# Changes in Articulatory Contact Pressure as a Function of Vocal Loudness
###### Abstract  
This study evaluated the impact of vocal loudness on the articulatory contact pressure (ACP) between the tongue and palate during the production of lingua-alveolar consonants. Fourteen adults with typical speech produced phrases with the phonemes /t, d, s/ embedded while ACP was sensed with a miniature pressure transducer attached to a palatal appliance. Stimuli were produced at four loudness levels: habitual, twice as load (loud), half as loud (soft), and whisper. There was a statistically significant difference in ACP as a function of loudness for all three phonemes (_p_ < 0.001 for each). Post hoc comparisons indicated that ACP during loud speech was significantly greater than habitual for each phoneme. ACP during soft speech was significantly less than habitual for /t/ and /d/, but not /s/. Whispered speech ACP values were significantly lower than soft for /t/ and /d/, but not /s/. The results indicate that changes in vocal loudness cause changes in ACP that are most evident for stop consonants /t, d/, and, to a lesser extent, the fricative /s/. A louder voice was associated with higher ACP. Elevated ACP may have implications for oral aerodynamics that could help explain why loud-focused clinical treatments improve articulation, although this remains to be empirically confirmed. loud; loudness; articulation; contact pressure; speech; tongue; palate +
Footnote †: journal: Medical  
In addition to variations as a function of stimulus features (i.e., phoneme type, syllable shape), there is evidence of altered ACP in individuals with speech disorders. Adults diagnosed with amyotrophic lateral sclerosis have been found to produce lingua-alveolar phonemes with significantly lower maximum ACP than age- and gender-matched adults without a speech disorder [8]. In contrast, higher ACP has been reported after the complete removal of the larynx (i.e., total laryngectomy), with the increased sense of speaking effort significantly correlated with ACP [9]. Elevated ACP has also been reported for bilabial plosives after total laryngectomy [10]. The findings from individuals without a larynx have been interpreted as most likely resulting from the person's attempt to overexaggregate their articulation to maximize speech intelligibility. Research has also shown that patients with a glossectomy produced the phonemes /t/, /t/, and /f/ with ACP that did not differ, which was in contrast to a non-glossectomy control group for whom ACP did differ across phonemes [3]. The fact that ACP does change in some patient populations relative to those with typical speech sound production highlights the potential use of ACP for diagnosing speech issues and potentially tracking change in speech status as a function of time, disease, recovery, or intervention (e.g., speech therapy, medication, surgery, etc.). One aspect of ACP production that has received almost no attention is the set of parameters that might alter the tongue-palate pressure. Changes to speech in terms of the rate, pitch, loudness, and articulatory precision are known to be influenced by a variety of factors such as the competing environmental noise [11], hearing status of the listener [12], distance between communication partners [13], language spoken by bilingual individuals [14; 15] ([PERSON] et al., 2015; [PERSON] et al., 2016), and differing language backgrounds of communication partners [16], among other factors. In clinical settings where the goal may be to rehabilitate or optimize speech, parameters such as the rate of speech [17; 18], loudness [19; 20], and articulatory precision [21; 22] may be the target of the intervention approach. Changing certain aspects of the speech production process such as the rate, loudness, or precision seems likely to cause changes in aspects of articulatory contact, including ACP. For example, healthy adults without communication disorders have been shown to significantly increase ACP when instructed to use 'clear speech' [23].