Rebecca Sandak

The neurobiology of adaptive learning in reading: a contrast of different training conditions.

AbstractfMRI was used to investigate the separate influences of orthographic, phonological, and semantic processing on the ability to learn new words and the cortical circuitry recruited to subsequently read those words. In a behavioral session, subjects acquired familiarity for three sets of pseudowords, attending to orthographic, phonological, or (learned) semantic features. Transfer effects were measured in an event-related fMRI session as the subjects named trained pseudowords, untrained pseudowords, and real words. Behaviorally, phonological and semantic training resulted in better learning than did orthographic training. Neurobiologically, orthographic training did not modulate activation in the main reading regions. Phonological and semantic training yielded equivalent behavioral facilitation but distinct functional activation patterns, suggesting that the learning resulting from these two training conditions was driven by different underlying processes. The findings indicate that the putative ventral visual word form area is sensitive to the phonological structure of words, with phonologically analytic processing contributing to the specialization of this region.

Effects of stimulus difficulty and repetition on printed word identification: An fmri comparison of nonimpaired and reading-disabled adolescent cohorts

Functional neuroimaging studies indicate that a primary marker of specific reading disability (RD) is reduced activation of left hemisphere (LH) posterior regions during performance of reading tasks. However, the severity of this disruption, and the extent to which these LH systems might be available for reading under any circumstances, is unclear at present. Experiment 1 examined the cortical effects of stimulus manipulations (frequency, imageability, consistency) that have known facilitative effects on reading performance for both nonimpaired (NI) and RD readers. Experiment 2 examined stimulus repetition, another facilitative variable, in an additional sample of adolescent NI and RD readers. For NI readers, factors that made words easier to process were associated with relatively reduced activation. For RD readers, facilitative factors resulted in increased activation in these same reading-related sites, suggesting that the LH reading circuitry in adolescent RD is poorly trained but not wholly disrupted.

A functional magnetic resonance imaging study of the tradeoff between semantics and phonology in reading aloud

Using functional magnetic resonance imaging, we explored the role of semantics in mediating orthographic-to-phonological processing in reading aloud, focusing on the interaction of imageability with spelling-to-sound consistency for low-frequency words. Behaviorally, high-imageable words attenuate the standard latency and accuracy disadvantage for low-frequency inconsistent words relative to their consistent counterparts. Neurobiologically, high-imageable words reduced consistency-related activation in the inferior frontal gyrus but increased posterior activation in the angular and middle temporal gyri, representing a possible neural signature of the tradeoff between semantics and phonology in reading aloud. We discuss implications for neurobiological models of reading in terms of understanding the interplay among areas associated with component processes and suggest that the results constitute an important step toward integrating neurobiological and computational models of reading.

Behavioral and neurobiological effects of printed word repetition in lexical decision and naming.

A series of experiments studied the effects of repetition of printed words on (1) lexical decision (LD) and naming (NAM) behavior and (2) concomitant brain activation. It was hypothesized that subword phonological analysis (assembly) would decrease with increasing word familiarity and the greater decrease would occur in LD, a task that is believed to be less dependent on assembly than naming. As a behavioral marker of assembly, we utilized the regularity effect (the difference in response latency between words with regular versus irregular spelling-sound correspondences). In addition to repetition, stimulus familiarity was manipulated by word frequency and case alternation. Both experiments revealed an initial latency disadvantage for low frequency irregular words suggesting that assembly is the dominant process in both tasks when items are unfamiliar. As items become more familiar with repetition, the regularity effect disappeared in LD but persisted in NAM. Brain activation patterns for repeated words that were observed in fMRI paralleled the behavioral studies in showing greater reductions in activity under lexical decision than naming for regions previously identified as involved in assembly.

An fMRI study of multimodal semantic and phonological processing in reading disabled adolescents

Using functional magnetic resonance imaging, we investigated multimodal (visual and auditory) semantic and unimodal (visual only) phonological processing in reading disabled (RD) adolescents and non-impaired (NI) control participants. We found reduced activation for RD relative to NI in a number of left-hemisphere reading-related areas across all processing tasks regardless of task type (semantic vs. phonological) or modality (auditory vs. visual modality). Moreover, activation differences in these regions, which included the inferior frontal gyrus, the superior temporal gyrus, and the occipitotemporal region, were largely independent of in-scanner performance in our auditory semantic task. That is, although RD participants and NI participants differed in performance in visually presented conditions, they did not differ significantly in the auditory condition, yet similar patterns of reduced activation were observed in these regions across conditions. These findings indicate a neurobiological marker in RD that is independent of task, modality, or performance. These findings are discussed in the context of current neurobiological models of RD.

Neurobiological Bases of Reading Comprehension: Insights From Neuroimaging Studies of Word-Level and Text-Level Processing in Skilled and Impaired Readers

For accurate reading comprehension, readers must first learn to map letters to their corresponding speech sounds and meaning, and then they must string the meanings of many words together to form a representation of the text. Furthermore, readers must master the complexities involved in parsing the relevant syntactic and pragmatic information necessary for accurate interpretation. Failure in this process can occur at multiple levels, and cognitive neuroscience has been helpful in identifying the underlying causes of success and failure in reading single words and in reading comprehension. In general, neurobiological studies of skilled reading comprehension indicate a highly overlapping language circuit for single-word reading, reading comprehension, and listening comprehension, with largely quantitative differences in a number of reading- and language-related areas. This article reviews relevant research from studies that have used neuroimaging techniques to study reading with a focus on the relationship between reading skill, single-word reading, and text comprehension.