EEG and fNIRS are associated with situation awareness (hazard) prediction during a driving task.

Situation awareness (SA) is important in many demanding tasks (e.g. driving). Assessing SA during training can indicate whether someone is ready to perform in the real world. SA is typically assessed by interrupting the task to ask questions about the situation or asking questions after task completion, assessing only momentary SA. An objective and continuous means of detecting SA is needed. We examined whether neurophysiological sensors are useful to objectively measure Level 3 SA (projection of events into the future) during a driving task. We measured SA by the speed at which participants responded to SA questions and the accuracy of responses. For EEG, beta and theta power were most sensitive to SA response time. For fNIRS, oxygenated haemoglobin (HbO) was most sensitive to accuracy. This is the first evidence to our knowledge that neurophysiological measures are useful for assessing Level 3 SA during an ecologically valid task.

We examine whether neurophysiological sensors are useful to objectively measure Level 3 situation awareness (SA) prediction during a driving task. EEG theta and beta, and fNIRS oxygenated haemoglobin were most sensitive to SA accuracy. This is evidence that neurophysiological measures can be used to assess hazard prediction (Level 3 SA).

Childhood stress, gender, and cognitive control: Midline theta power.

The emergence of psychiatric symptoms is a common consequence of childhood stress exposure. However, there are a dearth of reliable clinical hallmarks or physiological biomarkers to predict post-trauma symptom emergence. The objective of this study was to examine if childhood stressors and stress-related symptoms are associated with altered midline theta power (MTP) during cognitive control demands, and how these associations interact with gender and early adversity. N = 53 children (ages 9-13 years old) from a longitudinal study of children maltreated during early childhood and non-maltreated children participated in this study. EEG recorded neural activity during a Zoo-Themed Go/No-Go task. Stress-related symptoms, recent stressful events, and other adversity experiences were identified. MTP was analyzed with clinical variables in a series of follow-up analyses. The number of stressors in the past six months was negatively correlated with MTP in those with low preschool adversity, but not in those with high preschool adversity. MTP was higher in girls than in boys, and the associations of MTP with stressors and symptoms were moderated by gender. MTP was negatively associated with stressors in the past six months in girls, while in boys, MTP was associated with stress-related symptoms. Childhood stressful events were associated with reduced MTP during cognitive control demands, and this was finding was moderated by gender and early life adversity. These preliminary findings suggest that boys and girls may process stressful experiences in distinct ways, and preschool adversity may potentially blunt the interaction between current stress and neural dynamics. However, ongoing investigation is needed.

Effects of aging on externally cued and internally driven uncertainty representations.

OBJECTIVE: The Hick-Hyman law states that response time (RT) increases linearly with increasing information uncertainty. The effects of aging on uncertainty representations in choice RT paradigms remain unclear, including whether aging differentially affects processes mediating externally cued versus internally driven uncertainty. This study sought to characterize age-related differences in uncertainty representations using a card-sorting task. METHOD: The task separately manipulated internally driven uncertainty (i.e., probability of each stimulus type with fixed number of response piles) and externally cued uncertainty (i.e., number of response piles with fixed probability of each stimulus type). RESULTS: Older adults (OA) showed greater RT slowing than younger adults in response to uncertainty load, an effect that was stronger in the externally cued than internally driven condition. While both age groups showed lower accuracy and greater RTs in response to unexpected (surprising) stimuli in the internally driven condition at low uncertainty loads, OA were unable to distinguish between expected and nonexpected stimuli at higher uncertainty loads when the probability of each stimulus type was close to equal. Among OA, better performance on the internally driven, but not externally cued, condition was associated with better global cognitive performance and verbal fluency. CONCLUSIONS: Collectively, these findings provide behavioral evidence of age-related disruptions to bottom-up (externally cued) and top-down (supporting internally driven mental representations) resources to process uncertainty and coordinate task-relevant action. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Age-related differences in prefrontal glutamate are associated with increased working memory decay that gives the appearance of learning deficits.

