PMC

Spectral content of 2-kHz 95-Hz exponentially modulated ASSR signal. Y-axis shown in digital sample units, signal generated with overall digital amplitude of 10.

Swept method RACs for subject 18 (left) and 20 (right). RAC curve produced from identical EEG data with (solid line) and without (dashed line) variance weighted averaging. The axes are as for .

Schematic illustration of swept method averaging process. Upper panel shows the signal (grey line) and masker (black line) centre frequency plotted against test time in each sweep repetition. Lower panel represents the resultant RAC. Dashed arrows show the averaging process of the points of the EEG-waveform obtained for the upward and downward sweep direction.

Example of RACs recorded using the swept masker method. Solid lighter line shows the unmasked response amplitude recorded in the same test session as the RAC. Dashed lighter line shows the amplitude below which the response was not considered significantly higher than the background EEG-noise. Darker solid curve shows the response amplitudes, darker dashed line shows the ROEX curve fit to the response amplitudes.

Examples of ROEX curve fitting to RAC data. Left panel, example ROEX curve fitting with r parameters constrained (solid line) and unconstrained (dashed line). Right panel, example ROEX curve fitting with r parameters (r_upper and r_lower) separate for frequencies above and below the fitted tip (solid line) and with one single r parameter for all masker frequencies (dashed line). ROEX parameters as shown in .

Fixed and swept method RAC-tip estimation recording repeatability. Data points show the mean estimated RAC-tip frequency (x-axis) vs. the difference in tip frequency between two test runs (y-axis). The upper and lower dashed lines show the assumed mean difference ± the repeatability coefficient. The error bars show the 95% confidence limits for the repeatability coefficient.

Individual RACs recorded for the fixed and swept method for each subject in two sessions. Solid line shows the first test run recorded using the swept masking method. The filled circles represent the first test run recorded using the fixed masking method. The dashed line and unfilled circles are the second test run swept and fixed test method, respectively. Y-axis shows the response amplitude as a percentage of the not-masked amplitude recorded in the same test run as each RAC.

Gross mean RACs recorded in 20 subjects from two recording sessions for the fixed (left panel) and swept (right panel) masking method. Solid line is the mean relative amplitude, dashed line shows the ROEX curve fit of the mean. The mean amplitude ±1 SD is shown as the upper and lower dotted lines in the right panel and as error bars in the left panel.

Example RACs recorded using the fixed masker method. Solid lighter line shows the unmasked response amplitude recorded in the same test session as the RAC. Dashed lighter line with data points marked as ‘X’ shows the amplitude below which the response was not considered significantly higher than the background EEG-noise. Filled circular data points show the response amplitudes for each masker frequency, darker dashed line shows the ROEX curve fit to the response amplitudes.

Illustration of modulation envelope phase difference between the averaged upward and downward sweep direction analysis. Plots represent the 95 Hz modulation envelope. X-axis shows the time position in the sweep relative to the start of the sweep (Left panel) and end of the sweep (Right panel). Vertical lines show the first and second analysis points which were 0 ms and 20 ms on the left panel, 0 and −20 ms on the right panel.

Fixed and swept masking method RAC-tip estimation agreement for the first test run of each method. Data points show the mean estimated RAC tip from the two methods in the first recording (x-axis) vs. the difference in tip frequency between the two recording methods in the first test session. The upper and lower dashed lines show the mean tip difference ± the calculated limits of agreement. The error bars show the 95% confidence limits for the calculated limits of agreement.