Pupil responses in Experiment 2.

Mean pupil traces recorded for 28 listeners in Experiment 2: a sentence intelligibility task at two difficulty levels (0 and +14 dB SNR) under three luminance settings (dark, medium, and bright). Traces are all aligned by the onset of verbal response, and expressed in absolute units (top panels) to illustrate the massive light-evoked differences in pupil’s diameter, or corrected by their 1-sec baseline (bottom panels) to emphasize the peak pupil dilation. Shaded width represents 1 standard error from the mean.