proto-southwestern-tai revised: a new reconstruction - seals 22

Contact Induced Change? 9
There is therefore a certain amount of variation in the number of tokens produced by each
subject, with a tendency for educated speakers to skip fewer words.
The laryngeal activity of the subjects was recorded with an EG2-PC
electroglottograph (EGG) while they were reading the wordlist. Their speech was also
recorded acoustically via a microphone plugged into the EGG box. EGG (or
laryngography) consists in placing electrodes on each side of the speaker’s neck, at the
level of the larynx box, and to drive a low level electrical current (less than one volt)
between the two electrodes. Electrical conductivity will vary according to the degree of
opening of the glottis (closed glottis: good conductivity; open glottis: resistance), which
allows the researcher to measure the patterns of opening and closing of the vocal folds in
real time and therefore to infer their rate of vibration (f0, the phonetic correlate of pitch)
and the degree of closure of the glottis (open quotient, the articulatory correlate of voice
quality). The EG2-PC laryngograph also allows the researcher to measure the vertical
position of the larynx. However, these results are beyond the scope of this paper and will
not be discussed here.
In order to obtain perfectly synchronized signals, the outputs of the EGG and of the
microphone were channelled through a National Instrument data acquisition box. The
signal was then acquired on a laptop computer at a sampling rate of 22,050 Hz with a
MATLAB script.
2.4 Data processing and result extraction
The acoustic signal acquired with MATLAB was converted into a wav sound file that was
used to determine the boundaries of the segments to be measured. The beginning and
endpoints of the onsets, vowels and codas (if applicable) of each target word in the
wordlist were labelled in Praat textgrids. Since the acoustic indicators investigated here (f0,
open quotient, formants) can only be realized on voiced sonorants and since there are
relatively few words with onset sonorants in the wordlist, only measurements made on
vowels will be reported in section 3.
A MATLAB routine combining Alexis Michaud’s MATLAB-based EGG analysis
scripts and a Praat script was then used to extract the f0 (pitch), open quotient (% of the
glottal cycle during which the glottis is open), the frequency of the first and second
formants and the duration of the segments under investigation. Target segments were
measured at five sampling points: their onsets, offsets and three intermediate points. For
measurements made from individual glottal cycles (f0 and open quotient), the cycle that
was measured was the one whose peak was the closest to the sampling point, while being
within the same segment.
2.4.1 F0 (pitch)
The number of glottal cycles per second (f0), which is the articulatory correlate of pitch,
was measured directly from the EGG signal (a second was actually divided by the duration
of the target cycle). The major advantage of this type of measurement is that we can avoid
inaccuracies that are common when pitch trackers are attempting to locate glottal cycles on
waveforms that include the acoustic effect of the supraglottal cavity. A few suspicious
measurements were removed from the dataset by excluding values that were more than two
standard deviations away from the mean (calculated independently for each speaker). Since