Reason for crossed projections in the nervous system?

[Edwin Keulers]

In article <48ajig$se3 at news.cuny.edu>,
   Etha Schlemermeyer <etha at genectr.hunter.cuny.edu> wrote:
>
>> 
>>    Cajal thought it was to compensate for optical inversion of the images
>>    projected onto the retinas.  See "Recollections of my Life" pp. 470-475.
>> 
>>                                      John A. Kiernan
>>                                      Department of Anatomy
>>                                      Univ. of Western Ontario
>>                                      LONDON, Canada  N6A 5C1
>>                                      e-mail: kiernan at uwo.ca
>> 
>But you need to compensate for Up-down, not for right-left. ??
>
>Etha

Why would the brain need to compensate for up-down or right-left? There is no 
homunculus watching a screen or something! And even if it were it could be 
standing on it's head. If everything is cross-linked one could interpret the 
whole brain being inverted and upside down so the brain wouldn't have to be 
'aware' of this.