Higher-order cognitive functions, such as executive function (EF) and intelligence, are crucial to the everyday functioning of human beings. Gaining knowledge about these functions is important for our general understanding of human nature as well as for our ability to help those who may not develop these processes optimally. The present thesis focused particularly on the EF component working memory (WM), described as the ability to maintain informa-tion in consciousness during short time periods with the purpose of using that information in complex cognition. The major aims of the thesis were to increase our understanding of higher-order cognition in children as well as of deficiencies in intelligence found in children with Attention Deficit Hyperactivity Disorder (ADHD). We approached these aims by studying the interrelations among EF-related components in terms of their independent contributions to intellectual functioning. We also studied whether the lower intelligence in children with ADHD was mediated by fundamental EF-related components or whether these deficiencies went beyond the weaknesses in these specific cognitive functions. Interpreting the present data, we suggest that intellectual functioning in children is best viewed as representing a system of primarily independent parts that may be accompanied by an overarching common mechanism. The multiple components involve, but are surely not limited to, WM functions, inhibitory functions, sustained attention, and processing speed. One of these functions, WM, was found to be further partitioned into domain-specific executive WM processes and domain-specific short-term storage processes, all of which constitute important aspects of higher-order cognitive functioning. We have further learned that deficits in fluid intelligence in children with ADHD may entail more than weaknesses in specific central cognitive functions. This additional deficit is cautiously interpreted as involving supe-rior executive attention functions setting the stage for the development and integration of the EF system as well as the “intelligence system”.

Two aspects of cognitive control were investigated using the item-recognition task and the verb generation task. The item-recognition task had two conditions, high and low interference. The verb generation task was manipulated in three ways, for different levels of interference and time interval. The intention was to more deeply investigate one aspect of the item-recognition task, comparing response times for different trial types in different conditions, and to investigate a fatigue effect between the item-recognition and verb generation task. Thirty-two participants were tested at two occasions, in a within-subjects design. Results for the verb generation task revealed effects for levels of interference and time interval, although there was no difference in the manipulation. Results for the item-recognition task revealed effects for condition and trial type, as well as an interaction effect between these. The non-familiar trials in the high interference condition resulted in faster response times compared to the same kind of trials in the low condition. The result from the item-recognition task extends those from previous studies, revealing details for differences between trial types. This finding demonstrates a carry-over facilitation effect.

Working memory (WM) is essential for our ability to function cognitively. In this thesis we set out to examine the effects of computerized WM training in adults, through a randomized, comparison group controlled and double blind design. We measured this using a neuropsychological test called Paced Auditory Serial Addition Task (PASAT), which measures executive functions. The participants (N106), divided into four groups, young (20-30), old (60-70) and training-low dose. They trained with a computerized WM training program called Rememo© at home for five days a week during a period of five weeks. Before and after training they took the test, and then again after three months. The training gave significant improvement on PASAT performance in both young and old, and that the effect was significant at follow up. In conclusion, WM training has an effect even outside the specific tasks trained, which gives strong support to the theory of generalization and also support findings of plasticity in the aging brain.

This paper presents verbal working memory test results towards establishing the effects of menstrual cycle on working memory of women. The study comprised of a subject-set of twenty healthy young women with a regular 28 – 32 day menstrual cycles. Subjects were tested twice, once during their menstrual phase and second during their ovulation phase (on approximately day 12). Working memory tests were performed in a random sequence i.e. for some subjects during the menstrual phase (low estrogen level) working memory test occurred before their ovulation phase (high estrogen level) memory test and vice versa for other subjects. Study revealed that the test scores in the ovulatory phase were significantly higher than those in the menstrual phase. These findings suggest that higher levels of estrogen may improve working memory. Moreover, effects of estrogen on mood were also considered during both phases of menstruation. The fluctuation in estrogen levels seems to have an effect on women’s mood during menstrual and ovulation phases.

Den socialt kompetente har hög social status, många vänner, ett funktionellt beteende och sociala förmågor så som empati och hjälpsamhet. Avsaknad av social kompetens innebär bland annat känslomässiga och beteendemässiga problem. I denna studie medverkade totalt 30 gymnasieelever som genomgick två arbetsminnestest samt fyllde i en självvärderingsenkät som mäter social kompetens. Syftet var att undersöka om det finns ett samband mellan en tonårings arbetsminne och sociala kompetens. Studien begränsades till att mäta arbetsminnets fonologiska och visuellspatiala lagringsenheter samt två sociala förmågor; prosocialt beteende och initiativtagande. Inga signifikanta korrelationer mellan arbetsminne och social kompetens kunde påvisas. Eventuellt kan de icke existerande korrelationerna bero på att fel del av arbetsminnet eller fel del av den social kompetens stod i fokus för studien.

