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TOUCH

TOUCH. PSYCHOPHYSIOLOGY. L. Négyessy PPKE, 2010. Haptic exploration of local shape Static stimuli. min. 0,5 mm  : 3%. 1-2 mm. 2,8 mm. 0,17 mm. Thresholds I. Braille dots’ height: 500 µ m. Vibrating stimuli. OPTACON. 6 x 18 = 108 blunt pins 230 Hz. d’.

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TOUCH

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  1. TOUCH PSYCHOPHYSIOLOGY L. Négyessy PPKE, 2010

  2. Haptic exploration of local shapeStatic stimuli min. 0,5 mm : 3% 1-2 mm 2,8 mm 0,17 mm

  3. Thresholds I Braille dots’ height: 500 µm

  4. Vibrating stimuli OPTACON 6 x 18 = 108 blunt pins 230 Hz

  5. d’ Discriminabitlity (d’) of complex waveformsfor low frequencies Thresholds II

  6. The 4 channel model- psychophysics Threshold

  7. The 4 channel model- neurophysiology Sensory Afferents Conduct.: 35-70 m/s (Hand scan: 60-80 mm/s)

  8. Receptive field organization (finger pad)

  9. Aperiodic grating Braille reading SAI channel Form perception:dots, edges, curves

  10. Receptive field characteristics relevant to form perception RAI & SAI channels

  11. Surround supression skin mechanics

  12. Perception of texture:roughness

  13. Fine texture perception: SAI spatial variation* *Mean absolute difference in firing rates between SAI afferents with RFs separated by ~2mm

  14. SAI spatial variation code for fine textures (0.2-1mm)

  15. Summary of form & texture perceptioncoding of spatial features Evidences of SA1 specialization for the representation of spatial information: • SA1 responses to stimulus elements on a surface are independent of the force of application. • SA1-receptive fields grow minimally (relative to RA receptive fields) with increasing indentation depth. • SA1 afferents possess a response property, surround suppression, which confers response properties similar to those produced by surround inhibition in the central nervous system. This response property is a consequence of sensitivity to strain energy density, not a synaptic mechanism. • SA1 spatial resolution is affected minimally by changes in scanning velocity at velocities up to at least 80 mm s–1. • SA1 afferents are at least ten times more sensitive to dynamic than to static stimuli. • SA1 responses to repeated skin indentation are practically invariant: the variability is about one impulse per trial regardless of the number of action potentials evoked. • The RA system has greater sensitivity but poorer spatial resolution and limited dynamic range.

  16. Vibrotactile perception:flutter, vibration

  17. Periodic Stimulus Firing rate Periodic St Periodicity (IS interval) Aperiodic St Firing rate monkey ideal obs. Periodic+aperiodic St Only firing rate periodicity firing rate RA channel Thresholds ratios: psychometric/neurometric thresholds

  18. ideal obs. of St motion P channel 10 nm skin motion at 200 Hz

  19. Response to vibrating stimulus

  20. Summary of vibrotactile perception- coding of temporal features P channel • intense filtering (at nearly 60 dB per decade) of low-frequency stimuli • respond to stimuli less than 100–150 Hz with a phase-locked, Poisson discharge, therefore a whole population firing randomly but at a rate proportional to the instantaneous stimulus amplitude can represent the stimulus waveform accurately RA channel • RA neurons of S1, like their afferent fibers, fire periodically, in phase with mechanical oscillations • RA neurons modulate their firing rates as a function of the stimulus frequency • Flutter is encoded by firing rate of RA neurons

  21. AdaptationPeripheral mechanisms

  22. Time course of adaptation and recovery

  23. RA interference in spatial processing

  24. Tool use

  25. Coding object size

  26. Grasping and manipulation

  27. Grasping and manipulation

  28. SUMMARY • The 4 channel model of vibrotactile discrimination • RF correlates of the 4 channel model • Elements of form perception • Texture (roughness) perception • Vibrotactile perception • Object manipulation

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