Example of soft onset of phonation.
At the start of the film the vocal folds are abducted for
respiration. Adduction then starts at about 50 ms. Note that the
vocal folds start to vibrate (at about 120ms) before adduction is
complete. i.e for the first few cycles they vibrate without forming
a firm closure. This would be characteristic of what is called
breathy phonation
(for this speaker an audio signal is also available, which
confirms this impression).
Note that this speaker leaves a very slight gap open between
the arytenoids even after completion of adduction. This is quite
common and perfectly normal.
Although the changes in the vertical orientation of the vocal
folds are not so easy to see in this example, nonetheless the
good image quality gives a good impression of the
displacements occuring on the surface of the vocal folds, with
their gelatine-like consistency.
A few cycles of fully developed phonation from the previous film.
Unlike in the previous example the vocal folds adduct
completely before phonation starts. Notice how the adduction in
the region of the false vocal folds relaxes somewhat just before
the vocal folds start to vibrate. Initially, vibration is just in the
anterior part of the glottis, but spreads over the first couple of
cycles to include the whole length.
It is easier in this example than in the previous example of the female speaker to see the
changes in vertical orientation of the vocal folds over the course
of each vibratory cycle.
A few cycles of fully developed phonation.
Similar to previous example (male speaker 1), but with an even "harder" onset.
During the first 200ms strong adduction takes place, then for the
next 100ms little change occurs, the view of the true vocal folds
being considerably obscured by the strong adduction of the
false vocal folds. Then following relaxation of the false vocal
folds over about the following 70ms phonation starts. Thus, both
this example and the previous one have glottal stops preceding
phonation onset.
A few cycles of fully developed phonation.
This example shows the pattern of vibration in the presence of
paresis of the recurrent laryngeal nerve. This affects the
innervation all laryngeal muscles except the cricothyroid, and
thus means that the tension in the affected vocal fold cannot be
regulated properly, and that it also cannot be properly adducted
(or abducted). The two vocal folds thus effectively try to vibrate
at different frequencies, which means that a clear division of the
glottal vibratory cycle into open and closed phases cannot be
achieved. In a severe case such as this almost no sound
production is possible, but note that even under such
unfavourable conditions some vibration does occur.
The detailed film shows a striking consequence of the difference
in the vibratory properties of the two vocal folds: phases occur
where both vocal folds are tending to move in the same
direction.