Marcella Laiacona

WHAT ARE THE FACTS OF SEMANTIC CATEGORY-SPECIFIC DEFICITS? A CRITICAL REVIEW OF THE CLINICAL EVIDENCE

In this study we provide a critical review of the clinical evidence available to date in the field of semantic category-specific deficits. The motivation for undertaking this review is that not all the data reported in the literature are useful for adjudicating among extant theories. This project is an attempt to answer two basic questions: (1) what are the categories of category-specific deficits, and (2) is there an interaction between impairment for a type of knowledge (e.g., visual, functional, etc.) and impairment for a given category of objects (e.g., biological, artefacts, etc.). Of the 79 case studies in which the reported data are sufficiently informative with respect to the aims of our study, 61 presented a disproportionate impairment for biological categories and 18 presented a disproportionate impairment for artefacts. Less than half of the reported cases provide statistically and theoretically interpretable data. Each case is commented upon individually. The facts that emerge from our critical review are that (1) the categories of category-specific semantic deficits are animate objects, inanimate biological objects, and artefacts (the domain of biological objects fractionates into two independent semantic categories: animals, and fruit/vegetables); (2) the types of category-specific deficits are not associated with specific types of conceptual knowledge deficits. Other conclusions that emerge from our review are that the evidence in favour of the existence of cases of reliable category-specific agnosia or anomia is not very strong, and that the visual structural description system functions relatively autonomously from conceptual knowledge about object form.

Perceptual and Associative Knowledge in Category Specific Impairment of Semantic Memory: A Study of two Cases

We report two head-injured patients whose knowledge of living things was selectively disrupted. Their semantic knowledge was tested with naming and verbal comprehension tasks and a verbal questionnaire. In all of them there was consistent evidence that knowledge of living things was impaired and that of non-living things was relatively preserved. The living things deficit emerged irrespective of whether the question tapped associative or perceptual knowledge or required visual or non visual information. In all tasks the category effect was still significant after the influence on the performance of the following variables was partialled out: word frequency, concept familiarity, prototypicality, name agreement, image agreement and visual complexity. In the verbal questionnaire dissociations were still significant even after adjustment for the difficulty of questions for normals, that had proven greater for living things. Besides diffuse brain damage, both patients presented with a left posterior temporo-parietal lesion.

A cancellation test: its reliability in assessing attentional deficits in Alzheimer's disease.

The aim of the study is to provide (i) a standardized procedure for a Cancellation Test of Digits, designed to assess in the visual modality selective attention deficits in patients with Alzheimers disease, and (ii) a detailed analysis of how patients cope with it. Age-, education-, and sex-adjusted normative scores earned by 352 healthy controls are set forth, as well as data yielded by the Digit Cancellation Test in 74 Alzheimer patients, in 26 patients with a CT-assessed frontal lobe lesion and in a group of 24 healthy subjects urged to perform the task with a shortened time-constraint. Findings include discriminant power of Alzheimer patients versus healthy controls, sensitivity to cognitive evolution of the dementing process and analysis of errors. Attention data failed to supply psychometric support for the posterior-to-anterior algorithm of progressive cortical encroachment of Alzheimers disease suggested by PET-findings. Emphasis is put on methodological aspects of neuropsychological research on Alzheimer patients and on the analysis of processing components of the tests employed. Results are discussed in the light of the relationships between psychometric assessments and related functions, and underlying neuronal degeneration.

Group aggregates and individual reliability: The case of verbal short-term memory

Two experiments examined the generalizability of the effects of word length and phonological similarity with visual and auditory presentation in immediate verbal serial ordered recall. In Experiment 1, data were collected from 251 adult volunteers drawn from a broad cross-section of the normal population. Word length and phonological similarity in both presentation modes significantly influenced the group means. However, 43% of the subjects failed to show at least one of the effects, and the likelihood that effects appeared was highly correlated with verbal memory span. In Experiment 2, 40 subjects of the original sample were retested, 20 of whom had failed to show one or more effects in Experiment 1. Whether or not an effect had appeared for individual subjects on the first test session was a poor predictor of whether the effect would appear on retest. Finally, an analysis of subject reports demonstrated that the patterns of experimental data could be accounted for in part by the strategies that subjects reported using, and the effect of strategy was independent of the effect of span. The implications of these findings for theories of verbal short-term memory are discussed.

Gender affects word retrieval of certain categories in semantic fluency tasks.

Recent studies suggest that gender influences phonetically-cued fluency and some semantic memory tasks. In this study we analysed the effect of demographic variables on semantic fluency tasks. The semantic categories considered were: animals, fruits, tools and vehicles. The influence of age and education was common to all the categories considered and seems a general characteristic of the semantic fluency task. Gender had a significant effect only with fruits and tools, but a diverging role: females fared better with fruits and males with tools. We discuss whether the source of the gender effect should be located at the level of the semantic representation of each category or at the level of item recall in the short time (one minute) granted for the task.

