Subtracting report delays in the baseline condition from those obtained in the test condition allows us to isolate genuine attentional shift times. In agreement with previous studies, our results reveal that endogenous attention is much slower than exogenous attention (endogenous: 250 ms; exogenous: 100 ms). Surprisingly, the dependence of shift time on distance is minimal for exogenous attention, whereas it is steep for endogenous attention. In the final experiment, we find that endogenous shifts are faster across hemifields than within a hemifield suggesting that the two hemispheres can simultaneously process at least parts of these shifts.
分析一个场景需要将注意力从一个物体转移到另一个物体上。尽管有几项研究试图确定这些注意力转移的速度，但它们的估计存在很大差异。在这里，我们采用了由T. A. 卡尔森、H. 霍根多恩和F. A. J. 弗斯特拉滕（2006年）首创的一种方法，该方法直接测量纯粹的注意力转移时间。我们还测试了两个大脑半球中可用的独立资源是否可以并行处理注意力转移。我们在围绕注视点的环形中呈现10个“时钟”，每个时钟只有一根旋转的指针。要求观察者在短暂提示出现时报告其中一个时钟上指针的位置。报告时间与提示开始时的实际时间之间的延迟可用于推断处理时间和注意力转移时间。通过这种设置，我们使用了一种新颖的减法方法，该方法利用外源性和内源性提示的不同组合来确定两种注意力类型的转移时间。在一个实验中，受试者在一个区块中将注意力转移到一个由外源性提示的时钟上（基线条件），而在其他区块中，受试者再进行一次内源性转移到附近的一个时钟上（测试条件）。在另一个实验中，注意力被内源性提示到一个时钟上（基线条件），而在其他试验中，一个外源性提示将注意力进一步转移到附近的一个时钟上（测试条件）。从测试条件下获得的报告延迟中减去基线条件下的报告延迟，使我们能够分离出真正的注意力转移时间。与先前的研究一致，我们的结果表明内源性注意力比外源性注意力慢得多（内源性：250毫秒；外源性：100毫秒）。令人惊讶的是，对于外源性注意力，转移时间对距离的依赖性最小，而对于内源性注意力则很陡峭。在最后一个实验中，我们发现内源性转移在跨半球时比在一个半球内更快，这表明两个半球可以同时处理这些转移的至少一部分。
