Résumé
Future vertical lift (FVL) missions will be characterized by increased agility, degraded visual environments (DVE) and optionally piloted vehicles (OPVs). Increased agility will induce more frequent variations of linear and angular accelerations, while DVE will reduce the structure and quality of the out-the-window (OTW) scene. As rotorcrafts become faster and more agile, pilots are expected to navigate at low altitudes while traveling at high speeds. In contour terrain flight, the perception of self-position and orientation provided by visual, vestibular, and proprioceptive cues can vary from moment to moment due to visibility conditions and body alignment as a response to gravitoinertial forces and internally/externally induced perturbations. As a result, erroneous perceptions of the self and the environment can arise, leading ultimately to spatial disorientation (SD). In OPV conditions, the use of different autopilot modes transforms the pilot's role from active pilot to systems supervisor. This shift in paradigm, where pilotage is not the primary task, and where feedback from the controls is not available, has important consequences. Indeed, space perception can be strongly modulated by the nature of the displacement in space. Considering the relationships between the level of automation (LOA) and sense of agency (SoA), it is of particular interest to examine whether motor control mechanisms can modulate the level of visual-vestibular integration in tasks of movement perception vs. movement control. An experiment was conducted using the NASA AMES vertical motion simulator (VMS) to evaluate the effects of optical and gravitoinertial cues in the assessment of altitude in contour terrain flight. Seven U.S. Army pilots participated in the experiment. The aim of the proposed research was a) to establish the relative contribution of visual and gravitoinertial cues as a function of the quality of the visual cues (good vs. degraded) and the presence or absence of gravitoinertial cues; b) to determine the role of manual control vs. supervisory monitoring control on the estimation of altitude, and c) study the interactions between the nature and the quality of the sensory cues and the type of control. For the supervisory control condition, the results showed that the gravitoinertial component played a significant role in the estimation of ground height, but only in the case where the optical structure did not efficiently specify the actor-environment interaction. Meanwhile, the results for the manual control task provided evidence, at multiple levels, that the acceleration information, specified by the variations of the gravitoinertial field, has a relative character. Altogether, these results are in line with the Sensory Weighted Approach of perception, which proposes that each sensory cue is weighted depending on this reliability: gravitoinertial information is attenuated when the visual information is relevant while it enhances performance when the visual information is poor.