Word frequency modulates morpheme-based reading in poor and skilled Italian readers

A previous study reported that, similar to young and adult skilled readers, Italian developmental dyslexics read pseudowords made up of a root and a derivational suffix faster and more accurately than simple pseudowords. Unlike skilled readers, only dyslexic and reading-matched younger children benefited from morphological structure in reading words aloud. In this study, we show that word frequency affects the probability of morpheme-based reading, interacting with reading ability. Young skilled readers named lowbut not high-frequency morphologically complex words faster than simple words. By contrast, the advantage for morphologically complex words was present in poor readers irrespective of word frequency. Adult readers showed no facilitating effect of morphological structure. These results indicate that young readers use reading units (morphemes) that are larger than the singlegrapheme grain size. It is argued that morpheme-based reading is important for obtaining reading fluency (rather than accuracy) in transparent orthographies and is useful particularly in children with limited reading ability who do not fully master whole-word processing. In transparent orthographies, most letters are assigned the same pronunciation, regardless of the surrounding letter context. Consequently, accurate pronunciation is easily obtained by translating each letter into its corresponding phoneme. In principle, children learning to read a transparent orthography rely on small grainsize linguistic units (single letters and phonemes) even when larger reading units are available to them (Goswami, Ziegler, Dalton, & Schneider, 2003). They may © Cambridge University Press 2011 0142-7164/11 $15.00 Applied Psycholinguistics 32:3 514 Marcolini et al.: Morpheme-based reading in poor Italian readers achieve high levels of accuracy after only a few months of learning to read and are typically close to ceiling by the end of first grade. By contrast, children learning to read an irregular orthography achieve good reading accuracy much later (Goswami, Gombert, & Fraca de Barrera, 1998; Seymour, Aro, & Erskine, 2003) and probably never reach the same accuracy level as readers of a transparent orthography. However, acquiring transcoding accuracy is only part of becoming a mature skilled reader and reading fluency is a crucial component in this process (Wimmer, 2006). Reading based on small linguistic units may be correct in a transparent orthography, but it is very slow (Zoccolotti et al., 2005) and access to meaning is not efficient. What facilitates fluency is the adoption of reading units that are larger than single graphemes. Although adopting larger reading units is seldom necessary for accurate pronunciation in a transparent script, it is necessary to become a fast and fluent reader. Reading based on whole words develops early not only in deep but also in transparent orthographies (see, e.g., Marcolini, Burani, & Colombo, 2009; Orsolini, Fanari, Tosi, De Nigris, & Carrieri, 2006). In Italian, the use of whole-word reading units may speed up lexical access and reading aloud in typically developing readers and in children with developmental dyslexia (Barca, Burani, Di Filippo, & Zoccolotti, 2006; Paizi, Zoccolotti, & Burani, 2010). However, as children do not know all words, using them as reading units may prove difficult. Thus, morphemes (roots and affixes) may be useful in fostering reading, because they are larger linguistic units than graphemes but shorter than most words. Studies on opaque orthographies, such as English, Danish, and French, focus on reading accuracy. In these languages, word spelling is to some degree governed morphologically and knowledge of morphemes may help the child to assign the correct word pronunciation (Seymour, 1997; Verhoeven & Perfetti, 2003). The presence of known morphemes, such as stems and affixes, affects young readers’ accuracy in reading aloud, mainly when polymorphemic words are phonologically and semantically transparent with respect to the base word (Carlisle & Stone, 2003; Elbrö & Arnbak, 1996; Laxon, Rickard, & Coltheart, 1989) or when suffixes are frequent and productive (Mann & Singson, 2003). In Italian, as well as in other transparent orthographies, knowledge of morphemes is not necessary to assign the correct phonemes to graphemes; that is, there are no cases like the English word SHEPHERD, where the pronunciation of PH does not obey the usual print to sound conversion but is dictated by morphology, namely, by its constituents SHEEP and HERD. However, morphemes may have a role in speeding up reading, especially of newly encountered words, for which the whole-word orthographic representation is unavailable. Secondto sixth-grade Italian children benefited from the presence of morphemes in reading new polymorphemic stimuli similarly to adult readers (Burani, Marcolini, De Luca, & Zoccolotti, 2008; Burani, Marcolini, & Stella, 2002). Pseudowords made up of a root and a derivational suffix in a combination that does not exist in Italian (e.g., DONNISTA, “womanist”) were read faster than simple pseudowords matched for orthographic familiarity (e.g., DENNOSTO). An advantage in reading pseudowords composed of morphemes was reported by Burani et al. (2008) also for sixth-grade children with dyslexia. In the same Applied Psycholinguistics 32:3 515 Marcolini et al.: Morpheme-based reading in poor Italian readers study, developmental dyslexic and younger (second-grade) readers also benefited from the presence of morphemes in reading polymorphemic words, that is, words composed of a root and a derivational suffix (e.g., CASS-IERE, “cashier”) were read faster than simple words not parsable into a root and derivational suffix (e.g., CAMMELLO, “camel”). By