# Presentation: 578766

## Effect of Predictor Length and Encounter Geometry on 

- Estimates of Future Position

- Sheila Holland
- San Jose State University
- NASA-Ames Research Center

- For free-flight, pilots will require a tool that presents
- predictions of the future position of traffic.  This study examined
- the effects of predictor length and encounter angle on pilots’
- future position estimates, when presented with a straight line
- trajectory predictor.

## Research has shown that future position estimates are better when predictors are longer, but the resulting clutter could obscure other information on the display, especially when many aircraft are present. Research has also shown that pilots exhibit an angular bias in position predictions.  The bias seen resembles a well known visual illusion called the Poggendorff Effect.  If this illusion is occurring, it could have an impact on whether an intruding aircraft is considered threatening.  Since there is some evidence suggesting that longer predictor lines reduce this bias, the work presented here was performed to determine a sufficient predictor line length, while minimizing clutter. 

- Research has shown that future position estimates are better when predictors are longer, but the resulting clutter could obscure other information on the display, especially when many aircraft are present. Research has also shown that pilots exhibit an angular bias in position predictions.  The bias seen resembles a well known visual illusion called the Poggendorff Effect.  If this illusion is occurring, it could have an impact on whether an intruding aircraft is considered threatening.  Since there is some evidence suggesting that longer predictor lines reduce this bias, the work presented here was performed to determine a sufficient predictor line length, while minimizing clutter.

## The Poggendorff Illusion

- If you thought that the line on the right was lower than it should be, you are not alone.  Most people are susceptible to this illusion.  The lines do indeed intersect.  And this illusion has been shown to occur without the rectangle present.

- Do the lines intersect?

## Do the lines intersect?

- The power of this illusion diminishes the more horizontal the line gets. Again the two lines above intersect, but this time they look like they intersect. Therefore, it is expected that this illusion will affect pilots’ judgments when the intruder approaches along a diagonal path.

## Where will the intruding aircraft cross ownships path?

- While the question is different, pilots’ judgments of future position could be susceptible to the same illusion shown in the previous two figures.  In particular, it could lead to missed maneuver opportunities or unnecessary maneuvers.

## Four predictor lengths and six encounter angles were examined in the study.

- Predictor line lengths
- examined in study

## Average Performance for Five General Aviation Pilots

## As predicted by the Poggendorff illusion, error was most pronounced when the intruder was approaching from 45 degrees and 135 degrees.  In both cases, the predicted path was closer to the horizontal that the actual path. 

- The individual lines on the graph represent the data for the different predictor lengths. There was significantly less angular error for the longer predictors  (3 and 5 minutes) than there was for the shorter predictors (none and 1).  There wasn’t any difference between the 3 and 5 minute predictors.  This shows that while the longer predictors improve prediction performance, there is a point where a further increase in length is of no further use.