## 4 Experiments  
The first two experiments performed expanded on the tests done in [12; 14], this time using a dataset with 57 (study 1, expanding the dataset in [15]) subjects who performed the complete sequence of the data collection protocol. The goal here was to confirm our previous findings using a larger dataset. Both experiments consisted of classifying distinct groups of voice gestures as normal or simulated pressed productions, under the intra-subject constraint.  
For the first experiment, we used all vowels as individual gestures: i.e., /a/, /u/, and /i/; each produced under normal or simulated pressed conditions. Thus, a total of six classes were created, each with 50-55 valid samples due to a few occasional misarticulations or misses. The classification results are shown in the confusion matrix in Figure 4. The confusion matrix was arranged so that the normal and corresponding simulated pressed gestures are next to each other-- i.e., the indices (row and column) of the matrix correspond to: (1) /a / normal; (2) /a / pressed; (3) /u/ normal; (4) /u/ pressed; (5) /i/ normal; and (6) /i/ pressed. Hence, the reader should notice that error in the amount of about 5% of the cases relates to the confusion between the normal and their corresponding simulated pressed vowels--i.e., six of the second-diagonal elements with indices of (1,2) or (2,1); (3,4) or (4,3); and (5,6) or (6,5). The remaining approximate 10% of the error is spread through the remaining elements on each side (upper and lower halves) of the confusion matrix.  
For the second test, the entire set of normal vowel productions or simulated pressed vowel productions were assigned to one of two classes: _Negative_ and _Positive_, respectively. Each subject provided a total number of samples that varied between 108 and 165 for the Positive class, and between 55 and 165 for the Negative class. The test subjects were  
Figure 4: Confusion matrix for all six vowel gestures (three normal and three simulated pressed) computed over all test subjects and under the _intra-subject_ constraint. The entries in the table contain the percentages (top) and the actual number of samples detected (bottom). The numbers on the axes correspond to: (1) /a/ normal; (2) /a/ pressed; (3) /u/ normal; (4) /u/ pressed; (5) /i/ normal; and (6) /i/ pressed.  
tested separately (i.e., _intra-subject_ condition); their combined classification outcomes were averaged; and the results were shown in Table 2.  
As Figure 4 and Table 2 indicate, the overall accuracy of 84% for all six classes (first test) and 90% for two classes (second test) confirm the conclusions in [12; 14]. That is, (1) distinguishable sEMG patterns do emerge from individual voice gestures (vowels) measured from subjects' anterior necks; and similarly, (2) distinguishable sEMG patterns also emerge from simulated pressed voice gestures as a representation of vocal effort or strain. These conclusions led to the assumption that it could also be possible to distinguish normal vowel gestures from individuals without self-reported vocal fatigue from \"real\" vocally fatigued vowel gestures produced by individuals who actually reported vocal fatigue. Thus, the following experiments aimed to confirm this assumption.