User:Knguyend/sandbox
Visual word form area[edit]
The visual word form area or VWFA for short, is a region of the left inferior temporal lobe recognized for processing, learning and memory of words.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] Specifically in the temporal lobe, the fusiform gyrus allows for fast and automatic processing of visual words within 250 ms of perceiving a written word.[7][12] With such unique demands of the English language, processing of visual words in the fusiform gyrus allows access to word-associated knowledge, phonology and semantics. The visual word form is the combination of letters and symbols that make up a written word, despite variations in font, case, location and size.[7] Even visual words of mixed cases do not pose difficulty for this specialized area of the brain, suggesting a demand for such an area in the brain, that can be shaped by both short-term and long-term knowledge. [7][13]
Development of the Visual Word Form Area[edit]
In 1892, Joseph Jules Dejerine reported a case of a patient with damage to the left inferior occipitotemporal lobe that caused a selective loss for reading of letters and words.[1][4][14] He was the first to suggest word blindness resulted from damage to the fusiform gyrus from his studies on localization of the brain. He proposed that processing of visual words in the left visual field required use of the corpus callosum. The corpus callosum connects the left and right hemispheres to allow for communication. In other words, he suggested that even though word can be perceived in either the left or right visual field, word reading is specialized to the left hemisphere. After Dejerine's discovery, researchers did not deny the existence of the visual word system, but instead focused their studies on the underlying mechanisms of the visual word form area and how it came to be. His research is widely used as the basis for future research in the visual word form area. With recent emergence of writing and reading comprehension within the last century, some researchers argue that neuronal recycling is what allows for this enhanced perception of visual words, while others suggest that the development of localized word reading is innate. [4]
Neuronal Recycling[edit]
According to research, the development of the visual word form cannot be explained by natural selection. Stanislas Dehaene along with his colleagues became renowned for their work on the visual word form area.[1][4][5] Since the development of language and writing has only emerged within the last century, natural selection could not have influenced the human genome to specialize a brain region specific for reading. Instead, Dehaene and Cohen suggest that a neuronal recycling process occurs.[5] The basic idea is that neural processes specific to reading are recycled from neurons that were established for other vision processes. Over time, without any changes to the human genome, neurons originally intended for recognition of faces, can be recycled and used for recognition of visual words. [5]
Empirical Research[edit]
Evidence based research on patients with specific damage to their inferior temporal lobes and deficits to their word perception have revealed a modality specific function of the visual word form area. Research from neuropsychological studies and brain imaging studies have suggested evidence for specific tuning of the visual word form area.
| Deficit | Outcome |
|---|---|
| Pure Alexia | Impairment in word reading |
| Epilepsy | Seizures |
| Split-brain | Interfered connection between hemispheres |
Pure Alexia[edit]
Research on patients with a specific type of dyslexia known as pure alexia or word blindness has suggested evidence for localization of word perception in the visual word form area.[1] Cohen and his colleagues suggested this area in the midfusiform area to be the lesion site for pure alexics.'[1] Selective damage to the fusiform gyrus has been shown to cause impairment of reading words in rapid and parallel fashion. Patients who suffer from pure alexia have intact ability to write and speak, suggesting neuronal modularity of the fusiform gyrus. [5]
Epilepsy[edit]
epilepsy is a neurological disorder characterized by chronic seizures caused by abnormal neuronal activity. A patient study on epileptics revealed that a surgical lesion to the visual word form area to treat epilepsy suggested evidence for functional specificity of the fusiform gyrus.[4] Prior to surgery, functional magnetic resonance imaging (fMRI) showed activation of the fusiform gyrus when perceiving visual words. Following the surgery, results of a fMRI scan showed that the patient suffered an impairment to processing and reading of visual words but did not show difficultly recognizing objects, faces or other linguistic abilities.[1][4]
Split-brain Patients[edit]
Studies on split-brain patients have shown evidence for localization of word processing specific to the left inferior temporal hemisphere. Control patients who did not have damage to their corpus callosum were able to process visual words that were presented in both the left and right visual fields. However for callosal patients, visual word forms presented in the left visual field were unable to be perceived as a result of the inability for information to pass along the corpus callosum. In these patients, the visual word form system was only activated by words present in the right visual field. [15]
Debates[edit]
Neuropsychological studies on patients with damage to the fusiform gyrus and neuroimaging studies showing activation of the fusiform gyrus suggest the visual word form hypothesis is rather misleading. Research that debates one-to-one mapping of the visual word form area to reading of visual words do not deny the function of the fusiform gyrus, but suggest a more general explanation of visual processing.