contrast, sixth-grade and adult-skilled readers showed no difference in reading polymorphemic versus simple words. There may be a number of reasons why morphemes have similar facilitating effects on pseudoword reading across groups of readers while they have a differential impact on word reading depending on reading ability. Because letters (and phonemes) are assembled within morphemes, this should speed up the reading process with respect to the more analytical process of segmenting, transcoding, and reassembling smaller units (letters, graphemes, phonemes) into larger ones (Burani et al., 2008). Consequently, morphemic units may increase reading speed when the alternative reading procedure consists of relying on smaller reading units (i.e., single letters, graphemes, and phonemes), which are the only ones available for strings of letters never encountered in print. However, when a unit larger than the morpheme (i.e., the whole word) is available, morphemic parsing does not necessarily speed up processing. For experienced readers, morphemic parsing may be an efficient strategy only when the word is new or not familiar enough, that is, when the alternative is adopting smaller reading units. If a wholeword representation is present in the reader’s lexicon and can be obtained in a single fixation (Rayner & McConkie, 1976), morphemic parsing may not be necessary. This raises the question of whether the orthographic familiarity of the word constrains morpholexical reading. Models of adult word recognition assume that recourse to higher frequency constituents (morphemes) becomes increasingly important as whole-word frequency decreases, with morphemic processing maximally facilitating low-frequency (LF) words (Alegre & Gordon, 1999; Baayen, Wurm, & Aycock, 2007; Burani & Laudanna, 1992; Chialant & Caramazza, 1995; Schreuder & Baayen, 1995). In a race model of word processing (e.g., Schreuder & Baayen, 1995), there are two routes for identifying a word: a direct lookup and a compositional route. Which one predominates depends on the relative speed of the two processes. Each can be constrained by word frequency, with the direct lookup route predominating for high-frequency (HF) words and the compositional one predominating for LF polymorphemic words. For Italian, root frequency effects on LF words have been reported for lexical decision (Burani & Caramazza, 1987; Burani & Thornton, 2003) and word naming (Colombo & Burani, 2002). Converging evidence stems from eye movement studies. Holmes and O’Reagan (1992) varied the whole-word frequencies of French suffixed and monomorphemic words matched for length and frequency to the derived words. Gaze durations differed little between HF suffixed words and their monomorphemic controls, whereas they were shorter for the LF suffixed words, especially when the initial fixation was in a good position for viewing the root morpheme. Theoretical accounts of reading acquisition also predict that the facilitation obtained by morpheme-based processing may be particularly relevant for unfamiliar words and for poor or less-skilled readers. According to Reichle and Perfetti (2003), acquiring reading skill requires several encounters with printed words to Applied Psycholinguistics 32:3 516 Marcolini et al.: Morpheme-based reading in poor Italian readers build up orthographic representations that reflect familiarity and knowledge of the word. Because of insufficient reading practice, developing readers, and especially poor readers, may not have established the orthographic knowledge required for word-specific (whole-word) representations. Thus, rarely encountered LF words will have a low probability of being represented and processed as whole words. However, unfamiliar words that include a HF root will still be easily recognizable based on their familiar root. Two lexical decision studies support this expectation. Gordon (1989) showed that HF base words influenced the accuracy of 5to 9year-old children’s decisions on LF derived words. Burani et al. (2002) reported that 8and 10-year-old children were prone to accept as existing words new root + suffix combinations that included HF morphemes. Overall, the relative probability of the two reading procedures may depend both on word frequency and the reader’s processing ability. This is the main issue addressed in the present study. In our previous study (Burani et al., 2008), which showed that morphemic decomposition of words is limited to less skilled readers, the polymorphemic-suffixed words were selected from the medium-frequency to LF range (mean frequency = 27.4 out of 1 million) in a child-written frequency count (Marconi, Ott, Pesenti, Ratti, & Tavella, 1993). Very HF and very LF words were not included in the experimental sets. In the present experiment, highly familiar (polymorphemic and simple) words were contrasted with LF (polymorphemic and simple) words to assess whether readers’ reliance on morphemic reading would differ for HF versus LF root + suffix combinations, and whether this interacted with reading skill (care was taken that the present set of LF words had a lower frequency than the words used in our preceding study; Burani et al., 2008). Based on previous results, we expected all groups of readers to show word frequency effects, with HF words read faster than LF ones (see review in Paizi et al., 2010). However, poor readers were also expected to show faster naming latencies to polymorphemic than to simple words, irrespective of word frequency. By contrast, young and adult-skilled readers should read morphologically complex and simple HF words equally fast and accurately, because of their capacity to process familiar words as whole units, but might show an advantage of morphemic parsing for LF words that are less likely to be present in their lexicon.