From: rdd@cactus.org (Robert Dorsett)
Subject: Re: HUD question
Followup-To: sci.aeronautics
Organization: Capital Area Central Texas UNIX Society, Austin, Tx
Date: Fri, 6 Nov 1992 03:32:42 GMT

In article <9211051727.AA19848@tecnet1.jcte.jcs.mil> davehyde@tecnet1.jcte.jcs.mil writes:
>refocus your eyes periodically.  It has also been my observation that, on HUD-
>equipped airplanes I've flown, that I had to re-focus somewhat to read info on
>the HUD after looking through it to see outside.  I don't have an explanation
>for this, but I've seen it in several airplanes.

It appears that even the slightest accumulation of dust, grease, or other
particulate matter on the collimater will ruin the infinite-perspective
effect.


>And for my last observation....If you're in VMC and staring through a typical
>(as they exisit in production today) HUD, you won't see anything coming at you
>outside of boresight.  I.E. a HUD may not be the ideal thing for
>VFR...encouraging eyes-out but giving you a focal point.  It's still a "scan
>periodically" instrument, albeit with more information presented than most.

From HUMAN FACTORS IN AVIATION (Nagel & Wiener, Academic Press, 1988), p. 399:

"If information processing along one channel is unaffected by events on the
other, does this mean that processing between the two channels is serial
rather than parallel?  This hypothesis was supported in a simulator inves-
tigation by Fischer, Haines, and Price (1980), who examined the pilot's
ability to detect an unexpected obstacle on a visually simulated runway while
flying with or without a HUD.  Some of the pilots had failed even to notice
the object, a large aircraft partially on the runway.  When detected, reac-
tion time to detect the plane was actually longer with the HUD than with the
conventional head-down display.  To account for these results, it may be 
assumed that the attentional world was partitioned between near and far
channels, on the basis of optical and motion cues.  Then, in the serial 
processing mode, pilots focused on the near, while filtering out far, infor-
mation.  These findings tend to support Neisser and Becklan's (1975) conclu-
sion that parallel processing of information from two visual scenes may not
occur, even when these are superimposed in visual space.  Of course, such 
serial processing occurs with head-down displays as well.  However, in 
these conditions pilots presumably are aware that they *must* sample, since
physical constraints on peripheral vision prevent outside information from
registering while they are head-down.  Therefore, fairly rigid and optimal
scanning strategies will be invoked to check the far domain of the outside
world.  This optimal sampling may break down when scanning is no longer 
required in the HUD." (sic)

References cited:

Fischer, E., Haines, R., & Price, T. (1980) "Cognitive issues in head-up
displays (NASA Technical Report # 1711).  Washington, DC: NASA.

Neisser, V., & Becklan, R. (1975).  "Selective looking: attention to visually
specified events."  Cognitive Psychology, 7, 480-494.






---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd
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