THE ROLE OF RETINAL VERSUS PERCEIVED SIZE IN THE EFFECTS OF PITCHED DISPLAYS ON VISUALLY PERCEIVED EYE LEVEL

Visually perceived eye level (VPEL) was measured while subjects viewed two vertical lines which were either upright or pitched about the hor izontal axis. In separate conditions, the display consisted of a relat ively large pair of lines viewed at a distance of 1 m, or a display sc aled to one third the dimensions and viewed at a distance of either 1 m or 33.3 cm. The small display viewed at 33.3 cm produced a retinal i mage the same size as that of the large display at 1 m. Pitch of all t hree displays top-toward and top-away from the observer caused upward and downward VPEL shifts, respectively. These effects were highly simi lar for the large display and the small display viewed at 33.3 cm tie equal retinal size), but were significantly smaller for the small disp lay viewed at 1 m. In a second experiment, perceived size of the three displays was measured and found to be highly accurate. The results of the two experiments indicate that the effect of optical pitch on VPEL depends on the retinal image size of stimuli rather than on perceived size.