Visual object recognition in multiple sclerosis

Deficits in tasks measuring visual processing have been earlier reported in studies of MS. Yet, the nature and severity of visual-processing deficits in MS remains unclear. We used a new method in order to measure the different stages of visual processing in object recognition: shape recognition, familiarity recognition, semantic categorization, and identification with naming. Six two-choice reaction-time tasks were presented to 30 MS patients and 15 healthy controls. The patients were divided into cognitively preserved and cognitively deteriorated study groups according to their cognitive status. The purpose was to find out whether deficits at specific stages of visual processing can be found in cognitively deteriorated MS patients. Cognitively deteriorated MS patients did not perform as well as cognitively preserved MS patients or healthy controls. They were slower already at the early stage of visual processing where discrimination of whole objects from scrambled ones was required. They also had higher error rates in tasks requiring object familiarity detection and object identification with naming. Thus, cognitively deteriorated MS patients had difficulties in visual shape recognition and semantic-lexical processing. However, variation of performances was large within both of the patient groups indicating that even patients without a generalized cognitive decline may have deficits in some stages of the visual processing. We suggest that because of the heterogeneity of the patients, every single case needs to be examined separately in order to identify the possible deficits in visual processing.     

Are faces special in Alzheimer's disease? Cognitive conceptualisation, neural correlates, and diagnostic relevance of impaired memory for faces and names

Memory for faces and names has increasingly become a focus of cognitive assessment and research in Alzheimer's disease (AD). This paper reviews evidence from cognitive and clinical neuroscience regarding the question of whether AD is associated with a specific deficit in face recognition, face-name association, and retrieval of semantic information and names. Cognitive approaches conceptualizing face recognition and face-name association have revealed that, compared to other types of visual stimuli, faces are "special" because of their complexity and high intraclass similarity, and because their association with proper names is arbitrary and unique. Neuroimaging has revealed that due to this particular status, face perception requires a complex interplay of highly specialized secondary visual areas located in the occipitotemporal cortex with a widely distributed system of cortical areas subserving further task-dependent processing. Our review of clinical research suggests that AD-related deficits in face recognition are primarily due to mnestic rather than perceptual deficits. Memory for previously studied or famous faces is closely related to mediotemporal and temporocortical brain regions subserving episodic and semantic memory in general, suggesting that AD-related impairments in this domain are due to neural degeneration in these areas. Despite limited specificity due to the apparent absence of a "genuine" domain-specific deficit of face memory in AD, testing memory for faces and names is useful in clinical contexts, as it provides highly sensitive indices of episodic and semantic memory performance. Therefore, clinical assessment of face memory can usefully contribute to early detection of memory deficits in prodromal and initial stages of AD, and represents a basis for further attempts at rehabilitation. Further advantages, such as ecological validity, high task comprehensibility and, in the case of novel face learning, independence from premorbid intelligence level, render measures of face recognition valuable for clinical assessment in early AD.     

The Semantic Object Retrieval Test (SORT) in normal aging and Alzheimer disease.

OBJECTIVE: To characterize performance on a test of semantic object retrieval (Semantic Object Retrieval Test-SORT) in healthy, elderly subjects and patients with Alzheimer disease (AD). BACKGROUND: Although the initial presentation of patients with AD often reflects impairment in delayed recall for verbally encoded memory, common complaints of patients with early AD are actually related to semantic memory impairment. DESIGN: Thirty-eight AD patients and 121 healthy aging controls enrolled in an Alzheimer's Disease Center received a battery of standard neuropsychologic tests including the SORT. RESULTS: Compared with normal controls, AD patients had SORT memory impairments with significantly more false positive memory errors, fewer correctly produced names, and more substitutions in the name production aspect of the test. SORT had robust test-retest reliability in normals. CONCLUSIONS: The SORT task provides a direct, specific assessment of semantic memory, and has now been administered to 121 healthy, aging controls for normative ranges of performance, and to AD patients. The task detected semantic memory deficits in approximately half of patients with mild-moderate AD, which is comparable to other studies assessing semantic deficits in AD with less specific measures.     

