A Call for Computational Thinking in Undergraduate Psychology

Computational thinking is an approach to problem solving that is typically employed by computer programmers. The advantage of this approach is that solutions can be generated through algorithms that can be implemented as computer code. Although computational thinking has historically been a skill that is exclusively taught within computer science, there has been a more recent movement to introduce these skills within other disciplines. Psychology is an excellent example of a discipline that would benefit from computational thinking skills because of the nature of questions that are typically asked within the discipline. However, there has not been a formal curriculum proposed to teach computational thinking within psychology and the behavioural sciences. I will argue that computational thinking is a fundamental skill that can easily be introduced to psychology students throughout their undergraduate education. This would provide students with the skills necessary to become successful researchers, and would also provide a practical and marketable skill to all psychology graduates.

Vascular risk factor burden correlates with cerebrovascular reactivity but not resting state coactivation in the default mode network

PURPOSE

White matter hyperintensities (WMH) are prevalent among older adults and are often associated with cognitive decline and increased risk of stroke and dementia. Vascular risk factors (VRFs) are linked to WMH, yet the impact of multiple VRFs on gray matter function is still unclear. The goal of this study was to test for associations between the number of VRFs and cerebrovascular reactivity (CVR) and resting state (RS) coactivation among individuals with WMH.

MATERIALS AND METHODS

Twenty-nine participants with suspected WMH were grouped based on the number of VRFs (subgroups: 0, 1, or ≥2). CVR and RS coactivation were measured with blood oxygenation level-dependent (BOLD) imaging on a 3T magnetic resonance imaging (MRI) system during hypercapnia and rest, respectively. Default-mode (DMN), sensory-motor, and medial-visual networks, generated using independent component analysis of RS-BOLD, were selected as networks of interest (NOIs). CVR-BOLD was analyzed using two methods: 1) a model-based approach using CO2 traces, and 2) a dual-regression (DR) approach using NOIs as spatial inputs. Average CVR and RS coactivations within NOIs were compared between VRF subgroups. A secondary analysis investigated the correlation between CVR and RS coactivation.

RESULTS

VRF subgroup differences were detected using DR-based CVR in the DMN (F20,2  = 5.17, P = 0.015) but not the model-based CVR nor RS coactivation. DR-based CVR was correlated with RS coactivation in the DMN (r(2)  = 0.28, P = 0.006) but not the sensory-motor nor medial-visual NOIs.

CONCLUSION

In individuals with WMH, CVR in the DMN was inversely associated with the number of VRFs and correlated with RS coactivation.

Mistakes as stepping stones: Effects of errors on episodic memory among younger and older adults

The memorial costs and benefits of trial-and-error learning have clear pedagogical implications for students, and increasing evidence shows that generating errors during episodic learning can improve memory among younger adults. Conversely, the aging literature has found that errors impair memory among healthy older adults and has advocated for the use of errorless learning to rehabilitate memory. However, there is evidence that errors are not always beneficial for younger adults, nor always harmful for older adults. We propose that differences in the learning paradigms used in the younger and older adult literatures may account for these conflicting recommendations, namely that they typically engender conceptual and nonconceptual processing, respectively. In this study, we had younger and older adults study words under errorless and trial-and-error learning instructions and based either on conceptual (a flower--tulip) or lexical (ho___--house) cues. We found that relative to errorless learning, trial-and-error learning increased target memory in the conceptual condition but decreased it in the lexical condition. Critically, both age groups showed this pattern, implying that aging does not influence how we learn from mistakes. We suggest that conceptual guesses act as "stepping stones" toward the target whereas lexical guesses simply create retrieval noise. This suggestion was supported by the fact that participants of both ages remembered their prior guesses better in the conceptual than lexical condition and that memory for guesses mediated differences in target performance. These findings are discussed within the framework of current theories on the effects of error generation on episodic memory.

The benefits associated with volunteering among seniors: a critical review and recommendations for future research

There is an urgent need to identify lifestyle activities that reduce functional decline and dementia associated with population aging. The goals of this article are to review critically the evidence on the benefits associated with formal volunteering among older adults, propose a theoretical model of how volunteering may reduce functional limitations and dementia risk, and offer recommendations for future research. Database searches identified 113 papers on volunteering benefits in older adults, of which 73 were included. Data from descriptive, cross-sectional, and prospective cohort studies, along with 1 randomized controlled trial, most consistently reveal that volunteering is associated with reduced symptoms of depression, better self-reported health, fewer functional limitations, and lower mortality. The extant evidence provides the basis for a model proposing that volunteering increases social, physical, and cognitive activity (to varying degrees depending on characteristics of the volunteer placement) which, through biological and psychological mechanisms, leads to improved functioning; we further propose that these volunteering-related functional improvements should be associated with reduced dementia risk. Recommendations for future research are that studies (a) include more objective measures of psychosocial, physical, and cognitive functioning; (b) integrate qualitative and quantitative methods in prospective study designs; (c) explore further individual differences in the benefits associated with volunteering; (d) include occupational analyses of volunteers' specific jobs in order to identify their social, physical, and cognitive complexity; (e) investigate the independent versus interactive health benefits associated with volunteering relative to engagement in other forms of activity; and (f) examine the relationship between volunteering and dementia risk.

