Effect of stimulus parameters on fusional and stereoscopic performance.

The effect of stimulus size and complexity on the horizontal divergent diplopia threshold, stereoscopic range, reappearance of stereopsis, and re-fusion point was examined. It was found that the addition of random-dot (RD) backgrounds significantly increased both the diplopia threshold and re-fusion point, whereas the further addition of multiple depth planes did not. Stereopsis and diplopia were found to coexist in RD stereograms both when the disparity increased past the diplopia threshold and when it was decreasing toward the re-fusion point. This suggests that monocularly distinguishable contours must be added to RD stereograms to render them suitable for the measurement of fusional amplitudes.