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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.

The effects of prolonged (5 × 45 min) reading (loading) on time-based glottal waveform parameters of normal female and male subjects (n = 80) were studied. Two rest (morning and noon) and three loading (two in the morning and one in the afternoon) samples were recorded and analyzed. The glottal waveforms were obtained by inverse filtering of the acoustical signal using an automatic method. The following time-based parameters were analyzed from the estimated glottal flow waveform: (1) length of fundamental period (T); (2) open quotient (OQ); (3) speed quotient (SQ); (4) closing quotient (C1Q). The analysis was based on inverse filtering of the first stressed syllable of ‘paappa’ words produced with normal, maximally soft and maximally loud phonation. In the morning samples the loading affected only the T and OQ values of normal phonation in a statistically significant manner. In the afternoon all the quotient values changed statistically significantly in loud and normal phonation. On the basis of increased SQ and decreased C1Q values of females it is hypothesized that the female voices tended to change towards hyperfunction due to vocal loading.

The effects of prolonged (5 × 45 min) reading in different environmental and ergonomic conditions on time-based glottal waveform parameters of normal female and male subjects (n = 80) were studied. The exposure groups (n = 5 females and males per cell) consisted of eight combinations of the following factors: (1) normal ( < 65 dB) or high ( > 65 dB) speech output level; (2) sitting or standing posture; (3) low (25 ± 5%) or high (65 ± 5%) relative humidity of ambient air. Two rest (morning and noon) and three loading (two in the morning and one in the afternoon) samples were recorded and analyzed. The glottal waveforms were obtained by inverse filtering of the acoustical signal using an automatic method. The following time-based parameters were analyzed from the estimated glottal now waveform: (1) length of fundamental period; (2) open quotient; (3) speed quotient, and (4) closing quotient. The analysis was based on inverse filtering of the first stressed syllable of ‘paappa’ words repeated 3x5 times with normal, maximally soft and maximally loud phonation. Humidity was a significant factor in serveral instances. The interactions between gender and the loading factors were striking.