Figure 3. Responses of two single SA-I afferents to torques during the three phases of stimulation.

A, typical response pattern of SA-I afferents. This afferent showed a scaling effect for torque magnitude in the clockwise direction but showed little effect in the anticlockwise direction, thus exemplifying the rotational direction selectivity of SA-I afferents. The pattern was similar during all three phases of stimulation. B, response pattern of a SA-I afferent showing positive or negative response scaling depending on the direction and phase of the torque. During the loading and plateau phases, the afferent's response was positively scaled by torque in the anticlockwise direction and negatively scaled (suppressed) in the clockwise direction. The reverse effect was observed during the unloading phase; the afferent was excited in the clockwise direction and suppressed in the anticlockwise direction. Afferent responses were measured as spike counts during the respective phases of stimulation and were averaged over six trials.