A systematic review of type 2 diabetes mellitus and hypertension in imaging studies of cognitive aging: time to establish new norms

The rising prevalence of type 2 diabetes (T2DM) and hypertension in older adults, and the deleterious effect of these conditions on cerebrovascular and brain health, is creating a growing discrepancy between the "typical" cognitive aging trajectory and a "healthy" cognitive aging trajectory. These changing health demographics make T2DM and hypertension important topics of study in their own right, and warrant attention from the perspective of cognitive aging neuroimaging research. Specifically, interpretation of individual or group differences in blood oxygenation level dependent magnetic resonance imaging (BOLD MRI) or positron emission tomography (PET H2O(15)) signals as reflective of differences in neural activation underlying a cognitive operation of interest requires assumptions of intact vascular health amongst the study participants. Without adequate screening, inclusion of individuals with T2DM or hypertension in "healthy" samples may introduce unwanted variability and bias to brain and/or cognitive measures, and increase potential for error. We conducted a systematic review of the cognitive aging neuroimaging literature to document the extent to which researchers account for these conditions. Of the 232 studies selected for review, few explicitly excluded individuals with T2DM (9%) or hypertension (13%). A large portion had exclusion criteria that made it difficult to determine whether T2DM or hypertension were excluded (44 and 37%), and many did not mention any selection criteria related to T2DM or hypertension (34 and 22%). Of all the surveyed studies, only 29% acknowledged or addressed the potential influence of intersubject vascular variability on the measured BOLD or PET signals. To reinforce the notion that individuals with T2DM and hypertension should not be overlooked as a potential source of bias, we also provide an overview of metabolic and vascular changes associated with T2DM and hypertension, as they relate to cerebrovascular and brain health.

Combined effects of type 2 diabetes and hypertension associated with cortical thinning and impaired cerebrovascular reactivity relative to hypertension alone in older adults

OBJECTIVE

Type 2 diabetes mellitus is characterized by metabolic dysregulation in the form of hyperglycemia and insulin resistance and can have a profound impact on brain structure and vasculature. The primary aim of this study was to identify brain regions where the combined effects of type 2 diabetes and hypertension on brain health exceed those of hypertension alone. A secondary objective was to test whether vascular impairment and structural brain measures in this population are associated with cognitive function.

RESEARCH DESIGN AND METHODS

We enrolled 18 diabetic participants with hypertension (HTN + T2DM, 7 women, 71.8 ± 5.6 years) and 22 participants with hypertension only (HTN, 12 women, 73.4 ± 6.2 years). Cerebrovascular reactivity (CVR) was assessed using blood oxygenation level dependent (BOLD) MRI during successive breath holds. Gray matter structure was evaluated using cortical thickness (CThk) measures estimated from T1-weighted images. Analyses of cognitive and blood data were also performed.

RESULTS

Compared to HTN, HTN + T2DM had decreased CVR and CThk in a spatially overlapping region of the right occipital lobe (P < 0.025); CVR group differences were more expansive and included bilateral occipito-parietal areas (P < 0.025). Whereas CVR showed no significant associations with measures of cognitive function (P > 0.05), CThk in the right lingual gyrus ROI and regions resulting from a vertex-wise analysis (including posterior cingulate, precuneus, superior and middle frontal, and middle and inferior temporal regions (P < 0.025) were associated with executive function.

CONCLUSIONS

Individuals with T2DM and HTN showed decreased CVR and CThk compared to age-matched HTN controls. This study identifies brain regions that are impacted by the combined effects of comorbid T2DM and HTN conditions, with new evidence that the corresponding cortical thinning may contribute to cognitive decline.

Obstacles to remediating coping following traumatic brain injury

BACKGROUND

Coping has been suggested as the final common pathway related to outcome after traumatic brain injury (TBI). Different types of coping have been related to either positive or negative psychosocial outcomes. As a result, a small set of studies have attempted to remediate coping through intervention, but the effectiveness of these studies has been modest.

