Resting-state functional connectivity, as measured by functional magnetic resonance imaging (fMRI), is often treated as a trait, used, for example, to draw inferences about individual differences in ...cognitive function, or differences between healthy or diseased populations. However, functional connectivity can also depend on the individual's mental state. In the present study, we examined the relative contribution of state and trait components in shaping an individual's functional architecture. We used fMRI data from a large, population-based human sample (N = 587, age 18-88 years), as part of the Cambridge Centre for Aging and Neuroscience (Cam-CAN), which were collected in three mental states: resting, performing a sensorimotor task, and watching a movie. Whereas previous studies have shown commonalities across mental states in the average functional connectivity across individuals, we focused on the effects of states on the pattern of individual differences in functional connectivity. We found that state effects were as important as trait effects in shaping individual functional connectivity patterns, each explaining an approximately equal amount of variance. This was true when we looked at aging, as one specific dimension of individual differences, as well as when we looked at generic aspects of individual variation. These results show that individual differences in functional connectivity consist of state-dependent aspects, as well as more stable, trait-like characteristics. Studying individual differences in functional connectivity across a wider range of mental states will therefore provide a more complete picture of the mechanisms underlying factors such as cognitive ability, aging, and disease.
The brain's functional architecture is remarkably similar across different individuals and across different mental states, which is why many studies use functional connectivity as a trait measure. Despite these trait-like aspects, functional connectivity varies over time and with changes in cognitive state. We measured connectivity in three different states to quantify the size of the trait-like component of functional connectivity, compared with the state-dependent component. Our results show that studying individual differences within one state (such as resting) uncovers only part of the relevant individual differences in brain function, and that the study of functional connectivity under multiple mental states is essential to disentangle connectivity differences that are transient versus those that represent more stable, trait-like characteristics of an individual.
Training with audiovisual (AO) speech can promote auditory perceptual learning of vocoded acoustic speech by adults with normal hearing. Pre-/perilingually deafened adults rely on visual speech even ...when they also use a cochlear implant. This study investigated whether visual speech promotes auditory perceptual learning in these cochlear implant users. In Experiment 1, 28 prelingually deafened adults with late-acquired cochlear implants were assigned to learn paired associations between spoken disyllabic C(=consonant)V(=vowel)CVC nonsense words and nonsense pictures (fribbles), under AV and then under auditory-only (AO) (or counter-balanced AO then AV) training conditions. After training on each list of paired-associates (PA), testing was carried out AO. Across AV and AO training, AO PA test scores improved as did identification of consonants in untrained CVCVC stimuli. However, whenever PA training was carried out with AV stimuli, AO test scores were steeply reduced. Experiment 2 repeated the experiment with 43 normal-hearing adults. Their AO tests scores did not drop following AV PA training and even increased relative to scores following AO training. Normal-hearing participants' consonant identification scores improved also but with a pattern that contrasted with cochlear implant users’: Normal hearing adults were most accurate for medial consonants, and in contrast cochlear implant users were most accurate for initial consonants. The results are interpreted within a multisensory reverse hierarchy theory, which predicts that perceptual tasks are carried out whenever possible based on immediate high-level perception without scrutiny of lower-level features. The theory implies that, based on their bias towards visual speech, cochlear implant participants learned the PAs with greater reliance on vision to the detriment of auditory perceptual learning. Normal-hearing participants' learning took advantage of the concurrence between auditory and visual speech.
The adaption of movement to changes in the environment varies across life span. Recent evidence has linked motor adaptation and its reduction with age to differences in “explicit” learning processes. ...We examine differences in brain structure and cognition underlying motor adaptation in a population-based cohort (n = 322, aged 18–89 years) using a visuomotor learning task and structural magnetic resonance imaging. Reduced motor adaptation with age was associated with reduced volume in striatum, prefrontal, and sensorimotor cortical regions, but not cerebellum. Medial temporal lobe volume, including the hippocampus, became a stronger determinant of motor adaptation with age. Consistent with the role of the medial temporal lobes, declarative long-term memory showed a similar interaction, whereby memory was more positively correlated with motor adaptation with increasing age. By contrast, visual short-term memory was related to motor adaptation, independently of age. These results support the hypothesis that cerebellar learning is largely unaffected in old age, and the reduction in motor adaptation with age is driven by a decline in explicit memory systems.
