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 | The examples and perspective in this article deal primarily with the English language and do not represent a worldwide view of the subject.(June 2023) |
The dual-route theory of reading aloud was first described in the early 1970s. [1] This theory suggests that two separate mental mechanisms, or cognitive routes, are involved in reading aloud, with output of both mechanisms contributing to the pronunciation of a written stimulus. [1] [2] [3]
The lexical route is the process whereby skilled readers can recognize known words by sight alone, through a "dictionary" lookup procedure. [1] [4] According to this model, every word a reader has learned is represented in a mental database of words and their pronunciations that resembles a dictionary, or internal lexicon. [3] [4] When a skilled reader sees and visually recognizes a written word, he/she is then able to access the dictionary entry for the word and retrieve the information about its pronunciation. [2] [5] The internal lexicon encompasses every learned word, even exception words like 'colonel' or 'pint' that don't follow letter-to-sound rules. This route doesn't enable reading of nonwords (e.g. 'zuce'), though some phonological output can still be produced by matching the word to an approximation in the lexicon (e.g. 'sare' activating visually similar known words like 'care' or 'sore'). [1] [5] There is still no conclusive evidence whether the lexical route functions as a direct pathway going from visual word recognition straight to speech production, or a less direct pathway going from visual word recognition to semantic processing and finally to speech production. [2]
The nonlexical or sublexical route, on the other hand, is the process whereby the reader can "sound out" a written word. This is done by identifying the word's constituent parts (letters, phonemes, graphemes), and then applying knowledge of how these parts are associated with each other, for example how a string of neighboring letters sound together. [1] [4] [5] This mechanism can be thought of as a letter-sound rule system that allows the reader to actively build a phonological representation and read the word aloud. [2] [3] The nonlexical route allows the correct reading of nonwords as well as regular words that follow spelling-sound rules, but not exception words. The dual-route hypothesis of reading has helped researchers explain and understand various facts about normal and abnormal reading. [2] [4] [5] [6]
According to research, the amount of time required to master reading depends on the language's adherence to phonological rules. [7] A written language is described as transparent when it strongly adheres to spelling-sound rules and contains few exception words. Because of this, the English language (low transparency) is considered less transparent than French (medium transparency) and Spanish (high transparency) which contain more consistent grapheme-phoneme mappings. This difference explains why it takes more time for children to learn to read English, due to its frequent irregular orthography, compared to French and Spanish. [7] The Spanish language's reliance on phonological rules can account for the fact that Spanish-speaking children exhibit a higher level of performance in nonword reading, compared to English and French-speaking children. Similarly, Spanish surface dyslexics exhibit less impairment in reading overall, because they can rely upon consistent pronunciation rules instead of processing many exception words as a whole in the internal lexicon. [7] The dual-route system thus provides an explanation for the differences in reading acquisition rates as well as dyslexia rates between different languages. [7]
Skilled readers demonstrate longer reaction times when reading aloud irregular words that do not follow spelling-sound rules compared with regular words. [8] When an irregular word is presented, both the lexical and nonlexical pathways are activated but they generate conflicting information that takes time to be resolved. The decision-making process that appears to take place indicates that the two routes are not entirely independent from one another. [8] This data further explains why regular words, that both follow spelling-sound rules and have been stored in long-term memory, are read faster since both pathways "agree" about the issue of pronunciation. [5] [8]
According to the current model of dual-route processing, each of the two pathways consumes different amounts of limited attentional resources. [8] The nonlexical pathway is thought to be more active and constructive as it assembles and selects the correct subword units from various potential combinations. For example, when reading the word "leaf", that its spelling adheres to sound rules, the reader must assemble and recognize the two-letter grapheme "ea" in order to produce the sound "ee" that corresponds to it. It engages in controlled processing and thus requires more attentional capacities, which can vary in amount depending on the complexity of the words being assembled. [8] On the other hand, the processing that takes place in the lexical pathway appears to be more automatic, since the word-sound units in it are pre-assembled. Lexical processing is thus considered to be more passive, consuming less attentional resources. [8]
The dual-route hypothesis to reading can help explain patterns of data connected to certain types of disordered reading, both developmental and acquired. [9]
Children with reading disorders rely primarily on the sub-lexical route while reading. [10] Research shows that children can decode non-words, letter by letter, accurately but with slow speed. However, in decision tasks, they have trouble differentiating between words and pseudohomophones (non words that sound like real words but are incorrectly spelled), thereby showing that they had impaired internal lexicons. [10] Because children with reading disorders (RD) have both slow reading speeds and impaired lexical routes, there are suggestions that the same processes are involved in lexical route and fast naming of words. [10] Other studies have also confirmed this idea that rapid naming of words is more strongly correlated with orthographical knowledge (lexical route) than with phonological representations (sub-lexical route). Similar results were observed for patients with ADHD. [10] Research concludes that reading disorders and ADHD have common properties: lexical route processing, rapid reading and sublexical route processing deficits as well. [10]
