Depth inversion in random-dot stereograms

Errors in the stereoscopic separation of surfaces represented with regular textures

Stereograms containing two similar or dissimilar linear textures, either on the same surface or at two different depths, were tested on seventy subjects. Whereas random textures usually produced correct percepts, regular textures consistently led to errors of stereoscopic interpretations, including a reversal of hollows into bumps, dissociation of single surfaces into two layers, and errors in relative positioning of two surfaces. Horizontal-vertical textures tended to be seen as flatter and further away from the observer than diagonal ones. Continuous textures tended to be seen closer than discontinuous ones. In the interpretation of the results, the possibility is raised that different textures are processed independently and that the brain has no reliable method for combining the conclusions into a rigorous global percept.

Random-dot stereograms of real objects: observation on stereo faces and moulds

A simple technique for producing random-dot stereograms of real objects is described. It is then shown that stereograms of inside-out faces (moulds) cease to be perceptually reversible only when the presentation is truly cyclopean. Further possible applications of the technique are outlined.