Top-down and bottom-up influences on the left ventral occipito-temporal cortex during visual word recognition: An analysis of effective connectivity (original) (raw)
Related papers
Taxi vs. Taksi: On Orthographic Word Recognition in the Left Ventral Occipitotemporal Cortex
Journal of Cognitive Neuroscience, 2007
The importance of the left occipitotemporal cortex for visual word processing is highlighted by numerous functional neuroimaging studies, but the precise function of the visual word form area (VWFA) in this brain region is still under debate. The present functional magnetic resonance imaging study varied orthographic familiarity independent from phonological–semantic familiarity by presenting orthographically familiar and orthographically unfamiliar forms (pseudohomophones) of the same words in a phonological lexical decision task. Consistent with orthographic word recognition in the VWFA, we found lower activation for familiar compared with unfamiliar forms, but no difference between pseudohomophones and pseudowords. This orthographic familiarity effect in the VWFA differed from the phonological familiarity effect in left frontal regions, where phonologically unfamiliar pseudowords led to higher activation than phonologically familiar pseudohomophones. We suggest that the VWFA not only computes letter string representations but also hosts word-specific orthographic representations. These representations function as recognition units with the effect that letter strings that readily match with stored representations lead to less activation than letter strings that do not.
Journal of Cognitive Neuroscience, 2011
■ Prior lesion and functional imaging studies have highlighted the importance of the left ventral occipito-temporal (LvOT) cortex for visual word recognition. Within this area, there is a posterioranterior hierarchy of subregions that are specialized for different stages of orthographic processing. The aim of the present fMRI study was to dissociate the effects of subword orthographic typicality (e.g., cider [high] vs. cynic [low]) from the effect of lexicality (e.g., pollen [word] vs. pillen [pseudoword]). We therefore orthogonally manipulated the orthographic typicality of written words and pseudowords (nonwords and pseudohomophones) in a visual lexical decision task. Consistent with previous studies, we identified greater activation for pseudowords than words (i.e., an effect of lexicality) in posterior LvOT cortex. In addition, we revealed higher activation for atypical than typical strings, irrespective of lexicality, in a left inferior occipital region that is posterior to LvOT cortex. When lexical decisions were made more difficult in the context of pseudohomophone foils, left anterior temporal activation also increased for atypical relative to typical strings. The latter finding agrees with the behavior of patients with progressive anterior temporal lobe degeneration, who have particular difficulty recognizing words with atypical orthography. The most novel outcome of this study is that, within a distributed network of regions supporting orthographic processing, we have identified a left inferior occipital region that is particularly sensitive to the typicality of subword orthographic patterns. ■
We investigated phonological processing in normal readers to answer the question to what extent phonological recoding is active during silent reading and if or how it guides lexico-semantic access. We addressed this issue by looking at pseudohomophone and baseword frequency effects in lexical decisions with event-related functional magnetic resonance imaging (fMRI). The results revealed greater activation in response to pseudohomophones than for well-controlled pseudowords in the left inferior/superior frontal and middle temporal cortex, left insula, and left superior parietal lobule. Furthermore, we observed a baseword frequency effect for pseudohomophones (e.g., FEAL) but not for pseudowords (e.g., FEEP). This baseword frequency effect was qualified by activation differences in bilateral angular and left supramarginal, and bilateral middle temporal gyri for pseudohomophones with low-compared to high-frequency basewords. We propose that lexical decisions to pseudohomophones involves phonology-driven lexico-semantic activation of their basewords and that this is converging neuroimaging evidence for automatically activated phonological representations during silent reading in experienced readers. Ó 2015 The Authors. Published by Elsevier Ltd. on behalf of IBRO. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/). (M. Braun). Abbreviations: AG, angular gyrus; ANOVA, analysis of variance; DRC, dual-route cascaded model; fMRI, functional magnetic resonance imaging; IPL, inferior parietal lobule; MROM-P, multiple read-out model including phonology; pIO, posterior inferior occipital gyrus; pSTS, posterior superior temporal sulcus; SFG, superior frontal gyrus; SMA, supplementary motor area; SMG, supramarginal gyrus; TMS, transcranial magnetic stimulation; vOT, ventral occipito-temporal cortex. Neuroscience 295 (2015) 151-163
The present fMRI study investigated the hypothesis that activation of the left ventral occipitotemporal cortex (vOT) in response to auditory words can be attributed to lexical orthographic rather than lexico-semantic processing. To this end, we presented auditory words in both an orthographic ("three or four letter word?") and a semantic ("living or nonliving?") task. In addition, a auditory control condition presented tones in a pitch evaluation task. The results showed that the left vOT exhibited higher activation for orthographic relative to semantic processing of auditory words with a peak in the posterior part of vOT. Comparisons to the auditory control condition revealed that orthographic processing of auditory words elicited activation in a large vOT cluster. In contrast, activation for semantic processing was only weak and restricted to the middle part vOT. We interpret our findings as speaking for orthographic processing in left vOT. In particular, we suggest that activation in left middle vOT can be attributed to accessing orthographic whole-word representations. While activation of such representations was experimentally ascertained in the orthographic task, it might have also occurred automatically in the semantic task. Activation in the more posterior vOT region, on the other hand, may reflect the generation of explicit images of word-specific letter sequences required by the orthographic but not the semantic task. In addition, based on cross-modal suppression, the finding of marked deactivations in response to the auditory tones is taken to reflect the visual nature of representations and processes in left vOT.