Pure Alexia[edit]
Although pure alexia has revealed modularity of brain regions associated with reading of, some researchers argue that pure alexia is not limited to visual word form processing and not limited to damage to the left fusiform gyrus. If this is the case, evidence for the visual word system is misleading. Price and her colleagues showed that the visual word form area is activated by normal subjects in tasks that do not engage word-association, such as naming of colours, naming pictures, reading Braille. [14] Other tasks such as repetition of spoken words also seemed to activate this region of the brain. Pure alexics are shown to have damage to more than just the fusiform gyrus, in areas including the cuneus, calcarine sulcus, and lingual gyrus, making it difficult to localize word reading to a specific region of the brain. [14] Patients with pure alexics often report difficulties with naming of colours and pictures, along with impaired reading ability. Classic interpretation from a neurological perspective proposes that word blindness is the result a disconnection of visual processing from language processing in the occipital and temporal cortices respectively, in the left hemisphere, suggesting a more general visual problem as opposed to a specific reading deficit.[14]
Fusiform Face Area[edit]
Studies have suggested that the visual word form area is not specifically tuned for processing of visual words, but is shown to activate for faces as well.[8] This research refutes localized models that suggest that specific regions in the brain have specific functions, exclusive to that area. For example, the fusiform face area (FFA) is a region of the temporal lobe believed to be specialized for recognition of faces. However, fMRI studies have shown that the visual word form area is not limited to word processing, and therefore the function of both the fusiform face area and visual word form area have a more general role in processing of visual information, rather than specific.[8]
Object naming[edit]
Studies on the visual word form area have shown that during tasks of object naming, the fusiform gyrus is active, even though it does not require visual word form processing. When subjects are asked to name, view or generate verbs to pictures of objects the visual word form area shows activation in functional brain images.[14] These results suggest that the visual word form area is not specific to reading of visual words, though there is evidence that the fusiform gyrus does play a significant role in visual word processing.
Category activation[edit]
Results of similar functional magnetic resonance imaging studies also showed that there was greater activation for reading of words that belonged to animal categories over words that belonged to tool categories.[14] No current research done has suggested reasons for why the visual word form area would show more activation for one category over another. Future research should look to study this.
Conclusions and Future Implications[edit]
Much debate over the visual word hypothesis has suggested evidence for a more general approach to looking at processing of visual words. Neuropsychological evidence from patient studies of the brain have revealed a large variation of deficits and degree to which the deficit can occur in patients with damage to the fusiform area.[11] In conclusion, there is no argument disputing that the visual word form area is involved in processing, learning and memory of visual words, however it is suggestive to say that the visual word form area is specifically tuned to word reading. It is clear that the visual word form area is responsive to visual input, but research has shown that it is not exclusive.[14] Neuroimaging studies using fMRI have suggested that activation of this brain region can occur during naming of colours, pictures and even during auditory processing of words, suggesting a more general function of the left temporal lobe related to visual processing. From an evolutionary perspective, it is not likely that the human genome coded for a specific region of the brain for reading, but that is not to say that reading of visual input is not activated in this area.[1][4] Future research should look to study the underlying cognitive and neural implications of this brain region to rule out any alternate explanations of the visual word hypothesis.[1]
See Also[edit]
References[edit]
- ^ a b c d e f g h Cohen, L., & Dehaene, S. (2004). Specialization within the ventral stream: the case for the visual word form area. NeuroImage, 22, 466-476.