Semantic knowledge in mild cognitive impairment and mild Alzheimer's disease

The aim of this study was to investigate memory in patients with mild cognitive impairment (MCI) and mild Alzheimer's disease (AD). Ten patients with MCI, 11 with AD and a group of age and education matched healthy control participants were assessed on a comprehensive battery of semantic memory tests, including traditional semantic memory measures and a non-verbal test of knowledge of object use. The MCI group was impaired on tests of category fluency and all three conditions of an object knowledge test (matching to recipient, function and action), plus a difficult object-naming test. The mild AD group showed additional impairments on traditional measures of semantic memory, including naming high frequency items, comprehension and semantic association. Together these findings suggest that semantic memory impairments occur early in the course of AD, more specifically in patients with "amnesic" MCI, and provide further evidence that impaired category fluency reflects semantic breakdown.     

Early episodic memory impairments in Alzheimer's disease

Patients with Alzheimer's disease (AD) show early episodic memory impairments. Such deficits reflect specific impairments affecting one or several stages of encoding, storage and retrieval processes. However, AD patients not only have great difficulty retrieving memories and information but also suffer from distortions of memory, as intrusions and false recognitions. Intrusions can be defined as the unintentional recall of inappropriate information in a laboratory-learning tasks such as word-list recall and story recall. False recognition refers to the erroneous recognition of information that was not previously presented. The first objective of this review is to present studies from the literature that allowed a better understanding of the nature of episodic memory deficits in AD, and to examine recent research on false memories. The second part of this review is aimed at presenting recent research conducted on prospective memory (PM) in Alzheimer's disease. Prospective memory situations involve forming intentions and then realizing those intentions at some appropriate time in the future. Everyday examples of prospective memory include remembering to buy bread on the way home from work, remembering to give friends a message upon next encountering them, and remembering to take medication. Patients suffering from AD show difficulties in performing prospective tasks in daily life, according to the complaints of their care givers, and these difficulties are massively present at the first stages of the disease. Nevertheless, very few studies have been dedicated to this subject, although the evaluation of PM could be helpful for the early diagnosis of AD.     

Learning and forgetting new names and objects in MCI and AD

We studied how subjects with mild cognitive impairment (MCI), early Alzheimer's disease (AD) and age-matched controls learned and maintained the names of unfamiliar objects that were trained with or without semantic support (object definitions). Naming performance, phonological cueing, incidental learning of the definitions and recognition of the objects were tested during follow-up. We found that word learning was significantly impaired in MCI and AD patients, whereas forgetting patterns were similar across groups. Semantic support showed a beneficial effect on object name retrieval in the MCI group 8 weeks after training, suggesting that the MCI patients’ preserved semantic memory can compensate for impaired episodic memory. The MCI group performed equally well as the controls in the tasks measuring incidental learning and recognition memory, whereas the AD group showed impairment in this respect. Both the MCI and the AD group benefited less from phonological cueing than the controls. Our findings indicate that word learning is compromised in both MCI and AD, whereas long-term retention of newly learned words is not affected to the same extent. Incidental learning and recognition memory seem to be well preserved in MCI.     

