The Role of Orthography in Segmentation of Speech Sounds

Many pre-literate children, illiterate adults, and patients with acquired dyslexia have difficulty segmenting speech sounds despite intact or relatively spared spoken language abilities. Although it is unclear whether segmentation skills are a pre-requisite to or a consequence of reading ability, skilled readers may exploit orthographic knowledge during speech segmentation by invoking a strategy of visualizing the words to facilitate performance. To determine the role of orthographic knowledge in speech segmentation, 16 literate adults performed sound and letter judgment tasks on auditorily presented word pairs in which the consistency of orthographic and phonological information of the initial consonant was systematically varied (e.g., ‘card-cost,’ ‘card-kin,’ ‘guard-gem,’ ‘guard-jam’). Participants decided whether the first sound or letter was same or different. Task order was varied to explore possible strategic effects depending on the sequence of judgments. Participants were highly accurate on sound and letter judgments. For both tasks, responses to consistent phonological and orthographic pairs such as ‘card-cost’ were significantly more accurate than to conflicting pairs (e.g., ‘same’ sound pairs with conflicting spelling such as ‘card-kin,’ or ‘same’ letter pairs with conflicting initial phonemes such as ‘guard-gem’). In addition, ‘different’ judgments were slower on pairs with conflicting sound or spelling information in both tasks. Orthographic interference effects were found for the sound judgments even for participants who had not yet performed letter judgments. This effect could not be attributed to relying on a visualization strategy alone because of evidence of phonological interference effects during letter judgment, suggesting that orthographic and phonological knowledge in skilled readers may play an integrated role in segmentation of speech sounds. INTRODUCTION Typically, models of speech perception do not include a role for orthographic information (Klatt, 1979; Marslen-Wilson & Warren, 1994). However, lesion studies (e.g., Berndt, Haendiges, Mitchum, & Wayland, 1996) and priming studies (e.g., Jakimik, Cole, & Rudnicky, 1985) have suggested connections between spelling and speech perception. In particular, evidence has shown that many pre-literate children, illiterate adults, and patients with acquired dyslexia have difficulty segmenting speech sounds despite intact or relatively spared spoken language abilities (Berndt et al., 1996). Although it is unclear whether segmentation skills are a pre-requisite to or a consequence of reading ability, skilled readers may exploit orthographic knowledge during speech segmentation. Dijkstra et al. (1995) found phoneme monitoring response times were slowed for phonemes with secondary spellings compared to phonemes with a primary spelling. Such results have suggested that orthography affects the perception of spoken words (Ziegler & Ferrand, 1998). Burton et al. Orthography in Segmentation of Speech From Sound to Sense: June 11 – June 13, 2004 at MIT C-2 One possibility is that listeners may invoke a strategy of visualizing the words to facilitate performance of these tasks. Alternatively, in literate readers, associations of orthographic and phonological information may be strongly learned associations that may automatically influence speech tasks, even those that do not require explicit access to such knowledge (e.g., phoneme discrimination, lexical decision). To determine whether such orthographic effects are playing a role in a speech segmentation, we designed a phoneme discrimination experiment in which initial consonants with inconsistent mapping, such as ‘g,’ which can be pronounced as /g/ or /j/, were selected as initial consonants. We compared pairs of words in which sound and spelling of the initial phoneme had consistent mapping between members of the pair to those with mismatch of sound and spelling. If listeners do not access orthographic information during phoneme discrimination, no differences in sound judgments between pairs with matching and mismatching spelling should be expected. On the other hand, as has been suggested by previous studies, if orthographic knowledge plays a role in speech segmentation, pairs with conflicting sound and spelling information may degrade accuracy and/or slow response time.