CONCLUSION

We propose that three primary factors are limiting our ability to effectively remediate coping following TBI through intervention TBI: 1) limited understanding of inter-patient variability following TBI; 2) limited understanding of the mechanisms underlying coping following TBI; and 3) reliance on self-report measures of coping. We discuss these obstacles in the context of a model of frontal lobe function, and in light of recent behavioural work on coping.

Managing executive dysfunction following acquired brain injury and stroke using an ecologically valid rehabilitation approach: a study protocol for a randomized, controlled trial

Background

We have been investigating an ecologically valid strategy-training approach to enable adults with executive dysfunction to attain everyday life goals. Here, we report the protocol of a randomized controlled trial of the effects of this training compared to conventional therapy in a sample of community-dwelling adults with acquired brain injury and/or stroke.

Methods/design

We will recruit 100 community-dwelling survivors at least six months post-acquired brain injury or stroke who report executive dysfunction during a telephone interview, confirmed in pre-training testing. Following pre-training testing, participants will be randomized to the ecologically valid strategy training or conventional therapy and receive two one-hour sessions for eight weeks (maximum of 15 hours of therapy). Post-testing will occur immediately following the training and three months later. The primary outcome is self-reported change in performance on everyday life activities measured using the Canadian Occupational Performance Measure, a standardized, semi-structured interview. Secondary outcomes are objective measurement of performance change from videotapes of treatment session, Performance Quality Rating Scale; executive dysfunction symptoms, Behavioural Rating Inventory of Executive Function – Adult; participation in everyday life, Mayo-Portland Adaptability Inventory Participation Index; and ability to solve novel problems, Instrumental Activities of Daily Living Profile.

Discussion

This study is of a novel approach to promoting improvements in attainment of everyday life goals through managing executive dysfunction using an ecologically valid strategy training approach, the Cognitive Orientation to daily Occupational Performance. This study compares the efficacy of this approach with that of conventional therapy. The approach has the potential to be a valuable treatment for people with chronic acquired brain injury and/or stroke.

Trial registration

clinicaltrials.gov, Trial Identification Number: NCT01414348

Visual selective attention in amnestic mild cognitive impairment

OBJECTIVES

Subtle deficits in visual selective attention have been found in amnestic mild cognitive impairment (aMCI). However, few studies have explored performance on visual search paradigms or the Simon task, which are known to be sensitive to disease severity in Alzheimer's patients. Furthermore, there is limited research investigating how deficiencies can be ameliorated with exogenous support (auditory cues).

METHOD

Sixteen individuals with aMCI and 14 control participants completed 3 experimental tasks that varied in demand and cue availability: visual search-alerting, visual search-orienting, and Simon task.

RESULTS

Visual selective attention was influenced by aMCI, auditory cues, and task characteristics. Visual search abilities were relatively consistent across groups. The aMCI participants were impaired on the Simon task when working memory was required, but conflict resolution was similar to controls. Spatially informative orienting cues improved response times, whereas spatially neutral alerting cues did not influence performance. Finally, spatially informative auditory cues benefited the aMCI group more than controls in the visual search task, specifically at the largest array size where orienting demands were greatest.

DISCUSSION

These findings suggest that individuals with aMCI have working memory deficits and subtle deficiencies in orienting attention and rely on exogenous information to guide attention.

Comparing sensitivity to facial asymmetry and facial identity

Bilateral symmetry is a facial feature that plays an important role in the aesthetic judgments of faces. The extent to which symmetry contributes to the identification of faces is less clear. We investigated the relationship between facial asymmetry and identity using synthetic face stimuli where the geometric identity of the face can be precisely controlled. Thresholds for all observers were 2 times lower for discriminating facial asymmetry than they were for discriminating facial identity. The advantage for discriminating asymmetrical forms was not observed using nonface shape stimuli, suggesting this advantage is face-specific. Moreover, asymmetry thresholds were not affected when faces were either inverted or constructed about a nonmean face. These results, taken together, suggest that facial asymmetry is a characteristic that we are exquisitely sensitive to, and that may not contribute to face identification. This conclusion is consistent with neuroimaging evidence that suggests that face symmetry and face identity are processed by different neural mechanisms.

Contributions of frontal and medial temporal lobe functioning to the errorless learning advantage

Among individuals with episodic memory impairments, trial-and-error learning is less successful than when errors are avoided. This "errorless learning advantage" has been replicated numerous times, but its neurocognitive mechanism is uncertain, with existing evidence pointing to both medial temporal lobe (MTL) and frontal lobe (FL) involvement. To test the relative contribution of MTL and FL functioning to the errorless learning advantage, 51 healthy older adults were pre-experimentally assigned to one of four groups based on their neuropsychological test performance: Low MTL-Low FL, Low MTL-High FL, High MTL-Low FL, High MTL-High FL. Participants learned two word lists under errorless learning conditions, and two word lists under errorful learning conditions, and memory was tested via free recall, cued recall, and source recognition. Performance on all three tests was better for those with High relative to Low MTL functioning. An errorless learning advantage was found in free and cued recall, in cued recall marginally more so for those with Low than High MTL functioning. Participants with Low MTL functioning were also more likely to misclassify learning errors as target words. Overall, these results are consistent with a MTL locus of the errorless learning advantage. The results are discussed in terms of the multi-componential nature of neuropsychological tests and the impact of demographic and mood variables on cognitive functioning.

