# Changes in Articulatory Contact Pressure as a Function of Vocal Loudness
## 2 Materials and Methods
### Speech Stimuli  
The stimuli sampled in this study were three lingua-alveolar phonemes (/t, d, s/) in the syllable-initiating position of the monosyllable words /tp/, /dp/, and /sp/ that were placed in the carrier phrase \"you CVC here\", which was produced using a person's habitual speaking rate, loudness, and articulation. These stimuli were also sampled in three other loudness modes, namely, whisper, soft, and loud. This set of consonants provided the opportunity to sample ACP across phonemes that varied in terms of their voicing feature (/t/ vs. /d/) and manner of production (/t/ vs. /s/). The CVC vowel was held constant, as was the vowel preceding and following the CVC word. The consonant chosen to end the CVC stimulus allowed for a meaningful American English word and avoided tongue contact on the alveolar ridge to make it easier to identify the tongue-palate pressure peak for the CVC-initiating consonant.  
The stimuli were presented on a computer screen with instructions to say the phrase using a specific loudness level, as depicted in Figure 1. A direct magnitude estimation (DME) procedure was utilized to elicit the soft and loud conditions. This procedure allows individuals to perceptually judge their loudness level relative to a \"standard\" (i.e., a modulus), which in this case was the loudness level they typically use during daily communication (i.e., termed habitual for this study). An arbitrary value of 100 is assigned to this loudness and then they are asked to vary their loudness based on their auditory perception of their voice (i.e., their loudness) relative to this modulus. DME procedures have been utilized for other tasks requiring auditory perceptual judgements such as voice quality, speech intelligibility, and stuttering severity [41; 42; 43]. For the loud condition, participants were prompted to double their loudness and produce the stimulus at a value of 200. Likewise, for the soft condition, they were instructed to use a loudness level that was half of their habitual level, or a value of 50. The whisper condition was represented on the DME scale as a value of 0 and participants were also verbally instructed to whisper as if they were telling a secret in a quiet room. The target loudness level for a given production was indicated by altering the displayed text to show the intended loudness condition presented in red font with a double circle around it. Although it was not necessary for participants to precisely double the perceived loudness (roughly considered to be about 10 dB) or halve their loudness (roughly 10 dB less than usual) in the loud and soft conditions, as a group they did consistently adjust in the expected directions and magnitude, as reflected in the sound level meter recordings that were obtained. The mean habitual loudness for the group summed across all three sentences and repetitions was measured at 63.2 dB (sd: 1.61) compared to 71.8 db (sd: 2.67) in the loud condition and 55.3 dB (sd: 3.1) in the soft condition; the whisper condition was measured at 51.9 dB (sd: 1.0).  
Each CVC stimulus was produced five times for each phoneme in a block in each of the four loudness conditions (whisper, soft, habitual, and loud) for a total of 60 productions per participant and 840 samples in total across the 14 participants. The order of the sentences was randomized within each loudness condition, and the loudness conditions were randomized across participants. The pace of the stimulus presentation was controlled by a researcher and allowed for taking a breath and taking a drink of water if needed.