Deficits in complex motor functions, despite no evidence of procedural learning deficits, among HIV+ individuals with history of substance dependence.

Human immunodeficiency virus (HIV) and drugs of abuse affect common neural systems underlying procedural memory, including the striatum. The authors compared performance of 48 HIV seropositive (HIV+) and 48 HIV seronegative (HIV-) participants with history of cocaine and/or heroin dependence across multiple Trial Blocks of three procedural learning (PL) tasks: Rotary Pursuit (RP), Mirror Star Tracing (MST), and Weather Prediction (WP). Groups were well matched on demographic, psychiatric, and substance use parameters, and all participants were verified abstinent from drugs. Mixed model analyses of variance revealed that the individuals in the HIV+ group performed more poorly across all tasks, with a significant main effect of HIV serostatus observed on the Mirror Star Tracing and a trend toward significance obtained for the Rotary Pursuit task. No significant differences were observed on the Weather Prediction task. Both groups demonstrated significant improvements in performance across all three procedural learning tasks. It is important to note that no significant Serostatus × Trial Block interactions were observed on any task. Thus, the individuals in the HIV+ group tended to perform worse than those in the HIV- group across all trial blocks of procedural learning tasks with motor demands, but showed no differences in their rate of improvement across all tasks. These findings are consistent with HIV--associated deficits in complex motor skills, but not in procedural learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A neuropsychological investigation of multitasking in HIV infection: Implications for everyday functioning.

Objective: A subset of individuals with HIV-associated neurocognitive impairment experience related deficits in “real world” functioning (i.e., independently performing instrumental activities of daily living [IADL]). While performance-based tests of everyday functioning are reasonably sensitive to HIV-associated IADL declines, questions remain regarding the extent to which these tests' highly structured nature fully captures the inherent complexities of daily life. The aim of this study was to assess the predictive and ecological validity of a novel multitasking measure in HIV infection. Method: Participants included 60 individuals with HIV infection (HIV+) and 25 demographically comparable seronegative adults (HIV?). Participants were administered a comprehensive neuropsychological battery, questionnaires assessing mood and everyday functioning, and a novel standardized test of multitasking, which involved balancing the demands of four interconnected performance-based functional tasks (i.e., financial management, cooking, medication management, and telephone communication). Results: HIV+ individuals demonstrated significantly worse overall performance, fewer simultaneous task attempts, and increased errors on the multitasking test as compared to the HIV? group. Within the HIV+ sample, multitasking impairments were modestly associated with deficits on standard neuropsychological measures of executive functions, episodic memory, attention/working memory, and information processing speed, providing preliminary evidence for convergent validity. More importantly, multivariate prediction models revealed that multitasking deficits were uniquely predictive of IADL dependence beyond the effects of depression and global neurocognitive impairment, with excellent sensitivity (86%), but modest specificity (57%). Conclusions: Taken together, these data indicate that multitasking ability may play an important role in successful everyday functioning in HIV+ individuals. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The Role of the Prefrontal Cortex in the Maintenance of Verbal Working Memory: An Event-Related fMRI Analysis.

Neuroimaging studies have been inconclusive in characterizing the role of the prefrontal cortex (PFC) for maintaining increasingly larger amounts of information in working memory (WM). To address this question, the authors collected event-related functional MRI data while participants performed an item-recognition task in which the number of to-be-remembered letters was parametrically modulated. During maintenance of information in WM, the dorsolateral and the ventrolateral PFC exhibited linearly increasing activation in response to increasing WM load. Prefrontal regions could not be distinguished from one another on the basis of load sensitivity, but the dorsolateral PFC had stronger functional connectivity with the parietal and motor cortex than the ventrolateral PFC. These results suggest an increasingly important role for the PFC in actively maintaining information as the amount of that information increases. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Risky decision making assessed with the gambling task in adults with HIV.

Decision making was assessed using a laboratory gambling task in 67 adults with the Human Immunodeficiency Virus (HIV+) and in 19 HIV-seronegative (HIV-) control participants. Neurocognitive test performance across several domains was also analyzed to examine potential cognitive mechanisms of gambling task performance. As predicted, the HIV+ group performed worse on the gambling task, indicating greater risky decision making. Specifically, the HIV+ group selected more cards from the "risky" or disadvantageous deck that included relatively large payoffs but infrequent large penalties. The control group also selected such risky cards but quickly learned to avoid them. Exploratory analyses also indicated that in the HIV+ group, but not in the control group, gambling task performance was correlated with Stroop Interference performance and long delay free recall on the California Verbal Learning Test, suggesting the role of inhibitory processes and verbal memory in the poorer gambling task performance in HIV. These findings indicate the usefulness of the gambling task as a laboratory tool to examine risky decision making and cognition in the HIV population. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Explaining age differences in temporal working memory.