Mild cognitive impairment is associated with impaired visual-motor planning when visual stimuli and actions are incongruent

BACKGROUND/AIMS

This study examined cognitive-motor integration in adults with mild cognitive impairment (MCI). Previously, we showed that the performance of early-stage Alzheimer's disease patients declined significantly as a visually-guided movement went from having a standard mapping (vision and action spatially aligned) to having a non-standard mapping (vision and action incongruent). The present study extends this line of research by examining the performance of individuals affected by MCI.

METHODS

The participants made finger movements over a clear touchscreen placed in two separate spatial planes to either constantly present or remembered visual targets. These spatial plane conditions were repeated with the direction of cursor motion rotated 180° from that of hand motion. We also tested an 'arbitrary' condition where symbols instructed the participants to move their hand in certain directions.

RESULTS

We observe that adults with MCI took significantly longer to plan movements requiring intermediate levels of non-standard mapping, relative to healthy older adults.

CONCLUSIONS

These data suggest that movements requiring rule integration is affected even in individuals at a very early stage of cognitive decline. Cognitive-motor integration may provide a sensitive means to detect functional difficulty in early cognitive impairment.

Right frontal lobe mediation of recollection- and familiarity-based verbal recognition memory: evidence from patients with tumor resections

Medial-temporal, parietal, and pFC regions have been implicated in recollection and familiarity, but existing evidence from neuroimaging and patient studies is limited and conflicting regarding the role of specific regions within pFC in these memory processes. We report a study of 20 patients who had undergone resection of right frontal lobe tumors and 20 matched healthy control participants. The location and extent of lesions were traced on the patients' scans. A process dissociation procedure was employed to yield estimates of the contributions of recollection and familiarity in verbal recognition performance. Group comparisons revealed deficits in recollection but not familiarity in the patient group relative to their healthy counterparts. We found a positive relationship between estimates of familiarity and lesion sizes in the right inferior pFC (BA 11, 47) which was significant upon bootstrap resampling. These results are discussed in terms of prior work linking this area to an overextended sense of familiarity.

Errorless learning of computer-generated words in a patient with semantic dementia

This study explores the effectiveness and feasibility of an errorless learning approach administered via a computer-based treatment for anomia to CS, an individual with semantic dementia. Using a multiple baseline across behaviours design, we explored treatment specific effects, maintenance and generalisation of gains derived from the MossTalk Words((R)) therapy programme. CS was treated on three lists of words, each containing items for which CS retained some semantic knowledge and some for which he did not. CS was tested immediately after therapy, and one and three months later. Improved naming was maintained on all lists at all testing intervals. In addition, among those words for which CS retained some semantic knowledge, he maintained the ability to name all practised words, but only half of the not practised words. This study underscored the feasibility of computer-based treatments for anomia in progressive disorders, demonstrated the effectiveness of an errorless approach in semantic dementia in re-training lost words, and provided justification for training words that patients still have in their daily vocabulary. The results are discussed in relation to other treatment studies in progressive aphasia and in the context of factors necessary for therapeutic success in semantic dementia.

Verbal fluency, trail making, and Wisconsin Card Sorting Test performance following right frontal lobe tumor resection

Three commonly used clinical tests of frontal-executive function are verbal fluency, the Trail Making Test, and the Wisconsin Card Sorting Test, but few lesion studies of regional specificity within the frontal lobe (FL) exist for them. We examined 20 patients with right FL tumor resection, and mapped their damage to explore brain-behavior relations with greater precision. Across tests, the patients performed poorly and they also showed a deficit in switching but not clustering in verbal fluency. Within the right FL, however, we found none of the regional differences reported in studies of mixed-etiology FL patients, possibly due to the gradual neural reorganization that can occur with brain tumors. We discuss the importance of etiology in examining brain-behavior relations.

