Working memory and language comprehension: A meta-analysis

A resource model of the neural basis of executive working memory

Working memory (WM) refers to the temporary storage and processing of goal-relevant information. WM is thought to include domain-specific short-term memory stores and executive processes, such as coordination, that operate on the contents of WM. To examine the neural substrates of coordination, we acquired functional magnetic resonance imaging data while subjects performed a WM span test designed specifically to measure executive WM. Subjects performed two tasks (sentence reading and short-term memory for five words) either separately or concurrently. Dual-task performance activated frontal-lobe areas to a greater extent than performance of either task in isolation, but no new area was activated beyond those activated by either component task. These findings support a resource theory of WM executive processes in the frontal lobes.

Working memory capacity and time course of predictive inferences

A naming task assessed activation of inference concepts during reading. A predicting, or a control, context sentence was followed by a target word to be named, which represented the predicted event or an inconsistent event. The interval between the end of the context and the onset of the target word varied between 50 and 1050 msec. Individual differences in working memory capacity were assessed by the reading span task. As reflected by facilitation in naming latencies in the predicting condition, relative to the control condition, (a) inferences were not made within the first 50 msec after the context, regardless of reading span; (b) only the high-span participants drew inferences within a 550-msec interval; and, (c) both the high- and the low-span participants generated them within a 1050-msec interval. These results indicate that high working memory capacity accelerates the time course of predictive inferences, although they do not become automatic. We propose that this effect occurs because these inferences involve time-consuming elaborations that place demands on the effortful and limited resources of working memory. Deficiencies in word knowledge, speed of lexical access, or comprehension of explicit information do not account for low-span readers' difficulties in generating predictive inferences.

Dopamine and the origins of human intelligence

A general theory is proposed that attributes the origins of human intelligence to an expansion of dopaminergic systems in human cognition. Dopamine is postulated to be the key neurotransmitter regulating six predominantly left-hemispheric cognitive skills critical to human language and thought: motor planning, working memory, cognitive flexibility, abstract reasoning, temporal analysis/sequencing, and generativity. A dopaminergic expansion during early hominid evolution could have enabled successful chase-hunting in the savannas of sub-Saharan Africa, given the critical role of dopamine in counteracting hyperthermia during endurance activity. In turn, changes in physical activity and diet may have further increased cortical dopamine levels by augmenting tyrosine and its conversion to dopamine in the central nervous system (CNS). By means of the regulatory action of dopamine and other substances, the physiological and dietary changes may have contributed to the vertical elongation of the body, increased brain size, and increased cortical convolutedness that occurred during human evolution. Finally, emphasizing the role of dopamine in human intelligence may offer a new perspective on the advanced cognitive reasoning skills in nonprimate lineages such as cetaceans and avians, whose cortical anatomy differs radically from that of primates.

Cognitive approaches to the development of short-term memory

The capacity to retain information for brief periods of time increases dramatically during the childhood years. The increases in temporary storage of speech-based material that take place in the period spanning the pre-school years and adolescence reflect complex changes in many of the different component processes, including perceptual analysis, construction and maintenance of a memory trace, retention of order information, rehearsal, retrieval and redintegration. Another crucial capacity that undergoes a similar striking development is complex working memory, the ability to manipulate and store material simultaneously. Possible sources of age-related changes in working memory include increases in processing efficiency and attentional capacity, and task-switching. These two short-term memory systems might play significant but distinct roles in supporting the acquisition of knowledge and skills during childhood. Whereas phonological short-term memory is linked specifically with the learning of the phonological structures of new words, complex working memory appears to support processing and learning in a wide range of contexts, in both childhood and adulthood.