The ability to use past experience to effectively guide decision-making declines in older adulthood. Such declines have been theorized to emerge from either impairments of striatal reinforcement learning systems (RL) or impairments of recurrent networks in prefrontal and parietal cortex that support working memory (WM). Distinguishing between these hypotheses has been challenging because either RL or WM could be used to facilitate successful decision-making in typical laboratory tasks. Here we investigated the neurocomputational correlates of age-related decision-making deficits using an RL-WM task to disentangle these mechanisms, a computational model to quantify them, and magnetic resonance spectroscopy to link them to their molecular bases. Our results reveal that task performance is worse in older age, in a manner best explained by working memory deficits, as might be expected if cortical recurrent networks were unable to sustain persistent activity across multiple trials. Consistent with this, we show that older adults had lower levels of prefrontal glutamate, the excitatory neurotransmitter thought to support persistent activity, compared to younger adults. Individuals with the lowest prefrontal glutamate levels displayed the greatest impairments in working memory after controlling for other anatomical and metabolic factors. Together, our results suggest that lower levels of prefrontal glutamate may contribute to failures of working memory systems and impaired decision-making in older adulthood.

Age-related enhancement in visuomotor learning by a dual-task.

Many daily activities require performance of multiple tasks integrating cognitive and motor processes. While the fact that both processes go through deterioration and changes with aging has been generally accepted, not much is known about how aging interacts with stages of motor skill acquisition under a cognitively demanding situation. To address this question, we combined a visuomotor adaptation task with a secondary cognitive task. We made two primary findings beyond the expected age-related performance deterioration. First, while young adults showed classical dual-task cost in the early motor learning phase dominated by explicit processes, older adults instead strikingly displayed enhanced performance in the later stage, dominated by implicit processes. For older adults, the secondary task may have facilitated a shift to their relatively intact implicit learning processes that reduced reliance on their already-deficient explicit processes during visuomotor adaptation. Second, we demonstrated that consistently performing the secondary task in learning and re-learning phases can operate as an internal task-context and facilitate visuomotor memory retrieval later regardless of age groups. Therefore, our study demonstrated age-related similarities and differences in integrating concurrent cognitive load with motor skill acquisition which, may in turn, contributes to the understanding of a shift in balance across multiple systems.

Double dissociation in radial and rotational motion sensitivity.

Neurophysiological experiments have shown that a shared region of the primate visual system registers both radial and rotational motion. Radial and rotational motion also share computational features. Despite these neural and computational similarities, prior experiments have disrupted radial, but not rotational, motion sensitivity -a single dissociation. Here we report stimulus manipulations that extend the single dissociation to a double dissociation, thereby showing further separability between radial and rotational motion sensitivity. In Exp 1 bilateral plaid stimuli with or without phase-noise either radiated or rotated before changing direction. College students reported whether the direction changed first on the left or right-a temporal order judgment (TOJ). Phase noise generated significantly larger disruptions to rotational TOJs than to radial TOJs, thereby completing the double dissociation. In Exp 2 we conceptually replicated this double dissociation by switching the task from TOJs to simultaneity judgments (SJs). Phase noise generated significantly larger disruptions to rotational SJs than to radial SJs. This disruption pattern reversed after changing the plaids' motion from same- to opposite-initial directions. The double dissociations reported here revealed distinct dependencies for radial and rotational motion sensitivity. Radial motion sensitivity depended strongly on information about global depth. Rotational motion sensitivity depended strongly on positional information about local luminance gradients. These distinct dependencies arose downstream from the neural mechanisms that detect local linear components within radial and rotational motion. Overall, the differential impairments generated by our psychophysical experiments demonstrate independence between radial and rotational motion sensitivity, despite their neural and computational similarities.

Impaired integration of object feature knowledge in amnestic mild cognitive impairment.

OBJECTIVE: Accessing semantic representations of real-world objects requires integration of multimodal perceptual features that are represented across relevant neocortical areas. Early Alzheimer's disease (AD) neuropathology, including neurofibrillary tangles in the perirhinal cortex as well as disrupted cortico-cortical connectivity, would be expected to disrupt the integration of object features. This integration deficit may underlie AD patients' semantic memory deficits and would be predicted to be more prominent for living objects, which tend to be more defined by sensory features compared with nonliving objects. METHOD: Two experiments were conducted to assess feature integration in cognitively healthy older adults and patients with amnestic mild cognitive impairment (MCI). In both experiments, pictures of real-world objects were presented in congruent or incongruent colors. Participants were instructed to make a speeded color congruency judgment (Experiment 1) or name the presented surface color (Experiment 2). RESULTS: Across experiments, MCI patients showed a selective integration deficit for living, but not nonliving, objects across both experimental paradigms that was consistent with a deterioration in semantic structural representations rather than a deficit in controlled semantic retrieval. Planned secondary analyses with a subset of patients (Experiment 1) for whom PET imaging was available indicated that the degree of impairment was associated with the magnitude of cortical amyloid burden. CONCLUSIONS: These findings suggest that early AD pathology leads to impaired integration of distributed semantic object representations. The development of integration tasks as sensitive markers of early AD pathology may lead to more effective diagnostic tools for early detection and intervention. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Age-related changes in the neural dynamics of bottom-up and top-down processing during visual object recognition: an electrophysiological investigation.

