Test of a Model of Visual Spatial Discrimination and Its Application to Helicopter Control.

Abstract : A series of 4 laboratory studies and 3 field studies using a helicopter in hovering flight were undertaken to validate and test the assumptions made in and the predictions made from the Thielges-Matheny 'Analysis of Visual Discrimination in Helicopter Control'. The results of the field studies generally were in accordance with the predictions made from the model. In particular, certain results suggest that improved hover accuracy is obtained when the pilot is required or otherwise induced to use an eye-line-of-regard depressed substantially below his customary visual scan pattern. The laboratory studies were concerned primarily with validating the assumptions made in the Thielges-Matheny model concerning visual discrimination of changes in angular separation or relationship of two points in the visual field. The results of the laboratory studies show that the simple Weber ratio is not an adequate index of discriminability of displacement of one point with respect to the other. One of the results, that detection of motion across the imaginary line separating the two points is at least as easy as detection of displacement along that line, allows a considerable simplification of the model without changing its more important predictions. The most striking finding of the laboratory studies is the appearance of an 'Angular shrinkage illusion' which causes the angular separation of two points to be recalled as less than it actually was.