Louw Stefan, Kappers Astrid M L, Koenderink Jan J
Helmholtz Instituut, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
Perception. 2005;34(7):869-85. doi: 10.1068/p5425.
We studied human haptic perception of sine-wave gratings. In the first experiment we measured the dependence of amplitude detection thresholds on the number of cycles and on the wavelength of the gratings. In haptic perception of sine-wave gratings, the results are in agreement with neural summation. The rate at which detection thresholds decrease with increasing number of cycles is much higher than can be accounted for by probability summation alone. Further, neural summation mechanisms describe the detection thresholds accurately over the whole spatial range probed in the experiment, that is wavelengths from 14 mm up to 225 mm. Earlier, we found a power-law dependence of thresholds on the spatial width of Gaussian profiles (Louw et al, 2000 Experimental Brain Research 132 369-374). The current results extend these findings; the power-law dependence holds not only for Gaussian profiles, but also for a broad range of sine-wave gratings with the number of cycles varying between 1 and 8. Haptic perception involves tactual scanning combined with an active, dynamic exploration of the environment. We measured characteristics of the velocity and force with which stimuli were scanned while performing a psychophysical task. One particularly surprising finding was that, without being instructed, participants maintained an almost constant scanning velocity during each 45-min session. A constant velocity in successive trials of the experiment might facilitate or even be necessary for discrimination. Further, a large systematic dependence of velocity on scanning length was found. An eightfold increase in scanning length resulted in about a fourfold increase in scanning velocity. A second experiment was conducted to study the influence of scanning velocity on psychophysical detection thresholds. This was done by systematically imposing specific scanning velocities to the participants while the thresholds were measured. The main result of the second experiment was that psychophysical detection thresholds are constant over a relatively broad range of scanning velocities.
我们研究了人类对正弦波光栅的触觉感知。在第一个实验中，我们测量了振幅检测阈值与光栅周期数和波长的依赖关系。在正弦波光栅的触觉感知中，结果与神经总和一致。检测阈值随周期数增加而降低的速率远高于仅由概率总和所能解释的速率。此外，神经总和机制在实验所探测的整个空间范围内（即波长从14毫米到225毫米）准确地描述了检测阈值。此前，我们发现阈值对高斯轮廓空间宽度存在幂律依赖关系（Louw等人，2000年，《实验脑研究》132卷，369 - 374页）。当前结果扩展了这些发现；幂律依赖关系不仅适用于高斯轮廓，也适用于周期数在1到8之间变化的广泛正弦波光栅。触觉感知涉及触觉扫描以及对环境的主动、动态探索。我们在执行心理物理学任务时测量了扫描刺激的速度和力的特征。一个特别令人惊讶的发现是，在没有得到指示的情况下，参与者在每个45分钟的时间段内保持几乎恒定的扫描速度。实验连续试验中的恒定速度可能有助于甚至是辨别所必需的。此外，还发现速度对扫描长度有很大的系统依赖性。扫描长度增加八倍导致扫描速度增加约四倍。进行了第二个实验来研究扫描速度对心理物理学检测阈值的影响。这是通过在测量阈值时系统地给参与者施加特定的扫描速度来完成的。第二个实验的主要结果是，心理物理学检测阈值在相对较宽的扫描速度范围内是恒定的。
