Auditory Spectral Integration in the Perception of Static Vowels

Purpose: To evaluate potential contributions of broadband spectral integration in the perception of static vowels. Specifically, can the auditory system infer formant frequency information from changes in the intensity weighting across harmonics when the formant itself is missing? Does this type of integration produce the same results in the lower (first formant [F1]) and higher (second formant [F2]) regions? Does the spacing between the spectral components affect a listener's ability to integrate the acoustic cues? Method: Twenty young listeners with normal hearing identified synthesized vowel-like stimuli created for adjustments in the F1 region (/boolean AND/-/a/, /T/-/epsilon/) and in the F2 region (/boolean AND/-/ae/). There were 2 types of stimuli: (a) 2-formant tokens and (b) tokens in which 1 formant was removed and 2 pairs of sine waves were inserted below and above the missing formant; the intensities of these harmonics were modified to cause variations in their spectral center of gravity (COG). The COG effects were tested over a wide range of frequencies. Results: Obtained patterns were consistent with calculated changes to the spectral COG, in both the F1 and F2 regions. The spacing of the sine waves did not affect listeners' responses. Conclusion: The auditory system may perform broadband integration as a type of auditory wideband spectral analysis.