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Units of measurement (e.g., metre, week, gram) are critically important concepts in everyday life. Little is known about how knowledge of units is represented in the brain or how this relates to other forms of semantic knowledge. As unit terms are intimately connected with numerical quantity, we might expect knowledge for these concepts to be supported by parietally-mediated representations of space, time and magnitude. We investigated knowledge for measurement units in patients with posterior cortical atrophy (PCA), who display profound impairments of spatial and numerical cognition associated with occipital and parietal lobe atrophy. Relative to healthy controls, PCA patients displayed impairments for a range of unit-based knowledge, including the ability to specify the dimension which a unit refers to (e.g., grams measure mass), to select the appropriate units to measure everyday quantities (e.g., grams for sugar) and to determine the relative magnitudes of different unit terms (e.g., gram is smaller than kilogram). In most cases, their performance was also significantly poorer than a patient control group diagnosed with typical Alzheimer's disease. Our results suggest that impairment to systems that code numerical and spatial magnitudes has an effect on non-numerical verbal knowledge for measurement units. Units of measurement appear to lie at the intersection of the brain's verbal and numerical semantic systems, making them a critical class of concepts in which to investigate how magnitude-based codes contribute to verbal semantic representation. • Unit-based knowledge is impaired in PCA. • Deficits on coding of numerical magnitudes may impact non-numerical verbal knowledge. • Unit of measurement may be a tool to help elucidate magnitude-based semantic representations. [ABSTRACT FROM AUTHOR]

Simultanagnosia is a neuropsychological deficit of higher visual processes caused by temporo-parietal brain damage. It is characterized by a specific failure of recognition of a global visual Gestalt, like a visual scene or complex objects, consisting of local elements. In this study we investigated to what extend this deficit should be understood as a deficit related to specifically the visual domain or whether it should be seen as defective Gestalt processing per se. To examine if simultanagnosia occurs across sensory domains, we designed several auditory experiments sharing typical characteristics of visual tasks that are known to be particularly demanding for patients suffering from simultanagnosia. We also included control tasks for auditory working memory deficits and for auditory extinction. We tested four simultanagnosia patients who suffered from severe symptoms in the visual domain. Two of them indeed showed significant impairments in recognition of simultaneously presented sounds. However, the same two patients also suffered from severe auditory working memory deficits and from symptoms comparable to auditory extinction, both sufficiently explaining the impairments in simultaneous auditory perception. We thus conclude that deficits in auditory Gestalt perception do not appear to be characteristic for simultanagnosia and that the human brain obviously uses independent mechanisms for visual and for auditory Gestalt perception. [ABSTRACT FROM AUTHOR]

Spelling is a complex cognitive task where central and peripheral components are involved in engaging resources from many different cognitive processes. The present paper aims to both characterize the oral spelling deficit in a population of patients affected by a neurodegenerative condition and to clarify the nature of the graphemic representation within the currently available spelling models. Indeed, the nature of graphemic representation as a linear or multi-componential structure is still debated. Different hypotheses have been raised about its nature in the orthographic lexicon, with one positing that graphemes are complex objects whereby quantity and identity are separately represented in orthographic representations and can thus be selectively impaired. Posterior cortical atrophy (PCA) is a neurodegenerative condition that mainly affects visuoperceptual and visuospatial functions. Spelling impairments are considered part of the disease. Nonetheless the spelling deficit has received little attention so far and often it has been interpreted in relation to peripheral impairments such as writing difficulties associated with visuoperceptual and visuospatial deficits. In the present study we provide a detailed characterization of the oral spelling profile in PCA. The data suggest that multiple deficits underpin oral spelling problems in PCA, with elements of surface and phonological dysgraphia but also suggesting the involvement of the graphemic buffer. A large phenotypic individual variability is reported. Moreover, the larger proportion and the specific nature of errors involving geminate (i.e., double) as compared to non-geminate (i.e., non-double) letters suggest that a further central impairment might be associated with the abstract graphemic representation of letter numerosity. The present study contributes to the clinical characterization of PCA and to the current debate in the cognitive literature on spelling models; findings, despite not definitive, support the hypothesis that graphemic representations are multidimensional mental objects that separately encode information about grapheme identity and quantity. [ABSTRACT FROM AUTHOR]

