1. The responses of cutaneous mechanoreceptors in feline hairy skin were examined in vivo with systematic variations in the velocity and direction of stimulus motion across the receptive fields (RF). The mechanoreceptor classes studied were guard hair afferents, field afferents, down hair afferents, and slowly adapting type I (SAI) mechanoreceptors. A camel's hair brush, moved by a high-precision motor, provided surface-parallel stimulation at velocities ranging from 0.4 to 100 cm/s. The stimulating device and protocols were similar to those previously used to evaluate human perception, thus allowing direct comparison of the two sets of data. 2. Each mechanoreceptor produced highly reliable mean firing rates with repeated stimulation. All mechanoreceptors showed a growth in evoked activity with increased stimulus velocity. With few exceptions, the relationship between brush velocity and mean firing rate was well described by a power function throughout the range of velocities tested. The exponents of these power functions, reflecting the degree of velocity dependency for each mechanoreceptor, were largest for the field type 1 units (F1) and guard hair type 1 units (G1). 3. The capacity of the mechanoreceptors to discriminate velocity was examined in the context of signal detection theory. For each unit, a velocity discriminability estimate (velocity δ'e) was calculated for responses to 5 versus 10 cm/s brushing and 10 versus 20 cm/s. The G1 and F1 units exhibited the largest velocity δ'e values, which were comparable to human velocity discriminability (d'e) values. Thus these data show the quantitative parallel between the velocity discriminability of G1 and F1 mechanoreceptors and of human perception similarly tested. 4. Most mechanoreceptors generated different response rates with stimuli moving in opposing directions (in the proximal-distal axis of the hindlimb). However, no mechanoreceptor class showed a consistently preferred direction of movement. A directional δ'e value was calculated for each mechanoreceptor at each stimulus velocity. These values were quite variable, even within a single mechanoreceptor class. In general, a mechanoreceptor's directional δ'e value either 1) decreased with increasing velocity or 2) remained constant across velocities. The way in which human directional discriminability varies with stimulus velocity did not parallel the way in which mechanoreceptor's directional δ'e values varied with the same range of stimulus velocities. 5. Some mechanoreceptors were tested with both the standard-sized brush, which was smaller than most mechanoreceptors' RFs, and a much larger brush, which was at least twice the size of the mechanoreceptors' RFs. When the larger brush was used, most mechanoreceptors exhibited higher firing rates when the leading edge and the trailing edge moved through the RF and less of a response when the middle of the brush moved through the RF. The exceptions to this were the down-hair afferents, which showed the same consistent rate of activity throughout the brush sweep.
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