[R-sig-ME] theoretical question about random effects specifications

[Dan McCloy]

In psycholinguistic research, it seems to be common to have random
effects for both subjects (study participants) and items (stimulus
conditions).  I have a somewhat more complicated experiment, where
each stimulus involves one of 180 different sentences, read by one of
20 different talkers.  It is possible (indeed, likely) that responses
will cluster based on who the talker is, and it is also likely that
certain sentences are harder than others.  So the experimental design
would seem to demand random effects for listener, talker, and
sentence.  However, there is a distinct possibility that some
sentences are easy with some talkers and hard with other talkers
(i.e., due to dialect differences that are particularly strong for
certain words).  Question (1):  is it best to account for this
possibility by including a random effect for "stim" (i.e.,
talker-sentence pairing)?  Question (2):  if so, should I include the
separate random effects for talker and sentence in addition to "stim",
or is that redundant?  Question (3):  I've seen some models referenced
on this list and others that use what seem to be interactions between
random effects terms:  (1|x:y) or (1|x/y).  Is there a reference
somewhere where I could read up on these aspects of model
specification?  I tried running one or two of those, and they didn't
seem to behave like interactions between fixed effects (which I'm more
familiar with).