Surface dyslexia, first described by Marshall and Newcombe, is characterized by the inability to read words that do not follow traditional pronunciation rules. English is also an example of a language that has numerous exceptions to the rules of pronunciation and thus presents a particular challenge to those with surface dyslexia. Patients with surface dyslexia may fail to read such words as "yacht", or "island" for example, because they do not follow prescribed rules of pronunciation. The words will typically be sounded out using "regularizations", such as pronouncing "colonel" as "Kollonel". [11] Words like "state", and "abdominal", are examples of words that people with surface dyslexia will not have a problem pronouncing, as they do follow proscribed pronunciation rules. [12] Surface dyslexics will read some irregular words correctly if they are high frequency words such as "have" and "some". [11] It has been postulated that surface dyslexics are able to read regular words by retrieving the pronunciation through semantic means. [12]
Surface dyslexia is also semantically mediated. Meaning that there is a relationship between the word and its meaning and not just the mechanisms in how it is pronounced. People with surface dyslexia also have the ability to read words and non-words alike. This means the physical production of phonological sounds is not affected by surface dyslexia. [12]
The mechanism behind surface dyslexia is thought to be involved with the phonologic output of the lexicon and is also often attributed to the disruption of semantics. It is also hypothesized that three deficits cause surface dyslexia. The first deficit is at the visual level in recognizing and processing the irregular word. The second deficit may be located at the level of the output lexicon. This is because patients are able to recognize the semantic meaning of irregular words even if they pronounce them incorrectly in spoken word. This suggests the visual word form system and semantics are relatively preserved. The third deficit is likely related to semantic loss. [11]
While surface dyslexia can be observed in patients with lesions in their temporal lobe, it is primarily associated with patients who have dementias. Such as Alzheimer's or frontotemporal dementia. Surface dyslexia is also a characteristic of semantic dementia, in which subjects lose knowledge of the world around them. [12]
Treatments for surface dyslexia involves neuropsychological rehabilitation. The aim of the treatment is to improve the operation of the sub-lexical reading route, or the patient's ability to sound out new words. As well as the operation of the visual word recognition system, to increase the recognition of words. On a more micro level, treatment can also focus on the ability to sound out individual letters before the patient goes on to increasing the ability to sound out entire words. [13]
Acquired phonological dyslexia is a type of dyslexia that results in an inability to read nonwords aloud and to identify the sounds of single letters. However, patients with this disability can holistically read and correctly pronounce words, regardless of length, meaning, or how common they are, as long as they are stored in memory. [2] [4] This type of dyslexia is thought to be caused by damage in the nonlexical route, while the lexical route, that allows reading familiar words, remains intact. [2]
A computational model of a cognitive task is essentially a computer program that aims to mimic human cognitive processing. [5] [14] This type of model helps bring out the precise parts of a theory and disregards the ambiguous sections, as only the clearly understood parts of the theory can be converted into a computer program. The ultimate goal of a computational model is to resemble human behavior as closely as possible, such that factors affecting the functioning of the program would similarly affect human behavior and vice versa. [14] Reading is an area that has been extensively studied via the computational model system. The dual-route cascaded model (DRC) was developed to understand the dual-route to reading in humans. [14] Some commonalities between human reading and the DRC model are: [5]
The DRC model has been useful as it was also made to mimic dyslexia. Surface dyslexia was imitated by damaging the orthographic lexicon so that the program made more errors on irregular words than on regular or non-words, just as is observed in surface dyslexia. [6] Phonological dyslexia was similarly modeled by selectively damaging the non-lexical route thereby causing the program to mispronounce non words. As with any model, the DRC model has some limitations and a newer version is currently being developed. [14]
Dyslexia, previously known as word blindness, is a learning disability that affects reading. Different people are affected to different degrees. Problems may include difficulties in spelling words, reading quickly, writing words, "sounding out" words in the head, pronouncing words when reading aloud and understanding what one reads. Often these difficulties are first noticed at school. The difficulties are involuntary, and people with this disorder have a normal desire to learn. People with dyslexia have higher rates of attention deficit hyperactivity disorder (ADHD), developmental language disorders, and difficulties with numbers.
A lexicon is the vocabulary of a language or branch of knowledge. In linguistics, a lexicon is a language's inventory of lexemes. The word lexicon derives from Greek word λεξικόν, neuter of λεξικός meaning 'of or for words'.
Psycholinguistics or psychology of language is the study of the interrelation between linguistic factors and psychological aspects. The discipline is mainly concerned with the mechanisms by which language is processed and represented in the mind and brain; that is, the psychological and neurobiological factors that enable humans to acquire, use, comprehend, and produce language.
