Tuning of the human left fusiform gyrus to sublexical orthographic structure

Abstract

Neuropsychological and neurophysiological evidence point to a role for the left fusiform gyrus in visual word recognition, but the specific nature of this role remains a topic of debate. The aim of this study was to measure the sensitivity of this region to sublexical orthographic structure. We measured blood oxygenation (BOLD) changes in the brain with functional magnetic resonance imaging while fluent readers of English viewed meaningless letter strings. The stimuli varied systematically in their approximation to English orthography, as measured by the probability of occurrence of letters and sequential letter pairs (bigrams) comprising the string. A whole-brain analysis showed a single region in the lateral left fusiform gyrus where BOLD signal increased with letter sequence probability; no other brain region showed this response pattern. The results suggest tuning of this cortical area to letter probabilities as a result of perceptual experience and provide a possible neural correlate for the 'word superiority effect' observed in letter perception research.Much evidence supports the idea that perceptual systems become selectively efficient at processing inputs that are encountered frequently. In learning a written language, for example, human brains appear to become tuned to the recurring visual patterns of the language represented in its orthographic structure. This is illustrated by the fact that letters embedded in words (such as S in the English word FLASH) or in word-like letter strings (S in FRISH) are more efficiently recognized than letters embedded in unusual letter strings (S in RFHSL) (McClelland and Rumelhart, 1981;Reicher, 1969). Such evidence suggests that normal readers use information about frequently recurring letter combinations, encoded as a result of experience with a specific written language, to more efficiently perceive and identify letters and letter strings.Neuropsychological evidence for an orthographic processor in the brain comes from patients who exhibit 'letter-by-letter reading' after left occipitotemporal brain injury (Binder and Mohr, 1992;Cohen et al., 2003;Leff et al., 2001;Sakurai et al., 2000). Such patients have normal language functions, including good recognition of single letters, but show profoundly impaired processing of letter strings, suggesting focal damage to systems responsible for storing or using orthographic information (Behrmann et al., 1998;Patterson and Kay, 1982;Warrington and Shallice, 1980). This localization is supported by neuroimaging experiments in normal readers, which have identified a region in the lateral left fusiform (occipitotemporal) gyrus that responds more strongly to words and word-like nonwords than to consonant letter strings or nonsense characters Dehaene et al., 2001;Polk and Farah, 2002 1999). Several elegant studies showed that this orthographic system employs an abstract code that is unaffected by changes in letter case (Dehaene et al., 2001Polk and Farah, 2002).Although activation in this brain region appears to be relat...

Aging Influences the Neural Correlates of Lexical Decision but Not Automatic Semantic Priming

“…For example, degrading stimulus quality increases RT more in older adults than younger adults, whereas the effects of varying word frequency remain relatively consistent in aging (Madden 1988;Allen et al 1995). In addition, at the functional neuroanatomic level, extrastriate regions showing greater activation in the young group have been associated with orthographic processes (Petersen et al 1990;Cohen et al 2003;Binder et al 2003Binder et al , 2006. In contrast, inferior temporal regions showing greater activation in the older group have typically been associated with semantic knowledge (Nobre et al 1994;Martin et al 1995;Martin and Chao 2001;Sharp et al 2004), and the mid-LIPC region (ca.…”

“…There is evidence that different regions within this network play different roles in LD. Extrastriate regions have been linked with orthographic processes such as visual feature extraction and mapping visual patterns onto lexical representations (Petersen et al 1990;Binder et al 2003Binder et al , 2006Cohen et al 2003;Gold et al 2006). In contrast, inferior temporal regions have most typically been associated with semantic processes (Nobre et al 1994;Martin et al 1995;Martin and Chao 2001;Sharp et al 2004), and left inferior frontal regions have been shown to contribute to multiple high-level linguistic processes (Petersen et al 1988;Demb et al 1995;Thompson-Schill et al 1997;Badre et al 2005;Gold et al 2005, Gold et al 2006.…”

The balance between memory and unification in semantics: A dynamic account of the N400

“…7 We shall not comment on the purely visual aspects of word recognition or on visual-to-lexical transcoding (Perfetti, 1999). Here we only assume that structures in the inferior temporal lobe can act as interfaces between the visual system and the lexicon (Binder et al, 2003;Binder, Medler, Westbury, Liebenthal, & Buchanan, 2006;Cohen et al, 2000;Devlin, Jamison, Gonnerman, & Matthews, 2006;Nobre, Allison, & McCarthy, 1994), perhaps in cooperation with other brain areas (Mechelli, Gorno-Tempini, & Price, 2003;Price & Devlin, 2003). The mapping from visual input to lexical structures stored in the Memory component is represented by arrow 1 in Figure 3.…”

It's a word: Early electrophysiological response to the character likeness of pictographs

“…One set of studies showed that its sensitivity to visual words is independent of changes in case, font, size, and location (Dehaene et al, 2001(Dehaene et al, , 2004Polk & Farah, 2002) but is dependent on orthographic regularity and GPC rules (Bentin et al, 1999;Fiebach, Friederici, Muller, & von Cramon, 2002;Hsu et al, 2009). Based on such evidence, several researchers suggested that N170's specialization was orthography (Binder, Medler, Westbury, Liebenthal, & Buchanan, 2006;Vinckier et al, 2007).…”