Local tactile coding in the human fingertip

人类通常被认为是使用光谱分解或平均来识别振动触觉信号。这些是通用的“全局”代码，需要在很长一段时间内整合信号。然而，自然振动触觉信号可能包含简短的签名事件，可以检测到并用于纹理推断，即时，最小的集成，暗示迄今为止被忽视的“局部代码”。在本提案中，我们将首先研究这些特征是否存在于人类指尖无毛皮肤的乳头状脊中，以及它们是否通过局部编码传递影响感知机制的纹理信息。在该项目的第一个资助期，我们采用脉动刺激和被动（无手指运动）变化检测心理物理任务来揭示人类利用局部线索。我们的研究结果表明，人类不仅使用局部线索，而且局部线索甚至可能在感知中起主导作用，而且它们很容易被储存在工作记忆中。与此同时，我们还研究了生物力学、神经编码和老鼠的心理物理学，以便能够将我们在人类身上的结果与啮齿动物身上基于须的突出触觉系统进行比较。我们已经发现证据表明，在须和人类指尖触觉系统中进化出了非常相似的编码策略。在第二个资助期的拟议工作计划中，我们将以这些成果为基础，首先调查自我运动对感知的作用。我们将系统地比较使用被动辨别的心理物理表现与手指/手臂触诊运动时的心理物理表现。然后，我们将研究局部编码的生物力学基础。局部编码可能与主要存在的摩擦粘滑运动有关，如大鼠的触须。对于指尖，迄今为止还没有在单个乳头脊的水平上显示出这一点，也没有足够的时间分辨率。我们将首先采用显微刺激单乳头脊结合测量识别性能在人类。此外，使用超快速摄像技术，我们将监测指纹在特定表面上摩擦的时空分辨率，以揭示单个乳头状脊的摩擦粘滑运动的存在。

Humans are classically thought to use either spectral decomposition or averaging to identify vibrotactile signals. These are general purpose ‘global’ codes that require integration of the signal over long stretches of time. Natural vibrotactile signals, however, likely contain short signature events that can be detected and used for inference of textures, instantaneously, with minimal integration, suggesting a hitherto ignored ‘local code’. In this proposal we will firstly investigate whether such signatures exist in papillary ridges of glabrous skin in the human fingertip and whether they convey texture information that affects perceptual mechanisms using a local code. In the 1st funding period of this project we employed pulsatile stimuli and a passive (no finger movement) change detection psychophysical task to reveal that humans make use of local cues. Our results suggest that humans not only do use local cues but that local cues may even play a dominant role in perception, and that they can readily be stored in working memory. In parallel we have worked in biomechanics, neuronal coding and psychophysics in rats to be able to compare our results in humans with the prominent whisker-based tactile system in rodents. We have found evidence to suggest that quite similar coding strategies evolved in whisker and human fingertip-based tactile systems. In the proposed work program for a 2nd funding period we will build on these achievements to firstly investigate the role of egomovement for perception. We will systematically compare psychophysical performance using passive discrimination to that during palpation movements of the finger/arm. We will then investigate the biomechanical underpinnings of local coding. Local codes may be related to the dominant presence of frictional stick-slip movement of the integument, as shown to be the case for rat’s vibrissae. For fingertips this has hitherto not been shown on the level of single papillary ridges and with sufficient temporal resolution. We will firstly employ microscopic stimulation of single papillary ridges combined with measuring discrimination performance in humans. Further, using ultra-fast videography, we will monitor the fingerprint as it rubs across defined surfaces, at a spatio-temporal resolution needed to reveal the presence of frictional stick-slip movements of single papillary ridges.