Abstract
Classically, texture discrimination has been thought to be based on ‘global’ codes, i.e. frequency (signal analysis based on Fourier analysis) or intensity (signal analysis based on averaging), which both rely on integration of the vibrotactile signal across time and/or space. Recently, a novel ‘local’ coding scheme based on the waveform of frictional movements, discrete short lasting kinematic events (i.e. stick-slip movements called slips) has been formulated. We performed biomechanical measurements of relative movements of a rat vibrissa across sandpapers of different roughness. We find that the classic global codes convey some information about texture identity, but are consistently outperformed by the slip-based local code. Moreover, the slip code also surpasses the global ones in coding for active scanning parameters. This is remarkable as it suggests that the slip code would explicitly allow the whisking rat to optimize perception by selecting goal-specific scanning strategies.
Highlights
Sensory processing leads to a representation of a sensory object in terms of spatio-temporal brain activity
Given the presence of slips, the question arises whether a global code can be considered as optimal to read out texture information contained in slips, or in how far it is able to contribute texture information from other segments of the vibrotactile signal, like oscillations or creepy movements[12,13,14]
We compared biomechanical variables of vibrissa movement, while in dynamic contact with textures, with respect to their ability to provide the basis for texture discrimination
Summary
Sensory processing leads to a representation of a sensory object in terms of spatio-temporal brain activity. By actively whisking against objects, rats choose an active perceptual strategy by selecting several behavioral parameters, amongst them (1) distance of the rat’s head to the object (which determines axial and lateral forces acting on the vibrissa15), (2) velocity of whisking, and (3) the identity of the vibrissa(e) used to touch These parameters of active scanning in turn will determine the frictional movements and the probability of occurrence (rate) and the waveform (kinematic parameters) of slips. In this report we will assess texture coding using the different hypothetical coding symbols and determine in how far parameters of active touch modify this code This knowledge will be decisive to gain insights on what an effective neuronal efference copy[16] must look like, if it is to effectively separate textural information from the imprints of active scanning
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