When recognizing objects in our environments, we rely on both what we see and what we know. While older adults often display increased sensitivity to top-down influences of contextual information during object recognition, the locus of this increased sensitivity remains unresolved. To examine the effects of aging on the neural dynamics of bottom-up and top-down visual processing during rapid object recognition, we probed the differential effects of object perceptual ambiguity and scene context congruity on specific EEG event-related potential components indexing dissociable processes along the visual processing stream. Older adults displayed larger behavioral scene congruity effects than young adults. Older adults' larger visual P2 amplitudes to object perceptual ambiguity (as opposed to the scene congruity P2 effects in young adults) suggest continued resolution of perceptual ambiguity that interfered with scene congruity processing, while post-perceptual semantic integration (as indexed by N400) remained largely intact. These findings suggest that compromised bottom-up perceptual processing in healthy aging leads to an increased involvement of top-down processes to resolve greater perceptual ambiguity during object recognition.

Age-related changes in the functional integrity of the phasic alerting system: a pupillometric investigation.

Enhanced processing following a warning cue is thought to be mediated by a phasic alerting response involving the locus coeruleus-noradrenergic (LC-NA) system. We examined the effect of aging on phasic alerting using pupil dilation as a marker of LC-NA activity in conjunction with a novel assessment of task-evoked pupil dilation. While both young and older adults displayed behavioral and pupillary alerting effects, reflected in decreased RT and increased pupillary response under high (tone) versus low (no tone) alerting conditions, older adults displayed a weaker pupillary response that benefited more from the alerting tone. The strong association between dilation and speed displayed by older adults in both alerting conditions was reduced in young adults in the high alerting condition, suggesting that in young (but not older) adults the tone conferred relatively little behavioral benefit beyond that provided by the alerting effect elicited by the target. These findings suggest a functioning but deficient LC-NA alerting system in older adults, and help reconcile previous results concerning the effects of aging on phasic alerting.

Global depth perception alters local timing sensitivity.

Dynamic environments often contain features that change at slightly different times. Here we investigated how sensitivity to these slight timing differences depends on spatial relationships among stimuli. Stimuli comprised bilaterally presented plaid pairs that rotated, or radially expanded and contracted to simulate depth movement. Left and right hemifield stimuli initially moved in the same or opposite directions, then reversed directions at various asynchronies. College students judged whether the direction reversed first on the left or right-a temporal order judgment (TOJ). TOJ thresholds remained similar across conditions that required tracking only one depth plane, or bilaterally synchronized depth planes. However, when stimuli required simultaneously tracking multiple depth planes-counter-phased across hemifields-TOJ thresholds doubled or tripled. This effect depended on perceptual set. Increasing the certainty with which participants simultaneously tracked multiple depth planes reduced TOJ thresholds by 45 percent. Even complete certainty, though, failed to reduce multiple-depth-plane TOJ thresholds to levels obtained with single or bilaterally synchronized depth planes. Overall, the results demonstrate that global depth perception can alter local timing sensitivity. More broadly, the findings reflect a coarse-to-fine spatial influence on how we sense time.

Phasic alerting enhances spatial orienting in healthy aging but not in mild cognitive impairment.

