Effects of scene content and horizon on glideslope control

This study is part of a continuing program of research whose goal is the identification of the sources of information used by pilots performing visually guided landing approaches. One source of information that has received empirical support is the horizon-aimpoint angle, which subtends the distance from the horizon to the runway aimpoint. This angle remains invariant for a constant angle of approach, and thus serves as a means to determine deviations from the specified glideslope. It has been shown that a high or low horizon biases glideslope control in a systematic fashion, and that the addition of a perspective gradient weakens this bias. The first experiment reported examines the effect of the density of the perspective gradient on glideslope control, to see if a gradient of sufficient density can eliminate the bias induced by a high or low horizon. The second experiment explored the differential effects of a perspective gradient and moderately realistic scene detail when restricted to the foreground or background fields of a visual scene