Gesture comprehension,knowledge and production in Alzheimer’s disease

Background and purpose: Although apraxia is a typical consequence of Alzheimer’s disease (AD), the profile of apraxic impairments is still subject to debate. Here, we analysed apraxia components in patients with AD with mild‐to‐moderate or moderately severe dementia. Methods: Thirty‐one patients were included. We first evaluated simple gestures, that is, the imitation of finger and hand configurations, symbolic gestures (recognition, production on verbal command and imitation), pantomimes (recognition, production on verbal command, imitation and production with the object), general knowledge and complex gestures (tool–object association, function–tool association, production of complex actions and knowledge about action sequences). Tests for dementia (Mini Mental State Examination and the Dementia Rating Scale), language disorders, visual agnosia and executive function were also administered. Results: Compared with controls, patients showed significant difficulties (P ≤ 0.01) in subtests relating to simple gestures (except for the recognition and imitation of symbolic gestures). General knowledge about tools, objects and action sequences was less severely impaired. Performance was frequently correlated with the severity of dementia. Multiple‐case analyses revealed that (i) the frequency of apraxia depended on the definition used, (ii) ideomotor apraxia was more frequent than ideational apraxia, (iii) conceptual difficulties were slightly more frequent than production difficulties in the early stage of AD and (iv) difficulties in gesture recognition were frequent (especially for pantomimes). Conclusion: Patients with AD can clearly show gesture apraxia from the mild–moderate stage of dementia onwards. Recognition and imitation disorders are relatively frequent (especially for pantomimes). We did not find conceptual difficulties to be the main problem in early‐stage AD.     

Visual object recognition deficits in early Parkinson's disease

The nature of the visual perception deficits in Parkinson's disease (PD) has remained unclear. The present study explored whether there emerge deficits in the different stages of visual object recognition in early PD. Twenty-eight patients and 14 healthy controls were studied. A set of reaction time tasks were applied to measure the different stages of object recognition. The results indicate some selective problems in both basic perceptual and semantic visual processing at an early stage of cognitive deterioration in PD.     

Perception, attention, and working memory are disproportionately impaired in dementia with Lewy bodies compared with Alzheimer's disease

OBJECTIVE: To test the hypotheses that visuoperceptual and attentional ability are disproportionately impaired in patients having dementia with Lewy Bodies (DLB) compared with Alzheimer's disease (AD). METHODS: A comprehensive battery of neuropsychological tasks designed to assess working, episodic, and semantic memory, and visuoperceptual and attentional functions was given to groups of patients with DLB (n=10) and AD (n=9), matched for age, education, and mini mental state examination (MMSE), and to normal controls (n=17). RESULTS: Both patient groups performed equally poorly on tests of episodic and semantic memory with the exception of immediate and delayed story recall, which was worse in the AD group. Digit span was by contrast spared in AD. The most striking differences were on tests of visuoperceptual/spatial ability and attention. Whereas patients with AD performed normally on several subtests of the visual object and space perception battery, the DLB group showed substantial impairments. In keeping with previous studies, the AD group showed deficits in selective attention and set shifting, but patients with DLB were more impaired on virtually every test of attention with deficits in sustained, selective, and divided attention. CONCLUSIONS: Patients with DLB have substantially greater impairment of attention, working memory, and visuoperceptual ability than patients with AD matched for overall dementia severity. Semantic memory seems to be equally affected in DLB and AD, unlike episodic memory, which is worse in AD. These findings may have relevance for our understanding of the genesis of visual hallucinations, and the differential diagnosis of AD and DLB.     

Perceptual and Semantic Representations at Encoding Contribute to True and False Recognition of Objects