OBJECTIVE: Previous studies in young adults have demonstrated strong functional links between phasic alerting and exogenous orienting. The present study examined changes in the dynamic interaction between these attentional networks in healthy aging and in amnestic mild cognitive impairment. METHOD: Healthy young adults, healthy older adults, and patients with amnestic mild cognitive impairment (MCI) were asked to identify as quickly as possible the color of a target stimulus that appeared within one of 2 peripheral boxes. Orienting was manipulated by a brief flashing of the same (valid cue) or opposite (invalid cue) box in which the target subsequently appeared. Alerting was manipulated by presenting an auditory white noise burst simultaneously with the visual orienting cue on half of the trials. RESULTS: All 3 groups displayed significant alerting and orienting effects but differed in the nature of the interaction between alerting and orienting. As expected, young adults displayed increased orienting under high alerting conditions through a selective enhancement of validly cued targets. While older adults displayed a greater effect of alerting on orienting compared to young adults, MCI patients did not display a significant interaction between attentional networks. CONCLUSIONS: Results provide support for the presence of increased compensatory interactions between attentional networks in healthy aging that may be no longer effective with the emergence of clinical symptoms in MCI. The demonstration of qualitatively distinct effects of healthy aging and MCI suggests that behavioral tests of attentional network interactions may serve as cognitive markers in individuals at increased risk for developing AD. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

What underlies visual selective attention development? Evidence that age-related improvements in visual feature integration influence visual selective attention performance.

Visual selective attention (VSA) improves across childhood. Conjunction search tasks require integrating multiple visual features in order to find a target among distractors and are often used to measure VSA. Motivated by the visual system's architecture and developmental changes in neural connectivity, we predicted that feature integration across separate visual pathways (e.g., color and motion) should develop later than feature integration within the same visual pathways (e.g., luminance and motion). A total of 89 4- to 10-year-old children completed a visual search task that manipulated whether feature integration was between separate parallel visual pathways or within the same visual pathway. We first examined whether color-motion integration was associated with a performance cost relative to luminance-motion integration across childhood. We found that color-motion integration was worse than luminance-motion integration in early childhood but that this difference decreased with age. We also examined whether luminance-motion and color-motion visual search performance developed differently across childhood. Reaction time (RT) visual search slopes for the luminance-motion condition were both stable across childhood and steeper overall than those for the color-motion condition. In contrast, RT search slopes for the color-motion condition became steeperincrease across childhood. Finally, we found that age-related improvements in color-motion integration, relative to luminance-motion integration, were associated with longer color-motion search rates across childhood. These data suggest that age-related improvements in color-motion feature integration may increase competition between color-motion targets and distractors, thereby increasing the amount of time needed to process distractors as nontargets during the selection process.

Forward to the past: Revisiting the role of immediate recognition in the assessment of episodic memory.

Introduction: During the clinical assessment of episodic memory, encoding ability is typically inferred from immediate recall performance. This dependency on effortful retrieval may not be optimal for estimating encoding, particularly in the presence of executive dysfunction. We examined whether a test of immediate recognition memory could meaningfully supplement recall in estimating encoding and provide unique information about memory retention.Method: Fifty older adult outpatients were administered a neuropsychological test battery including original and revised versions of the Hopkins Verbal Learning Test; the former (HVLT) assesses recognition memory immediately after learning trials, while the latter (HVLT-R) assesses only delayed recognition. Hierarchical regressions evaluated the incremental value of immediate recognition in predicting both delayed verbal and visual recognition. ANCOVA was performed on subgroups defined by the number of impaired performances on executive functioning tests (EF-intact, EF-1, EF-2) to examine the influence of executive impairment on measures of immediate recall and recognition. Recall- and recognition-based estimates of verbal memory retention were also compared across groups to determine whether they yield distinct patterns of memory consolidation.Results: Immediate verbal recognition accounted for significant variance in both delayed verbal and visual recognition beyond immediate recall, age, and education. Although subgroups were demographically similar, EF-1 and EF-2 performed significantly worse than EF-intact across verbal and visual memory recall. Contrastingly, there were no group differences in immediate recognition. Subgroups attained similar scores on a conventional, recall-based memory retention measure, but EF-2 showed relatively greater forgetting on a recognition-based retention measure.Conclusions: Immediate verbal recognition is an independent determinant of delayed memory performance but is not captured in current test paradigms. Study results provide proof-of-concept that recognition testing at learning can provide a more comprehensive index of encoding ability than recall alone, may facilitate disentangling memory functions from executive deficits, and could have important downstream implications for estimating memory consolidation.

Alzheimer's disease and the processing of uncertainty during choice task performance: Executive dysfunction within the Hick-Hyman law.