To determine the cognitive mechanisms underlying age differences in temporal working memory (WM), the authors examined the contributions of item memory, associative memory, simple order memory, and multiple item memory, using parallel versions of the delayed-matching-to-sample task. Older adults performed more poorly than younger adults on tests of temporal memory, but there were no age differences in nonassociative item memory, regardless of the amount of information to be learned. In contrast, a combination of associative and simple order memory, both of which were reduced in older adults, completely accounted for age-related declines in temporal memory. The authors conclude that 2 mechanisms may underlie age differences in temporal WM, namely, a generalized decline in associative ability and a specific difficulty with order information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impaired visual working memory consolidation in schizophrenia.

This study investigated working memory (WM) consolidation, that is, the time required to create durable WM representations, at different levels of WM load in schizophrenia. Twenty-three schizophrenia spectrum patients and 16 control subjects participated in a change-detection task in which a sample array of 1-3 squares appeared followed by a delay and a test array. An array of pattern masks was inserted into the delay interval--covering the locations of the sample-array squares--100-800 ms after the offset of the sample array. If a durable WM representation is formed prior to mask onset, the mask should not impair performance. The degree of masking at an interval reflects the degree of WM consolidation at that time. Neither group showed masking at set size 1. Unlike controls, patients demonstrated robust masking effects at set size 2. Both groups showed masking at set size 3, but masking effects were larger and longer lasting in patients. These data demonstrate abnormally prolonged WM consolidation in schizophrenia. This impairment may slow the formation of stable representations of the visual environment, impacting everyday visually guided behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working Memory Consolidation Is Abnormally Slow in Schizophrenia.

This study reports evidence that patients with schizophrenia demonstrate a slowing of working memory (WM) consolidation, which is the process of transforming transient perceptual representations into durable WM representations. Sixteen schizophrenia patients and 16 healthy control participants performed a task measuring the visual WM consolidation rate in a change-detection paradigm. A target display containing 3 colored squares was followed by a variable delay of 17-483 ms, a pattern mask, and then a test stimulus. This pattern mask does not interfere with perception but disrupts WM consolidation. Control participants reached no-mask performance by 250 ms, indicating completed WM consolidation, whereas patients failed to reach no-mask performance by 483 ms. Slowed consolidation may play an important and largely unrecognized role in schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of working memory in spatial S-R correspondence effects.

This study investigates the impact of working memory (WM) load on response conflicts arising from spatial (non) correspondence between irrelevant stimulus location and response location (Simon effect). The dominant view attributes the Simon effect to automatic processes of location-based response priming. The automaticity view predicts insensitivity of the Simon effect to manipulations of processing load. Four experiments investigated the role of spatial and verbal WM in horizontal and vertical Simon tasks by using a dual-task approach. Participants maintained different amounts of spatial or verbal information in WM while performing a horizontal or vertical Simon task. Results showed that high load generally decreased, and sometimes eliminated, the Simon effect. It is interesting to note that spatial load had a larger impact than verbal load on the horizontal Simon effect, whereas verbal load had a larger impact than spatial load on the vertical Simon effect. The results highlight the role of WM as the perception-action interface in choice-response tasks. Moreover, the results suggest spatial coding of horizontal stimulus-response (S-R) tasks, and verbal coding of vertical S-R tasks. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Familiarity enhances visual working memory for faces.

Although it is intuitive that familiarity with complex visual objects should aid their preservation in visual working memory (WM), empirical evidence for this is lacking. This study used a conventional change-detection procedure to assess visual WM for unfamiliar and famous faces in healthy adults. Across experiments, faces were upright or inverted and a low- or high-load concurrent verbal WM task was administered to suppress contribution from verbal WM. Even with a high verbal memory load, visual WM performance was significantly better and capacity estimated as significantly greater for famous versus unfamiliar faces. Face inversion abolished this effect. Thus, neither strategic, explicit support from verbal WM nor low-level feature processing easily accounts for the observed benefit of high familiarity for visual WM. These results demonstrate that storage of items in visual WM can be enhanced if robust visual representations of them already exist in long-term memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working memory and connectionist models of parsing: A reply to MacDonald and Christiansen (2002).

The authors take issue with 3 claims made by M. C. MacDonald and M. H. Christiansen (2002): (a) tha connectionist models of syntactic processing do not have components that function in the sarne way as limitations on working memory (WM) in production system models of psychological processes; (b) that individual differences in WM are related to the efficiency of syntactic processing because both are affected by reading experience; and (c) that individual differences in the nature of phonologica representations affect the efficiency of syntactic processing. The authors argue that the concept of WM cannot be eliminated from models of language processing and that the literature supports the view that syntactic processing involves a specialized WM system. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Age-related deficits in generation and manipulation of mental images: I. The role of sensorimotor speed and working memory.

