Lengthened voiced stops and the airstream through the nose

Question

I am going through Catford's Practical Introduction to Phonetics, experiments 31-32. After explaining how to produce voiced stops [b], [d], [g] by superimposing a closure upon the voiced air-stream, the author asks the reader to try producing their lengthened variants — [b b], [d d], [g g] by prolonging "the period of closure while keeping the voice going throughout" (p. 44). Catford then remarks that it may be difficult keep the voicing going long enough for lengthened voiced stops and offers a method of doing so by starting to lower the larynx at the moment when the closure is made.

My two questions are:

1. I think I am struggling to do this correctly. Most of the times when I try to pronounce lengthened voiced stops as described above, I feel that the air goes through my nose as well, so the produced lengthened [b], for example, inevitably involves the humming sound of [m]. Are there any tricks to prevent the air from going to the nose, or is it impossible in this case?
2. In the languages which have geminated voiced stops, are they pronounced by passing the air only through the oral cavity, without any voicing going through the nose?

Answer 1

It is possible that you do lower the velum when you do this, and velum lowering is one of the methods that is used to alleviate the pressure buildup of voiced stops, but it is also possible that your feelings about what you are doing is wrong. You could be reacting to pressure against your velum and/or the acoustic consequences of acoustic transduction of glottal pulses beating on the thinned-out soft palate, leading to vibrations in the nasopharynx. If you put your thumb on your nose-holes, you should be able to feel whether there is actual air escaping though the nasal passages, and you can more clearly detect the vocal fold vibrations causing tour nose to vibrate a tiny amount (if there is nasal air flow).

Voiced geminate stops are rare enough in the world's languages, and nasal airflow studies are rare enough, that it is risky trying to make any generalizations about nasalization as a compensatory articulatory process for coping with pressure buildup. Fujimoto and Funatsu find that there is not any nasal airflow in the production of Japanese geminate voiced stops (instead, there is devoicing). I know of no airflow study that shows nasalization of geminate voiced stops, but nobody has does an airflow study of Luganda, for example. Ghalib apparently gathered data on nasal airflow during geminate vs. singleton stop production in Iraqi Arabic, but doesn't report a general pattern for nasal airflow (it was apparently collected but not analyzed). There is no increase in nasal airflow in the provided mingogram trace in appendix 4, but that is just a single token. I would say that we just don't know if phonetic nasalization of voiced geminates occurs. There are no reported instances of phonological nasalization (/bb/ → [mm], neutralizing with /mm/).

Answer 2

If you're producing nasals then you must be allowing your velum to drop. No fair. You have to find some way to enlarge the closed air cavity above your larynx. There are several ways to do this. One is to lower your larynx, as Catford suggests. Watch your throat in a mirror and you may be able to see your larynx bobbing downward, if you're doing this successfully. Exaggerate this a little and you'll be making implosives (and the attempt to keep voiced stops from being devoiced by back-pressure above the larynx has been suggested as an origin for the implosive series' in some languages).

Or, you can relax your cheek muscles enough that they bulge out to make more room in your mouth. For labials, you can let your lips bulge. I call this the Bing Crosby maneuver, since I think he did this in his singing. It gave the impression that he was very relaxed in his performances.

Or, you can drop your jaw. That might affect vowel quality.