Reversibility of the Necker Cube: I. An Examination of the Concept of “Satiation of Orientation”

A central fatigue factor (satiation of orientation) is proposed to account for reversals of the Necker cube. During viewing, the figure process mediating one orientation becomes satiated, a threshold level is reached and a reversal is reported. The conception places no special importance on retinal locus of the figure since it is not any one part of the central process that satiates but rather the process mediating one particular orientation. To support this analysis, the cube was presented tachistoscopically so that growth of satiation would be interrupted before threshold was reached. When presented repetitively, the satiation summated with residual satiation generated by preceding exposures until the threshold was reached and a reversal was reported. When, however, the interval between successive exposures of the cube was lengthened to permit the satiative processes to decay to a minimal value after each exposure, then no summation took place, the threshold was never reached and reversals were never reported.

The viewing-from-above bias and the silhouette illusion

The silhouette illusion published online a number of years ago by the Japanese Flash designer Nobuyuki Kayahara has received substantial attention from the online community. One feature that seems to make it interesting is an apparent rotational bias: Observers see it spinning more often clockwise than counter-clockwise. Here, we show that this rotational bias is in fact due to the visual system's preference for viewpoints from above rather than from below.