Dyslexia and access to Lexicon
Dyslexia is a learning disorder that primarily affects the skills involved in reading and writing; that is, in the access to the lexicon. Some people with dyslexia maybe presents some type of neurological and / or sensorial alteration that justifies this disorder. In addition, in most cases it is about people who have had school opportunities to develop a correct learning. In dyslexia, usually both reading process and writing process are affected.
Commonly, phonological awareness skills, verbal or phonological memory and verbal processing speed are altered.
- Phonological awareness: it is the ability to identify and manipulate the sounds of words. It is recognized as the fundamental ability to perform the processes of analysis and synthesis inherent in the written language.
- Verbal or phonological memory: it consists in the ability to retain the sequential order of verbal matter during a short period of time. For example: remember a list of words or instructions.
- Verbal processing speed: this is the time it takes to process familiar verbal information such as spellings or digits.
Access to the lexicon: How do we Access to our lexicon?
To study the process of access to the lexicon, chronometric methods such as lexical decision tasks have been used. The variables used are the following:
- Frequency: the most frequent words are recognized more easily. That is, the reaction time is shorter and fewer mistakes are made. It has an effect on the words content, not on the words function. For example: the word house has a higher frequency than the word cricket; because the first one is used more times.
- Familiarity: it is a similar concept to frequency; but it occurs on an individual or group scale. For example: the word test tube is not a frequent word in our normal lexicon, but it is for people who work in a laboratory.
- Age of acquisition: the words that are learned earlier in life, are recognized faster and fewer mistakes are made.
- Cumulative frequency: explains the 3 previous effects. The more times a person has been exposed to a word, the shorter the reaction time and the fewer errors accessing on lexicon.
- Length: the shorter the word, the fewer errors and the less reaction time. In the auditory recognition the length is measured with syllables and in the visual recognition the length is measured in letters. For example: since the frequency of both words is the same, the word duck will be recognized before the word library, due to its length.
- Lexicality (or word effect vs. no word): the time it takes to respond positively to a word is always less than the time it takes to respond negatively to a non-word.
- Neighbouring: this factor is used in written words. One word will be next to another, when it is written in the same way except one letter. For example, the following words would be neighbours: bed, bad …. The recognition of a rare word slows down if one of its neighbouring words is very frequent.
- Imaginability (or correction / abstraction): if a word is related to a conceptual representation easily imaginable, it will be recognized before than an abstract type. For example: the word table will be recognized earlier because it is a tangible and easily imaginable concept, that the word adds that it is an abstract concept.
- Semantic facility: the recognition of a word is easier if it is preceded by another word with which it has a semantic relationship. For example: the word hospital will be recognized before and with fewer errors if it is preceded by the word doctor.
Behrmann, M., & Bub, D. (1992). Surface dyslexia and dysgraphia: Dual routes, single lexicon. Cognitive Neuropsychology, 9(3), 209-251.
Caramazza, A., Miceli, G., Silveri, M. C., & Laudanna, A. (1985). Reading mechanisms and the organisation of the lexicon: Evidence from acquired dyslexia. Cognitive Neuropsychology, 2(1), 81-114.