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, Jon Andoni Duñabeitia (codir. tes.) , Moisés Betancort Montesinos (tut. tes.) , Marta Vergara Martínez (secret.) , Cristina Baus (voc.) Learning to read is probably one of the most important milestones in our lives. Acquiring this ability opens up a host of opportunities and also brings about changes in our brains (Carreiras et al., 2009). Hearing children with typical development and academic progress acquire reading after an appropriate amount of instruction. This process is easier in languages with a transparent orthography, such as Spanish, in which there is a regular correspondence between letters and phonemes. However, children with learning disabilities and most deaf children do not achieve fluent reading. Most deaf people do not reach proficient levels of reading with respect to their hearing peers (Conrad, 1979; Traxler, 2000). Only 10% of deaf adults become skilled readers (Marschark, 1997).
Much research on deaf readers has been conducted in languages with an opaque orthography and most of these studies do not show activation of phonological coding in visual word processing. Several works have claimed to show that the basis of visual word recognition rests on phonological representation, depending on the degree of transparency of the language in which reading occurs (Ehri, 1986; Frith, 1985; Harm & Seidenberg, 2004; Share, 1995). According to Frost and Katz (1992), phonological processes are required in transparent orthographies for visual word recognition. In addition, others authors (Carreiras et al., 2009; Pollatsek et al., 2005) showed that accessing phonological encoding when reading a transparent language like Spanish is automatic. This suggests that phonological processing is an obligatory step for word identification in transparent languages.
There are very few studies on deaf people and reading in Spanish. Most have focused on educational perspectives, and research on reading in Spanish (a language with transparent orthography) by deaf individuals from the point of view of cognitive neuroscience is limited. The studies that make up this thesis project focus on deaf skilled readers of Spanish. Although much previous work on deaf readers has been limited to children in the process of developing their language skills, this study looks at skilled adult readers. These are individuals who have overcome the difficulties of learning to read and we are interested in finding out how they have managed this by examining what mechanisms underlie their reading skills. The aim of this project is to investigate the role of phonological and orthographic processes of deaf and hearing skilled readers of Spanish, and to discover whether both groups show similar or different patterns in this respect.
The experimental section is divided into three parts and contains descriptions of several experiments, including behavioral responses and electrophysiological activity.
Experiment 1 investigates phonological processes using two tasks. Experiment 1a involves a lexical decision task with two types of nonwords: pseudohomophones (nonwords that sound like real words) and control nonwords. Experiment 1b involves a go/no go semantic categorization task with a masked priming technique, using nonwords as primes. Through this experiment we want to verify what role phonology plays during visual word recognition in deaf readers and to assess the differences and similarities in the reliance on phonological processes during word reading between deaf and hearing readers with similar reading proficiency levels.
Experiment 2 focuses on the role of orthographic processes, using the same tasks as in Experiment 1. Experiment 2a, a lexical decision task, involves two types of nonwords: transposed-letter nonwords and replaced-letter nonwords. Experiment 2b explores the same manipulation with a masked priming go/no go semantic categorization task. The goal of this experiment is to investigate whether deaf and hearing skilled readers respond similarly or differently to orthographic manipulations, such as the transposition of letters, during visual word recognition.
Experiment 3 investigates orthographic sub-processes in more detail using three explicit perceptual matching tasks based on a same-different judgment. We study two key steps for orthographic processing: letter position coding (Experiment 3a) and letter identity coding, focusing on visual similarity (Experiment 3b) and abstract identity by changing cases (Experiment 3c). As suggested by Pelli et al. (2006), word recognition is based on the analysis of letters. Therefore, in order to further investigate the differences and similarities in orthographic processing between deaf and hearing skilled readers, we assessed the perceptual processing of letter position and identity (in relation to visual similarity and abstract identity).
The present project revealed both differences and similarities between hearing and deaf skilled readers. In particular, the findings suggest that, in contrast to hearing readers, phonological activation is not necessary for deaf readers when reading words in a language with a transparent orthography, such as Spanish. Deaf and hearing readers were both sensitive to orthographic manipulations, suggesting that orthographic awareness alone may sustain proficient reading, without the need for phonological coding, although language competence, including sign language knowledge, may provide support for the development of reading skills. Automatic phonological processing may commonly be the default mechanism for reading in transparent orthographies, but it is clearly not required for successful visual word recognition. The special case of skilled deaf readers demonstrates that word recognition may rely solely on other processes, such as visual-orthographic processing or the decoding of the written word through sub-lexical units of sign language.
