Re: Driving and 3d

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Fri, 22 Aug 1997 21:29:09 -0500
>From: "P3D  Dr. George A. Themelis"  <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
>Subject: Re: Driving and 3d

>>>Have you even experienced lack of stereopsis
>>>with both your healthy eyes wide open?  

>>just close one eye while driving. 

>I asked about having both eyes open, on purpose.  I tend to believe
>that TEMPORARILY closing one eye is a poor imitation of not having 
>stereopsis FOR YOUR ENTIRE LIFE.

>>*****  If one does *not* have stereopsis functionality, that is a
>>significant amount of less information available to the driver. 

>Information that the driver needs while he/she is driving?

>Because I have not experienced lack of stereopsis with both eyes
>open, I cannot speak for the effects of this deficiency during
>driving... But logic suggests that since most objects are beyond
>20 feet and everything is in constant motion (motion parallax
>is experienced without stereopsis, correct?) lack of stereopsis
>would not be missed...

Your line of reasoning appears to include a strong implicit assumption
that quality of visual information for a driver is judged by a Boolean
criterion - that either "there is sufficient visual information for
driving" or "there is not sufficient visual information for driving".
Of your multiple recent posts on this subject, all that I have read
appear to support this viewpoint.

I disagree with this viewpoint. Humans use many visual cues and many
sources of information while driving. There is a tremendous variation
in the amount of relevant information availble while driving, and the
safety and enjoyability of driving is strongly affected by the amount of
information availble. As an analogy, far less visual information is
available to the driver at night than during the day, and even when
other factors are the same I consider night driving to be less enjoyable
and more hazardous than day driving in terms of the risk of hitting
obstacles, etc. Driving at night in an unfamiliar city in the rain is
a classic example of a situation in which the visual information available
to the driver is far less than what the driver would like - the feat may
be attempted, but generally the driver wishes it were a sunny day.

Motion parallax and angular displacement between headlights do provide some
depth cues, and people with or without stereoscopic vision both use these
cues, but the characteristics of depth perception using these cues differ
from the characteristics of stereoscopic depth perception - for example,
motion parallax requires integration over time, generally a longer time for
greater accuracy, while stereoscopic perception provides depth perception
"at a glance" - very rapidly. Having both sets of cues allows them to be
compared to one another, for greater total accuracy of distance judgement.

Regarding the case you mention of a person who has never had sterescopic
vision, it's true that people who lack one sense tend to improve their
interpretation of other senses to compensate, but that's not to say they
will get up to the level of capability they would have achieved if they
had the missing sense. And it doesn't mean that people with stereo vision
don't make use of it while driving.

My mother recently scratched her eye and had to wear an eyepatch for a
few days. It was not a permanent situation, but considerably longer than
a few seconds of covering one eye. She was sufficiently concerned over the
reduced ability to perceive depth (not just reduction of field of view)
that she arranged to have someone else drive for her during that time.

In conclusion, I strongly disagree with the contention that for a driver,
the lack of stereopsis would not be missed.

John R



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