Simultanagnosia caused by posterior temporo-parietal brain damage is characterized through an inability to recognize a global Gestalt from an arrangement of single objects while perception of single objects appears widely intact. We asked whether recognition of single objects in simultanagnosia is still intact if objects are really large, i.e. if they exceed the size of a usual computer screen. Single objects were presented in three different sizes: ‘regular’, ’medium’, and ‘large’. Simultanagnosia patients demonstrated a decrease of recognition performance with increasing object size; recognition of ‘large’ objects was significantly impaired while perception of ‘regular’ sized objects was unaffected. The results argue against the traditional view of preserved recognition of single objects in simultanagnosia. They provide evidence for a more general perceptual impairment that emerges irrespective of presenting single or multiple objects, but whenever the visual system has to assemble information over larger spatial distances or other demanding viewing conditions. It appears that perception of large single objects requires intact abilities of dorsal Gestalt processing, in addition to regular functions of ventral object recognition. [ABSTRACT FROM AUTHOR]

A growing amount of empirical data is showing that the ability to manipulate quantities in a precise and efficient fashion is rooted in cognitive mechanisms devoted to specific aspects of numbers processing. The analog number system (ANS) has a reasonable representation of quantities up to about 4, and represents larger quantities on the basis of a numerical ratio between quantities. In order to represent the precise cardinality of a number, the ANS may be supported by external algorithms such as language, leading to a “precise number system”. In the setting of limited language, other number-related systems can appear. For example the parallel individuation system (PIS) supports a “chunking mechanism” that clusters units of larger numerosities into smaller subsets. In the present study we investigated number processing in non-aphasic patients with corticobasal syndrome (CBS) and posterior cortical atrophy (PCA), two neurodegenerative conditions that are associated with progressive parietal atrophy. The present study investigated these number systems in CBS and PCA by assessing the property of the ANS associated with smaller and larger numerosities, and the chunking property of the PIS. The results revealed that CBS/PCA patients are impaired in simple calculations (e.g., addition and subtraction) and that their performance strongly correlates with the size of the numbers involved in these calculations, revealing a clear magnitude effect. This magnitude effect was correlated with gray matter atrophy in parietal regions. Moreover, a numeral-dots transcoding task showed that CBS/PCA patients were able to take advantage of clustering in the spatial distribution of the dots of the array. The relative advantage associated with chunking compared to a random spatial distribution correlated with both parietal and prefrontal regions. These results shed light on the properties of systems for representing number knowledge in non-aphasic patients with CBS and PCA. [ABSTRACT FROM AUTHOR]

Abstract: The integration of visual elements into global perception seems to be implemented separately to single object perception. This assumption is supported by the existence of patients with simultanagnosia who can identify single objects but are incapable of integrating multiple visual items. We investigated a case of simultanagnosia due to posterior cortical atrophy without structural brain damage who demonstrated an incomplete simultanagnosia. The patient successfully recognized a global stimulus in one trial but failed to do so just a few seconds later. Using event-related fMRI, we contrasted post hoc selected trials of successful global perception with trials of global recognition failure. We found circumscribed clusters of activity at the right and left primary intermediate sulci and a bilateral cluster at the ventral precuneus. The integration of multiple visual elements resulting in a conscious perception of their gestalt seems to rely on these bilateral structures in the human lateral and medial inferior parietal cortex. [Copyright &y& Elsevier]