•Reduced motor adaptation with age relates to less graey matter in motor regions.•These regions are striatum, premotor and prefrontal cortex, but not the cerebellum.•With age, motor adaptation is more positively related to medial temporal lobe areas.•Motor adaptation relates to short-term memory measures regardless of age.•With age, motor adaptation is more positively related to long-term memory scores.
A lexical modeling methodology was employed to examine how the distribution of phonemic patterns in the lexicon constrains lexical equivalence under conditions of reduced phonetic distinctiveness ...experienced by speech-readers. The technique involved (1) selection of a phonemically transcribed machine-readable lexical database, (2) definition of transcription rules based on measures of phonetic similarity, (3) application of the transcription rules to a lexical database and formation of lexical equivalence classes, and (4) computation of three metrics to examine the transcribed lexicon. The metric percent words unique demonstrated that the distribution of words in the language substantially preserves lexical uniqueness across a wide range in the number of potentially available phonemic distinctions. Expected class size demonstrated that if at least 12 phonemic equivalence classes were available, any given word would be highly similar to only a few other words. Percent information extracted (PIE) D. Carter, Comput. Speech Lang. 2, 1-11 (1987) provided evidence that high-frequency words tend not to reside in the same lexical equivalence classes as other high-frequency words. The steepness of the functions obtained for each metric shows that small increments in the number of visually perceptible phonemic distinctions can result in substantial changes in lexical uniqueness.
Healthy ageing has disparate effects on different cognitive domains. The neural basis of these differences, however, is largely unknown. We investigated this question by using Independent Components ...Analysis to obtain functional brain components from 98 healthy participants aged 23-87 years from the population-based Cam-CAN cohort. Participants performed two cognitive tasks that show age-related decrease (fluid intelligence and object naming) and a syntactic comprehension task that shows age-related preservation. We report that activation of task-positive neural components predicts inter-individual differences in performance in each task across the adult lifespan. Furthermore, only the two tasks that show performance declines with age show age-related decreases in task-positive activation of neural components and decreasing default mode (DM) suppression. Our results suggest that distributed, multi-component brain responsivity supports cognition across the adult lifespan, and the maintenance of this, along with maintained DM deactivation, characterizes successful ageing and may explain differential ageing trajectories across cognitive domains.
Most prior research has focused on characterizing averages in cognition, brain characteristics, or behavior, and attempting to predict differences in these averages among individuals. However, this ...overwhelming focus on mean levels may leave us with an incomplete picture of what drives individual differences in behavioral phenotypes by ignoring the variability of behavior around an individual's mean. In particular, enhanced white matter (WM) structural microstructure has been hypothesized to support consistent behavioral performance by decreasing Gaussian noise in signal transfer. Conversely, lower indices of WM microstructure are associated with greater within-subject variance in the ability to deploy performance-related resources, especially in clinical populations. We tested a mechanistic account of the "neural noise" hypothesis in a large adult lifespan cohort (Cambridge Centre for Ageing and Neuroscience) with over 2500 adults (ages 18-102; 1508 female; 1173 male; 2681 behavioral sessions; 708 MRI scans) using WM fractional anisotropy to predict mean levels and variability in reaction time performance on a simple behavioral task using a dynamic structural equation model. By modeling robust and reliable individual differences in within-person variability, we found support for a neural noise hypothesis (Kail, 1997), with lower fractional anisotropy predicted individual differences in separable components of behavioral performance estimated using dynamic structural equation model, including slower mean responses and increased variability. These effects remained when including age, suggesting consistent effects of WM microstructure across the adult lifespan unique from concurrent effects of aging. Crucially, we show that variability can be reliably separated from mean performance using advanced modeling tools, enabling tests of distinct hypotheses for each component of performance.
Human cognitive performance is defined not just by the long-run average, but trial-to-trial variability around that average. However, investigations of cognitive abilities and changes during aging have largely ignored this variability component of behavior. We provide evidence that white matter (WM) microstructure predicts individual differences in mean performance and variability in a sample spanning the adult lifespan (18-102). Unlike prior studies of cognitive performance and variability, we modeled variability directly and distinct from mean performance using a dynamic structural equation model, which allows us to decouple variability from mean performance and other complex features of performance (e.g., autoregression). The effects of WM were robust above the effect of age, highlighting the role of WM in promoting fast and consistent performance.
