BACKGROUND: Ischemic hypoxia induced by suprathreshold G-force loading can adversely affect vision, cognition, and lead to loss of consciousness (LOC). The purpose of this study was to determine whether reductions in cerebral oxygenation, caused by subthreshold G-forces (up to 4 G_z and of limited durations that do not lead to LOC), would affect visual perception and working memory performance.METHODS: Sixteen subjects performed visual perception and working memory tasks both before and during G_z exposures (1, 2.2, 3, 4 with leg pressurization, 4 with leg and abdomen pressurization) within a human-use centrifuge.RESULTS: As measured using near-infrared spectroscopy, blood oxygenation over medial prefrontal cortex was similar in the 1 and 2.2 G_z conditions, but was reduced to a similar extent in the 3 and 4 G_z conditions. In parallel, visual perception accuracy was reduced in the 3 and 4 G_z conditions, with no difference between the 3 and 4 G_z conditions. No change in reaction time was seen. Conversely, neither accuracy nor reaction time changes were observed for the visual working memory task.DISCUSSION: These results indicate that although visual working memory is not affected, the ability to visually discriminate between stimuli is reduced at G-forces as low as 3 and 4 G_z. This may have important ramifications for pilots who are routinely subjected to such forces.