The effects of microgravity on tongue height

Résumé

A previous investigation comparing astronaut speech during and after the Apollo 11 mission reported a significant increase across all vowel formants during microgravity exposure. This result was interpreted as indicating that the tongue is lowered in microgravity conditions [Yu & Hansen, 2017, JASA, 141(3), 1605-1614]. However, we note that the microgravity condition speech data used in this analysis were routed through telephone channels while the earth condition data were not. As telephone speech is characterized by a marked increase to formants [Nolan, 2002. Forensic Ling. 9(1), 74-82], it is unclear whether any observed effect was due to microgravity or telephone bandwidths.  Using higher quality audio from the STS-129 and 135 missions and linear mixed effects models, we compared the first vowel formant (F1) of two astronauts immediately before and during exposure to microgravity during space travel. We found no significant interaction of condition in our models, suggesting microgravity does not have a substantial effect on tongue height. We conclude that previous observations of microgravity-induced tongue lowering may actually be a product of telephone bandwidth changes. Future investigations of astronaut speech should take care to ensure audio bandwidth is comparable across conditions.