Word Recognition in Auditory Cortex
Georgetown University-Graduate School of Arts & Sciences, 2013
Although spoken word recognition is more fundamental to human communication than text recognition, knowledge of word-processing in auditory cortex is comparatively impoverished. This dissertation synthesizes current models of auditory cortex, models of cortical pattern recognition, models of single-word reading, results in phonetics and results in language acquisition to form a novel model of auditory word-form recognition. The model is expounded and assessed empirically in two studies and discussed with respect to results from clinical neuroscience. Study 1 uses a series of meta-analyses to quantitatively synthesize functional brain imaging results. The analytical method assesses the anatomical concordance of prior results for a given experimental paradigm. Through consideration of multiple paradigms and stimulus types, it assesses concordance for several experimental phenomena pertinent to aspects of the model presented. Two novel findings are reported. First, a processing cascade for speech sounds is observed in left auditory cortex, extending from mid superior temporal gyrus (STG) to anterior STG to anterior superior temporal sulcus (STS). This corresponds with increasing scales of speech sound processing, from phonemes to words to phrases. Second, correlates of selectivity and invariance for speech sounds are observed within the same left mid-to-anterior STG region, the former being with respect to both artificial control stimuli and non-speech natural sounds, the latter being with respect to categoryspecific neural adaptation. Study 2 tests predictions about the types of speech sounds encoded by auditory cortex. Data from linguistic corpora are used to model the natural statistics of the heard phonetic environment. These statistics are then used to characterize the regularity of phoneme orderings within non-word stimuli. Two novel results are reported. First, using functional magnetic resonance imaging (fMRI), sensitivity to the natural statistics of phoneme ordering is observed in left anterior STG, as predicted iv by distributional learning and hierarchical feature coding. Second, correlation is observed between activity in left anterior-lateral planum temporale (PT) and phoneme-level prediction error for an ideal observer, consistent with predictive coding. According to the model presented, PT is the site of subphonemic representation. Error signal in PT is therefore suggestive of inaccurate top-down contextual predictions for acoustic-phonetic features.
The present fMRI study used a spelling task to investigate the hypothesis that the left ventral occipitotemporal cortex (vOT) hosts neuronal representations of whole written words. Such an orthographic word lexicon is posited by cognitive dual-route theories of reading and spelling. In the scanner, participants performed a spelling task in which they had to indicate if a visually presented letter is present in the written form of an auditorily presented word. The main experimental manipulation distinguished between an orthographic word spelling condition in which correct spelling decisions had to be based on orthographic whole-word representations, a word spelling condition in which reliance on orthographic whole-word representations was optional and a phonological pseudoword spelling condition in which no reliance on such representations was possible. To evaluate spelling-specific activations the spelling conditions were contrasted with control conditions that also presented auditory words and pseudowords, but participants had to indicate if a visually presented letter corresponded to the gender of the speaker. We identified a left vOT cluster activated for the critical orthographic word spelling condition relative to both the control condition and the phonological pseudoword spelling condition. Our results suggest that activation of left vOT during spelling can be attributed to the retrieval of orthographic whole-word representations and, thus, support the position that the left vOT potentially represents the neuronal equivalent of the cognitive orthographic word lexicon. Hum Brain Mapp 00:000-000, 2015.
Modulation of brain regions involved in word recognition by homophonous stimuli: An fMRI study
Brain Research, 2011
We used rapid event-related fMRI to explore factors modulating the activation of orthographic and phonological representations of print during a visual lexical decision task. Stimuli included homophonous word and nonword stimuli (MAID, BRANE), which have been shown behaviorally to produce longer response times due to phonological mediation effects. We also manipulated participants' reliance on orthography by varying the extent to which nonword foils were orthographically typical (wordlike context) or atypical (non-wordlike context) of real words. Key findings showed that reading lowfrequency homophones in the wordlike context produced activation in regions associated with phonological processing (i.e., opercular region of the left inferior frontal gyrus [IFG; BA 44]), the integration of orthography and phonology (i.e., the inferior parietal lobule (IPL), and lexicosemantic processing (i.e., left middle temporal gyrus, [MTG]). Pseudohomophones in the wordlike context produced greater activity relative to other nonword trials in regions engaged during both phonological processing (i.e., left IFG/precentral gyrus; BA 6/9]), and semantic processing (triangular region of the left IFG; BA 47). Homophonous effects in the non-wordlike context were primarily isolated to medial extrastriate regions, hypothesized to be involved in low level visual processing and not reading-related processing per se.
European Journal of Neuroscience, 2008
Letters and speech sounds are the basic units of correspondence between spoken and written language. Associating auditory information of speech sounds with visual information of letters is critical for learning to read; however, the neural mechanisms underlying this association remain poorly understood. The present functional magnetic resonance imaging study investigates the automaticity and behavioral relevance of integrating letters and speech sounds. Within a unimodal auditory identification task, speech sounds were presented in isolation (unimodally) or bimodally in congruent and incongruent combinations with visual letters. Furthermore, the quality of the visual letters was manipulated parametrically. Our analyses revealed that the presentation of congruent visual letters led to a behavioral improvement in identifying speech sounds, which was paralleled by a similar modulation of cortical responses in the left superior temporal sulcus. Under low visual noise, cortical responses in superior temporal and occipito-temporal cortex were further modulated by the congruency between auditory and visual stimuli. These crossmodal modulations of performance and cortical responses during an unimodal auditory task (speech identification) indicate the existence of a strong and automatic functional coupling between processing of letters (orthography) and speech (phonology) in the literate adult brain.
Phonological and orthographic components of word recognition
2000
activated by both decision-making tasks; more intense and widespread activation was seen there during phonological, pseudowords) and lexical decision-making tasks were used with 15 O PET to examine the neural correlates of phonological than during orthographic, decision making, with the activation during phonological decision-making extending and orthographic processing in 14 healthy right-handed men (aged 18-40