To successfully move through the world, the brain constructs spatial representations that situate the body within the environment. Communicating spatial directions poses specific challenges to this process, in part because the format through which the information is communicated must be interpreted to match the visual scene the navigator is viewing while traversing that space. For example, if a navigator needs to turn left to reach a goal, the information may be presented in the form of words ("turn left"), schemas (arrows pointing left), or images of the specific left turn. Previous research has suggested unique representations exist for spatial directions within and across modalities. Behavioral data reveal, for instance, that interpreting images seems to require spatial information, whereas words or schemas can be processed using a visual-matching strategy. In the current pre-registered study, we tested two patients with posterior cortical atrophy, who did not have spatial neglect, to determine whether they had general impairments interpreting spatial directions across formats, or specific impairments in particular formats. Our results are consistent with the specific impairment prediction, supporting the idea that interpreting spatial directions in images requires action-relevant spatial processing. We conducted single-case analyses for the patients we tested in comparison to a group of non-clinically diagnosed older adults. Of the two patients, one showed a classical dissociation between a color control task and spatial directions across all modalities. This patient also showed a classical dissociation between images (most impaired) and schemas, and between schemas and words (least impaired). Our findings lend support for a hypothesized hub in the spatial navigation network, which converts format-specific information into actionable spatial directions, and has implications for designing the built environment to optimize for spatial behavior. • Posterior cortical atrophy (PCA) is a neurodegenerative condition affecting the parietal lobes • We tested two PCA patients on spatial directions in images, words, and schemas • One patient was unimpaired. The other was impaired on images, not words or schemas • Results suggest distinct neural processing of the different formats • Giving PCA patients spatial directions in words or schemas may improve navigation [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is now conceptualized as a biological entity defined by amyloid and tau deposition and neurodegeneration, with heterogeneous clinical presentations. With the aid of in vivo biomarkers, clinicians are better poised to examine clinical syndromic variability arising from a common pathology. Word retrieval deficits, measured using verbal fluency and confrontation naming tests, are hallmark features of the early clinical stages of the amnestic presentations of AD, specifically in category fluency and naming with relatively spared letter fluency. As yet, there is no consensus regarding performance on these tests in atypical clinical phenotypes of AD, including posterior cortical atrophy (PCA) and logopenic primary progressive aphasia (lvPPA), in individuals who are amyloid-positive (Aβ+) but present with different clinical profiles and patterns of neurodegeneration compared to amnestic AD. The goal of the current study is to determine how Aβ+ individuals across the syndromic spectrum of AD perform on three different word retrieval tasks. A secondary goal is to determine the neuroanatomical substrates underlying word retrieval performance in these Aβ+ individuals. Thirty-two Aβ+ participants with the amnestic presentation, 16 with Aβ+ PCA, 22 with Aβ+ lvPPA, and 99 amyloid-negative (Aβ-) control participants were evaluated with verbal fluency and visual confrontation naming tests as well as high-resolution MRI. The Aβ+ patient groups were rated at very mild or mild levels of severity (CDR 0.5 or 1) and had comparable levels of global cognitive impairment (average MMSE = 23.7 ± 3.9). Behaviorally, we found that the word retrieval profile of PCA patients is comparable to that of amnestic patients, characterized by intact letter fluency but impaired category fluency and visual confrontation naming, while lvPPA patients demonstrated impairment across all tests of word retrieval. Across all AD variants, we observed that letter fluency was associated with cortical thickness in prefrontal, central precuneus, lateral parietal and temporal cortex, while category fluency and naming were associated with cortical thickness in left middle frontal gyrus, posterior middle temporal gyrus, and lateral parietal cortex. Visual confrontation naming was uniquely associated with atrophy in inferior temporal and visual association cortex. We conclude that a better understanding of the word retrieval profiles and underlying neurodegeneration across the AD syndromic spectrum will help improve interpretation of neuropsychological profiles with regard to the localization of neurodegeneration, particularly in the atypical AD variants. • PCA and amnestic AD showed intact letter but impaired category fluency and naming. • lvPPA demonstrated impairment across all tests of word retrieval. • Each task was associated with atrophy in overlapping and unique cortical regions. [ABSTRACT FROM AUTHOR]