Purpose: The goal of this review article is to reinvigorate interest in lipreading and lipreading training for adults with acquired hearing loss. Most adults benefit from being able to see the talker ...when speech is degraded; however, the effect size is related to their lipreading ability, which is typically poor in adults who have experienced normal hearing through most of their lives. Lipreading training has been viewed as a possible avenue for rehabilitation of adults with an acquired hearing loss, but most training approaches have not been particularly successful. Here, we describe lipreading and theoretically motivated approaches to its training, as well as examples of successful training paradigms. We discuss some extensions to auditory-only (AO) and audiovisual (AV) speech recognition. Method: Visual speech perception and word recognition are described. Traditional and contemporary views of training and perceptual learning are outlined. We focus on the roles of external and internal feedback and the training task in perceptual learning, and we describe results of lipreading training experiments. Results: Lipreading is commonly characterized as limited to viseme perception. However, evidence demonstrates subvisemic perception of visual phonetic information. Lipreading words also relies on lexical constraints, not unlike auditory spoken word recognition. Lipreading has been shown to be difficult to improve through training, but under specific feedback and task conditions, training can be successful, and learning can generalize to untrained materials, including AV sentence stimuli in noise. The results on lipreading have implications for AO and AV training and for use of acoustically processed speech in face-to-face communication. Conclusion: Given its importance for speech recognition with a hearing loss, we suggest that the research and clinical communities integrate lipreading in their efforts to improve speech recognition in adults with acquired hearing loss.
Slowing is a common feature of ageing, yet a direct relationship between neural slowing and brain atrophy is yet to be established in healthy humans. We combine magnetoencephalographic (MEG) measures ...of neural processing speed with magnetic resonance imaging (MRI) measures of white and grey matter in a large population-derived cohort to investigate the relationship between age-related structural differences and visual evoked field (VEF) and auditory evoked field (AEF) delay across two different tasks. Here we use a novel technique to show that VEFs exhibit a constant delay, whereas AEFs exhibit delay that accumulates over time. White-matter (WM) microstructure in the optic radiation partially mediates visual delay, suggesting increased transmission time, whereas grey matter (GM) in auditory cortex partially mediates auditory delay, suggesting less efficient local processing. Our results demonstrate that age has dissociable effects on neural processing speed, and that these effects relate to different types of brain atrophy.
Studies of audiovisual perception of spoken language have mostly modeled phoneme identification in nonsense syllables, but it is doubtful that models or theories of phonetic processing can adequately ...account for audiovisual word recognition. The present study took a computational approach to examine how lexical structure may additionally constrain word recognition, given the phonetic information available under vocoded audio, visual and audiovisual stimulus conditions. Subjects made phonemic identification judgments on recordings of spoken nonsense syllables. Hierarchical cluster analysis was used first to select classes of perceptually equivalent phonemes for each of the stimulus conditions, and then a machine-readable phonemically transcribed lexicon was retranscribed in terms of these phonemic equivalence classes. Several statistics were computed for each of the transcriptions, including percent information extracted, percent words unique and expected class size. The findings suggest that superadditive levels of audiovisual enhancement are more likely for monosyllabic than for multisyllabic words. That is, impoverished phonetic information may be sufficient to recognize multisyllabic words, but the recognition of monosyllabic words seems to require additional phonetic information.
Cardiovascular ageing contributes to cognitive impairment. However, the unique and synergistic contributions of multiple cardiovascular factors to cognitive function remain unclear because they are ...often condensed into a single composite score or examined in isolation. We hypothesized that vascular risk factors, electrocardiographic features and blood pressure indices reveal multiple latent vascular factors, with independent contributions to cognition. In a population-based deep-phenotyping study (n = 708, age 18-88), path analysis revealed three latent vascular factors dissociating the autonomic nervous system response from two components of blood pressure. These three factors made unique and additive contributions to the variability in crystallized and fluid intelligence. The discrepancy in fluid relative to crystallized intelligence, indicative of cognitive decline, was associated with a latent vascular factor predominantly expressing pulse pressure. This suggests that higher pulse pressure is associated with cognitive decline from expected performance. The effect was stronger in older adults. Controlling pulse pressure may help to preserve cognition, particularly in older adults. Our findings highlight the need to better understand the multifactorial nature of vascular aging.
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