Spatial augmented reality (SAR) technology allows one to change the appearance of objects by projecting directly onto their surface without the requirement of wearing glasses, and therefore can be used in many practical applications. In this article, we present a human–subject study, which investigates the research question whether it is possible to use SAR to change one's perception of depth and spatial relationships among objects and humans in a real-world environment. Such projected illusions could open up new possibilities, for example, supporting people who suffer from poor depth perception by compensating distance and size misperceptions. We present three monoscopic projection-based techniques that we adapted from visual arts: (i) color temperature, (ii) luminance contrast, and (iii) blur, and show that each of them can significantly change depth perception, even in a real-world environment when displayed with other distance cues. We discuss practical implications and individual differences in the perception of depth between observers, and we outline future directions to influence and improve human depth perception in the real world.

When walking within a CAVE-like system, accommodation distance, parallax, and angular resolution vary according to the distance between the user and the projection walls, which can alter spatial perception. As these systems get bigger, there is a need to assess the main factors influencing spatial perception in order to better design immersive projection systems and virtual reality applications. In this paper, we present two experiments that analyze distance perception when considering the distance toward the projection screens and parallax as main factors. Both experiments were conducted in a large immersive projection system with up to 10-meter interaction space. The first experiment showed that both the screen distance and parallax have a strong asymmetric effect on distance judgments. We observed increased underestimation for positive parallax conditions and slight distance overestimation for negative and zero parallax conditions. The second experiment further analyzed the factors contributing to these effects and confirmed the observed effects of the first experiment with a high-resolution projection setup providing twice the angular resolution and improved accommodative stimuli. In conclusion, our results suggest that space is the most important characteristic for distance perception, optimally requiring about 6- to 7-meter distance around the user, and virtual objects with high demands on accurate spatial perception should be displayed at zero or negative parallax.