The Hick-Hyman law states that choice response time (RT) increases linearly with increasing information uncertainty. Neuroimaging studies suggest that the representation of uncertainty in support of response generation is mediated by the cognitive control network (CCN), which is disrupted in Alzheimer's disease (AD). Thus, we predicted that patients with AD would be sensitive to increased uncertainty particularly under conditions that place demands on the internal representation of uncertainty, and that choice RT performance under these conditions would be associated with performance on tests of executive function. Cognitively normal older adults (CN) and patients with AD completed card-sorting tasks that separately manipulated either externally cued uncertainty (i.e., number of sorting piles with a fixed probability of each stimulus type) or more internally driven uncertainty (i.e., the probability of each stimulus type with a fixed number of sorting piles). Consistent with our predictions, AD patients were impaired relative to CN particularly on the internally driven uncertainty task, and RT in this task was associated with performance on neuropsychological measures of executive functioning but not episodic memory. We suggest that this pattern of findings is consistent with presumed disruptions to the CCN in AD and provides neuropsychological evidence in support of the role of the CCN in the representation of uncertainty.

Change in retinal structural anatomy during the preclinical stage of Alzheimer's disease.

INTRODUCTION: We conducted a 27-month longitudinal study of mid-life adults with preclinical Alzheimer's disease (AD), using spectral domain optical coherence tomography to compare changes in volume and thickness in all retinal neuronal layers to those of age-matched healthy control subjects. METHODS: Fifty-six older adults (mean age = 65.36 years) with multiple risk factors for AD completed spectral domain optical coherence tomography retinal imaging and cognitive testing at baseline. Twenty-seven months later, they completed the same examinations and an 18F-florbetapir positron emission tomography imaging study. RESULTS: Compared to healthy control subjects, those in the preclinical stage of AD showed a significant decrease in macular retinal nerve fiber layer (mRNFL) volume, over a 27-month follow-up interval period, as well as a decrease in outer nuclear layer and inner plexiform layer volumes and thickness in the inferior quadrant. However, only the mRNFL volume was linearly related to neocortical positron emission tomography amyloid standardized uptake value ratio after controlling for any main effects of age (R2 = 0.103; ρ = 0.017). Furthermore, the magnitude of mRNFL volume reduction was significantly correlated with performance on a task of participants' abilities to efficiently integrate visual and auditory speech information (McGurk effect). DISCUSSION: We observed a decrease in mRNFL, outer nuclear layer, and inner plexiform layer volumes, in preclinical AD relative to controls. Moreover, the largely myelinated axonal loss in the RNFL is related to increased neocortical amyloid-ß accumulation after controlling for age. Volume loss in the RNFL, during the preclinical stage, is not related to performance on measures of episodic memory or problem solving. However, this retinal change does appear to be modestly related to relative decrements in performance on a measure of audiovisual integration efficiency that has been recently advanced as a possible early cognitive marker of mild cognitive impairment.

Detection of Risky Driving Behaviors in the Naturalistic Environment in Healthy Older Adults and Mild Alzheimer's Disease.

Analyzing naturalistic driving behavior recorded with in-car cameras is an ecologically valid method for measuring driving errors, but it is time intensive and not easily applied on a large scale. This study validated a semi-automated, computerized method using archival naturalistic driving data collected for drivers with mild Alzheimer's disease (AD; n = 44) and age-matched healthy controls (HC; n = 16). The computerized method flagged driving situations where safety concerns are most likely to occur (i.e., rapid stops, lane deviations, turns, and intersections). These driving epochs were manually reviewed and rated for error type and severity, if present. Ratings were made with a standardized scoring system adapted from DriveCam®. The top eight error types were applied as features to train a logistic model tree classifier to predict diagnostic group. The sensitivity and specificity were compared among the event-based method, on-road test, and composite ratings of two weeks of recorded driving. The logistic model derived from the event-based method had the best overall accuracy (91.7%) and sensitivity (97.7%) and high specificity (75.0%) compared to the other methods. Review of driving situations where risk is highest appears to be a sensitive data reduction method for detecting cognitive impairment associated driving behaviors and may be a more cost-effective method for analyzing large volumes of naturalistic data.

Differential Contributions of Selective Attention and Sensory Integration to Driving Performance in Healthy Aging and Alzheimer's Disease.

