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Pattern recognition and visual word forms Epigraph “But if any see fit not to agree with the opinions here expressed. . .still let them note the great magnitude of experiments. . .we have dug them up and demonstrated them with much pains and sleepless nights and great money expense. Enjoy them you, and if ye can, employ them for better purposes.” --William Gilbert, 1600 In other words: Even if you don’t like the theories, you have to explain the data. The great “visual word form area” debate Is the “visual word form area” specialized for visual word forms? Larger debates: Domain general vs. Domain specific Organization-by-material vs. Organizationby-process Roles of learning, expertise and evolution in shaping brain function. Fusiform Gyrus and the “Visual Word Form Area” Fusiform gyrus VWFA: Fusiform Gyrus and the “Visual Word Form Area” Hypothesized to “contains a population of neurons that, as an ensemble, is tuned to invariant stimulus properties and structural regularities of written words” (McCandliss et al., 2003) Fusiform Gyrus and the “Visual Word Form Area” Model of functional anatomy for invariant word perception ose a simple anatomical and functional model of the visual word reading, which follows the general principles that govern cognition in the visual system of primates (Fig. I). Separate s in left and right hemispheres are integrated in the left d Visual Word Form Area (VWFA), which mediates between pecific input, and more abstract linguistic areas responsible for emantic and phonological processes. Although the precise ns from VWFA to systems involved in lexical, semantic and VWFA: phonological processes are currently less clearly defined, functional areas probably include the left angular gyrus [52], left inferior frontal cortex [53], and temporal regions anterior to the VWFA [54]. Finally, ventral visual regions receive top-down attentional influences associated with left and right parietal regions that are likely to affect all processing levels, and whose impairment might therefore lead to various forms of neglect dyslexia. Hypothesized to “contains a population of neurons that, as an ensemble, is tuned to invariant stimulus properties and structural regularities of written words” (McCandliss et al., 2003) Anatomy and connectivity Phonology Lexico-semantic features VWF Visuospatial attention Functional properties W-O-R-D V4 V4 V2 V2 V1 V1 dr oW Visuospatial attention • Sequence of abstract letter identities • Font invariant Wdo • Location invariant • Increasing receptive field size • Increasingly abstract features Word TRENDS in Cognitive Sciences ntative model of functional anatomical pathways involved in visual perception of words. Letter strings are first processed in ventral occipital regions (V1 to lateral to the stimuli, building up increasingly abstract visual representations (right). For stimuli in the left visual field, information is conveyed from the right Fusiform Gyrus and the “Visual Word Form Area” Response properties (McCandliss et al., 2003): Responds reliably to letters and words. May also respond to faces and objects. Responds more to letters than pseudo-letters Modality-specific (doesn’t respond to spoken words) Invariant with regard to retinal location, letter case, size and font (neural priming studies) Insensitive to lexical properties (e.g. frequency) Left Fusiform is Activated by Visual Word Forms (Cohen et al., 2002) Passive viewing of words, letter strings and checkerboards Words & Letters > Checkerboards in left, but not right, fusiform cluster. Left Fusiform is Activated by Visual Word Forms (Cohen et al., 2002) Passive viewing of words, letter strings and checkerboards Words > letters in left fusiform cluster. Left Fusiform is Activated by Visual Word Forms (Cohen et al., 2002) How does the VWFA become specialized? Written language is a recent cultural development (~5400 years ago), so can’t be evolution. Children do not show letter/word specific activation in VWFA before learning to read. Initial properties intrinsic to the region and its connectivity must determine its subsequent specialization for reading. May be specialized for foveal objects, local object features, and invariance for position and size. Expertise for reading in the fusiform gyrus (McCandliss et al., 2003) Expertise in different visual categories (e.g. birds, cars) linked to enhanced perception of category members via more holistic processing of the stimulus, through functional re-organizaiton of visual areas. Expertise for word reading may be similar. Expertise for reading in the fusiform gyrus (McCandliss et al., 2003) Literate adults group letters together into a single perceptual unit (visual word form). Speed of word recognition is unaffected by the number of letters for 3-6 letter words. Suggests processed in parallel Expertise for reading in the fusiform gyrus (McCandliss et al., 2003) Hypothesis: reading experience drives progressive specialization of a pre-existing inferotemporal pathway for visual object recognition. Expertise for reading in the fusiform gyrus (McCandliss et al., 2003) Evidence: Younger children do show word length effects for 3-6 letter words. ERP data shows 10-year-olds have adult-like response to high frequency, but not low frequency, words. Activation level of VWFA correlated with phonemegrapheme decoding ability, controlling for age. VWFA less active in adults with developmental dyslexia. “The myth of the VWFA” (Price & Devlin, 2003) Is the VWFA really specialized for word forms? Neuropsychological evidence: “pure alexics” usually have much larger lesions (including cuneus, calcarine sulcus and lingual gyrus in addition to fusiform) “pure alexics” often have other perceptual problems (e.g. color naming, picture processing) “The myth of the VWFA” (Price & Devlin, 2003) 476 C.J. Price, J.T. Devlin / NeuroImage 19 (2003) 473– 481 Is the VWFA really specialized for word forms? Functional imaging evidence: Also active when subjects name familiar objects, make manipulation responses to pictures of unfamiliar objects, name colors and perform auditory and tactile word processing tasks. “The myth of the VWFA” (Price & Devlin, 2003) So what does the “VWFA” do then? 3 possibilities: 1. Different populations of neurons in the same region, one for VWFs and others for naming, object perception etc. Not very neurally plausible. Would require single-cell evidence. “The myth of the VWFA” (Price & Devlin, 2003) So what does the “VWFA” do then? 3 possibilities: 2. A single cognitive function, not yet identified underlies all these multimodal responses. “The myth of the VWFA” (Price & Devlin, 2003) So what does the “VWFA” do then? 3 possibilities: 3. the same population of neurons could support different cognitive processes, depending on their interactions with other cortical and subcortical areas. Visual Perceptual Learning of Words and the VWFA Debate (Xue & Poldrack, 2007) Korean characters presented in pairs: same/different judgment. Scanned before and after training. Difficulty controlled by amount of visual noise. English word control task. Figure 1. Example of the stimuli. (A) Korean characters. The top and bottom show an example character with left–right–bottom, and top–middle–bottom structure, respectively. The letters of the character are marked with different colors. (B) English words. All English words Visual Perceptual Learning of Words and the VWFA Debate (Xue & Poldrack, 2007) At pre-training scan, both words and Korean characters strongly activated VWFA. Not sig. different. After training, less VWFA activation for Korean characters, both with same level of noise as pre-training scan, and same level of performance (by increasing noise). Suggest that “VWFA is neither specific to words nor sensitized by visual expertise with specific writing systems”