Learning to See Words

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328

Spoken word recognition requires complex, invariant representations. Using a meta-analytic approach incorporating more than 100 functional imaging experiments, we show that preference for complex sounds emerges in the human auditory ventral stream in a hierarchical fashion, consistent with nonhuman primate electrophysiology. Examining speech sounds, we show that activation associated with the processing of short-timescale patterns (i.e., phonemes) is consistently localized to left mid-superior temporal gyrus (STG), whereas activation associated with the integration of phonemes into temporally complex patterns (i.e., words) is consistently localized to left anterior STG. Further, we show left midto anterior STG is reliably implicated in the invariant representation of phonetic forms and that this area also responds preferentially to phonetic sounds, above artificial control sounds or environmental sounds. Together, this shows increasing encoding specificity and invariance along the auditory ventral stream for temporally complex speech sounds.functional MRI | meta-analysis | auditory cortex | object recognition | language S poken word recognition presents several challenges to the brain. Two key challenges are the assembly of complex auditory representations and the variability of natural speech (SI Appendix, Fig. S1) (1). Representation at the level of primary auditory cortex is precise: fine-grained in scale and local in spectrotemporal space (2, 3). The recognition of complex spectrotemporal forms, like words, in higher areas of auditory cortex requires the transformation of this granular representation into Gestalt-like, object-centered representations. In brief, local features must be bound together to form representations of complex spectrotemporal contours, which are themselves the constituents of auditory "objects" or complex sound patterns (4, 5). Next, representations must be generalized and abstracted. Coding in primary auditory cortex is sensitive even to minor physical transformations. Object-centered coding in higher areas, however, must be invariant (i.e., tolerant of natural stimulus variation) (6). For example, whereas the phonemic structure of a word is fixed, there is considerable variation in physical, spectrotemporal form-attributable to accent, pronunciation, body size, and the like-among utterances of a given word. It has been proposed for visual cortical processing that a feed-forward, hierarchical architecture (7) may be capable of simultaneously solving the problems of complexity and variability (8-12). Here, we examine these ideas in the context of auditory cortex.In a hierarchical pattern-recognition scheme (8), coding in the earliest cortical field would reflect the tuning and organization of primary auditory cortex (or core) (2, 3, 13). That is, single-neuron receptive fields (more precisely, frequency-response areas) would be tuned to particular center frequencies and would have minimal spectrotemporal complexity (i.e., a single excitatory zone and one-to-two inhibitory side bands). ...

Section: And Cohen and Colleagues' (2004) Hypothesis Of An Auditory Wsupporting

confidence: 69%

Phoneme and word recognition in the auditory ventral stream

DeWitt

Rauschecker²

2012

419

328

“…Variation in the quality of early-life language input, the differential effect of children's reading experience, the timing of instruction with respect to these processes, and genetic factors could all contribute. Learning to read influences the development of the brain: Cerebral gray matter circuits and the white matter connecting them learn to extract the statistical regularities of text written in a person's native language (5). We hypothesized that learning to read depends in part on the capacity of white-matter pathways to develop in response to literacy training.…”

Section: Discussionmentioning

confidence: 99%

“…Our primary objective was to test the hypothesis that plasticity in key white-matter fascicles is related to children's reading development. We focused on the left hemisphere arcuate fasciculus and ILF because these tracts project to cortical circuits that are believed to be essential for skilled reading (3,5,6). We used the right hemisphere homologs of these pathways as well as sensory-motor tracts as control pathways to assess the anatomical specificity of our findings.…”

Section: Methodsmentioning

confidence: 99%

“…Only in the last decade has it become possible to study the microstructural properties of the white matter in the living human brain, and only in recent years has there been an opportunity to trace the developmental progression of these fascicles systematically. During this decade it has been shown that learning to read is associated with corresponding changes in sensory and language circuits in the brain (2)(3)(4)(5).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Development of white matter and reading skills

