The Effect of Shadows on Performing Stereo visual Pointing Tasks: Is Shadow-Free Open Surgery Ideal?

Abstract

Surgical overhead luminaires and head-mounted luminaires are important tools for surgeons. The optical design of these luminaires focuses on providing shadow free light. Shadows, however, are reported as important cues for depth perception in mono- and stereo-visual situations. Because surgeons repeatedly touch delicate tissue with their instruments, their depth-perception should not be hampered. Two experiments were performed to evaluate the influence of shadow on human performance when executing stereo-visual pointing tasks. Experiment 1 studied the effect of the existence of shadows and Experiment 2 studied the effect of the direction of shadows. Subjects were instructed to point random sequences of virtual targets accurately under different shadow situations. Performance was characterized with spatial error E (distance to target, mm). Experiment 1 showed that both large and small high-contrast shadows gave significantly smaller spatial error E (4.8, 4.6 mm, respectively) than either low-contrast shadows (5.6 mm) or no shadows (6.3 mm). Experiment 2 showed that the Error varied (2.1 to 3.2 mm) for different illumination directions. The Error decreased with an increasing angle between the line-of-sight and line-of-light. Illuminating from the center or from the left side of the observer gave better results then from the right side. To maximize depth-perception, surgical luminaires should provide a clear shadow from a light source that illuminates from within the vertical plane through the line-of-sight, and with a 90° angle with respect to the line-of-sight.

Keywords:

• Surgery
• depth perception
• pointing tasks
• stereo-vision
• shadow.