OBJECTIVES: Patients with Alzheimer's disease (AD) demonstrate deficits in cross-cortical feature binding distinct from age-related changes in selective attention. This may have consequences for driving performance given its demands on multisensory integration. We examined the relationship of visuospatial search and binding to driving in patients with early AD and elderly controls (EC). METHODS: Participants (42 AD; 37 EC) completed search tasks requiring either luminance-motion (L-M) or color-motion (C-M) binding, analogs of within and across visual processing stream binding, respectively. Standardized road test (RIRT) and naturalistic driving data (CDAS) were collected alongside clinical screening measures. RESULTS: Patients performed worse than controls on most cognitive and driving indices. Visual search and clinical measures were differentially related to driving behavior across groups. L-M search and Trail Making Test (TMT-B) were associated with RIRT performance in controls, while C-M binding, TMT-B errors, and Clock Drawing correlated with CDAS performance in patients. After controlling for demographic and clinical predictors, L-M reaction time significantly predicted RIRT performance in controls. In patients, C-M binding made significant contributions to CDAS above and beyond demographic and clinical predictors. RIRT and C-M binding measures accounted for 51% of variance in CDAS performance in patients. CONCLUSIONS: Whereas selective attention is associated with driving behavior in EC, cross-cortical binding appears most sensitive to driving in AD. This latter relationship may emerge only in naturalistic settings, which better reflect patients' driving behavior. Visual integration may offer distinct insights into driving behavior, and thus has important implications for assessing driving competency in early AD. (JINS, 2018, 24, 486-497).

Dissociable Effects of Aging and Mild Cognitive Impairment on Bottom-Up Audiovisual Integration.

Effective audiovisual sensory integration involves dynamic changes in functional connectivity between superior temporal sulcus and primary sensory areas. This study examined whether disrupted connectivity in early Alzheimer's disease (AD) produces impaired audiovisual integration under conditions requiring greater corticocortical interactions. Audiovisual speech integration was examined in healthy young adult controls (YC), healthy elderly controls (EC), and patients with amnestic mild cognitive impairment (MCI) using McGurk-type stimuli (providing either congruent or incongruent audiovisual speech information) under conditions differing in the strength of bottom-up support and the degree of top-down lexical asymmetry. All groups accurately identified auditory speech under congruent audiovisual conditions, and displayed high levels of visual bias under strong bottom-up incongruent conditions. Under weak bottom-up incongruent conditions, however, EC and amnestic MCI groups displayed opposite patterns of performance, with enhanced visual bias in the EC group and reduced visual bias in the MCI group relative to the YC group. Moreover, there was no overlap between the EC and MCI groups in individual visual bias scores reflecting the change in audiovisual integration from the strong to the weak stimulus conditions. Top-down lexicality influences on visual biasing were observed only in the MCI patients under weaker bottom-up conditions. Results support a deficit in bottom-up audiovisual integration in early AD attributable to disruptions in corticocortical connectivity. Given that this deficit is not simply an exacerbation of changes associated with healthy aging, tests of audiovisual speech integration may serve as sensitive and specific markers of the earliest cognitive change associated with AD.

Motion discrimination in dementia with Lewy bodies and Alzheimer disease.

OBJECTIVE: Visual processing abilities of patients with dementia with Lewy bodies (DLB) or Alzheimer disease (AD) dementia were assessed psychophysically using a simple horizontal motion discrimination task that engages the dorsal visual processing stream. METHODS: Participants included patients with mild dementia with DLB, AD dementia or Parkinson disease (PD) with dementia (PDD), without dementia with PD, and normal controls. Participants indicated the left or right direction of coherently moving dots that were embedded within dynamic visual noise provided by randomly moving dots. The proportion of coherently moving dots was increased or decreased across trials to determine a threshold at which participants could correctly indicate their direction with greater than 80% accuracy. RESULTS: Motion discrimination thresholds of patients with DLB and PDD were comparable and significantly higher (i.e., worse) than those of patients with AD dementia. The thresholds of patients with AD dementia and patients with PD were normal. These results were confirmed in subgroups of patients with DLB/PDD and AD dementia with autopsy-confirmed disease. A motion discrimination threshold greater than 0.23 distinguished between DLB/PDD and AD dementia with 67% sensitivity and 85% specificity. CONCLUSIONS: Differential deficits in detecting direction of simple horizontal motion suggest that dorsal processing stream dysfunction is greater in DLB and PDD than in AD dementia. Therefore, impaired performance on simple visual motion discrimination tasks that specifically engage occipitoparietal brain regions suggests the presence of Lewy body pathology.