Another study also challenges the notion of working memory being
   deficient in people who are deaf because HEARING people who used
   British Sign Language had the same inability to reach the
   magical 7 +/-2 level of serial recall. This doesn't answer the
   OP - but the point is: our phonological loop (which is where the
   speaking-words-in-our-mind) is not terribly important in
   measures of intellectual ability. What does this imply for the
   OP? Not much, except we give our "thinking in spoken words" part
   of our mind perhaps a little more credit than it might be due.
   Or rather: We *too* do not think exclusively in auditory words.
   [1]http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4419661/ "A
   disadvantage for serially-presented linguistic material is also
   found when deaf participants undertake the digit span or letter
   span task in a sign language. Deaf native American Sign Language
   (ASL) signers recall on average only 5 * 1 digits in forward
   tasks, compared to hearers who recall an average of 7 * 2 digits
   (Boutla et al., 2004; Bavelier et al., 2006). Hall and Bavelier
   (2010, p. 54) have concluded that *speech-based representations
   are better suited for the specific task of perception and memory
   encoding of a series of unrelated verbal items in serial order
   through the phonological loop.* Conway et al. (2009) go further
   and propose the *auditory scaffolding hypothesis,* whereby one's
   experience with sound helps provide a scaffold for the
   development of those general cognitive abilities that are
   required for the representation of temporal or sequential
   patterns. However, Bavelier and colleagues' work shows that
   hearing English-ASL bilingual adults also show the same
   disadvantage for sign span compared to spoken span (Bavelier et
   al., 2008), which challenges the auditory scaffolding hypothesis
   because these individuals have had rich auditory input since
   birth. In any case, it is clear that performance on spoken
   serial recall tasks may not be directly comparable to
   performance on signed serial recall tasks."   ===
   [2]http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2945821/ Among
   hearing people, the phonological loop is partially relied upon
   for working memory but not exclusively. There's a heuristic - a
   "rule of thumb" that's used as a baseline, of 7 distinct items
   in working memory, +/- two, but according to this study, people
   born deaf do not have diminished working memory capacity,
   although they DO have fewer "items" available to recall in a
   serial fashion - at least *seem-to*. IN this article the
   rule-of-thumb itself is questioned because the 7 +/-2 was rather
   over-reaching... and in fact people who have hearing, their
   levels of serial item recall is typically at the same levels as
   ASL users with only minor adjustments to lab study. So, point
   is: The "extra two" that are sometimes measured are _likely_
   echoing in the phonological loop. Meaning: There's not much
   significance to the phonological loop to working memory.

References

   Visible links
   1. https://l.facebook.com/l.php?u=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC4419661%2F&h=qAQHtap0U
   2. https://l.facebook.com/l.php?u=http%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC2945821%2F&h=tAQHB8qcH