Agraphia is an acquired neurological disorder causing a loss in the ability to communicate through writing, either due to some form of motor dysfunction or an inability to spell. The loss of writing ability may present with other language or neurological disorders; disorders appearing commonly with agraphia are alexia, aphasia, dysarthria, agnosia, acalculia and apraxia. The study of individuals with agraphia may provide more information about the pathways involved in writing, both language related and motoric. Agraphia cannot be directly treated, but individuals can learn techniques to help regain and rehabilitate some of their previous writing abilities. These techniques differ depending on the type of agraphia.
Reading for special needs has become an area of interest as the understanding of reading has improved. Teaching children with special needs how to read was not historically pursued due to perspectives of a Reading Readiness model. This model assumes that a reader must learn to read in a hierarchical manner such that one skill must be mastered before learning the next skill. This approach often led to teaching sub-skills of reading in a decontextualized manner. This style of teaching made it difficult for children to master these early skills, and as a result, did not advance to more advanced literacy instruction and often continued to receive age-inappropriate instruction.
In psycholinguistics, language processing refers to the way humans use words to communicate ideas and feelings, and how such communications are processed and understood. Language processing is considered to be a uniquely human ability that is not produced with the same grammatical understanding or systematicity in even human's closest primate relatives.
In cognitive psychology, the word superiority effect (WSE) refers to the phenomenon that people have better recognition of letters presented within words as compared to isolated letters and to letters presented within nonword strings. Studies have also found a WSE when letter identification within words is compared to letter identification within pseudowords and pseudohomophones.
Pure alexia, also known as agnosic alexia or alexia without agraphia or pure word blindness, is one form of alexia which makes up "the peripheral dyslexia" group. Individuals who have pure alexia have severe reading problems while other language-related skills such as naming, oral repetition, auditory comprehension or writing are typically intact.
Speech production is the process by which thoughts are translated into speech. This includes the selection of words, the organization of relevant grammatical forms, and then the articulation of the resulting sounds by the motor system using the vocal apparatus. Speech production can be spontaneous such as when a person creates the words of a conversation, reactive such as when they name a picture or read aloud a written word, or imitative, such as in speech repetition. Speech production is not the same as language production since language can also be produced manually by signs.
Deep dyslexia is a form of dyslexia that disrupts reading processes. Deep dyslexia may occur as a result of a head injury, stroke, disease, or operation. This injury results in the occurrence of semantic errors during reading and the impairment of nonword reading.
Indirect memory tests assess the retention of information without direct reference to the source of information. Participants are given tasks designed to elicit knowledge that was acquired incidentally or unconsciously and is evident when performance shows greater inclination towards items initially presented than new items. Performance on indirect tests may reflect contributions of implicit memory, the effects of priming, a preference to respond to previously experienced stimuli over novel stimuli. Types of indirect memory tests include the implicit association test, the lexical decision task, the word stem completion task, artificial grammar learning, word fragment completion, and the serial reaction time task.
The history of dyslexia research spans from the late 1800s to the present.
The mental lexicon is defined as a mental dictionary that contains information regarding the word store of a language user, such as their meanings, pronunciations, and syntactic characteristics. The mental lexicon is used in linguistics and psycholinguistics to refer to individual speakers' lexical, or word, representations. However, there is some disagreement as to the utility of the mental lexicon as a scientific construct.
Surface dyslexia is a type of dyslexia, or reading disorder. According to Marshall & Newcombe's (1973) and McCarthy & Warrington's study (1990), patients with this kind of disorder cannot recognize a word as a whole due to the damage of the left parietal or temporal lobe. Individuals with surface dyslexia are unable to recognize a word as a whole word and retrieve its pronunciation from memory. Rather, individuals with surface dyslexia rely on pronunciation rules. Thus, patients with this particular type of reading disorder read non-words fluently, like "yatchet", but struggle with words that defy pronunciation rules. For example, a patient with surface dyslexia can correctly read regular words like "mint", but will fail when presented with a word that disobeys typical pronunciation rules, like "pint". Often, semantic knowledge is preserved in individuals with surface dyslexia.
Phonological dyslexia is a reading disability that is a form of alexia, resulting from brain injury, stroke, or progressive illness and that affects previously acquired reading abilities. The major distinguishing symptom of acquired phonological dyslexia is that a selective impairment of the ability to read pronounceable non-words occurs although the ability to read familiar words is not affected. It has also been found that the ability to read non-words can be improved if the non-words belong to a family of pseudohomophones.
Bilingual lexical access is an area of psycholinguistics that studies the activation or retrieval process of the mental lexicon for bilingual people.
Dynaread Special Education Corporation is a provider of dyslexia remediation services specifically designed for older struggling readers.
Max Coltheart is an Australian cognitive scientist who specialises in cognitive neuropsychology and cognitive neuropsychiatry.
Kathleen Rastle is a cognitive psychologist and Professor of Cognitive Psychology at Royal Holloway, University of London where she was previously the Head of Department of Psychology (2015-2019). Her research has made fundamental contributions to understanding of reading and learning to read.
Silent reading is reading done silently, or without speaking the words being read.