Headphone screening to facilitate web-based auditory experiments
Psychophysical experiments conducted remotely over the internet permit data collection from large numbers of participants but sacrifice control over sound presentation and therefore are not widely employed in hearing research. To help standardize online sound presentation, we introduce a brief psychophysical test for determining whether online experiment participants are wearing headphones. Listeners judge which of three pure tones is quietest, with one of the tones presented 180° out of phase across the stereo channels. This task is intended to be easy over headphones but difficult over loudspeakers due to phase-cancellation. We validated the test in the lab by testing listeners known to be wearing headphones or listening over loudspeakers. The screening test was effective and efficient, discriminating between the two modes of listening with a small number of trials. When run online, a bimodal distribution of scores was obtained, suggesting that some participants performed the task over loudspeakers despite instructions to use headphones. The ability to detect and screen out these participants mitigates concerns over sound quality for online experiments, a first step toward opening auditory perceptual research to the possibilities afforded by crowdsourcing.
KeywordsPsychometrics/testing Stimulus control Audition
This work was supported by an NSF CAREER award and NIH grant 1R01DC014739-01A1 to J.H.M. The authors thank Malinda McPherson, Alex Kell, and Erica Shook for sharing data from Mechanical Turk experiments, Dorit Kliemann for help recruiting subjects for in-lab validation experiments, and Ray Gonzalez and Kelsey R. Allen for organizing code for distribution.
Code implementing the headphone screening task can be downloaded from the McDermott lab website (http://mcdermottlab.mit.edu/downloads.html).
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