Composite neuropsychological batteries and demographic correction: Standardization based on equivalent scores, with a review of Published Data

Equivalent Scores (ES; Capitani & Laiacona, 1988) is a 5-point scale that offers a solution to the problem of standardizing neuropsychological scores after adjustment for age and education, given that the common z-standardization is not generally applicable in these cases. ES are discussed, and their properties and limits are compared with those of z-standardization. In a battery of ES-standardized tests, the average ES (AES) for the whole battery can provide a measure of the overall cognitive level, free of the influence of age and education. We report empirical data from a battery composed of 10 ES-standardized tests, in order to discuss general properties of ES standardization. The expected mean of the AES is constant, regardless of the number or type of tests included. The standard deviation of the AES, however, is variable: it decreases in proportion to the number of tests, but increases in proportion to their intercorrelation. We provide general indications concerning the normality threshold, which are applicable to all batteries of ES-standardized tests regardless of the number and type.

Semantic category dissociations: a longitudinal study of two cases.

We report the neuropsychological findings of two patients (LF and EA) with herpes simplex encephalitis. Both patients presented a greater deficit for living than non-living categories in a number of tasks, although EA was much more impaired than LF. We controlled the several stimulus variables that might affect the performance and could demonstrate that the dissociation was not artifactual. Neither LF nor EA revealed a selective or preferential involvement of perceptual semantic knowledge, and both showed a homogeneous impairment of perceptual and associative encyclopaedic notions. At a second examination, carried out from 1 to 2 years later, LF showed a good recovery, whereas EAs improvement was confined to the non-living categories. The lesion of both patients affected the left temporal pole and the basal neocortical regions of the left temporal lobe. The involvement of limbic areas was more marked in LF, while the Wernicke area and the posterior parts of the middle and inferior temporal gyri were only involved in EA. Besides the basal temporal areas, also the posterior temporal regions are likely to play a role in determining the clinical picture of such patients, and their prospect of recovery.

Crossed aphasia: one or more syndromes?

Seven strongly right-handed patients developed aphasia following a right hemisphere vascular lesion documented by computerized tomography. One patient had a severe unilateral neglect, indication of its presence were evident in three and absent in three patients. The Token Test scores were significantly higher than in matched controls. Two patients had Broca aphasia, four had Wernicke aphasia and one had agraphia. The correlation between type of aphasia and locus of lesion was not much different from that normally found in standard left hemisphere brain damaged aphasics.

Picture reality decision, semantic categories and gender: A new set of pictures, with norms and an experimental study

We present a new corpus of 80 pictures of unreal objects, useful for a controlled assessment of object reality decision. The new pictures were assembled from parts of the Snodgrass and Vanderwart [J. Exp. Psychol., Hum. Learning Memory 6; 1980: 174] set and were devised for the purpose of contrasting natural categories (animals, fruits and vegetables), artefacts (tools, vehicles and furniture), body parts and musical instruments. We examined 140 normal subjects in a free-choice and a multiple-choice object decision task, assembled with 80 pictures of real objects and above 80 new pictures of unreal objects in order to obtain a difficulty index for each picture. We found that the tasks were more difficult with pictures representing natural entities than with pictures of artefacts. We found a gender by category interaction, with a female superiority with some natural categories (fruits and vegetables, but not animals), and a male advantage with artefacts. On this basis, the difficulty index we calculated for each picture is separately reported for males and females. We discuss the possible origin of the gender effect, which has been found with the same categories in other tasks and has a counterpart in the different familiarity of the stimuli for males and females. In particular, we contrast explanations based on socially determined gender differences with accounts based on evolutionary pressures. We further comment on the relationship between data from normal subjects and the domain-specific account of semantic category dissociations observed in brain-damaged patients.

Semantic category dissociations in naming : is there a gender effect in Alzheimer’s disease?

Several studies on picture naming in Alzheimers disease have reported inconsistent findings regarding semantic category dissociation. To clarify this point, 26 patients suffering from dementia of the Alzheimers type (DAT) were given a naming task, based on 60 black and white drawings, which allowed us to take into account several variables that might influence performance, notably word frequency, stimulus familiarity and prototypicality, name and image agreement and visual complexity. On a raw analysis, DAT patients as a group gave a lower performance with stimuli of Living Categories (LC) than with stimuli of Non-Living Categories (NLC), but when all the confounding factors were taken into account the category effect disappeared. Nevertheless, with a multiple single case approach, some patients presented a true dissociation: 11 were significantly better with Non-Living stimuli, and 3 with Living stimuli. In order to find what factors were involved in determining this distribution, we took the distribution of asymmetry indices of each patient, and plotted the individual category effect against the level of the general performance. In our sample, the distribution of asymmetry indices was skewed, and included a definite cluster of male subjects who were better at performing with Non-Living stimuli. Multivariate analysis suggested that the greater discrepancy shown by male patients was due to a protection acting on Non-Living stimuli rather than to a selective hampering of Living stimuli. The greater personal experience of males with Non-Living things could explain the relative preservation of these in male DAT subjects.