Evaluating synthetic speech workload with oculo-motor indices: preliminary observations for Japanese speech

Pupillometry has recently been introduced as a method to evaluate cognitive workload of synthetic speech. Prior research conducted on English speech indicates that in noisy listening conditions, pupil dilation is significantly
higher for synthetic speech as compared to natural speech. In a lab-based listening experiment, we evaluated participants' (n=16) pupil responses to Japanese speech (natural vs. synthetic) at three different signal-to-noise levels (-1dB, -3dB and -5dB). Our research expands on previous work by evaluating pupillary responses both in terms of temporal changes in pupil size and degree of pupil oscillations. We observe statistically significant differences in pupil sizes at the recall stage between each type of speech. For pupil oscillations, we register statistically significant differences in frequency power spectrum densities (PSDs). Our investigation proposes an expansion of the current synthetic speech evaluation methods that are based on pupillary responses and outlines possible avenues for future research that arise from the findings of this work.