Fingertip force,surface geometry,and the perception of roughness by active touch

Ss made magnitude estimates of the perceived roughness of grooved metal plates under conditions of active touch with controlled finger force. The wider the grooves in the plate, the narrower the lands between the grooves, or the greater the finger force, the greater was the perceived roughness. Increase in finger force also slightly increased the slope of the magnitude estimation function, suggesting not only that the roughness of a uniform surface but also the contrasts in the roughness of differing parts of a patterned surface would be altered by changes in the manner of feeling the surface. An analogous effect has been reported in vision, in that increases in illumination increase the apparent contrast of a surface.