Visual precueing of individual phonemes can facilitate speech perception

Is the phoneme a psychologically accessible unit of speech perception? One approach to this question is to determine whether speech perception can be facilitated by advance information about individual phonemes. Naive, untrained subjects listened to monosyllabic words embedded in white noise. After listening to each word, subjects chose between two visually presented letters, one of which was the initial letter of the spoken word. (Each word began with a letter which has a reliable grapheme-phoneme correspondence.) On half of such trails, the letter alternatives were also presented as a precue before the spoken word. Results showed that precueing the alternative letters significantly improved performance. The improvement with letter precues (5.5% higher accuracy) was approximately as large as the improvement with whole-word precues, measured in a control condition (6.5% higher accuracy.) These results show that people are able to use the familiar English letter representations of phonemes as cues to improve perceptual processing. This phenomenon can be accounted for by a system of phoneme detectors whose thresholds are lowered by precueing the corresponding letter.