Relative availability of surface and object properties during early haptic processing.

How the relative order in which 4 property classes of haptically perceived surfaces becomes available for processing after initial contact was studied. The classes included material, abrupt-surface discontinuity, relative orientation, and continuous 3-D surface contour properties. Relative accessibility was evaluated by using the slopes of haptic search functions obtained with a modified version of A. Treisman's (A. Treisman & S. Gormican, 1988) visual pop-out paradigm; the y0 intercepts were used to confirm and fine-tune order of accessibility. Target and distractors differed markedly in terms of their value on a single dimension. The results of 15 experiments show that coarse intensive discriminations are haptically processed early on. In marked contrast, most spatially encoded dimensions become accessible relatively later, sometimes considerably so.