Yeatman

Dougherty

Ben-Shachar

et al. 2012

Self Cite

331

356

White matter tissue properties are highly correlated with reading proficiency; we would like to have a model that relates the dynamics of an individual's white matter development to their acquisition of skilled reading. The development of cerebral white matter involves multiple biological processes, and the balance between these processes differs between individuals. Cross-sectional measures of white matter mask the interplay between these processes and their connection to an individual's cognitive development. Hence, we performed a longitudinal study to measure white-matter development (diffusion-weighted imaging) and reading development (behavioral testing) in individual children (age 7-15 y). The pattern of white-matter development differed significantly among children. In the left arcuate and left inferior longitudinal fasciculus, children with above-average reading skills initially had low fractional anisotropy (FA) that increased over the 3-y period, whereas children with belowaverage reading skills had higher initial FA that declined over time. We describe a dual-process model of white matter development comprising biological processes with opposing effects on FA, such as axonal myelination and pruning, to explain the pattern of results.R eading requires efficient communication within a network of visual, auditory, and language-processing regions that are separated by many centimeters. Hence, the white-matter fascicles that connect these regions are critical for proficient reading (1). Only in the last decade has it become possible to study the microstructural properties of the white matter in the living human brain, and only in recent years has there been an opportunity to trace the developmental progression of these fascicles systematically. During this decade it has been shown that learning to read is associated with corresponding changes in sensory and language circuits in the brain (2-5).Diffusion measurements of the white-matter pathways (3, 5-7) and neurological case studies (8, 9) suggest that in typical development and education both the left hemisphere arcuate fasciculus and inferior longitudinal fasciculus (ILF) carry signals important for reading. Studies in adults, adolescents, and schoolage children have reported differences between good and poor readers in white-matter volume and diffusion properties in the vicinity of these pathways (10-14). One possibility is that these differences are present from an early age, remain constant through development, and constrain children's aptitude for reading. An alternative possibility is that there is an interaction between the biological development and timing of instruction. Two case studies support this hypothesis. When damage to the arcuate fasciculus occurs at birth, normal reading skills can develop (15); when damage to the arcuate fasciculus occurs later, for example after reading instruction has begun, it can result in severe reading impairment (9). These cases suggest that learning depends on the circuits' current state and capacity for plasti...

“…The difference in tissue properties between the VOF and adjacent white matter can be appreciated in each individual brain (P < 0.0001), and likely influences the nature of the signals carried by the pathway. This interest has been driven by the discovery of categoryselective responses throughout VOT and LOT, including regions that are preferentially responsive to words (59)(60)(61), faces (62)(63)(64), body parts (48,64,65), places (66), and objects (67,68).…”

Section: Dorsal Vof Endpoints Project To the Transverse Occipital Sulcusmentioning

confidence: 99%

The vertical occipital fasciculus: A century of controversy resolved by in vivo measurements

Yeatman

Weiner

Pestilli

et al. 2014

Self Cite

244

275

The vertical occipital fasciculus (VOF) is the only major fiber bundle connecting dorsolateral and ventrolateral visual cortex. Only a handful of studies have examined the anatomy of the VOF or its role in cognition in the living human brain. Here, we trace the contentious history of the VOF, beginning with its original discovery in monkey by Wernicke (1881) and in human by Obersteiner (1888), to its disappearance from the literature, and recent reemergence a century later. We introduce an algorithm to identify the VOF in vivo using diffusion-weighted imaging and tractography, and show that the VOF can be found in every hemisphere (n = 74). Quantitative T1 measurements demonstrate that tissue properties, such as myelination, in the VOF differ from neighboring white-matter tracts. The terminations of the VOF are in consistent positions relative to cortical folding patterns in the dorsal and ventral visual streams. Recent findings demonstrate that these same anatomical locations also mark cytoarchitectonic and functional transitions in dorsal and ventral visual cortex. We conclude that the VOF is likely to serve a unique role in the communication of signals between regions on the ventral surface that are important for the perception of visual categories (e.g., words, faces, bodies, etc.) and regions on the dorsal surface involved in the control of eye movements, attention, and motion perception. T he vertical occipital fasciculus (VOF) is the only major fiber bundle connecting dorsal and ventral regions of occipital, parietal, and temporal cortex. The signals carried by the VOF are likely to play an essential role in an array of visual and cognitive functions. Characterizing the VOF connections and tissue structure in the living human brain is important for the study of human vision and cognitive neuroscience alike.Carl Wernicke discovered the VOF (1). For the next 30 y, the VOF was included in many major neuroanatomy atlases and journal articles (1-14). However, Wernicke's study contradicted a widely accepted principle of white-matter organization proposed by Meynert, Wernicke's mentor. Over the subsequent decades, there emerged a camp of neuroanatomists who acknowledged Wernicke's discovery and another group that, like Meynert, disregarded the discovery. Due to its controversial beginnings, haphazard naming convention, and the difficulty of standardizing postmortem procedures, the VOF largely disappeared from the literature for most of the next century. A century later, Yeatman et al. (15) rediscovered the VOF using diffusion magnetic resonance imaging (dMRI); they were the first to characterize the VOF cortical projections in the living, behaving, human brain.Why would such an important pathway disappear from the literature for so long? The disappearance can be traced to controversies and confusions among some of the most prominent neuroanatomists of the 19th century (1-13, 16-18). Modern, in vivo, MRI measurements and algorithms allow for precise, reproducible, scalable computations that can resolve these cen...