Temporal aspects of orientation pooling using visual noise stimuli

Previous psychophysical studies have shown that oriented signals are pooled over space to support better perceptual performance. We have investigated whether oriented signals may also be pooled over time. Using an orientation-in-noise paradigm, the threshold to discriminate large orientation differences was measured as the minimum amount of signal required to discriminate an oriented stimulus from unoriented noise. Discrimination thresholds were better with dynamic stimuli, containing multiple independent samples over time, than with static stimuli presented for an equal duration. Thresholds for dynamic stimuli showed gradual improvement from very brief (12 ms) to remarkably long presentation times (>4 s). Spatial integration of orientation signals is very efficient and can be understood in terms of a model based on signal detection theory, with performance limited by early and late stages of intrinsic noise. The nature of temporal integration is different, however, and is more consistent with probability summation of the outputs from low-level orientation detectors operating at a very brief timescale but whose outputs can be combined over a very long duration to yield better perceptual performance.

Evaluating shape after-effects with radial frequency patterns

Mechanisms selective for complex shape are vulnerable to adaptation techniques historically used to probe those underlying performance in lower-level visual tasks. We explored the nature of these shape after-effects using radial frequency patterns. Adapting to a radial frequency pattern resulted in a strong and systematic after-effect of a pattern that was 180 degrees out of phase with the adapting pattern. This after-effect was characterized as both a shift in the point of subjective equality and an increase in response uncertainty. The after-effect transferred across adapting pattern contrast and adaptor amplitude, suggesting an involvement from shape-specific mechanisms located at higher processing stages along the visual pathway. Moreover, our results suggested that the shift in the point of subjective equality was guided by global processing mechanisms, whereas the increase in uncertainty reflected activity from local processing mechanisms. Together, these results suggest that shape-specific after-effects reflect gain control processes at various stages of processing along the ventral pathway.

The mnemonic mechanisms of errorless learning

Errorless learning enhances memory relative to errorful, trial-and-error learning, but the extent to which this advantage relies on implicit or explicit memory processes is not clear. Previous attempts to determine the mnemonic mechanisms of errorless learning have relied on contrasts between patient groups or between tasks, but both approaches are problematic. In this study, healthy younger and older adults were engaged in errorless or errorful learning using a process dissociation procedure that provides separate estimates of explicit recollection and implicit familiarity within-subjects and within-task (Hay & Jacoby, 1996). Consistent with much prior research, we found an age-related decrement in recollection, but age-invariance in familiarity. In the young adults, errorless learning reduced the misleading familiarity of prior errors, but this benefit was offset by the non-elaborative nature of the errorless learning condition that also reduced recollection. In the older adults, who are less able to oppose familiarity-based errors because of their lower recollection, errorless learning only reduced the misleading impact of previous errors. Our results support Baddeley and Wilson's (1994) position that the errorless learning effect is mediated by implicit memory processes: individuals with reduced explicit memory benefit from errorless learning because errorless learning bypasses the need to engage explicit error elimination processes. We do not recommend standard errorless learning for individuals with intact explicit memory, such as students trying to learn information in preparation for an examination.

The case for the development and use of "ecologically valid" measures of executive function in experimental and clinical neuropsychology

This article considers the scientific process whereby new and better clinical tests of executive function might be developed, and what form they might take. We argue that many of the traditional tests of executive function most commonly in use (e.g., the Wisconsin Card Sorting Test; Stroop) are adaptations of procedures that emerged almost coincidentally from conceptual and experimental frameworks far removed from those currently in favour, and that the prolongation of their use has been encouraged by a sustained period of concentration on "construct-driven" experimentation in neuropsychology. This resulted from the special theoretical demands made by the field of executive function, but was not a necessary consequence, and may not even have been a useful one. Whilst useful, these tests may not therefore be optimal for their purpose. We consider as an alternative approach a function-led development programme which in principle could yield tasks better suited to the concerns of the clinician because of the transparency afforded by increased "representativeness" and "generalisability." We further argue that the requirement of such a programme to represent the interaction between the individual and situational context might also provide useful constraints for purely experimental investigations. We provide an example of such a programme with reference to the Multiple Errands and Six Element tests.

The toronto mindfulness scale: Development and validation

In this study, the authors both developed and validated a self-report mindfulness measure, the Toronto Mindfulness Scale (TMS). In Study 1, participants were individuals with and without meditation experience. Results showed good internal consistency and two factors, Curiosity and Decentering. Most of the expected relationships with other constructs were as expected. The TMS scores increased with increasing mindfulness meditation experience. In Study 2, criterion and incremental validity of the TMS were investigated on a group of individuals participating in 8-week mindfulness-based stress reduction programs. Results showed that TMS scores increased following treatment, and Decentering scores predicted improvements in clinical outcome. Thus, the TMS is a promising measure of the mindfulness state with good psychometric properties and predictive of treatment outcome.

