Are judgments of semantic relatedness systematically impaired in Alzheimer's disease?

The Dynamic Interplay between Loss of Semantic Memory and Semantic Learning Capacity: Insight from Neologisms Learning in Semantic Variant Primary Progressive Aphasia

Semantic Variant of Primary Progressive Aphasia (svPPA) has often been considered as a loss of knowledge stored in semantic memory, but might also be due to a general disruption of mechanisms allowing the acquisition, storage, and retrieval of semantic memories. In order to assess any parallelism in svPPA patients between loss of semantic knowledge and inability to acquire new semantic information, we administered a battery of semantic learning tasks to healthy individuals and svPPA patients, where they were requested to learn new conceptual representations and new word forms, and to associate the former with the latter. A strong relation was found between loss of semantic knowledge and disruption of semantic learning: (a) patients with severe svPPA had the lowest scores in the semantic learning tasks; (b) significant correlations were found between scores obtained in semantic learning tasks and scores obtained in semantic memory disorders in svPPA patients.

Stability and change in the organisation of collective memory representations

In this study, we investigated the impact of a highly consequential public event, the July 15 Coup Attempt, on the structure and organisation of events in Turkish collective memory. To do this, we followed up on our earlier work (Mutlutürk, Tekcan, & Boduroglu, 2021) that used the multidimensional scaling approach to identify critical dimensions in public event representational space. Participants rated the similarity of 15 key public events in a pairwise fashion, across three waves of data collection. They were also asked to report for which political party they had voted in the most recent election. We replicated our earlier results that public events were distinguished based on their political and nonpolitical characteristics; political events were clustered based on their specific attributes. Despite substantial stability in the organisation of collective memories across three time points, the post-coup representational space among voters of the ruling party changed, eliminating clusters within the political dimension and resulting in the ruling party achieving a central and anchor status. These findings suggest that, transformative events may have the potential to impact the structure and organisation of collective memory representations and sociopolitical identity may have to do with the stability of collective memories.

Semantic Feature Disturbance in Alzheimer Disease: Evidence from an Object Decision Task

BACKGROUND AND OBJECTIVE

It is widely held that semantic disturbance in Alzheimer disease (AD) involves the loss of distinctive features but the relative sparing of nondistinctive features. Many previous studies of semantic feature disturbance have used cognitively challenging tasks with verbal stimuli that allow for potential cognitive confounds. Our objective was to use a task with lower memory demands to investigate distinctive feature disturbance in AD.

METHODS

We used an object decision task to compare the processing of distinctive and nondistinctive semantic features in people with AD and age-matched controls. The task included six conditions based on the relationship between each prime and target object. We tested the processing of distinctive and nondistinctive features by selectively altering distinctive and nondistinctive semantic features between prime and target pairs.

RESULTS

Performance accuracy was significantly lower for participants with AD than for age-matched controls when distinctive features were manipulated, but no difference was found when nondistinctive features were manipulated.

CONCLUSIONS

Our results provide evidence of semantic content disturbance in AD in the context of a task with low cognitive demands.

Biases for affective versus sexual content in multidimensional scaling analysis: an individual difference perspective

Visual sexual stimuli can motivate sexual behaviors that can risk or enhance health. How one allocates attention to a sexually motivating stimulus may be important for predicting its effect on sexual feelings, sexual risk behaviors, and sexual problems. A large sample (N = 157) of men and women rated the similarity of all possible pairs of photographs of women, which had been pretested to vary in their sexual and affective content. Multidimensional scaling was used to extract two dimensions of sex and affect, including the extent to which each person relied on each dimension in making their similarity judgments. These individual weights were then used to predict sexual variables of interest. Participants who relied more on the affect information judging photograph similarity were more likely to be female, viewed erotica less frequently, reported fewer sexual partners, reported less sexual desire, and more sexual problems. Those who relied more on the erotic content in making their similarity judgments were more likely to be male, viewed more erotica weekly, experienced higher sexual desire, and were more likely to have taken an HIV test. The "double edge sword" of attention weight to affect in sexual cues is discussed for its potential to both enhance and harm sexual health.

The versatility of SpAM: a fast, efficient, spatial method of data collection for multidimensional scaling

Although traditional methods to collect similarity data (for multidimensional scaling [MDS]) are robust, they share a key shortcoming. Specifically, the possible pairwise comparisons in any set of objects grow rapidly as a function of set size. This leads to lengthy experimental protocols, or procedures that involve scaling stimulus subsets. We review existing methods of collecting similarity data, and critically examine the spatial arrangement method (SpAM) proposed by Goldstone (1994a), in which similarity ratings are obtained by presenting many stimuli at once. The participant moves stimuli around the computer screen, placing them at distances from one another that are proportional to subjective similarity. This provides a fast, efficient, and user-friendly method for obtaining MDS spaces. Participants gave similarity ratings to artificially constructed visual stimuli (comprising 2-3 perceptual dimensions) and nonvisual stimuli (animal names) with less-defined underlying dimensions. Ratings were obtained with 4 methods: pairwise comparisons, spatial arrangement, and 2 novel hybrid methods. We compared solutions from alternative methods to the pairwise method, finding that the SpAM produces high-quality MDS solutions. Monte Carlo simulations on degraded data suggest that the method is also robust to reductions in sample sizes and granularity. Moreover, coordinates derived from SpAM solutions accurately predicted discrimination among objects in same-different classification. We address the benefits of using a spatial medium to collect similarity measures.

Multidimensional scaling

The concept of similarity, or a sense of 'sameness' among things, is pivotal to theories in the cognitive sciences and beyond. Similarity, however, is a difficult thing to measure. Multidimensional scaling (MDS) is a tool by which researchers can obtain quantitative estimates of similarity among groups of items. More formally, MDS refers to a set of statistical techniques that are used to reduce the complexity of a data set, permitting visual appreciation of the underlying relational structures contained therein. The current paper provides an overview of MDS. We discuss key aspects of performing this technique, such as methods that can be used to collect similarity estimates, analytic techniques for treating proximity data, and various concerns regarding interpretation of the MDS output. MDS analyses of two novel data sets are also included, highlighting in step-by-step fashion how MDS is performed, and key issues that may arise during analysis. WIREs Cogn Sci 2013, 4:93-103. doi: 10.1002/wcs.1203 This article is categorized under: Psychology > Perception and Psychophysics.

Anomia as a marker of distinct semantic memory impairments in Alzheimer's disease and semantic dementia

OBJECTIVE

Many neurologically constrained models of semantic memory have been informed by two primary temporal lobe pathologies: Alzheimer's disease (AD) and Semantic Dementia (SD). However, controversy persists regarding the nature of the semantic impairment associated with these patient populations. Some argue that AD presents as a disconnection syndrome in which linguistic impairment reflects difficulties in lexical or perceptual means of semantic access. In contrast, there is a wider consensus that SD reflects loss of core knowledge that underlies word and object meaning. Object naming provides a window into the integrity of semantic knowledge in these two populations.

METHOD

We examined naming accuracy, errors and the correlation of naming ability with neuropsychological measures (semantic ability, executive functioning, and working memory) in a large sample of patients with AD (n = 36) and SD (n = 21).

RESULTS

Naming ability and naming errors differed between groups, as did neuropsychological predictors of naming ability. Despite a similar extent of baseline cognitive impairment, SD patients were more anomic than AD patients.

CONCLUSIONS

These results add to a growing body of literature supporting a dual impairment to semantic content and active semantic processing in AD, and confirm the fundamental deficit in semantic content in SD. We interpret these findings as supporting of a model of semantic memory premised upon dynamic interactivity between the process and content of conceptual knowledge.