Fig 1.
Stimuli and behavioral results.
(a) Cochleograms of 3 stimulus types. A Gammatone filterbank of 64 banks was used to decompose the stimuli. The prior distributions of segment duration for the 3 stimuli are shown on the right. (b) Behavioral performance. The blue, gray, and red lines show d-prime values for θ, α, and γ sounds across different signal-to-noise ratios (SNRs), respectively. The 3 separately plotted results at the top-right corner are d-prime values in clean stimulus conditions. Error bars: ±1 standard error of the mean. Data are deposited in the Dryad repository: http://dx.doi.org/10.5061/dryad.f357r [121].
Fig 2.
Z-scores of intertrial phase coherence (zITC) to 3 clean stimuli and their response topographies.
(a) Top panel, spectra of zITC for θ, α, and γ sounds. The dashed line (z-score of 1.64) is equivalent to an alpha level of 0.05 (1-tailed, corrected). The shaded areas represent ±1 standard error of the mean. The bottom panel shows zITC for θ, α, and γ sounds in 4 frequency bands, theta (4–7 Hz), alpha (8–12 Hz), beta (13–30 Hz), and gamma (31–45 Hz). The color scheme of blue, gray, and red in both panels represents zITC of θ, α, and γ sounds, respectively. The error bars represent ±1 standard error of the mean. (b) Topographies of zITC for each sound at each frequency band. Auditory response patterns (compared to, for example, classic evoked M100 responses) are observed clearly in the theta band for θ sounds as well as for the α and γ sounds. In the gamma band, the topographies show the auditory response pattern only for the γ sound. No clear pattern is observed in other frequency bands. Data are deposited in the Dryad repository: http://dx.doi.org/10.5061/dryad.f357r [121].
Fig 3.
Time-frequency analyses of evoked power.
Evoked power responses to θ, α, and γ sounds, respectively. The vertical dashed lines indicate the onset of the auditory stimuli. The dashed boxes in the panels mark the frequency bands of evoked power responses corresponding to the stimulus modulation rates. θ sounds evoke power increase in the theta band and γ sounds in the gamma band. Data are deposited in the Dryad repository: http://dx.doi.org/10.5061/dryad.f357r [121].
Fig 4.
Mutual information between cochlear-scaled correlation and phase of neural oscillations.
(a) Cochlear-scaled correlation of θ, α, and γ sounds. (b) Mutual information results. The colors represent mutual information computed using the phase of the neural oscillation to different sounds: blue, θ sound; gray, α sound; red, γ sound. The inset bar graphs show the averaged mutual information within frequency ranges that show significant main effects of the stimulus type. The robust phase coherence observed in the theta band for θ sound and in the gamma band for γ sound is caused by tracking acoustic structures instead of simply being evoked by general acoustic stimuli. The shaded areas represent ±1 standard error of the mean. Data are deposited in the Dryad repository: http://dx.doi.org/10.5061/dryad.f357r [121].
Fig 5.
(a) Confusion matrices for phase-based and power-based classifications. “Stimulus label” represents the actual stimulus type and “classified label” represents the classified bin. Color bar codes the percentage of trials classified into each bin. (b) Classification performance for each sound using phase and power. Phase-based classification performs significantly better than power-based classification. The blue, gray, and red bars represent θ, α, and γ sounds, respectively. (c) Frequency band contributions to phase-based classification of each sound. “N” indicates classification without the given frequency band; “Y” indicates classification with the given frequency band. Phase in the theta band improves performance for classifying all stimuli and phase in the gamma band contributes to classifying γ sound. The color scheme is as in (b). The error bars represent ±1 standard error of the mean. Data are deposited in the Dryad repository: http://dx.doi.org/10.5061/dryad.f357r [121].
Fig 6.
Temporal progression of classification performance in the theta and the gamma bands.
(a) Classification performance along each time point. Upper panel: classification results using phase series of the theta and the gamma bands for θ sounds, from 500 ms before the onset of stimuli to 2,000 ms after the onset of stimuli; middle panel shows results for α sounds; lower panel shows results for γ sounds. Classification results using the theta band in black and the gamma band in green. Lines represent the mean classification results averaged across subjects. The bolded parts represent clusters significantly larger than baseline, D′ = 0. Significant clusters are observed in the theta band after the onset of stimuli for all 3 sounds. In the gamma band, the significant clusters are found mainly for γ sounds. (b) Classification results averaged from 300 to 1,900 ms after the onset of stimuli for each band. The upper panel represents the classification results using the theta band for θ, α, and γ sound and the low panel the classification results using the gamma band. Classification performance for θ sounds using the theta band is significantly larger than that for α and γ sounds, whereas classification performance for γ sound using the gamma band is larger than that for θ and α sounds. The error bars and shaded areas represent ±1 standard error of the mean. Data are deposited in the Dryad repository: http://dx.doi.org/10.5061/dryad.f357r [121].
Fig 7.
Selected channels pooled across subjects.
The plot shows a layout of channels that are selected based on the peak of M100 response across 15 subjects. Twenty channels are selected for each subject (10 in each hemisphere). The channels selected for analysis are indicated by black circles. The contours indicate the extent of overlap across subjects. Data are deposited in the Dryad repository: http://dx.doi.org/10.5061/dryad.f357r [121].