Ayala Naila, Binsted Gordon, Heath Matthew
School of Kinesiology and Graduate Program in Neuroscience, University of Western Ontario, London, ON, N6A 3K7, Canada.
Faculty of Health and Social Development, University of British Columbia, Kelowna, BC, Canada.
Exp Brain Res. 2018 Aug;236(8):2439-2446. doi: 10.1007/s00221-018-5311-6. Epub 2018 Jun 19.
Recent work proposed that biomechanical constraints in aperture separation limit the utility of Weber's law in determining whether dissociable visual codes support grasping and manual estimation. We tested this assertion by having participants precision grasp, manually estimate and complete a method of adjustment task to targets scaled within and beyond the range of their maximal aperture separation (i.e., from 20 to 140% of participant-specific maximal aperture separation: MAS). For grasping and manual estimation tasks, just-noticeable-difference (JND) scores were computed via the within-participant standard deviations in peak grip aperture, whereas method of adjustment JNDs were computed via the within-participant standard deviations in response output. Method of adjustment JNDs increased linearly across the range of targets; that is, responses adhered to Weber's law. Manual estimation JNDs linearly increased for targets 20-100% of MAS and then decreased for targets 120-140% of MAS. In turn, grasping JNDs for targets 20% through 80% of MAS did not differ and were larger than targets 100-140% of MAS. That manual estimation and grasping showed a decrease in JNDs for the largest targets indicates that participants were at their biomechanical limits in aperture shaping, and the fact that the target showing the JND decrease differed between tasks (i.e., manual estimation = 100% of MAS; grasping = 80% of MAS) is attributed to the fact that grasping-but not manual estimation-requires a safety-margin task-set. Accordingly, manual estimations and grasping across a range of functionally 'graspable' targets, respectively, adhered to and violated Weber's law-a result interpreted to reflect the use of dissociable visual codes.
最近的研究提出，孔径分离中的生物力学限制限制了韦伯定律在确定可分离视觉编码是否支持抓握和手动估计方面的效用。我们通过让参与者精确抓握、手动估计并完成一项调整任务方法来测试这一断言，该任务针对的目标尺寸在其最大孔径分离范围之内和之外（即参与者特定最大孔径分离：MAS的20%至140%）。对于抓握和手动估计任务，通过峰值抓握孔径的参与者内部标准差计算最小可觉差（JND）分数，而调整任务方法的JND则通过响应输出的参与者内部标准差计算。调整任务方法的JND在目标范围内呈线性增加；也就是说，反应符合韦伯定律。手动估计的JND在MAS的20%-100%目标范围内线性增加，然后在MAS的120%-140%目标范围内下降。相应地，MAS的20%至80%目标的抓握JND没有差异，且大于MAS的100%-140%目标的抓握JND。最大目标的手动估计和抓握的JND下降表明参与者在孔径塑造方面达到了生物力学极限，并且任务中显示JND下降的目标不同这一事实（即手动估计 = MAS的100%；抓握 = MAS的80%）归因于抓握（而非手动估计）需要安全边际任务集这一事实。因此，手动估计和抓握在一系列功能上“可抓握”的目标上，分别符合和违反了韦伯定律——这一结果被解释为反映了可分离视觉编码的使用。
