This thesis describes a psychophysical experiment carried out to assess the perceptual influence of approximating ambient occlusion in real-time rendering. Three different screen-space ambient occlusion techniques of differing physical accuracy were implemented for the experiment. The results of the experiment show that screen-space ambient occlusion can increase the perceived realism of visually complex synthetic images. Visual complexity was also found to have an influence on the required physical accuracy of the ambient occlusion algorithm. Specifically, as the visual complexity increases, the required physical accuracy of ambient occlusion decreases. In a visually complex, ecologically valid scenario, experiment participants were not able to discern a difference between two different screen-space ambient occlusion techniques with significant observable quality differences. The results of the experiment suggest that in practical application scenarios such as computer games, it is prudent to investigate the need for, and impact of, screen-space ambient occlusion for individual scenes or environments. In many cases, low accuracy ambient occlusion can be sufficient, and in some cases it can be turned off completely; thus allowing for more computation time to be utilized on other perceptually important rendering tasks.