Vocal analysis related to changes in frequency of pure tone auditory feedback.

Abstract

Many studies have shown that subjects show a change of vocal fundamental frequency (F0) when phonating subjects hear their vocal pitch feedback shifted upward or downward. This study was performed to demonstrate whether vocal parameters [F0, intensity, jitter, shimmer, and noise to harmonic ratio (NHR)] in normal males respond to changes in frequency of pure tone masking.
Twenty healthy male subjects participated in this study. Subjects vocalized /a/ vowel sounds while listening to a pitch- shift pure tone through headphones (upward pitch-shift in succession: 1 kHz to 2 kHz and 1 kHz to 4 kHz at 50 dB or 80 dB, respectively, downward pitch-shift in succession: 1 kHz to 250 Hz and 1 kH to 500 Hz at 50 dB or 80 dB, respectively).
Vocal intensity, F0, was increased, whereas jitter was decreased as the pitch of pure tone was shifted upward. However, there was no correlation between shimmer and NHR with pitch-shift feedback for pure tones. Unlike vocal pitch- shift feedback in other studies, upward pitch-shift feedback of pure tones caused the vocal F0 and intensity to change in the same direction as pitch-shift.
The results of this study demonstrated that auditory kinesthetic feedback is affected by pitch-shift in pure tone.

Full text

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Yonsei Med J 49(4):610 - 614, 2008
DOI 10.3349/ymj.2008.49.4.610
Yonsei Med J Vol. 49, No. 4, 2008
Purpose: Many studies have shown that subjects show a
change of vocal fundamental frequency (F0) when phonating
subjects hear their vocal pitch feedback shifted upward or
downward. This study was performed to demonstrate whether
vocal parameters [F0, intensity, jitter, shimmer, and noise to
harmonic ratio (NHR)] in normal males respond to changes
in frequency of pure tone masking. Materials and Methods:
Twenty healthy male subjects participated in this study.
Subjects vocalized /a/ vowel sounds while listening to a pitch-
shift pure tone through headphones (upward pitch-shift in
succession: 1kHz to 2 kHz and 1 kHz to 4 kHz at 50 dB or
80 dB, respectively, downward pitch-shift in succession: 1 kHz
to 250Hz and 1kH to 500 Hz at 50dB or 80 dB, respectively).
Results: Vocal intensity, F0, was increased, whereas jitter was
decreased as the pitch of pure tone was shifted upward.
However, there was no correlation between shimmer and NHR
with pitch-shift feedback for pure tones. Unlike vocal pitch-
shift feedback in other studies, upward pitch-shift feedback of
pure tones caused the vocal F0 and intensity to change in the
same direction as pitch-shift. Conclusion: The results of this
study demonstrated that auditory kinesthetic feedback is
affected by pitch-shift in pure tone.
Key Words: Pitch, feedback
INTRODUCTION
Auditory feedback through acoustic auto-moni-
toring of vocal output plays an important role in
the control of phonation. Vocal intensity tends to
increase in response to masking noise, and this is
known as the Lombard effect. In addition to vocal
intensity, F0 is closely linked to the auditory
system.1
Severalexperimental
demonstrated that subjects change their F0 with
distortion of their vocal feedback.2Tanabe et al.3
showed that another control loop related to vocal
output is feedback from the laryngeal sensory
receptors. This is a complex neuromuscular reflex
system referred to as kinesthetic feedback.4Some
reports showed that kinesthetic receptors are
important for fine control of F0 frequency.5
Although vocal intensity and F0 in response to a
change of intensity in masking noise have been
relatively well studied, there are no previous
investigations on the relationship between vocal
parameters and frequency of pure tone masking.
Some studies have showed that vocal F0 is
reduced to compensate for the disparity of a
perceived vocal pitch that is greater than the
intended pitch,6suggesting that certain ranges of
frequency of the feedback signal can be involved
in vocal control. In addition to vocal pitch-shift
feedback, changes in vocal F0 have also been
observed in response to non-vocal sounds such as
clicks.7,8
However,vocal
differs from non-vocal pitch-shift feedback in that
the latency of response to non-vocal sounds has
been shown to be shorter than vocal pitch-shift
response. The term "pitch-shift response" refers to
this process. Therefore, pitch-shift response helps
to stabilize vocal F0 around an actual or intended
target F0. However, earlier studies are limited by
the use of stimuli that were short and presented
suddenly.
In our study, we investigated whether auditory
kinesthetic feedback was sensitive to pitch-shift
studieshave
pitch-shiftfeedback
Vocal Analysis Related to Changes in Frequency of Pure
Tone Auditory Feedback
Sang-Hyuk Lee, Kyung-Chul Lee, Jae-Ho Ban, No-Hee Lee, and Sung-Min Jin
Department of Otorhinolaryngology-Head and Neck Surgery, Kangbuk Samsung Hospital, Sungkyunkwan University School of
Medicine, Seoul, Korea.
Received November 1, 2007
Accepted January 8, 2008
Reprint address: requests to Dr. Sung Min Jin, Department of
Otorhinolaryngology-Head and Neck Surgery, Kangbuk Samsung
Hospital, Sungkyunkwan University School of Medicine, 108
Pyoung-dong, Jongro-gu, Seoul 110-746, Korea. Tel: 82-2-2001-
2264, Fax: 82-2-2001-2273, E-mail: strobojin@hanmail.net

