Comparing vowel formant thresholds from two tasks: Classification versus 2‐alternative forced choice (2AFC) adaptive tracking

Abstract

Accurate classification of vowels in American English is difficult because of the number of acoustically similar vowels. Previous experiments in our lab [Kewley‐Port et al., J. Acoust. Soc. Am. 118, 1929–1930 (2005)] described a new method to obtain formant thresholds using a classification task rather than the more typical 2AFC task. The goal of the present experiment was to directly compare formant thresholds estimated from a classification task with a modified 2AFC paradigm using adaptive tracking. Stimuli, generated by STRAIGHT, consisted of separate continua for formants F1 and F2 based on natural productions of ‘‘bid’’ shifted to ‘‘bed,’’ and ‘‘cut’’ shifted to ‘‘cot.’’ Separate 7‐ and 14‐step continua were created for the classification and 2AFC tasks, respectively. Eight subjects participated first in the classification task, followed by the 2AFC task. Classification threshold results here replicated those observed in our previous experiments. Within‐subject comparisons of the classification and 2AFC data refined our method for calculating a classification threshold from logistic psychometric functions. Individual thresholds calculated using this refined method were very similar to those from the 2AFC task. Results demonstrate the viability of using a more natural, single‐interval classification task to estimate formant discrimination thresholds. [Work supported by Grant NIHDCD‐02229.]