A pharyngealised velar [k\] or uvular [q\] (to use an ad hoc simplification of the SAMPA transcription) would work particularly well as the original phonetic value of *q (and, likewise, [x\] or [X\] for *h2). Pharyngeal constriction (whether involving tongue-root retraction, larynx raising or sphincteric pharyngeal contraction), has the effect of raising F1 and lowering F2 and F3, thus producing an acoustic effect of lowness and backness that may spread to an adjacent frontish vowel (*e > *a) even if the position of the dorsum is actually high. Some conventional notations make pharyngealised dorsals appear prohibited, since they would have to be [+high] and [+low] at the same time, but since pharyngealisation is actually independent of the shape of the body of the tongue, the problem is only notational (and therefore illusory). Such sounds have been reported from a number of languages.
----- Original Message -----
From: Miguel Carrasquer
To: cybalist@yahoogroups.com
Sent: Sunday, September 29, 2002 1:53 AM
Subject: Re: [tied] *h3 (More deja-vu)

>What are the typological grounds for the statement that uvulars
>trigger a-colouring (and not o-colouring, for instance)? What would
>be a possible (neuro)physiological explanation? Just wondering.

Ladefoged & Maddieson (Sounds of the World's Languages, p. 36) describe a study
where in an Arabic speaker uvular /q/ lowers F2 of a following /a/ or /i/, while
(slightly) raising F2 of a following /u/, as compared to velar /k/.  This
amounts to a backing of the vowel (F1 is correlated with high/low, (F2-F1) with
front/back).  The effect is comparable to that of pharyngealization, or
"[A]-colouring" (Arabic /q/ is historically a pharyngealized /k/).