Phonetic biases in voice key response time measurements

Voice response time (RT) measurements from 4 large-scale studies of oral reading of English monosyllables were analyzed for evidence that voice key measurements are biased by the leading phonemes of the response. Words with different initial phonemes did have significantly different RTs. This effect persisted after contributions of nine covariables, such as frequency, length, and spelling consistency, were factored out, as well as when variance associated with error rate was factored out. A breakdown by phoneme showed that voiceless, posterior, and obstruent consonants were detected later than others. The second phonemes of the words also had an effect on RT: Words with high or front vowels were detected later. Phoneme-based biases due to voice keys were large (range about 100 ms) and pervasive enough to cause concern in interpreting voice RT measurements. Techniques are discussed for minimizing the impact of these biases.