The authors investigated age-related slowing of information processing in mental imagery tasks. Eighty-five healthy adults (ages 18 to 77) performed a visual, sensorimotor, reaction-time task; a visual-perceptual choice reaction task; and 3 mental imagery tasks that varied in apparent difficulty and involved stimuli at 2 levels of graphic complexity. Age was associated with prolongation of response time across all tasks and both levels of stimulus complexity. Accuracy of response was adversely affected by increase in stimulus complexity in all tasks, whereas it was negatively related to age only on the tasks with substantial mental imagery requirements. Slowing of information processing and reduction in accuracy were mediated by declines in working memory but not by decrease of sensorimotor speed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neuropsychological performance and CD4 levels in HIV-1 asymptomatic infection

The performance of 68 HIV-1 seropositive asymptomatic (HIV+) subjects stratified on CD4 levels were compared with 82 HIV-1 seronegative (HIV-) subjects on a battery of neuropsychological, mood state, and perceived health status measures. The neuropsychological test battery included measures of attention, reaction time, memory, intellectual ability, psychomotor speed, frontal lobe or "executive" function, and decision time. None of the HIV+ subjects were taking antiviral agents. The groups did not differ for age, mood state, or WAIS-R Verbal and Performance IQ scores. Due to group differences for education and weekly ethanol consumption, both variables were used as covariates in multivariate analyses of variance. Relatively few differences were observed between subgroups of HIV+ patients or between these subgroups and control subjects. These data suggest that factors other than absolute levels of immunosuppression as expressed by CD4 levels alone, appear to be responsible for the deficits observed in HIV+ asymptomatic patients.     

Optimizing cognitive load for learning from computer-based science simulations.

How can cognitive load in visual displays of computer simulations be optimized? Middle-school chemistry students (N = 257) learned with a simulation of the ideal gas law. Visual complexity was manipulated by separating the display of the simulations in 2 screens (low complexity) or presenting all information on 1 screen (high complexity). The mode of visual representation in the simulation was manipulated by presenting important information in symbolic form only (symbolic representations) or by adding iconic information to the display (iconic + symbolic representations), locating the sliders controlling the simulation separated from the simulation or integrating them, and graphing either only the most recent simulation result or showing all results taken. Separated screen displays and the use of optimized visual displays each promoted comprehension and transfer, especially for low prior-knowledge learners. An expertise reversal effect was found for learners' prior general science knowledge. Results indicate that intrinsic and extraneous cognitive load in visual displays can be manipulated and that learners' prior knowledge moderates the effectiveness of these load manipulations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A theory of visual information acquisition and visual memory with special application to intensity-duration trade-offs.

Describes a theory of memory for visual material in which the visual system acts as a linear filter operating on a stimulus to produce a function, a(t), relating some sensory response to t (the time since stimulus onset). Stimulus information is acquired at a rate proportional to the product of the magnitude by which a(t) exceeds some threshold, and the amount of as-yet-unacquired information. Recall performance is assumed to equal the proportion of acquired information. The theory accounts for data from 2 digit-recall experiments in which stimulus temporal waveform was manipulated. The authors comment on the theory's account of the relation between 2 perceptual events: the phenomenological experience of the stimulus, and the memory representation that accrues from stimulus presentation. It is asserted that these 2 events, although influenced by different variables, can be viewed as resulting from 2 characteristics of the same sensory-response function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of alcohol on working memory: Distinguishing multiple processes.

The authors assessed effects of alcohol consumption on different types of working memory (WM) tasks in an attempt to characterize the nature of alcohol effects on cognition. The WM tasks varied in 2 properties of materials to be retained in a 2-stimulus comparison procedure. Conditions included (a) spatial arrays of colors, (b) temporal sequences of colors, (c) spatial arrays of spoken digits, and (d) temporal sequences of spoken digits. Alcohol consumption impaired memory for auditory and visual sequences but not memory for simultaneous arrays of auditory or visual stimuli. These results suggest that processes needed to encode and maintain stimulus sequences, such as rehearsal, are more sensitive to alcohol intoxication than other WM mechanisms needed to maintain multiple concurrent items, such as focusing attention on them. These findings help to resolve disparate findings from prior research on alcohol's effect on WM and on divided attention. The results suggest that moderate doses of alcohol impair WM by affecting certain mnemonic strategies and executive processes rather than by shrinking the basic holding capacity of WM. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of working memory capacity in retrieval.