When encoding new episodic memories, visual and semantic processing is proposed to make distinct contributions to accurate memory and memory distortions. Here, we used fMRI and preregistered representational similarity analysis to uncover the representations that predict true and false recognition of unfamiliar objects. Two semantic models captured coarse-grained taxonomic categories and specific object features, respectively, while two perceptual models embodied low-level visual properties. Twenty-eight female and male participants encoded images of objects during fMRI scanning, and later had to discriminate studied objects from similar lures and novel objects in a recognition memory test. Both perceptual and semantic models predicted true memory. When studied objects were later identified correctly, neural patterns corresponded to low-level visual representations of these object images in the early visual cortex, lingual, and fusiform gyri. In a similar fashion, alignment of neural patterns with fine-grained semantic feature representations in the fusiform gyrus also predicted true recognition. However, emphasis on coarser taxonomic representations predicted forgetting more anteriorly in the anterior ventral temporal cortex, left inferior frontal gyrus and, in an exploratory analysis, left perirhinal cortex. In contrast, false recognition of similar lure objects was associated with weaker visual analysis posteriorly in early visual and left occipitotemporal cortex. The results implicate multiple perceptual and semantic representations in successful memory encoding and suggest that fine-grained semantic as well as visual analysis contributes to accurate later recognition, while processing visual image detail is critical for avoiding false recognition errors.SIGNIFICANCE STATEMENT People are able to store detailed memories of many similar objects. We offer new insights into the encoding of these specific memories by combining fMRI with explicit models of how image properties and object knowledge are represented in the brain. When people processed fine-grained visual properties in occipital and posterior temporal cortex, they were more likely to recognize the objects later and less likely to falsely recognize similar objects. In contrast, while object-specific feature representations in fusiform gyrus predicted accurate memory, coarse-grained categorical representations in frontal and temporal regions predicted forgetting. The data provide the first direct tests of theoretical assumptions about encoding true and false memories, suggesting that semantic representations contribute to specific memories as well as errors.     

Visual object and face processing in mild-to-moderate Alzheimer's disease: from segmentation to imagination

Little is known about the fate of higher level visual perception and visual mental imagery in the early stages of Alzheimer's disease (AD). In this study, we assessed these abilities in a group of mild-to-moderate AD patients using tasks selected to satisfy two main criteria. First, they have been shown to be sensitive to impairments of perception and imagery caused by other neurological conditions. Second, they test specific stages of visual perception and cognition in a reasonably selective manner. These stages were (in their normal order of occurrence during perception): the segmentation of different local points of the visual field into regions belonging to distinct objects; the representation of the shapes of these segmented regions in the image; the construction of more abstract shape representations that possess constancy over changes in size, location, orientation or illumination (assessed separately for faces and objects); the use of these perceived shape representations to access stored shape representations; and the access of lexical semantic representations from these high-level visual representations. Additional tasks tested the top-down activation of earlier visual representations from the semantic level in visual mental imagery. Our findings indicate small, but in most cases reliable, impairments in visual perception, which are independent of degree of cognitive decline. Deficits in basic shape processing influenced performance on some higher level visual tasks, but did not contribute to poor performance on face processing, or to the profound deficit on object naming. The latter of these is related to semantic-lexical impairment.     

Visual attention impairments in Alzheimer's disease

BACKGROUND: Impaired attention can hinder information processing at multiple levels and may explain aspects of functional decline in aging and dementia. Impairments of attention in early AD may contribute to performance reductions in other cognitive domains, including memory and executive functions.Method:- The authors analyzed the scores on a battery of tests of attention and cognitive abilities in 64 older individuals: 42 with mild AD and 22 control subjects without dementia. The authors tested the hypotheses that patients with AD would have impairments of visual attention, and that these impairments would correlate with dysfunction in other key cognitive domains. RESULTS: Patients with AD performed significantly worse than control subjects on measures of sustained attention, divided attention, selective attention, and visual processing speed. The differences were not due to differences in age, education, or basic visual function. Strong relationships were identified between reduced attention skills and overall cognitive impairment. CONCLUSIONS: Deterioration of attention abilities occurs in early stages of AD, and likely contributes to functional decline in these patients. More routine assessment of visual attention deficits could give a more accurate measure of functionally useful perception in patients with AD who show normal visual acuity and visual fields, perhaps providing useful clues to diagnosis and staging.     

