Fig 1.
A. Subjective sleepiness. Sleepiness was evaluated by self-reports on the Stanford Scale before sleep deprivation (Control) and after two nights of mild sleep deprivation (Sleep deprived). The abscissa indicates the time of day when sleepiness reports were collected. B. Average reported sleepiness before and after sleep restriction. Lines connect data points for each participant.
Fig 2.
A. Spectro-Temporal Modulations before sleep deprivation. Projections on the rate-scale and rate-frequency planes are shown. Arbitrary model units. B. As in A., but after sleep deprivation. C. Acoustic difference before and after sleep deprivation, shown as 2 * abs(B-A) / (A+B). Units of percent. D. Speech features before (green) and after (orange) sleep deprivation. Displayed are four openSMILE features related to average pitch (mean of the fundamental frequency f0), pitch variation (standard deviation of f0), voice creakiness (jitter) and voice breathiness (logarithm of the Harmonic to Noise Ratio). Lines connect data points for each participant.
Fig 3.
Machine learning classification results with STM input features.
A. Balanced Accuracies for the population-level classifier using the generic STM representation as input feature space. Two cross-validation procedures are reported (see text). Error bars show standard deviations. Stars indicate the significance level of t-tests against chance level (** < .01; *** < .001). B. Balanced Accuracies for the classifiers tuned to individual participants, obtained with the 50-splits, 25% test cross-validation procedure. Participants are ranked according to classification accuracy.
Fig 4.
Classification accuracy for voice variability unrelated versus related to sleep deprivation.
Balanced Accuracies for discriminating reading sessions recorded both before or after sleep deprivation (“Within”) or for discriminating one reading sessions recorded before and one reading session recorded after sleep deprivation (“Across”). As 15 out of 22 classifiers produced accuracies above 0.9 for the Across comparison, BAccs were converted to rationalized arcsine units (RAU). Points represent individual participants. The median and interquartile intervals are also shown.
Fig 5.
Machine learning classification results with openSMILE input features.
Format as in Fig 3. In particular, for B., participants’ labels (#) are identical to Fig 3.
Fig 6.
Interpretation of the population-level classifier.
Discriminative features (see main text) are shown in the input STM space, for the rate-scale and frequency-scale projections. Red areas indicate features positively associated to sleep deprivation by the classifier. Blue areas correspond to features negatively associated to sleep deprivation by the classifier. Color bar indicate the averaged value of the reverse correlation mask. Values are low because of the relative low consistency of the interpretation masks for this population-level classifier.
Fig 7.
Interpretation of the participant-level classifiers.
A. As for Fig 6, but for individual participants identified by their participant #. B. Projection of participants # in the interpretation-PCA space of all participant’s masks (see text for details). C. and D. Variance of the idealized masks along the first two dimensions of the interpretation-PCA. Idealized masks are obtained by first sampling the PCA latent space between -2 and 2 for the two first dimensions with 30 values and then inverting the latent space into the input feature space by using the inverse transform of the PCA. Red areas show the discriminative features that vary the most along each interpretation-PCA dimension. Units: variance in the feature space.
Fig 8.
Relation between subjective sleepiness and voice classifiers.
A. Subjective sleepiness is plotted as a function of balanced accuracy of each participant-level classifier. B. Subjective sleepiness is plotted as a function of the coordinate of each participant-level classifier on the first dimension of the interpretation-PCA space. C. As in B., but for the second dimension of the interpretation-PCA space.