- ^ Cohen, L., Dehaene, S., Naccache, L., Lehericy, S., Dehaene-Lambertz, G., Hennaff, M, & Michel, F. (2000). The visual word form area: Spatial and temporal characterization of an initial stage of reading in normal subjects and posterior split-brain patients. Brain, 123, 291-307.
- ^ Cohen, L., Lehericy, S., Chochon, F., Lemer, C., Rivaud, S., & Dehaene, S. (2002). Language-specific tuning of visual cortex? Functional properties of the visual word form area. Brain, 125, 1054-1069.
- ^ a b c d e f g Dehaene, S., & Cohen, L. (2011). The unique role of the visual word form area in reading. Trends in Cognitive Sciences, 15:6, 254-262.
- ^ a b c d e Dehaene, S., Le Clech'H, G., Poline, J., Le Bihan, D., & Cohen, L. (2002). The visual word form area: A prelexical representation of visual words in the fusiform gyrus. NeuroReport, 13:3, 321-325.
- ^ Hillis, A. E., Newhart, M., Heidler, J., Barker, P., Herskovits, E., & Degaonkar, M. (2005). THe roles of the visual word form area in the reading. NeuroImage, 24, 548-559.
- ^ a b c d McCandliss, B. D., Cohen, L., & Dehaene, S. (2003). The visual word form area: expertise for reading in the fusiform gyrus. Trends in Cognitive Sciences, 7:7, 293-299.
- ^ a b c Mei, L., Xue, G., Chen, C., Zhang, M., & Dong, Q. (2010). The visual word form area is involved in successful memory encoding of words and faces. NeuroImage, 52, 371-378
- ^ Reinke, K., Fernandes, M., Schwindt, G., O'Craven, K., & Grady, C. L. (2008). Functional specificity of the visual word form area: General activation for words and symbols but specific network activation for words. Brain and Language, 104, 180-189.
- ^ Vigneau, M., Jobard, G., & Tzourio-Mazoyer, N. (2005). Word and non-word reading: What role for the visual word form area. Neuroimage, 27, 692-705.
- ^ a b Xue, G., & Poldrack, R. A. (2007). Neural substrates of visual perceptual learning of words: Implications for the visual word form area hypothesis. Journal of Cognitive Neuroscience, 19:10, 1643-1655.
- ^ Qiao, E., Vinckier, F., Szwed, M., Naccache, L., Valabregue, R., Dehaene, S., & Cohen, L. (2010). Unconsciously deciphering handwriting: Subliminal invariance for handwritten words in the visual word form area. NeuroImage, 49, 1786-1799.
- ^ Song, B., Hu, S., Luo, Y., & Liu, J. (2010). Short-term language experience shape the plasticity of the visual word form area. Brain Research, 1316, 83-91.
- ^ a b c d e f g Price, C. J., & Devlin, J. T. (2003). The myth of the visual word form area. NeuroImage, 19, 473-481.
- ^ Cohen, L., Dehaene, S., Naccache, L., Lehericy, S., Dehaene-Lambertz, G., Hennaff, M, & Michel, F. (2000). The visual word form area: Spatial and temporal characterization of an initial stage of reading in normal subjects and posterior split-brain patients. Brain, 123, 291-307.
Further Readings[edit]
- Cohen, L., & Dehaene, S. (2004). Specialization within the ventral stream: the case for the visual word form area. NeuroImage, 22, 466-476.
- Dehaene, S., & Cohen, L. (2011). The unique role of the visual word form area in reading. Trends in Cognitive Sciences, 15:6, 254-262.
- Price, C. J., & Devlin, J. T. (2003). The myth of the visual word form area. NeuroImage, 19, 473-481.