Biomedical subjects

Paavo Alku

Publications and source records attributed to Paavo Alku.

42 records · Page 3Linked to original sources

PubMed2002

Cortical processing of speech sounds and their analogues in a spatial auditory environment.

We used magnetoencephalographic (MEG) measurements to study how speech sounds presented in a realistic spatial sound environment are processed in human cortex. A spatial sound environment was created by utilizing head-related transfer functions (HRTFs), and using a vowel, a pseudo-vowel, and a wide-band noise burst as stimuli. The behaviour of the most prominent auditory response, the cortically generated N1m, was investigated above the left and right hemisphere. We found that the N1m responses elicited by the vowel and by the pseudo-vowel were much larger in amplitude than those evoked by the noise burst. Corroborating previous observations, we also found that cortical activity reflecting the processing of spatial sound was more pronounced in the right than in the left hemisphere for all of the stimulus types and that both hemispheres exhibited contralateral tuning to sound direction.

Acoustic Stimulation↗

PubMed2002

Normalized amplitude quotient for parametrization of the glottal flow.

Normalized amplitude quotient (NAQ) is presented as a method to parametrize the glottal closing phase using two amplitude-domain measurements from waveforms estimated by inverse filtering. In this technique, the ratio between the amplitude of the ac flow and the negative peak amplitude of the flow derivative is first computed using the concept of equivalent rectangular pulse, a hypothetical signal located at the instant of the main excitation of the vocal tract. This ratio is then normalized with respect to the length of the fundamental period. Comparison between NAQ and its counterpart among the conventional time-domain parameters, the closing quotient, shows that the proposed parameter is more robust against distortion such as measurement noise that make the extraction of conventional time-based parameters of the glottal flow problematic. Experiments with breathy, normal, and pressed vowels indicate that NAQ is also able to separate the type of phonation effectively.

Adult↗

PubMedDate not supplied

Dynamic extremes of voice in the light of time domain parameters extracted from the amplitude features of glottal flow and its derivative.

In the first part of the study, the subjects (4 females, 4 males) produced sustained breathy, normal and pressed types of phonation. The maximum AC flow (f(ac)) and the negative peak amplitude (d(min)) of the first derivative of the glottal flow were extracted from glottal volume velocity waveforms estimated by inverse filtering. The ratio between f(ac) and d(min) (amplitude quotient, AQ), which gives an estimate of the closing time of the glottal flow, and its normalised version (NAQ) were computed. The NAQ values correlated strongly with the closing quotient of glottal flow. In the second part of the study, the aim was to investigate the dynamic extremes of the human voice in terms of F(0), SPL, f(ac), d(min), AQ and NAQ as well as the intraoral pressure (p) used for subglottal pressure estimation. Eleven normal subjects (5 females, 6 males) participated in this experiment. The subjects started with the production of soft phonation (approximately 55 dB at 40 cm) and increased their vocal intensity at 5-dB steps up to the level of 105 dB. At the analysis stage, the voice samples were divided into three categories: soft (<70 dB), normal (70-90 dB) and loud (>90 dB). In soft and normal phonation, intensity change was correlated with changes in the shape of the glottal flow waveform, whereas the loud voice samples showed a large increase in F(0) and p values. At the loudest extreme, d(min) approached its maximum and AQ its minimum values and NAQ started to rise. In terms of the NAQ values of stressed syllables, the type of phonation was breathy in the soft intensity category, whereas in the normal and loud intensity categories it was within the range of the pressed type of phonation of sustained phonation samples.

Adult↗

PubMedDate not supplied

Loading-related subjective symptoms during a vocal loading test with special reference to gender and some ergonomic factors.

Vocal loading-related subjective symptoms were studied in a day-long vocal loading test. The voices of 40 female and 40 male voluntary young students were loaded by having them read aloud a novel for five times 45 min. The subjective symptoms that occurred during the vocal loading session were reported by filling in a questionnaire after each session. The responses loaded on five factors in a factor analysis: (1) 'central fatigue'; (2) 'symptoms of the neck, shoulders and back'; (3) 'drying in the mouth and throat'; (4) 'symptoms of the throat'; (5) 'symptoms of the voice'. The exposure groups (5 females and 5 males per cell) consisted of eight combinations of the following factors: (1) low (25 +/- 5%) or high (65 +/- 5%) relative humidity of ambient air; (2) low [<65 dB(SPL)] or high [>65 dB(SPL)] speech output level of vocal loading; (3) sitting or standing posture during vocal loading. The lowest mean score for symptoms pooled over the test were found in 'symptoms of the neck, shoulders and back' and the highest mean symptom score in 'drying in the mouth and throat' and 'symptoms of the throat'. Most symptoms were at their minimum during the first loading session and increased statistically significantly to a peak mean value after three or five vocal loading sessions. Statistically significant differences in the mean level between the gender or exposure groups emerged for 'central fatigue' (humidity had clear effects) and 'symptoms of the neck, shoulders and back' (gender, humidity and posture had clear effects). In these cases, females had more symptoms than males; the low-humidity group had more symptoms than the high-humidity group, and the standing subjects had more symptoms than the sitting subjects.

Adolescent↗

PubMedDate not supplied

Experiences of a short vocal training course for call-centre customer service advisors.

It is commonly known that occupational voice users suffer from voice symptoms to varying extents. The purpose of this study was to find out the effects of a short (2-day) vocal training course on professional speakers' voice. The subjects were 38 female and 10 male customer advisors, who mainly use the telephone during their working hours at a call centre. The findings showed that although the subjects did not suffer from severe voice problems, they reported that the short vocal training course had an effect of some of the vocal symptoms they had experienced. More than 50% of the females and males reported a decrease in the feeling of mucus and the consequent need to clear the throat, and diminished worsening of their voice. Over 60% thought that voice training had improved their vocal habits and none reported a negative influence of the course on their voice. Females also reported a reduction of vocal fatigue. The subjects were further asked to respond to 23 statements on how they experienced the voice training in general. The statements 'I learned things that I didn't know about the use of voice in general' and 'I got useful and important knowledge concerning my work' were highly assessed by both females and males. The results suggest that even a short vocal training course might affect positively the self-reported well-being of persons working in a vocally loading occupation. However, to find out the long-term effects of a short training course, a follow-up study would need to be carried out.

Adult↗

PubMedDate not supplied

Subtitled videos and mismatch negativity (MMN) investigations of spoken word processing.

The purpose of this study was to determine whether the presence of subtitles on a distracting, silent video affects the automatic mismatch negativity (MMN) response to simple tones, consonant-vowel (CV) nonwords, or CV words. Two experiments were conducted in this study, each including ten healthy young adult subjects. Experiment 1 investigated the effects of subtitles on the MMN response to simple tones (differing in frequency, duration, and intensity) and speech stimuli (CV nonwords and CV words with a /d/-/g/ contrast). Experiment 2 investigated the effects of subtitles on the MMN response to a variety of CV nonword and word contrasts that incorporated both small (e.g., /d/ vs. /g/) and/or large (e.g., /e:/ vs. /el/) acoustic deviances. The results indicated that the presence or absence of subtitles on the distracting silent video had no effect on the amplitude of the MMN or P3a responses to simple tones, CV nonwords, or CV words. In addition, the results also indicated that movement artifacts may be statistically reduced by the presence of subtitles on a distracting silent video. The implications of these results are that more "engaging" (i.e., subtitled) silent videos can be used as a distraction task for investigations into MMN responses to speech and nonspeech stimuli in young adult subjects, without affecting the amplitude of the responses.

Acoustic Stimulation↗