TOUCH

TOUCH

PSYCHOPHYSIOLOGY

L. Négyessy PPKE, 2010

2

Haptic exploration of local shape

Static stimuli

1-2 mm 2,8 mmmin. 0,5 mm: 3%

0,17 mm

3

Thresholds I

Braille dots’ height: 500 µm

4

6 x 18 = 108 blunt pins

230 Hz

Vibrating stimuliOPTACON

5

Thresholds II

Discriminabitlity (d’) of complex waveformsfor low frequencies

d’

6

The 4 channel model- psychophysics

Threshold

7

Sensory Afferents

Conduct.: 35-70 m/s(Hand scan: 60-80 mm/s)

The 4 channel model- neurophysiology

8

Receptive field organization (finger pad)

SAI RA P SAII?

RF size 1 mm2 0.82 mm2 diffuse diffuse

Aff. denz. 100 cm-2 150 cm-2 350/ finger ? (low)

Diverg.(RF area)

4-16(5 mm2)

4-16 (5 mm2)

1:1 1:1

Converg. 1:1 2-7 1:1 1:1

Adequ. stim. Strain energy density (point, edge, curve)

Slip, load force

High freq. vibration

Skin stretch

function Form, texture Grip control, fine

discr.

Distant events, tool use

Hand shape

9

Form perception:dots, edges, curves

Braille readingAperiodic grating

SAI channel

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 perception

coding 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

RA channel

Periodic StimulusFiring rate

Periodic StPeriodicity (IS interval)

Aperiodic StFiring rate

Periodic+aperiodic St Only firing rate

firing rate periodicity

monkey

ideal obs.

Thresholds ratios: psychometric/neurometric thresholds

18

P channel

10 nm skin motion at 200 Hz

ideal obs.

of St motion

19

Response to vibrating stimulus

20

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

Summary of vibrotactile perception- coding of temporal features

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