Working memory in aging: maintenance and suppression

The present research is focused on a fine-grained analysis of memory decline with aging, and the role of suppression mechanisms in age-related memory decline. Three groups of participants (continuous age ranges; young-old: 55-65 years, old: 66-75 years, and old-old: more than 75 years) were administered Forward and Backward span test, and a Working Memory task with Categorization (WMC). This new task requires lists of five words to be processed in order to individuate animal nouns, and that the last word of each list be contemporarily maintained. The words incorrectly recalled as target items, but presented during the task (intrusion errors), were computed in order to analyze the efficiency of suppression mechanisms. The findings indicated a continuous decline in working memory measures, and an early decline in short-term memory (passive storage) measures (between 60's and 70's). An age-related increase in intrusion errors was observed; the intrusion index was inversely related to working memory performance but, according to the hypotheses, was not related to short-term memory measures. These results suggest that the stronger working memory effect observed through age might be due to the combined influence of a decline in the capacity of short-term memory, and a loss of efficiency in suppression mechanisms.

The role of interference in memory span

In two experiments, we investigated the possibility that susceptibility to proactive interference (PI) affects performance on memory span measures. We tested both younger and older adults (older adults were tested because of the suggestion that they are differentially susceptible to PI). We used two different span measures and manipulated testing procedures to reduce PI for these tasks. For older adults, span estimates increased with each PI-reducing manipulation; for younger adults, scores increased when multiple PI manipulations were combined or when PI-reducing manipulations were used in paradigms in which within-task PI was especially high. The findings suggest that PI critically influences span performance. We consider the possibility that interference-proneness may influence cognitive behaviors previously thought to be governed by capacity.

Functional organization of activation patterns in children: whole brain fMRI imaging during three different cognitive tasks

1. Patterns of brain activation were measured with whole brain echo-planar functional magnetic resonance imaging (fMRI) at 3.0 Tesla in healthy children (N = 6) and in one child with a left-hemisphere encephalomalacic lesion as sequellae from early stroke. 2. Three cognitive tasks were used: auditory sentence comprehension, verb generation to line drawings, and mental rotation of alphanumeric stimuli. 3. There was evidence for significant bilateral activation in all three cognitive tasks for the healthy children. Their patterns of activation were consistent with previous functional imaging studies with adults. 4. The child with a left-hemisphere stroke showed evidence of homologous organization in the non-damaged hemisphere.

Cognition as a bridge between signal and dialogue: communication in the hearing impaired and deaf

This paper is an overview of the research we have carried out at Linköping University on cognitive aspects of visual language processing and related communicative forms. In the first section, a cognitive individual difference perspective on speechreading is introduced. In the second, compensatory perceptual mechanisms are discussed on the basis of behavioral and neurophysiological data. The third section addresses further the issue of perceptual versus cognitive compensation, and the fourth and fifth sections apply a set of cognitive tests based on the concept of working memory for poorly specified language input to data on the successes and failures with cochlear implants, tactile aids and hearing aids.

Individual and developmental differences in working memory across the life span

The effects of secondary tasks on verbal and spatial working memory were examined in multiple child, young adult, and older adult samples. Although memory span increased with age in the child samples and decreased with age in the adult samples, there was little evidence of systematic change in the magnitude of interference effects. Surprisingly, individuals who had larger memory spans when there was no secondary task showed greater interference effects than their age-mates. These findings are inconsistent with the hypothesis that age and individual differences in working memory are due to differences in the ability to inhibit irrelevant information, at least as this hypothesis is currently formulated. Moreover, our results suggest that different mechanisms underlie developmental and individual differences in susceptibility to interference across the life span. A model is proposed in which memory span and processing speed both increase with development but are relatively independent abilities within age groups.

A speechreading expert: the case of MM

The present case study of MM, who acquired both sign language and spoken language in her early preschool years-and then reached the normal milestones of development in each language--revealed that her speechreading expertise is associated with cognitive functions such as high working memory capacity and phonological skills. Her cognitive profile is in accord with previous case studies of extremely good speechreading skill. MM's enhanced right prefrontal/frontal cerebral blood flow activation during speechreading seems to be indicative of efficient visual scanning, but it is also possibly due to her strategy for phonological decoding of visual speech.