The nature of synthetic face adaptation

Recent evidence demonstrates that adapting to a face will systematically bias the perception of faces that lie along the same identity trajectory in geometric face space but not faces that lie along different identity trajectories. We explored this configural aftereffect using synthetic face stimuli developed to measure face-specific processing. Adapting to synthetic "anti-faces" resulted in an identity-specific aftereffect that was characterized by a marked decrease in the slope of the psychometric functions. Adaptation transferred across different face sizes, but not different face viewpoints nor faces constructed about a non-mean face. Performance was captured by a model where responses were modulated through a divisive gain control and an additive constant reflecting a shift in the origin of perceived face space. Together, these results suggest that face adaptation reflects activity from mechanisms common to various processing stages along the visual pathway.

Intensive methotrexate and cytarabine followed by high-dose chemotherapy with autologous stem-cell rescue in patients with newly diagnosed primary CNS lymphoma: an intent-to-treat analysis

PURPOSE

To assess the safety and efficacy of intensive methotrexate-based chemotherapy followed by high-dose chemotherapy (HDT) with autologous stem-cell rescue in patients with newly diagnosed primary CNS lymphoma (PCNSL).

PATIENTS AND METHODS

Twenty-eight patients received induction chemotherapy using high-dose systemic methotrexate (3.5 g/m2) and cytarabine (3 g/m2 daily for 2 days). Fourteen patients with chemosensitive disease evident on neuroimaging then received high-dose therapy using carmustine, etoposide, cytarabine, and melphalan with autologous stem-cell rescue.

RESULTS

The objective response rate to the induction-phase chemotherapy was 57%, and median overall survival is not yet assessable, with a median follow-up time of 28 months. The overall median event-free survival time is 5.6 months for all patients and 9.3 months for 14 patients who underwent transplantation. Six of these 14 patients (43%) remained disease-free at last follow-up. Treatment was well tolerated; there was one transplantation-related death. Prospective neuropsychologic evaluations have revealed no evidence of treatment-related neurotoxicity.

CONCLUSION

This treatment approach is feasible in patients with newly diagnosed PCNSL without evidence of significant related neurotoxicity. Although the transplantation results are similar to those achieved in patients with aggressive or poor-prognosis systemic lymphoma, the low response rate to induction chemotherapy and the significant number of patients who experienced relapse soon after HDT suggest that more aggressive induction chemotherapy may be warranted.

Orientation discrimination in visual noise using global and local stimuli

We have investigated orientation discrimination in visual noise using two types of high contrast, broadband stimuli. Discrimination thresholds are better for Local stimuli, in which the orientation signal is spatially limited, than for Global stimuli, in which the orientation signal extends across the entire stimulus. Performance improves with increasing stimulus area, reaching an optimum threshold of about 11% orientation signal. Thresholds were not influenced by brief presentation times or practice. These results, along with results from a simple computational model, suggest that human orientation discrimination for this kind of pattern is mediated by pooling local responses of low-level neural mechanisms and is limited by two stages of intrinsic neural noise.

Lateralization of prefrontal activity during episodic memory retrieval: evidence for the production-monitoring hypothesis

We propose a new hypothesis concerning the lateralization of prefrontal cortex (PFC) activity during verbal episodic memory retrieval. The hypothesis states that the left PFC is differentially more involved in semantically guided information production than is the right PFC, and that the right PFC is differentially more involved in monitoring and verification than is the left PFC. This "production-monitoring hypothesis" differs from the existing "systematic-heuristic hypothesis," which proposes that the left PFC is primarily involved in systematic retrieval operations, and the right PFC in heuristic retrieval operations. To compare the two hypotheses, we measured PFC activity using positron emission tomography (PET) during the performance of four episodic retrieval tasks: stem cued recall, associative cued recall, context recognition (source memory), and item recognition. Recall tasks emphasized production processes, whereas recognition tasks emphasized monitoring processes. Stem cued recall and context-recognition tasks underscored systematic operations, whereas associative cued recall and item-recognition tasks underscored heuristic operations. Consistent with the production-monitoring hypothesis, the left PFC was more activated for recall than for recognition tasks and the right PFC was more activated for recognition than for recall tasks. Inconsistent with the systematic-heuristic hypothesis, the left PFC was more activated for heuristic than for systematic tasks and the right PFC showed the converse result. Additionally, the study yielded activation differences outside the PFC. In agreement with a previous recall/recognition PET study, anterior cingulate, cerebellar, and striatal regions were more activated for recall than for recognition tasks, and the converse occurred for posterior parietal regions. A right medial temporal lobe region was more activated for stem cued recall and context recognition than for associative cued recall and item recognition, possibly reflecting perceptual integration. In sum, the results provide evidence for the production-monitoring hypothesis and clarify the role of different brain regions typically activated in PET and functional magnetic resonance imaging (fMRI) studies of episodic retrieval.