Previous research has indicated that meaningful background speech affects individuals reading comprehension performance differently and that this difference is related to working memory capacity. But what mechanism in working memory that is involved is not well understood. The present study’s main purpose was to investigate if individual differences in susceptibility to effects of speech on reading comprehension are moderated by working memory capacity as measured by the number updating task and two different mechanisms within this construct; delayed suppression (i.e. the inhibition of information that once was task-relevant but no longer is) and immediate suppression (i.e. the inhibition of processed but irrelevant information, while withholding attention focused on the to-be-recalled task-relevant items). Forty participants performed a number updating task and a reading comprehension task in silence and with meaningful background speech. The results indicated that the immediate suppression mechanism moderates the effects of background speech on reading comprehension. Those who can’t handle the interference from the background speech let the task-irrelevant information interfere with the ongoing cognitive task and therefore are more likely to be distracted by the background speech while reading a text.

The purpose of the present study was to examine working memory (WM) capacity, lexical access and phonological skills in 19 children with cochlear implants (CI) (5;7-13;4 years of age) attending grades 0-2, 4, 5 and 6 and to compare their performance with 56 children with normal hearing. Their performance was also studied in relation to demographic factors. The findings indicate that children with CI had visuospatial WM capacities equivalent to the comparison group. They had lower performance levels on most of the other cognitive tests. Significant differences between the groups were not found in all grades and a number of children with CI performed within 1 SD of the mean of their respective grade-matched comparison group on most of the cognitive measures. The differences between the groups were particularly prominent in tasks of phonological WM. The results are discussed with respect to the effects of cochlear implants on cognitive development.

This study used pre-existing data to examine whether children with ADHD, with and without working memory (WM) deficits, differ in their academic achievement and clinical profiles. 73 children (26% female), aged 6-12 years, with a confirmed diagnosis of ADHD had completed standardized achievement tests of reading, mathematics, and written language. Six WM measures and three parent and teacher questionnaires probing behaviour and executive functioning were administered. Of the sample, only 26% met the criteria for a WM deficit. Children with WM impairments were found to perform significantly worse than those without WM impairment on all achievement clusters, with no clinical profile differences. Poor WM is not universal in ADHD, but its presence is associated with lower academic achievement scores. Clinicians and educators should consider that underlying impairments in WM may be the contributing factors to academic difficulties in children with ADHD. Interventions targeting WM skills need to be implemented.

Examining the neural correlates associated with the moment a stimulus enters or exits conscious awareness is one way to potentially identify the neural mechanisms that give rise to consciousness. In the present study, we examined neural activity using electroencephalogram (EEG) recordings while participants observed a bilateral shape-from-motion (SFM) display. While the display is in motion, the observer perceives an object that is immediately segregated from a noisy background. After the motion stops, the observer’s experience of the object remains momentarily in awareness, before it eventually fades out of consciousness back into the noisy background. Consistent with subjective reports of perceptual experience, we observed a prominent sustained posterior contralateral negativity (SPCN), but only in conditions associated with sustained awareness. Importantly, the amplitude of the SPCN was correlated with individual differences in visual awareness, suggesting that this activity plays a significant role in the maintenance of objects in consciousness.

The term working memory (WM) refers to a set of cognitive processes that allows for the temporary storage and manipulation of information. Neural correlates of the N- back task, a well-established WM measure used in neuroimaging, have been studied extensively in adults but less so in developmental populations. This thesis determines the effect of age on brain activations that mediate cognitive processes for remembering non- verbal/visual stimuli. Block-design fMRI was used to record activity in 84 subjects (6-35 years) during a visual-patterns 0- and 1-back task. Regions activated during the 1-back condition were largely common to all age groups, with adults displaying the largest extent of activations. Children and adolescents showed similar 0-back activations (distinct from 1-back) while adults engaged an analogous 1-back activation pattern during 0-back, suggesting that brain mechanisms underlying memory and attentional processes required for this task in children and adolescents are not yet mature and that strategy usage is still developing.