Routine clinical diagnosis of primary progressive non-fluent aphasia

It may be difficult to distinguish between a primary progressive aphasia at a very mild stage from the beginning of Alzheimer's disease (AD). However, this may be achieved by carrying out simple neuro-psychological tests. Nine non-fluent PPA (NFPPA) and 76 AD patients with comparable MMSE as well as 58 control subjects were evaluated using simple tests: MMSE, fluency, apraxia, naming, digital span, story memory, 5 words memory test. NFPPA patients had significantly impaired functions during the semantic category fluency and naming tests as compared to AD patients, whereas they showed a better delayed recall of the 5 words and story memory tests. As compared to AD, MMSE of NFPPA patients was also better in the time orientation and word recall sub-tests, although inferior in words repetition and language items. Thus, with comparable MMSE, NFPPA patients have more lexico-semantic difficulties, but a better delayed verbal memory than AD patients. These simple tests easily confirm the language impairment of NFPPA patients as opposed to the mnestic difficulties of AD, even at very early stages of these pathologies.     

Lexical processing in Spanish patients with probable Alzheimer's disease

Twenty Spanish patients with probable Alzheimer's disease (AD) and 20 matched controls were given a battery of 17 tasks involving object recognition and the spoken and written perception and production of words and non-words. The AD patients were significantly impaired on nine of the tasks. Prominent among these were tasks that involve semantic processing, though non-word reading was also impaired. Performance on a category fluency task best discriminated AD patients from controls. It is proposed that impairment to semantic processing underlies most of the observed deficits on lexical processing tasks in patients with early AD, but that non-word reading may be sensitive to additional, mild impairments to phonological representations caused by extension of the degenerative process from anterior to posterior temporal regions.     

Episodic and semantic memory in mild cognitive impairment

Little is known about episodic and semantic memory in the early predementia stage of Alzheimer's disease (AD), which is referred to as mild cognitive impairment (MCI). To explore person knowledge, item recognition and spatial associative memory, we designed the Face Place Test (FPT). A total of 75 subjects participated: 22 patients with early AD, 24 with MCI and 29 matched controls. As predicted, AD patients showed significant deficits in person naming, item recognition and recall of spatial location (placing). Surprisingly, subjects with MCI were also impaired on all components. There was no significant difference between AD and MCI except on the placing component. Analysis of the relationship between semantic (naming) and episodic (recognition and placing) components of the FPT revealed a significant association between the two episodic tasks, but not between episodic and semantic performance. Patients with MCI show deficits of episodic and semantic memory. The extent of impairment suggests dysfunction beyond the medial temporal lobe. The FPT might form the basis of a sensitive early indicator of AD.     

Registering eye movements during reading in Alzheimer’s disease: Difficulties in predicting upcoming words

Reading requires the fine integration of attention, ocular movements, word identification, and language comprehension, among other cognitive parameters. Several of the associated cognitive processes such as working memory and semantic memory are known to be impaired by Alzheimer’s disease (AD). This study analyzes eye movement behavior of 18 patients with probable AD and 40 age-matched controls during Spanish sentence reading. Controls focused mainly on word properties and considered syntactic and semantic structures. At the same time, controls’ knowledge and prediction about sentence meaning and grammatical structure are quite evident when we consider some aspects of visual exploration, such as word skipping, and forward saccades. By contrast, in the AD group, the predictability effect of the upcoming word was absent, visual exploration was less focused, fixations were much longer, and outgoing saccade amplitudes were smaller than those in controls. The altered visual exploration and the absence of a contextual predictability effect might be related to impairments in working memory and long-term memory retrieval functions. These eye movement measures demonstrate considerable sensitivity with respect to evaluating cognitive processes in Alzheimer’s disease. They could provide a user-friendly marker of early disease symptoms and of its posterior progression.     