Aging gracefully: compensatory brain activity in high-performing older adults

Whereas some older adults show significant cognitive deficits, others perform as well as young adults. We investigated the neural basis of these different aging patterns using positron emission tomography (PET). In PET and functional MRI (fMRI) studies, prefrontal cortex (PFC) activity tends to be less asymmetric in older than in younger adults (Hemispheric Asymmetry Reduction in Old Adults or HAROLD). This change may help counteract age-related neurocognitive decline (compensation hypothesis) or it may reflect an age-related difficulty in recruiting specialized neural mechanisms (dedifferentiation hypothesis). To compare these two hypotheses, we measured PFC activity in younger adults, low-performing older adults, and high-performing older adults during recall and source memory of recently studied words. Compared to recall, source memory was associated with right PFC activations in younger adults. Low-performing older adults recruited similar right PFC regions as young adults, but high-performing older adults engaged PFC regions bilaterally. Thus, consistent with the compensation hypothesis and inconsistent with the dedifferentiation hypothesis, a hemispheric asymmetry reduction was found in high-performing but not in low-performing older adults. The results suggest that low-performing older adults recruited a similar network as young adults but used it inefficiently, whereas high-performing older adults counteracted age-related neural decline through a plastic reorganization of neurocognitive networks.

Divided attention during encoding and retrieval: differential control effects?

Previous studies have shown that divided attention (DA) during retrieval has little effect on recall of episodic memories, although DA during encoding has a large detrimental effect. One possible reason for this asymmetry is that stimulus presentation at encoding is under experimenter control, whereas retrieval operations and responses are under participant control. This experiment tested this possibility by presenting paired-associate word lists for learning and recall, either at a fixed 4-s rate or at a rate controlled by the participant. The results showed that the higher recall levels for DA at retrieval than for DA at encoding held under all combinations of experimenter and participant control. The implications of these results for a fuller understanding of encoding and retrieval processes are discussed.

Divided attention during encoding and retrieval: differential control effects?

Previous studies have shown that divided attention (DA) during retrieval has little effect on recall of episodic memories, although DA during encoding has a large detrimental effect. One possible reason for this asymmetry is that stimulus presentation at encoding is under experimenter control, whereas retrieval operations and responses are under participant control. This experiment tested this possibility by presenting paired-associate word lists for learning and recall, either at a fixed 4-s rate or at a rate controlled by the participant. The results showed that the higher recall levels for DA at retrieval than for DA at encoding held under all combinations of experimenter and participant control. The implications of these results for a fuller understanding of encoding and retrieval processes are discussed.

The effects of divided attention on encoding- and retrieval-related brain activity: A PET study of younger and older adults

Divided attention (DA) disrupts episodic encoding, but has little effect on episodic retrieval. Furthermore, normal aging is associated with episodic memory impairments, and when young adults are made to encode information under DA conditions, their memory performance is reduced and resembles that of old adults working under full attention (FA) conditions. Together, these results suggest a common neurocognitive mechanism by which aging and DA during encoding disrupt memory performance. In the current study, we used PET to investigate younger and older adults' brain activity during encoding and retrieval under FA and DA conditions. In FA conditions, the old adults showed reduced activity in prefrontal regions that younger adults activated preferentially during encoding or retrieval, as well as increased activity in prefrontal regions young adults did not activate. These results indicate that prefrontal functional specificity of episodic memory is reduced by aging. During encoding, DA reduced memory performance, and reduced brain activity in left-prefrontal and medial-temporal lobe regions for both age groups, indicating that DA during encoding interferes with encoding processes that lead to better memory performance. During retrieval, memory performance and retrieval-related brain activity were relatively immune to DA for both age groups, suggesting that DA during retrieval does not interfere with the brain systems necessary for successful retrieval. Finally, left inferior prefrontal activity was reduced similarly by aging and by DA during encoding, suggesting that the behavioral correspondence between these effects is the result of a reduced ability to engage in elaborate encoding operations.

Asymmetry between encoding and retrieval processes: evidence from divided attention and a calibration analysis

Two experiments provide further information on the effects of divided attention (DA) on encoding and retrieval processes. The first experiment examined the effects of decision and motor difficulty of a concurrent reaction time task. A calibration analysis was used in the second experiment to test the hypothesis that shifting attentional emphasis away from encoding to the secondary task reduces the level of processing the to-be-remembered items receive. Overall, the results confirm and extend the conclusions of Craik, Govoni, Naveh-Benjamin, and Anderson (1996) and Naveh-Benjamin, Craik, Guez, and Dori (1998), by pointing to clear differences between encoding and retrieval processes: Encoding is affected by simultaneous task demands, especially those associated with "central" resources involved in conscious decision making, whereas retrieval is obligatory in that it is largely immune to the effects of simultaneous demands. The results of the calibration analysis suggest that one reason for the poorer memory performance as a result of DA at encoding is a qualitative shift to less deep, elaborative strategies.

