This paper presents a speech perception experiment with vowels and consonants as phoneme detection targets in real English words. Phoneme targets were the two vowels /a/ and /i/, plus the two unvoiced stop consonants, /p/ and /t/. In contrast with a previous study that used the same materials, listeners heard the target phoneme specification immediately prior to stimulus presentation. The results showed that the reaction times for the vowels were not significantly longer than those to the consonants. It is concluded that vowels benefit more than consonants from having target specification and stimulus presentation occur closely together. It is proposed that the time lag between phoneme type and stimulus token reduces the effect of inherent perceptual ambiguity of vowels during a speeded response task.

Keywords: Human speech recognition, vowels, consonants, phoneme detection, reaction time, auditory memory.