J. Farley Norman¹, William B. Marcum¹, Maria Carmichael¹, Evan Hagan¹, Cain B. Del Savio¹, Ash Sheehan², Avery Sutton¹; ¹Western Kentucky University, ²Carol Martin Gatton Academy of Mathematics and Science

Thirty younger and older adults, ranging in age from 18 to 82 years, made ordinal depth judgments for locations on the surfaces of smoothly curved solid objects. The objects’ 3-D structure was defined by motion, image shading, and specular highlights; depth differences ranging from 0.4 to 1.2 cm were evaluated. The separation (in the projected images) between the surface regions to be judged ranged from near separations (4.0 cm or less) to far separations (7.0 cm or greater). The task was to indicate which of the highlighted surface regions was closer (to the observers) in depth. The observers’ d’ values ranged from near chance levels to 3.6, depending upon the image separation, the depth difference magnitude, and the individual observer. There were significant effects of image separation, depth difference magnitude, and age. Overall, the younger observers’ performance was 25.2 percent higher than that exhibited by the older observers (average d’ values for the younger and older observers were 1.643 and 1.312, respectively). The image separation had large effects: performance for near separations was 113 percent higher than for far separations when the depth difference was identical (average d’ values for near and far separations in this case were 2.031 and 0.954, respectively). Larger depth differences produced higher performance than smaller depth differences, with 0.4 cm increases in depth difference magnitude producing 64 percent increases in d’ for near separations and 73.6 percent increases in d’ for far separations. The current results both confirm (effects of image separation and depth difference magnitude) and extend previous findings (significant negative effect of age). While an age effect did occur, it was small (partial eta squared was 0.144). Older adults (at least up to the age of 82 years) therefore maintain an effective ability to judge ordinal depth relationships on solid object surfaces.