[OS X Emacs] matlab -nodesktop in Aquamacs

[Claire]

Hi 

I'm running Aquamacs 2.2 on Mac OSX 10.6.8 and I'd like to be
able to run Matlab within Aquamacs. Within my bash shell I 
have aliased matlab to "matlab -nodesktop".  However, when I 
type 

M-x matlab-shell

from within Aquamacs, matlab opens in the gui, i.e without the 
'nodesktop' flag. I tried adding the line: 

(setq matlab-shell-command-switches "-nodesktop")

to my Preferences.el file, but Aquamacs returns the error:

wrong type argument: listp, "-nodesktop".

Does anyone know what I'm doing wrong, and how to correct this?

Any help much appreciated.

Claire