Manzone Joseph, Davarpanah Jazi Shirin, Whitwell Robert L, Heath Matthew
School of Kinesiology, University of Western Ontario, London, Ontario, Canada.
Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada.
Vision Res. 2017 Jan;130:31-35. doi: 10.1016/j.visres.2016.09.018. Epub 2016 Nov 29.
Work by our group and others employed the within-participants variability in peak grip aperture as a 'just-noticeable-difference' (JND) in grasping. Notably, our group reported that grasping responses with decoupled spatial relations between stimulus and response (i.e., pantomime-grasping) produced JNDs that increased linearly with increasing target object size (i.e., adherence to Weber's law) and interpreted that result as law-based evidence of aperture shaping via relative visual information. In contrast, Utz et al. (2015) reported that pantomime-grasping elicits an inverse JND/object size relationship and proposed that JNDs in grasping do not reflect the sensory properties of a target object but rather reflect range effects in the biomechanical limits of aperture opening (i.e., the biomechanical hypothesis). Thus, the biomechanical hypothesis asserts that small objects have a larger range of possible aperture values than larger objects due to reduced biomechanical freedom associated with the hand's effective range of motion. To test the biomechanical hypothesis we measured participants' maximal thumb and forefinger separation and custom-built target objects with widths that matched decile increments (i.e., 10 through 80%) of each participant's effective range of motion. Results showed that JNDs increased linearly with increasing target object size - a result incompatible with the biomechanical hypothesis. Instead, the JND/object size relationship observed here supports convergent evidence that pantomime-grasping is a perception-based task mediated via relative visual information.
我们团队及其他人员的研究将抓握时峰值抓握孔径的参与者内部变异性用作抓握方面的“最小可觉差”（JND）。值得注意的是，我们团队报告称，刺激与反应之间空间关系解耦的抓握反应（即模拟抓握）产生的最小可觉差会随着目标物体尺寸的增加而线性增加（即符合韦伯定律），并将该结果解释为通过相对视觉信息进行孔径塑造的基于定律的证据。相比之下，乌茨等人（2015年）报告称，模拟抓握会引发最小可觉差与物体尺寸的反向关系，并提出抓握中的最小可觉差并不反映目标物体的感官属性，而是反映孔径打开的生物力学极限中的范围效应（即生物力学假说）。因此，生物力学假说断言，由于与手部有效运动范围相关的生物力学自由度降低，小物体比大物体具有更大的可能孔径值范围。为了检验生物力学假说，我们测量了参与者拇指和食指的最大间距以及定制的目标物体，这些物体的宽度与每个参与者有效运动范围的十分位数增量（即10%至80%）相匹配。结果表明，最小可觉差随着目标物体尺寸的增加而线性增加——这一结果与生物力学假说不相符。相反，此处观察到的最小可觉差与物体尺寸的关系支持了趋同证据，即模拟抓握是一项通过相对视觉信息介导的基于感知的任务。