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Vocal Response to Pitch-Shift Feedback of Puretone
Yonsei Med J Vol. 49, No. 4, 2008
with pure tones while vocalizing vowel sounds as
shown by vocal pitch-shift feedback. We also
analyzed the change in stability of phonation
(jitter, shimmer, and NHR) as well as vocal F0
elicited by perturbations in pitch of pure tones.
MATERIALS AND METHODS
Twenty healthy male subjects (28 - 33 years of
age; mean age, 29.7 years) participated in this
study. None of the subjects had a history of
neurological deficits; speech, language, auditory
or voice disorders, and were not trained singers
or regular smokers. Each subject passed a hearing
screening test at the 15 dB sound pressure level
(SPL) for 500, 1 k, 2 k, 4 k, and 8 kHz bilaterally.
Subjects were seated comfortably in a sound-
treated booth. They were instructed to vocalize
/a/ vowel sounds at a comfortable and steady
habitual pitch while listening to pitch-shift of pure
tones through headphones. All subjects were
tested for 8 binaural pitch-shift masking condi-
tions (increasing pitch-shift in succession: 1 kHz to
2 kHz and 1 kHz to 4 kHz at 50 dB or 80 dB,
respectively; decreasing pitch-shift in succession: 1
kHz to 250 Hz and 1 kHz to 500 Hz at 50 dB or
80 dB, respectively). While subjects sustained the
vowel sounds for 5 seconds, we changed the
frequency of masking at 3 seconds. The first and
last 500 ms of each vowel sound were discarded
to minimize any potential initiation and termina-
tion effects. Half of all subjects received increasing
pitch-shift masking after decreasing pitch-shift
masking with a break of 5 minutes between con-
ditions. The other half received increasing pitch-
shift masking followed by decreasing pitch-shift
masking. Vocal responses were analyzed by Kay
Elemetrics CSL Model 4300B (Kay Elemetrics
Corporation, Lincoln Park, NJ, USA). Vocalization
was transduced with an AKG c420 microphone
(AKG Acoustics Harman proGmbH, Munich,
Germany). We used an AC 40 (Interacoustics,
Denmark) for the delivery of pitch-shift pure tone.
RESULTS
The mean fundamental frequency, jitter, shimmer,
and NHR in each condition are shown in Fig. 1.
The mean vocal parameters for the pre- and
post-shift periods were separately measured. Each
vocal parameter from the pre-shift period was
subtracted from that of the post-shift period;
positive numbers indicate increasing changes and
negative numbers decreasing changes.
For change of vocal intensity, the mean vocal
intensity was significantly increased as pitch of
pure tone shifted upward for each of the condi-
tions (Fig. 1A). Sixteen subjects (1 kHz to 2 kHz
and 1 kHz to 4 kHz at 50 dB), 18 (1 kHz to 2 kHz
at 80 dB), and 19 (1 kHz to 4 kHz at 80 dB) out of
20 subjects had increased vocal intensity as pitch
tone shifted upward. However, there were no cor-
relation between vocal intensity and downward
pitch-shiftfeedback. The
response of vocal intensity was greater at the
pitch feedback of 80 dB than at 50 dB, and it was
greater at a pitch-shift of 1 k to 4 k than at 1 k to
2 k.
For change of fundamental frequency, the mean
vocal F0 increased as pitch of pure tone shifted
upward for each of the conditions (Fig. 1B). The
majority of subjects increased their F0 for an
upward pitch-shiftfeedback
However, there were no significant differences in
the change of F0 when subjects received a
downward pitch-shift feedback of pure tone at 50
dB and 80 dB. The percentage of subjects that
increased their F0 in response to an upward
pitch-shift feedback of pure tone was low by 60%
(1 k to 2 k at 50 dB), 65% (1 k to 4 k at 50 dB), 70%
(1 k to 2k at 80 dB), and 80% (1 k to 4 k at 80 dB).
For change of jitter in response to a shift in
masking frequency, jitter had a tendency to
decrease when masking frequency shifted upward
at 50 dB and 80 dB (Fig. 1C).
For change of shimmer or NHR in response to
shift-masking frequency, there were no correla-
tions between shimmer, NHR, and pitch-shift
feedback (Figs. 1D and E). The degree of change
in shimmer or NHR was negligible.
magnitudeofthe
ofpuretone.
DISCUSSION
Vocal reaction in response to noise is a physio-
logical reflex in preparation for the possibility of

