Listening effort elicited by energetic versus informational masking

Measuring the listening effort exerted by an individual to understand speech under auditory masking conditions can provide vital information not available from speech intelligibility scores alone. The goal of this study was to compare the amount of listening effort elicited in young, normal-hearing subjects during an intelligible speech masking condition producing a high degree of informational masking (due to listener uncertainty, e.g. target-masker confusions) versus in two speech spectrum-shaped noise masking conditions producing primarily energetic masking (due to spectrotemporal overlap between target and maskers). One noise masking condition involved unmodulated noise, while the other involved speech-envelope-modulated noise. Listening effort was measured simultaneously using two physiological metrics: pupil dilation and alpha power (via electroencephalography). The target speech comprised 5-word matrix-style sentences in both conditions. In each condition, the target-to-masker ratio was set at each subject’s 75% correct point on the psychometric function. Target and maskers were spatially separated. Results indicated that the intelligible speech masking condition elicited a greater change in pupil size than the unmodulated noise masking condition. This finding is consistent with the view that greater effort is involved in ignoring acoustically and linguistically similar sources than highly dissimilar, low-information value sources.