Selective attention in schizophrenia: relationship to verbal working memory

In previous work using the Stroop task to examine cognitive function in schizophrenia, we have suggested that reaction time (RT) facilitation and error interference should be more sensitive measures of cognitive function than RT interference. We examined this hypothesis in 36 DSM-IV schizophrenia and schizoaffective patients, who performed both the Stroop and the Speaking Span, a measure of verbal working memory. The results supported our hypotheses, demonstrating that RT facilitation and error interference were associated more strongly with working memory performance than RT interference. The robust correlations between these measures of selective attention and Speaking Span performance has implications for understanding the nature and selectivity of cognitive dysfunction in schizophrenia. We present several different hypotheses that may explain this relationship, including: (1) a generalized deficit; (2) a common cognitive disturbance; and (3) a common neurobiological dysfunction.

Increases in intrusion errors and working memory deficit of poor comprehenders

This study tests the hypothesis that the ability to inhibit already processed and actually irrelevant information could influence performance in the listening span test (Daneman & Carpenter, 1980) and have a crucial role in reading comprehension. In two experiments, the listening span test and a new working memory test were given to two groups of young adults, poor and good comprehenders, matched for logical reasoning ability. In Experiment 1, the poor comprehenders had a significantly lower performance in the listening span test associated to a higher number of intrusions--that is, recalled words that, in spite of being in sentence form, were not placed in the last position. In Experiment 2, a new working memory test was devised in order to analyse more effectively the occurrence of intrusions. Subjects were required to listen to a growing series of strings of animal and non-animal words. While listening, they had to detect when an animal word occurred, and at the end of each series they had to recall the last word of each string. The poor comprehenders obtained a significantly lower performance in the memory task and made a higher number of intrusions, particularly of animal words.

Components of verbal working memory: evidence from neuroimaging

We review research on the neural bases of verbal working memory, focusing on human neuroimaging studies. We first consider experiments that indicate that verbal working memory is composed of multiple components. One component involves the subvocal rehearsal of phonological information and is neurally implemented by left-hemisphere speech areas, including Broca's area, the premotor area, and the supplementary motor area. Other components of verbal working memory may be devoted to pure storage and to executive processing of the contents of memory. These studies rest on a subtraction logic, in which two tasks are imaged, differing only in that one task presumably has an extra process, and the difference image is taken to reflect that process. We then review studies that show that the previous results can be obtained with experimental methods other than subtraction. We focus on the method of parametric variation, in which a parameter that presumably reflects a single process is varied. In the last section, we consider the distinction between working memory tasks that require only storage of information vs. those that require that the stored items be processed in some way. These experiments provide some support for the hypothesis that, when a task requires processing the contents of working memory, the dorsolateral prefrontal cortex is disproportionately activated.

Assessment of syntax after adolescent brain injury: effects of memory on test performance

In this study, we investigated the influence of working memory load on performance of a task designed to measure receptive syntax ability. Subjects were 6 brain-injured adolescents and 6 hospitalized control subjects matched for age, sex, and general ability. Each subject was administered the Listening/Grammar subtest of the Test of Adolescent Language (TOAL-3) and a modified version of this subtest with identical syntax and fewer response choices (i.e., a reduced working memory processing and storage load). The syntactic structures tested on these tasks also were measured in spontaneous narratives. The brain-injured subjects' performance was significantly worse than that of controls on both versions of the syntax comprehension subtest. There was a significant group-by-task interaction, as brain-injured subjects' performance was significantly worse on the Listening/Grammar subtest than the modified subtest, whereas Control subjects'performance did not differ across the two tasks. In their spontaneous narratives, subjects in both groups produced the syntactic structures tested on the receptive syntax tasks, with no between-groups difference in syntax production. The results are discussed in terms of test validity and the impact of measurement methods on test performance in disordered groups.

Getting a grasp on working memory

Without it, you couldn't understand this sentence, add up a restaurant tab in your head, or even find your way home. The “it” is working memory, an erasable mental blackboard that allows you to hold briefly in your mind the information essential for comprehension, reasoning, and planning. Now, neurobiologists are beginning to identify the neural machinery underlying this critical ability. They have found that working memory relies on cooperation among scattered areas of the brain, with the prefrontal cortex apparently working as the orchestrator that coordinates the activity of these various regions.