[R] Proportion test in three-chices experiment

[Rafael Laboissiere]

Hi,

I wish to analyze with R the results of a perception experiment in which
subjects had to recognize each stimulus among three choices (this was a
forced-choice design).  The experiment runs under two different
conditions and the data is like the following:

   N1 : count of trials in condition 1
   p11, p12, p13: proportions of choices 1, 2, and 3 in condition 1
   
   N2 : count of trials in condition 2
   p21, p22, p23: proportions of choices 1, 2, and 3 in condition 2
   
How can I test whether the triple (p11,p12,p13) is different from the
triple (p21,p22,p23)?  Clearly, prop.test does not help me here, because
it relates to two-choices tests.

I apologize if the answer is trivial, but I am relatively new to R and
could not find any pointers in the FAQ or in the mailing list archives.

Thanks in advance for any help,

-- 
Rafael Laboissiere