Feeling textures through a probe: effects of probe and surface geometry and exploratory factors.

Vibratory roughness perception occurs when people feel a surface with a rigid probe. Accordingly, perceived roughness should reflect probe and surface geometry, exploratory speed, and force. Experiments 1 and 2 compared magnitude estimation of roughness with the bare finger and two types of probes, one designed to eliminate force moments, under the subject's active control. Experiments 3 and 4 varied speed under passive control. Log magnitude was consistently a quadratic function of log spacing between elements in the surface. The location of the function's peak was related to the drop point--that is, the spacing at which the probe can just drop between elements--which is affected by probe tip diameter, element height, and speed. Other parameters of the quadratic were affected by probe type and speed.