Variable Vulnerability of Words to Visual Impairment: Exploring grain-size Effects in Reading

Variable Vulnerability of Words to Visual Impairment: Exploring Grain-Size Effects in Reading Giovanni Pagliuca (gp517@york.ac.uk) University of York, UK Padraic Monaghan (p.monaghan@lancaster.ac.uk) Lancaster University, UK Rob McIntosh (r.d.mcintosh@ed.ac.uk) University of Edinburgh, UK & Goswami, 2005), grain sizes that are language specific and allow for an efficient mapping between the two levels or representation. In this view the ability to identify and make optimal use of orthographic clusters in reading plays a major role in defining the ability to read. One high-order cluster that has received particular attention in recent years as a potentially important grain size in reading is the grapheme. A grapheme is defined as a written representation of a phoneme (Berndt, Reggia, & Mitchum, 1987). For example, the word BREAD contains the five letters B, R, E, A, D, that map onto the four phonemes in /bred/. Therefore, four graphemes can be identified: B, R, EA, D, in virtue of the mapping between the letters and the phonemes. Graphemes therefore provide a direct mapping between orthography and phonology, and this mapping depends on the grain size of the orthographic representation. Two main studies suggested explicitly that graphemes might act as perceptual units in reading. Rey, Jacobs, Schmidt-Weigand and Ziegler (1998), found that word identification times were longer for low frequency words composed of few graphemes (i.e. /biJ/ as in BEACH) than for control words composed of many graphemes (i.e. /krIsp/ as in CRISP), but critically having the same number of letters. This graphemic effect slowed processing time due to the extra-cost of having to functionally group more than one letter into a single grapheme. The study thus offered empirical evidence of a “phonemic” effect in orthographic processing. A second study conducted by Rey, Ziegler and Jacobs (2000) implemented a letter detection paradigm to explore graphemic effects in reading. They asked participants to detect a single letter in words where the target letter was embedded in a multi-letter grapheme (i.e. ‘A’ in ‘BEACH’) or when it corresponded to a single-letter grapheme (i.e. ‘A’ in ‘PLACE’). Participants were slower in detecting the target in the former case than in the latter, suggesting that graphemes are processed as perceptual units in reading. This effect was found irrespective of the word frequency or phonemic similarity, and held for both English and French native speakers. The authors claim that the effect emerges from the difficulty in splitting the unit (grapheme) into its constituent letters in order to perform the task. However, neither of these studies directly tested participants on a reading task, and the claim that graphemes are “perceptual Abstract Languages vary in the grain size used to map orthography onto phonology, but the use of different grain sizes varies also within a language. A core question is what kind of information the reading system is using to map orthography onto phonology. A unit that has received particular attention in recent years is the grapheme. Graphemes are defined as written representations of phonemes, and they can be composed of multiple letters. If graphemes are functional reading units, then a word containing a multi-letter grapheme (digraph) should be read more accurately than a word without, given the same kind of perceptual noise to impair the orthographic input. We trained a neural network model to map English orthography onto phonology. Impairing the model revealed a distinction in performance with words with digraphs less affected by damage than control words. A behavioral experiment confirmed the prediction of the model. We discuss these results in light of a psycholinguistic grain size theory of reading. Keywords: grain size; reading; modeling Introduction The question of how we recognize words is one of the core issues in cognitive psychology, and has been investigated at length (for a review see Prinzmetal, 1995). There are two possibilities for how written words may be identified: whole word recognition (or holistic recognition) approaches and recognition by parts approaches. In the former approach, a word is hypothesized to be recognized as a single object, as suggested by word-superiority effects in reading (Wheeler, 1970). The latter approach has instead tried to identify smaller grain sizes as important for word recognition such that some combinations of letters and their features (Rastle & Coltheart, 1998; Martelli, Majaj, & Pelli, 2005), orthographic syllables (Carreiras, Alvarez, & De Vega, 1993), and/or onsets and rimes (Bowey, 1990) are the functional units of the reading system. The debate has sparked great interest especially for its developmental and pedagogical implications (Ziegler & Goswami, 2005; Stanovich & Stanovich, 1995). A main theoretical framework has been recently proposed which assumes that learning to read is learning to find shared grain sizes in orthography and in phonology (Ziegler