SENSORIMOTOR MECHANISMS IN WEIGHT DISCRIMINATION

The role of efferent and afferent signals in weight discrimination was investigated by using the tonic vibratory reflex contraction of the biceps muscle. Differential thresholds were obtained for 2 lifting conditions (normal and reflex) and 2 static conditions (with and without muscular tonus). Normal lifting gave finer discrimination than reflex lifting (experiment 1). Normal lifting was also superior to the 2 static conditions (experiment 2). Within the static conditions, the addition of muscular tonus gave finer discrimination. The reflex lifting condition gave thresholds similar to those for static holding with muscular tonus, lying between those for normal active lifting and those for static pressure. The reflex lifting and pressure-sensing thresholds were very much finer than the previous literature suggests. The relative contributions of efference and afference to weight discrimination are discussed.