Hemispheric asymmetries of hypometabolism associated with semantic memory impairment in Alzheimer's disease: a study using positron emission tomography with fluorodeoxyglucose-F18

Considerable disagreement exists about the neuroanatomical basis of conceptual-semantic impairments observed in a subgroup of patients with Alzheimer's disease (AD) at mild to moderate stages of the disease. Several studies of groups of patients have shown correlations between focal hypometabolism or hypoperfusion in left hemispheric areas and measures of verbal semantic memory impairment in AD patients. The question remains, however, whether left hemispheric hypometabolism is sufficient to produce such impairment in the single case and whether nonverbal semantic knowledge is also affected. We used positron emission tomography (PET) with fluorodeoxyglucose-F18 (FDG), statistical parametric mapping (SPM), and tests of verbal and nonverbal semantic memory in 11 AD patients with a mean score on the Mini-Mental State Examination of 22.6 (+/-2.8). Naming impairment was significantly associated with left hemispheric asymmetry of hypometabolism on a single-case basis. Our correlation analysis showed that metabolism in left anterior temporal, posterior inferior temporal, inferior parietal and medial occipital areas (Brodmann areas: 21/38, 37, 40 and 19) correlated with both verbal and nonverbal semantic performance. We conclude that left hemispheric synaptic dysfunction, as measured by regional glucose hypometabolism, was sufficient to produce semantic impairments in our patients. The majority of areas affected in our patients with semantic impairments were involved in multimodal or supramodal (verbal and nonverbal) semantic knowledge.     

The use of semantic knowledge in Alzheimer's disease: evidence for impairments of attention

The ability to access and use semantic knowledge was examined in 25 patients with Alzheimer's disease (AD) and 31 healthy controls. The AD patients exhibited intact automatic activation of semantic relationships on a semantic priming task. They also made active use of category information on a recognition memory test. However, the patients did not use semantic information to generate expectations on the semantic priming task and were inconsistent in their use of category information on the memory test. It is suggested that attentional deficits underlie the observed impairments and may in fact help explain the patterns of performance across tasks differing widely in their overt cognitive demands.     

Can the emotional connotation of concepts modulate the lexico-semantic deficits in Alzheimer's disease?

Semantic memory impairments are a common symptom of Alzheimer's disease (AD) and may occur at a relatively early stage. These disturbances can be evidenced by a hyperpriming effect (greater semantic priming in AD patients than in controls). Up till now, very few studies of semantic memory have included emotionally charged concepts. Our aim was therefore to study the semantic processing of such concepts, as opposed to neutral ones, in early AD. Given that emotional processes are relatively preserved at the beginning of the disease compared with other cognitive functions, we expected that an emotional connotation would influence the spreading activation of words and affect some of the impairments in semantic processing. We administered a semantic priming task (lexical decision task) implicitly assessing semantic memory to 26 patients with AD and 26 normal controls. Primes and targets either had a semantic relationship (e.g. tiger-lion), a semantic and emotional (positive or negative) relationship (e.g. slap-smack) or no relationship at all (e.g. chair-horse), or else belonged to a word-nonword condition (e.g. window-inuly). Compared with controls, the patients showed pathological hyperpriming effects in all conditions, especially in the emotional conditions. Hyperpriming implies a deterioration in specific attributes, as it is difficult to tell two concepts apart once their distinctive attributes have been lost. These results suggest that emotional concepts, like neutral ones, lose some of their distinctive attributes in early AD, and as the emotional processes are preserved, there is greater similarity between close emotional concepts than between close neutral concepts.     

Semantic memory impairment in the earliest phases of Alzheimer's disease

The presence and the nature of semantic memory dysfunction in Alzheimer's disease (AD) have been widely debated. This study aimed to determine the frequency of impaired semantic test performances in mild AD and to study whether incipient semantic impairments could be identified in predementia AD. Five short neuropsychological tests sensitive to semantic memory and easily applicable in routine practice were administered to 102 patients with mild AD (Mini-Mental State Examination score above 19), 22 predementia AD patients and 58 healthy subjects. 'Category fluency' and 'naming of famous faces' were the most frequently impaired tests in both patient groups. The study demonstrated that impairments on semantically related tests are common in mild AD and may exist prior to the clinical diagnosis. The results imply that assessment of semantic memory is relevant in the evaluation of patients with suspected AD.