Peripheral neural representation of the spatial frequency of a grating moving across the monkey's finger pad.

1. Responses in mechanoreceptive afferent fibres innervating the monkey's finger pads were examined when a ridged surface ("grating') was moved across the fibre's receptive field with a specified velocity and applied force. 2. The stimulus feature represented in single fibre responses was the temporal frequency of the moving grating (stimulus temporal frequency = velocity of moving surface/spatial period); information about the spatial period of the grating was represented equivocally. 3. Peripheral neural representation of the grating's spatial period (or spatial frequency) depended on information signalled by the responding fibre population rather than by individual fibres. 4. The three mechanoreceptive fibre populations responded differentially to a grating moving across the finger pad. Slowly adapting fibres coded best those stimulus combinations with a stimulus temporal frequency in the range 20-60 Hz, rapidly adapting fibres coded best those with frequencies of 60-200 Hz, and Pacinian fibres best defined those stimuli with a high temporal frequency (100-300 Hz). 5. Applying the moving grating to the skin with varying radial forces in the range 20-60 g wt. did not greatly modify the pattern of discharge in the responding fibre populations.