Berryhill Marian E, Hughes Howard C
Dartmouth College, Hanover, New Hampshire, USA.
Atten Percept Psychophys. 2009 Apr;71(3):503-14. doi: 10.3758/APP.71.3.503.
Flexible, context-dependent linkages between stimulus and response are fundamental to adaptive behavior. In the present article, we evaluate the limits of this flexibility by exploring the asymptotic efficiency of people's ability to switch between two different sensorimotor mappings. Two stimulus-response (S-R) mappings were learned, either both on the same hand (unimanual condition) or one mapping per hand (intermanual condition). The S-R mappings presented bivalent stimuli and employed the same response keys. A novel training regimen successfully reduced task-switch costs to approximately 20 msec, suggesting that residual switch costs cannot be eliminated. These costs cannot be entirely attributed to the cognitive control process of task-set reconfiguration, because they are observed over cued switch intervals of several seconds. Two additional issues in motor learning were addressed: the single or dual loci of manual motor control and the coordinate system of task representation. First, the results favored the notion of independent controllers for each hand instead of a single dominant controller, since intermanual performance was superior to unimanual performance. Second, a transfer task tested internal (egocentric) and external (allocentric) coordinate systems. Transfer was more effective using the external coordinate system, suggesting that the S-R mappings reflected the association between the bivalent stimuli and external goals (i.e., the individual keys) rather than the concrete pattern of muscle contractions (i.e., the finger pressing the key). Finally, retention tests revealed that these learned S-R associations were remarkably durable, since no decrements in fluent task-switching performance were observed after 10 months without practice.
刺激与反应之间灵活的、依赖情境的联系是适应性行为的基础。在本文中，我们通过探究人们在两种不同的感觉运动映射之间切换能力的渐近效率，来评估这种灵活性的限度。学习了两种刺激-反应（S-R）映射，要么两种都在同一只手上（单手条件），要么每只手一种映射（双手条件）。S-R映射呈现二价刺激并使用相同的反应键。一种新颖的训练方案成功地将任务切换成本降低到了大约20毫秒，这表明残余的切换成本无法消除。这些成本不能完全归因于任务集重新配置的认知控制过程，因为在几秒的提示切换间隔中都能观察到它们。还探讨了运动学习中的另外两个问题：手动运动控制的单一位点或双位点以及任务表征的坐标系。首先，结果支持每只手有独立控制器的观点，而非单一主导控制器，因为双手表现优于单手表现。其次，一项迁移任务测试了内部（以自我为中心）和外部（以他物为中心）坐标系。使用外部坐标系时迁移更有效，这表明S-R映射反映了二价刺激与外部目标（即各个按键）之间的关联，而非肌肉收缩的具体模式（即按下按键的手指）。最后，保持测试表明，这些习得的S-R关联非常持久，因为在10个月不练习后，流畅的任务切换表现没有下降。
