Table 2.
Overview of the speech variables related to their respective stage in the process of speech production (i.e., breathing, phonation and resonance), the stressors that impact them.
| Speech parameters | Speech process | Stressors impact | Remarks |
|---|---|---|---|
| • Respiration rate | Breathing | Physical load | Competition between ventilation processes speech |
| • Articulation rate | and metabolic demands muscles: inappropriate breathing | ||
| • Word duration | pause placements. | ||
| • Vowel duration | |||
| • Respiration time between words or sentences | |||
| • Voice Onset Time (VOT) | |||
| • Voicing and voiceless transients | |||
| Acute hypoxia | Different impact on speech between chronic and acute hypoxia. | ||
| Alcohol | Slurred speech. | ||
| Emergencies | Faster articulation rate. | ||
| F0-based variables: | |||
| • Mean F0 SD | Phonation | Physical activity | Fatigue vs. metabolic response? |
| • Min to max range | |||
| • F0 peaks | |||
| • F0 floor values | |||
| • Relative average perturbation | |||
| Acute hypoxia | Difference between chronic and acute hypoxia. | ||
| Alcohol | Replication study needed. | ||
| Sleep deprivation | Impact in correspondence with circadian rhythm. | ||
| Emergencies | Real-life stress clear impact but influence of voluntary control. | ||
| Cognitive workload | Challenge to differentiate between emotional and cognitive load. | ||
| Different types of emotions | Variable results. | ||
| • Jitter | Phonation | Emergencies | Decrease jitter: only one study with N = 1. |
| • Shimmer | |||
| Cognitive workload | Decrease jitter Decrease shimmer. | ||
| • Signal to noise ratio (SNR) | Phonation | Alcohol | Strong indicator in combination with F0. |
| • Harmonic to noise ratio (HNR) | |||
| Harmonic Richness Factor | Phonation | Physical activity | Subject dependent. |
| Harmonics | Phonation | Different emotions: anger, neutral with little sadness and loudness | Only one study found. |
| Formants | Resonance | Physical load | Only one study with lot of non-responders. |
| Emotional load – Emergency | Significant variations between stress and non-stress but not for all the types of vowels, with different senses of variation on vowel type with stress arousal. | ||
| Cognitive load | F1, F2, and F3 are vowel specific. F1/F2 ratio potential to differentiate between low and high cognitive load. | ||
| Glottal flow | Resonance | Physical load | Increased open and closing quotient indicative of a breathy voice – decreased open and closing quotient of a pressed voice. |
| NAQ | Resonance | Physical load | Potential for NAQ – F0 combination. |
| MFCC | Resonance | Sleep deprivation | Circadian pattern |
| Emotional load | Vowel-dependent? Important to preselect appropriate mel-filters. |