Here, we present the Oxford Cognitive Screen-Plus, a computerised tablet-based screen designed to briefly assess domain-general cognition and provide more fine-grained measures of memory and executive function. The OCS-Plus was designed to sensitively screen for cognitive impairments and provide a differentiation between memory and executive deficits. The OCS-Plus contains 10 subtasks and requires on average 24 min to complete. In this study, 320 neurologically healthy ageing participants (age M = 62.66, SD = 13.75) from three sites completed the OCS-Plus. The convergent validity of this assessment was established in comparison to the ACE-R, CERAD and Rey–Osterrieth. Divergent validity was established through comparison with the BDI and tests measuring divergent cognitive domains. Internal consistency of each subtask was evaluated, and test–retest reliability was determined. We established the normative impairment cut-offs for each of the subtasks. Predicted convergent and divergent validity was found, high internal consistency for most measures was also found with the exception of restricted range tasks, as well as strong test–retest reliability, which provided evidence of test stability. Further research demonstrating the use and validity of the OCS-Plus in various clinical populations is required. The OCS-Plus is presented as a standardised cognitive assessment tool, normed and validated in a sample of neurologically healthy participants. The OCS-Plus will be available as an Android App and provides an automated report of domain-general cognitive impairments in executive attention and memory.
Posterior cortical atrophy is dominated by progressive degradation of parieto-occipital grey and white matter, and represents in most cases a variant of Alzheimer's disease. Patients with posterior cortical atrophy are characterized by increasing higher visual and visuo-spatial impairments. In particular, a key symptom of posterior cortical atrophy is simultanagnosia i.e. the inability to perceive multiple visual objects at the same time. Two neuro-cognitive mechanisms have been suggested to underlie simultanagnosia, either reduced visual short-term memory capacity or decreased visual processing speed possibly resulting from white matter impairments over and above damage to cortical brain areas. To test these distinct hypotheses, we investigated a group of 12 patients suffering from posterior cortical atrophy with homogenous lesion sides in parieto-occipital cortices and varying severity of grey and white matter loss. More specifically, we (i) tested whether impaired short-term memory capacity or processing speed underlie symptoms of simultanagnosia; (ii) assessed the link to grey and white matter damage; and (iii) integrated those findings into a neuro-cognitive model of simultanagnosia in patients with posterior cortical atrophy. To this end, simultaneous perception of multiple visual objects was tested in patients with posterior cortical atrophy mostly with positive Alzheimer's disease biomarkers and healthy age-matched controls. Critical outcome measures were identification of overlapping relative to non-overlapping figures and visuo-spatial performance in tests sensitive to simultanagnosia. Using whole report of briefly presented letter arrays based on the mathematically formulated 'Theory of Visual Attention', we furthermore quantified parameters of visual short-term memory capacity and visual processing speed. Grey and white matter atrophy was assessed by voxel-based morphometry analyses of structural magnetic resonance data. All patients showed severe deficits of simultaneous perception. Compared to controls, we observed a specific slowing of visual processing speed, while visual short-term memory capacity was preserved. In a regression analysis, processing speed was identified as the only significant predictor of simultaneous perception deficits that explained a high degree of variance (70-82%) across simultanagnosia tasks. More severe slowing was also indicative for more severe impairments in reading and scene comprehension. Voxel-based morphometry yielded extensive reductions of grey and white matter in parieto-occipital and thalamic brain areas. Importantly, the degree of individual atrophy of white matter in left superior parietal lobe, but not of any grey matter region, was associated with processing speed. Based on these findings, we propose that atrophy of white matter commonly observed in posterior cortical atrophy leads to slowing of visual processing speed, which underlies the overt clinical symptoms of simultanagnosia.
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