Haptic perception of texture gradients

To pick up 3-D aspects of pictures is arguably the most difficult problem c oncerning tactile pictorial perception by the blind. The aim of the experim ents reported was to examine the potential utility of texture gradients in this context. Since there is no theoretical basis for predicting absolute v alues of 3-D properties from 2-D patterns read by the finger pads, the abil ities of participants to perceive gradients lying between known maxims and minima were assessed. Experiment 1 involved blindfolded sighted participant s making verbal magnitude estimations of texture-gradient magnitudes corres ponding to plane surfaces at different slants. In experiment 2 the particip ants' task was to orient a surface at a slant corresponding to the texture gradients depicted tactually, and experiment 3 required early-blind partici pants to attempt the same task. The results revealed that participants can scale the magnitudes of texture gradients with high precision and that they can also accurately produce surface slants from depictions, providing the extreme conditions are clearly defined and there are opportunities for lear ning. Texture gradients appear as informative to the blind as they do to th e sighted. To what extent these data can be generalised to other gradients and textures or to other projections of 3-D scenes remains to be investigat ed.