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Sang-Hyuk Lee, et al.
Yonsei Med J Vol. 49, No. 4, 2008
verbal communication. Pitch-shift response to
stabilize vocal F0 by correcting pitch perturbations
has been widely recognized.6This voice auditory
feedback response shows that vocal F0 is opposite
in direction to vocal pitch-shift.9When feedback
pitch is perceived to be lower, vocal F0 is
increased; conversely, when feedback pitch is
perceived to be higher, vocal F0 is decreased.
Speakers modulate their voices to compensate for
changes in pitch of voice auditory feedback.
Most earlierstudies
response to vocal pitch-shift feedback within a
narrow change of pitch (from 50 to 200 cents).10
However, in our study, we tested the effects of
pitch-shift feedback of pure
response in normal hearing subjects. We tested a
pitch-shift of pure tones in a different range from
speech frequency, which is middle- to low-tone
haveanalyzedvocal
tones on vocal
frequency and middle- to high-tone frequency.
Vocal F0 increases when vocal pitch feedback
shifts downward as mentioned above, however,
the shift that increases vocal F0 in response to
pitch of pure tone masking is not downward but
upward. Vocal F0 shows no change when pitch of
pure tone masking was shifts downward. For
vocal intensity, our study showed that vocal
intensity was also increased only when pitch of
pure tone masking was shifted upward. Most
subjects said that they felt as if their speaking was
distorted while hearing the upward pitch-shift of
pure tone masking. According to them, masking
noise seemed to be increasing while hearing an
upward pitch-shift of pure tone masking, and it
was much more intensive at the 80 dB. However,
subjects did not perceive similar changes in pure
tone masking when hearing a downward pitch-
Fig. 1. The mean change of vocal parameters in response to
8 pitch-shift masking conditions. The values of pre-shift
vocal parameters were subtracted from post-shift vocal
parameters at the 50 and 80 dB masking levels. (A) The
mean change of vocal intensity according to the change of
4 different shifts in masking frequency. (B) The mean
change of F0 according to the change of 4 shifts in masking
frequency. (C) The mean change of jitter according to the
change of 4 shifts in masking frequency. (D) The mean
change of shimmer according to the change of 4 shifts in
masking frequency. (E) The mean change of NHR according
to the change of four different shifts in masking frequency.
*Percentage of subjects that
toward the same direction of pitch-shift of pure tone.
changed vocalparameter
AB
CD
E

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Vocal Response to Pitch-Shift Feedback of Puretone
Yonsei Med J Vol. 49, No. 4, 2008
shift of pure tones.
The pathophysiology of our results is not clear.
However, some possibilities include the following.
First, pitch-shift feedback for pure tones resulted
in an overall following response of vocal F0 and
intensity. The following response means that
change of vocal F0 or intensity was in the same
direction as the pitch-shift stimulus. However, it
is well established that vocal pitch-shift feedback
results in an opposing response of the vocal F0:
that is, a change in vocal F0 is in the opposite
direction ofthepitch-shift
vocalizing at a particular pitch, subjects compare
pitch memory with auditory, proprioceptive, and
kinestheticfeedback.11
feedback, subjects may primarily rely on pitch
memory to adjust F0 output, thereby auditory
feedback aligning with memory, which results in
the opposing response. However, for pitch-shift
feedback with pure tones, the frequency of a pure
tone is a frequency different from vocal F0. When
external pitch feedback is clearly different from
subjects' vocal F0, it is likely that subjects tend to
ignore the compensation for the shift of pure tone
frequency. Subjects who follow the direction of
pitch-shiftstimulus may
reference to control vocal F0 and intensity.12
Because an external reference is different from
internal vocal F0, the external reference may
dominate thevocal
mechanism may result in the following response
to vocal F0 and intensity of the response to
pitch-shift feedback of pure tone masking.
Second, vocal F0 is related only to upward pitch
feedback, not the downward pitch feedback. An
increase in pitch of pure tone masking may have
a more noticeable effect than a decrease. one
report on the effects of frequency shift feedback
on vocal F0 showed a similar pattern; the change
of vocal F0 was larger for the upward shift than
the downward shift although the change of
direction was opposite to the stimulus.13
Third, the increase of vocal F0 in response to
upward pitch-shift feedback was related to vocal
intensity. Some investigators have reported that
an increase of F0 occurs concurrently with an
increase of vocal intensity with altered auditory
feedback.14
Inanaerodynamic
intensity usually increased with subglottic air
stimulus.6
When
Forvocal pitch-shift
adopt anexternal
controlsystem. This
study,vocal
pressure, which is associated with increase of F0.15
Although it is not known whether the change of
vocal F0 is secondary to vocal intensity, the
present study showed that pitch feedback for pure
tones could affect vocal F0 and vocal intensity.
As for the relationship between jitter and
pitch-shift feedback, it is important to consider
that the vocalis and cricothyroid muscles exert
morebalancedforce as
increases.15This may lead to increased stability as
reflected by a decrease of the jitter level. However,
shimmer and NHR showed no correlation with
pitch-shiftfeedback.Perhaps,
intensity was too small to change shimmer or
NHR.
The change of vocal parameters in response to
pitch changes of pure tones with unperturbed
vocal feedback has not previously been studied.
Unlike vocal pitch-shift feedback, upward pitch-
shift feedback differed from the subject's voice.
Thepresentresultsshowed
perception made subjects change their vocal F0
and intensity toward the same direction of the
pitch-shift. Therefore, the change of frequency of
puretonealso affects
feedback.
thevocalintensity
thechangeof
thatpuretone
auditory kinesthetic
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