Reduced benefit from long-term item frequency contributes to short-term memory deficits in dyslexia.

Dyslexia, a specific difficulty in acquiring proficient reading, is also characterized by reduced short-term memory (STM) capacity. Extensive research indicates that individuals with developmental dyslexia (IDDs) benefit less from exposure, and this hampers their long-term knowledge accumulation. It is well established that long-term knowledge has a great effect on performance in STM tasks, and thus IDDs' reduced benefit of exposure could potentially reduce their relative performance in such tasks, especially when frequent items, such as digit-words, are used. In this study we used a standard, widely used, STM assessment: the Digit Span subtest from the Wechsler Adult Intelligence Scale. The task was conducted twice: in native language and in second language. As exposure to native language is greater than exposure to second language, we predicted that IDDs' performance in the task administered in native language will reveal a larger group difference as compared to second language, due to IDDs' reduced benefit of item frequency. The prediction was confirmed, in line with the hypothesis that reduced STM in dyslexia to a large extent reflects reduced benefits from long-term item frequency and not a reduced STM per se.

Training-induced improvement in working memory tasks results from switching to efficient strategies.

It is debated whether training with a working memory (WM) task, particularly n-back, can improve general WM and reasoning skills. Most training studies found substantial improvement in the trained task, with little to no transfer to untrained tasks. We hypothesized that training does not increase WM capacity, but instead provides opportunities to develop an efficient task-specific strategy. We derived a strategy for the task that optimizes WM resources and taught it to participants. In two sessions, 14 participants who were taught this strategy performed as well as fourteen participants who trained for 40 sessions without strategy instructions. To understand the mechanisms underlying the no-instruction group's improvement, participants answered questionnaires during their training period. Their replies indicate that successful learners discovered the same strategy and their improvement was associated with this discovery. We conclude that n-back training allows the discovery of strategies that enable better performance with the same WM resources.

Short-term memory capacity and sensitivity to language statistics in dyslexia and among musicians.

Poor short-term memory (STM) capacity in individuals with dyslexia (IDDs) and enhanced STM capacity in musicians are well documented, yet their causes are disputed. Previous studies also found poor use of stimuli statistics by IDDs and enhanced use by musicians. We hypothesized that these observations are functionally related, as follows: Enhanced sensitivity to statistics facilitates musicians' benefit from each exposure, and reduced sensitivity to statistics hinders IDDs' benefit. Thus, larger group differences are expected for larger exposure: STM capacity, which is sensitive to item familiarity, will thus be larger among musicians, and smaller among IDDS, particularly for high-frequency items. Testing this hypothesis using syllable span, we found that musicians' advantage and IDDs' difficulty were indeed larger for high-frequency syllables than for low-frequency ones. By contrast, benefits from sequence repetition did not differ between musicians, controls and IDDs, suggesting that online sequence learning is based on a different mechanism. To test this dissociation we recruited, in addition to native Hebrew speakers, native English speakers, matched to the Hebrew-speaking controls. Their spans for high-frequency syllables in Hebrew, which do not have high frequency in English, were small - as expected from reduced exposure to these syllables. Yet, their benefit from sequence repetition was similar to that of the three Hebrew-speaking groups. Taken together, these experiments suggest that different sensitivities to item frequency explain some of the population-related variability in STM tasks. By contrast, benefits from sequence repetition do not depend on item familiarity, and do not differ between groups.

Auditory frequency discrimination is correlated with linguistic skills, but its training does not improve them or other pitch discrimination tasks.

Brain-training, aimed at advancing and improving cognitive and perceptual abilities, is vastly studied because of its immense promise. Yet, there are major controversies regarding its main claim that intensive weeks' training on a single challenging task could improve performance in related untrained tasks. Ample training studies showing transfer were criticized for flawed design. We now explored the impact of perceptual training (auditory frequency discrimination), applying a carefully controlled intensive training experiment. First, we administered a battery of perceptual, linguistic, and cognitive tasks to a large population to determine "near" to "far" tasks according to (pretraining) correlations in performance. This assessment revealed significant correlations between simple pitch discrimination and complex linguistic tasks, including reading and syntactic reasoning. Second, we administered a broad test battery before (and after) training, which included several tasks assessing pitch discrimination, and the linguistic tasks that showed pretraining correlation with auditory frequency discrimination. The test group trained with 2 tone frequency discrimination for 40 sessions. An active control group trained with a working memory (n-back) task for the same duration, and a passive control group was only tested before and after training. Pretraining performance levels were similar in the three groups. Our results were straightforward. No transfer was found to untrained tasks that rely on pith discrimination, or to linguistic tasks that showed pretraining correlation. Mild to marginal transfer was found only to pitch discrimination tasks using almost exactly the trained protocol. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Electrophysiological correlates of speech perception mechanisms and individual differences in second language attainment.

In an increasingly globalized world mastering a second language (L2) provides a clear advantage. However, after early childhood, not everyone can easily learn a foreign language. The present study explored whether the large variability found in L2 attainment in the normal population, not diagnosed as learning disabled, is related to preattentive speech perception abilities. Using event-related potentials (ERPs) we examined the mismatch negativity, P3a, and the late discriminative negativity (MMN-P3a-LDN) complex, which served as an index for preattentive foreign phonological contrast discrimination abilities. Our results show that, compared to unsuccessful L2 learners, successful L2 learners had shorter latencies of the MMN and P3a components and higher amplitudes of the LDN component. These results suggest that unsuccessful L2 learners have a deficient speech perception mechanism.

Crystal structure of a type-II cohesin module from the Bacteroides cellulosolvens cellulosome reveals novel and distinctive secondary structural elements.

The incorporation of enzymes into the multi-enzyme cellulosome complex and its anchoring to the bacterial cell surface are dictated by a set of binding interactions between two complementary protein modules: the cohesin and the dockerin. In this work, the X-ray crystal structure of a type-II cohesin from scaffoldin A of Bacteroides cellulosolvens has been determined to a resolution of 1.6 angstroms using molecular replacement. The type-II B. cellulosolvens cohesin (Bc-cohesin-II) is the first detailed description of a crystal structure for a type-II cohesin, and its features were compared with the known type-I cohesins from Clostridium thermocellum and Clostridium cellulolyticum (Ct-cohesin-I and Cc-cohesin-I, respectively). The overall jelly-roll topology of the type-II Bc-cohesin is very similar to that observed for the type-I cohesins with three additional secondary structures: an alpha-helix and two "beta-flaps" that disrupt the normal course of a beta-strand. In addition, beta-strand 5 is elevated by approximately 4 angstroms on the surface of the molecule, relative to the type-I Ct and Cc-cohesins. Like its type-I analogue, the hydrophobic/aromatic core of Bc-cohesin-II comprises an upper and lower core, but an additional aromatic patch and conserved tryptophan at the crown of the molecule serves to stabilize the alpha-helix of the type-II cohesin. Comparison of Bc-cohesin-II with the known type-I cohesin-dockerin heterodimer suggests that each of the additional secondary structural elements assumes a flanking position relative to the putative dockerin-binding surface. The raised ridge formed by beta-strand 5 confers additional distinctive topographic features to the proposed binding interface that collectively distinguish between the type-II and type-I cohesins.