A flight simulator was used to investigate the perception of self-motion and visual scene motion during the induction of saturated 10 deglsec yaw and 50 m/sec surge vection, and during subsequent impairment of saturated vection by inertial motions. The subjects (n = 5) did not perceive any selfacceleration or visual scene deceleration during the induction of saturated vection but perceived a rather sudden change in self-velocity and visual scene velocity. The mean group times to saturated veetion were 3.0 sec for yaw and 2.7 sec for surge. Above certain inertial motion amplitudes, the subjects reported additional self-motion from the applied inertial motions while experiencing saturated veetion. To impair saturated yaw vection, these amplitudes were 0.6 m/sec-, 0.4 m/sec-, 8 deg/sec-, and 5 deg/sec 2, for surge, sway, roll and yaw motions, respectively. To impair saturated surge vection, these amplitudes were 0.6 m/sec-, 0.3 m/sec-, 5 deg/sec-, and 4 deg/sec-, respectively. The results indicate that saturated vection is more robust for translations than for rotations because the rotational inertial amplitudes were closer to the amplitudes at which the applied inertial motion was perceived than the translational inertial amplitudes.

A flight simulator was used for two experiments to determine the amplitude combinations of visual scene motion (with respect to the observer) and inertial body motion (with respect to an earth-fixed frame) that provide the perception of an earth-stationary visual scene and realistic simulated self-motion. In the first experiment, this range was determined for simulated self-motion about the longitudinal body axis, while in the second, self-motion about the vertical body axis was considered. Both the inertial and the visual motions consisted of 0.75 s accelerations, followed by 1.50 s decelerations, and 0.75 s accelerations. The visual scene acceleration amplitude, W, was fixed at either 0, 2, 4, 8, or 12°/s2 while the inertial acceleration amplitude, I, was varied by a staircase procedure. Following the visual and inertial motions, the subjects pushed a button when they perceived the scene to be not earth-stationary. At each visual scene acceleration amplitude, the lower and upper inertial threshold amplitudes were determined, which bounded the range in which the visual scene was perceived to be earth-stationary. The lower and upper inertial thresholds were defined as the inertial motion amplitudes for which the inertial stimulations were too small or too large, respectively, to provide the perception of an earth-stationary visual scene. The lower inertial thresholds were determined for W=2 through W=12°/s2 and were found to be well approximated by the linear relation I=−0.37+0.60W for the roll motions tested, and I=1.1+0.33W for the yaw motions tested. The upper inertial thresholds were determined for W=0 through W=12°/s2 and were found to be well approximated by the linear relation I=2.7+1.7W for roll and I=2.2+1.4W for yaw. With the assumption that the lower and upper inertial threshold amplitudes are symmetric about the W=0 condition, the present results infer a strong nonlinearity of the thresholds near W=0.

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