Zhang Zheng, Tannan Vinay, Holden Jameson K, Dennis Robert G, Tommerdahl Mark
Department of Biomedical Engineering, University of North Carolina School of Medicine, Chapel Hill, NC, USA.
Biomed Eng Online. 2008 Mar 10;7:12. doi: 10.1186/1475-925X-7-12.
The traditional two-point discrimination (TPD) test, a widely used tactile spatial acuity measure, has been criticized as being imprecise because it is based on subjective criteria and involves a number of non-spatial cues. The results of a recent study showed that as two stimuli were delivered simultaneously, vibrotactile amplitude discrimination became worse when the two stimuli were positioned relatively close together and was significantly degraded when the probes were within a subject's two-point limen. The impairment of amplitude discrimination with decreasing inter-probe distance suggested that the metric of amplitude discrimination could possibly provide a means of objective and quantitative measurement of spatial discrimination capacity.
A two alternative forced-choice (2AFC) tracking procedure was used to assess a subject's ability to discriminate the amplitude difference between two stimuli positioned at near-adjacent skin sites. Two 25 Hz flutter stimuli, identical except for a constant difference in amplitude, were delivered simultaneously to the hand dorsum. The stimuli were initially spaced 30 mm apart, and the inter-stimulus distance was modified on a trial-by-trial basis based on the subject's performance of discriminating the stimulus with higher intensity. The experiment was repeated via sequential, rather than simultaneous, delivery of the same vibrotactile stimuli.
Results obtained from this study showed that the performance of the amplitude discrimination task was significantly degraded when the stimuli were delivered simultaneously and were near a subject's two-point limen. In contrast, subjects were able to correctly discriminate between the amplitudes of the two stimuli when they were sequentially delivered at all inter-probe distances (including those within the two-point limen), and improved when an adapting stimulus was delivered prior to simultaneously delivered stimuli.
Subjects' capacity to discriminate the amplitude difference between two vibrotactile stimulations was degraded as the inter-stimulus distance approached the limit of their two-point spatial discriminative capacity. This degradation of spatial discriminative capacity lessened when an adapting stimulus was used. Performance of the task, as well as improvement on the task with adaptation, would most likely be impaired if the cortical information processing capacity of a subject or subject population were systemically altered, and thus, the methods described could be effective measures for use in clinical or clinical research applications.
传统的两点辨别（TPD）测试是一种广泛使用的触觉空间敏锐度测量方法，但因其基于主观标准且涉及许多非空间线索而被批评为不精确。最近一项研究的结果表明，当同时施加两个刺激时，当两个刺激相对靠近放置时，振动触觉幅度辨别能力变差，并且当探头处于受试者的两点阈限时，辨别能力会显著下降。随着探头间距离减小，幅度辨别能力受损表明幅度辨别指标可能提供一种客观和定量测量空间辨别能力的方法。
采用二选一强迫选择（2AFC）跟踪程序来评估受试者辨别位于相邻皮肤部位的两个刺激之间幅度差异的能力。两个25Hz的颤动刺激，除了幅度有恒定差异外完全相同，同时施加于手背。刺激最初间隔30mm，刺激间距离根据受试者辨别强度较高刺激的表现逐次试验进行调整。通过顺序而非同时施加相同的振动触觉刺激来重复该实验。
本研究获得的结果表明，当同时施加刺激且刺激靠近受试者的两点阈限时，幅度辨别任务的表现显著下降。相比之下，当在所有探头间距离（包括两点阈限内的距离）顺序施加刺激时，受试者能够正确辨别两个刺激的幅度，并且在同时施加刺激之前先施加一个适应刺激时，辨别能力有所提高。
随着刺激间距离接近其两点空间辨别能力的极限，受试者辨别两个振动触觉刺激之间幅度差异的能力会下降。当使用适应刺激时，这种空间辨别能力的下降会减轻。如果受试者或受试者群体的皮质信息处理能力被系统性改变，任务表现以及适应后任务的改善很可能会受损，因此，所描述的方法可能是临床或临床研究应用中的有效测量方法。