The verbal fluency task that requires generation of category exemplars and appears to be an example of what M. Moscovitch (1995) calls a strategic test of memory retrieval. Four experiments explored the role of individual differences in working memory (WM) capacity on verbal fluency under various secondary load conditions. High WM participants consistently recalled more exemplars. However, load conditions caused a decline in recall only for high WM participants. Low WM participants showed no effect of secondary workload on exemplar generation. WM group differences and load effects were observed even in the 1st min of retrieval, which suggests that differences were not due to differences in knowledge. A model of retrieval is supported that relies on cue-based-automatic activation, monitoring of output for errors, controlled suppression of previously recalled items, and controlled strategic search. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequence Effects in the Categorization of Tones Varying in Frequency.

In contrast to exemplar and decision-bound categorization models, the memory and contrast models described here do not assume that long-term representations of stimulus magnitudes are available. Instead, stimuli are assumed to be categorized using only their differences from a few recent stimuli. To test this alternative, the authors examined sequential effects in a binary categorization of 10 tones varying in frequency. Stimuli up to 2 trials back in the sequence had a significant effect on the response to the current stimulus. The effects of previous stimuli interacted with one another. A memory and contrast model, according to which only ordinal information about the differences between the current stimulus and recent preceding stimuli is used, best accounted for these data (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intraindividual variability in HIV infection: Evidence for greater neurocognitive dispersion in older HIV seropositive adults.

Objective: Both the prevalence and incidence of HIV infection among older adults are on the rise. Older adults are at increased risk of HIV-associated neurocognitive disorders, which have historically been characterized as an inconsistent or “spotty” pattern of deficits. Dispersion is a form of intraindividual variability (IIV) that is defined as within-person variability in performance across domains and has been associated with poorer neurocognitive functioning and incipient decline among healthy older adults. To our knowledge, no studies have yet examined dispersion in an aging HIV-infected sample. Method: For the current study we examined the hypothesis that age and HIV infection have synergistic effects on dispersion across a battery of clinical and experimental cognitive tasks. Our well-characterized sample comprised 126 HIV-seropositive individuals (HIV+) and 40 HIV-seronegative comparison individuals (HIV?), all of whom were administered a comprehensive neuropsychological battery. Results: Consistent with our hypothesis, an age by HIV serostatus interaction was observed, with the older HIV+ group demonstrating a higher level of dispersion relative to older HIV? and younger HIV+ individuals, even when potentially confounding demographic and medical factors were controlled. Conclusion: Our results demonstrate that older HIV+ adults produce greater dispersion, or intraindividual variability in performance across a range of tests, which may be reflective of cognitive dyscontrol to which this population is vulnerable, perhaps driven by the combined effects of aging and HIV infection on prefrontostriatal systems. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The relationship between processing speed and working memory demand in systemic lupus erythematosus: Evidence from a visual n-back task.

Objective: Working memory (WM) deficits have been reported previously in systemic lupus erythematosus (SLE), but the relationship between information processing speed (PS) and WM deficits in SLE is unknown. This study examined whether or not PS slowing could account for the WM deficits observed in SLE. Method: A visual n-back task was used to measure simple and complex PS and WM in 40 SLE patients and 36 healthy controls. Simple PS was defined as reaction time (RT) to correct responses under a very low WM load condition (0-back), while complex PS was defined as RT to correct responses under moderate and high WM load conditions (1 and 2-back). Results: The results showed that SLE patients performed as well as the controls at the lower WM load conditions but had fewer correct responses than controls under the highest WM load condition (2-back). SLE patients had slower RTs than controls under all conditions, but they had relatively greater RT slowing than controls under the higher WM load conditions. Further, when RT for simple PS was subtracted from complex PS, SLE patients still showed slower complex PS for the 1- and 2-back compared with controls. Both simple and complex PS slowing were related to poorer accuracy scores on the 2-back condition, only for the SLE group. Conclusions: The n-back task provides a sensitive measure of PS and WM. The results suggest that PS deficits alone could not account for the WM deficits in SLE. Disease duration, disease activity, and depression did not appear to account for the observed PS and WM deficits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

N-methyl-D-aspartate receptor antagonist MK-801 and spatial memory representation: Working memory is impaired in an unfamiliar but not in a familiar environment.

Female Sprague-Dawley rats were injected with the noncompetitive N-methyl-D-aspartate (NMDA) antagonist MK-801 or saline 30 min before daily testing in spatial working-memory (WM) and reference memory (RM) procedures in an 8-arm radial maze. MK-801 impaired RM and WM acquisition but not performance when rats were trained to criterion before drug administration. Neither a 2-hr nor a 4-hr delay between the first and last 2 correct WM choices impaired long-term WM. MK-801 impaired WM performance in trained rats only when rats were tested in a new environment. Thus, 2 mechanisms may be required for relational memory: an NMDA-dependent mechanism for acquiring long-term spatial representations and an NMDA-insensitive mechanism for operating on these stored representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)