The effect of divided attention on encoding and retrieval in episodic memory revealed by positron emission tomography

The effects of divided attention (DA) on episodic memory encoding and retrieval were investigated in 12 normal young subjects by positron emission tomography (PET). Cerebral blood flow was measured while subjects were concurrently performing a memory task (encoding and retrieval of visually presented word pairs) and an auditory tone-discrimination task. The PET data were analyzed using multivariate Partial Least Squares (PLS), and the results revealed three sets of neural correlates related to specific task contrasts. Brain activity, relatively greater under conditions of full attention (FA) than DA, was identified in the occipital-temporal, medial, and ventral-frontal areas, whereas areas showing relatively more activity under DA than FA were found in the cerebellum, temporo-parietal, left anterior-cingulate gyrus, and bilateral dorsolateral-prefrontal areas. Regions more active during encoding than during retrieval were located in the hippocampus, temporal and the prefrontal cortex of the left hemisphere, and regions more active during retrieval than during encoding included areas in the medial and right-prefrontal cortex, basal ganglia, thalamus, and cuneus. DA at encoding was associated with specific decreases in rCBF in the left-prefrontal areas, whereas DA at retrieval was associated with decreased rCBF in a relatively small region in the right-prefrontal cortex. These different patterns of activity are related to the behavioral results, which showed a substantial decrease in memory performance when the DA task was performed at encoding, but no change in memory levels when the DA task was performed at retrieval.

The attentional demands of encoding and retrieval in younger and older adults: 2. Evidence from secondary task reaction time distributions

Three studies examined the effects of encoding or retrieval on properties of secondary task reaction time (RT) distributions in younger and older adults. Relative to full attention conditions, encoding and retrieval increased secondary task RT medians and standard deviations more for older adults than for younger adults, and the age-related RT increase was most pronounced among the slowest RTs. Hierarchical regression analyses revealed two age-related mechanisms underlying these effects, which were interpreted as cognitive slowing and reductions in attentional resources. Cognitive slowing affects the entire RT distribution regardless of the memory task. By contrast, reduced attentional resources result in very long RTs, especially when the tasks require self-initiated encoding or retrieval operations.

Age-related differences in neural activity during item and temporal-order memory retrieval: a positron emission tomography study

Positron emission tomography (PET) was used to investigate the hypothesis that older adults' difficulties with temporal-order memory are related to deficits in frontal function. Young (mean 24.7 years) and old (mean 68.6 years) participants studied a list of words, and were then scanned while retrieving information about what words were in the list (item retrieval) or when they occurred within the list (temporal-order retrieval). There were three main results. First, whereas the younger adults engaged right prefrontal regions more during temporal-order retrieval than during item retrieval, the older adults did not. This result is consistent with the hypothesis that context memory deficits in older adults are due to frontal dysfunction. Second, ventromedial temporal activity during item memory was relatively unaffected by aging. This finding concurs with evidence that item memory is relatively preserved in old adults and with the notion that medial temporal regions are involved in automatic retrieval operations. Finally, replicating the result of a previous study (Cabeza, R., Grady, C. L., Nyberg, L., McIntosh, A. R. , Tulving, E., Kapur, S., Jennings, J. M., Houle, S., and Craik, F. I. M., 1997), the old adults showed weaker activations than the young adults in the right prefrontal cortex but stronger activations in the left prefrontal cortex. The age-related increase in left prefrontal activity may be interpreted as compensatory. Taken together, the results suggest that age-related changes in brain activity are rather process- and region-specific, and that they involve increases as well as decreases in neural activity.

The attentional demands of encoding and retrieval in younger and older adults: 2. Evidence from secondary task reaction time distributions

Three studies examined the effects of encoding or retrieval on properties of secondary task reaction time (RT) distributions in younger and older adults. Relative to full attention conditions, encoding and retrieval increased secondary task RT medians and standard deviations more for older adults than for younger adults, and the age-related RT increase was most pronounced among the slowest RTs. Hierarchical regression analyses revealed two age-related mechanisms underlying these effects, which were interpreted as cognitive slowing and reductions in attentional resources. Cognitive slowing affects the entire RT distribution regardless of the memory task. By contrast, reduced attentional resources result in very long RTs, especially when the tasks require self-initiated encoding or retrieval operations.