Five different disparities were used to obtain the thresholds. Figure 7 shows the effect of disparity on the duration thresholds for stereoacuity. Although duration thresholds increase more quickly in down-gaze as target duration is reduced, this difference is not statistically significant. Too short of a duration would not be sufficient to induce adaptive vestibulo-ocular changes and too long of a duration would run the risk of causing motion sickness. These alterations were not quantified, so it is unknown whether a significant elevation of stereoacuity should occur.
Stimulation exceeding one hour causes motion sickness symptoms in susceptible subjects.
The degradation of visual performance as a result of TTD-induced adaptation is being assessed by comparing duration thresholds for stereoacuity before and after TTD stimulation. Based on the results in Fig. 7, a 4 arc-min disparity is used for this experiment. Surrounding the subject is a lightweight box, lined on the inside with black stripes that accentuate the 3-D structure of the box. These experiments to identify the optimal duration of TTD stimulation are currently in progress.