Contrasting domain-general and domain-specific accounts in cognitive neuropsychology: An outline of a new approach with developmental prosopagnosia as a case.

The backbone of cognitive neuropsychology is the observation of (double) dissociations in performance between patients, suggesting some degree of independence between cognitive processes (domain specificity). In comparison, observations of associations between disorders/deficits have been deemed less evidential in neuropsychological theorizing about cognitive architecture. The reason is that associations can reflect damage to independent cognitive processes that happen to be mediated by structures commonly affected by the same brain disorder rather than damage to a shared (domain-general) mechanism. Here we demonstrate that it is in principle possible to discriminate between these alternatives by means of a procedure involving large unbiased samples. We exemplify the procedure in the context of developmental prosopagnosia (DP), but the procedure is in principle applicable to all neuropsychological deficits/disorders. A simulation of the procedure on a dataset yields estimates of dissociations/associations that are well in line with existing DP-studies, and also suggests that seemingly selective disorders can reflect damage to both domain-general and domain-specific cognitive processes. However, the simulation also highlights some limitations that should be considered if the procedure is to be applied prospectively. The main advantage of the procedure is that allows for examination of both associations and dissociations in the same sample. Hence, it may help even the balance in the use of associations and dissociations as grounds for neuropsychological theorizing.

Patterns of perceptual performance in developmental prosopagnosia: An in-depth case series.

Developmental prosopagnosia (DP) is a syndrome characterized by lifelong impairment in face recognition in the absence of brain damage. A key question regarding DP concerns which process(es) might be affected to selectively/disproportionally impair face recognition. We present evidence from a group of DPs, combining an overview of previous results with additional analyses important for understanding their pattern of preserved and impaired perceptual abilities. We argue that for most of these individuals, the common denominator is a deficit in (rapid) processing of global shape information. We conclude that the deficit in this group of DPs is not face-selective, but that it may appear so because faces are more visually similar-and recognized at a more fine-grained level-than objects. Indeed, when the demand on perceptual differentiation and visual similarity are held constant for faces and objects, we find no evidence for a disproportionate deficit for faces in this group of DPs.

Whole-object effects in visual word processing: Parallels with and differences from face recognition.

Visual words and faces differ in their structural properties, but both are objects of high expertise. Holistic processing is said to characterize expert face recognition, but the extent to which whole-word processes contribute to word recognition is unclear, particularly as word recognition is thought to proceed by a component-based process. We review the evidence for experimental effects in word recognition that parallel those used to support holistic face processing, namely inversion effects, the part-whole task, and composite effects, as well as the status of whole-word processing in pure alexia and developmental dyslexia, contrasts between familiar and unfamiliar languages, and the differences between handwriting and typeset font. The observations support some parallels in whole-object influences between face and visual word recognition, but do not necessarily imply similar expert mechanisms. It remains to be determined whether and how the relative balance between part-based and whole-object processing differs for visual words and faces.

Face recognition in developmental dyslexia: evidence for dissociation between faces and words.

Developmental dyslexia is primarily a reading disorder, but recent studies have indicated that face processing problems may also be present. Using a case-series approach, we tested face recognition and visual word recognition in 24 high school students diagnosed with developmental dyslexia. Contrary to previous findings, no face recognition problems were found on the group-level. Rather, a significant classical dissociation with impaired word reading and normal face recognition was demonstrated on a group-level and for six individuals with developmental dyslexia. However, four individuals with dyslexia did show face recognition problems. Thus, while problems in face recognition can be present in developmental dyslexia, the dissociation strongly suggests that face recognition can also be preserved. Combined with previously reported dissociations between face and word recognition in developmental prosopagnosia, this constitutes a double dissociation.

Pure Alexia: A Combined First-Person Account and Neuropsychological Investigation.

Pure alexia is an acquired reading disorder where patients' ability to read words and text is severely impaired, while their writing is left unaffected. Patients with pure alexia typically recover some reading ability over time, although most never regain their premorbid reading skills. A few studies have reported some behavioral and imaging correlates of such remission; however, little is known about the patients' experience of their reading impairment. This paper contains a first-person account of pure alexia, describing the first author's (K.H.) experience of his remission from severe reading problems immediately following a posterior cerebral artery stroke to the mild pure alexia characterizing his reading ability today. To provide a context for this account, we also present neuropsychological and reading data obtained from K.H. at several time points during his recovery.

A free and simple computerized screening test for visual field defects.

About 30-40% of stroke patients suffer from visual field defects following injury. These can interfere with the standard neuropsychological assessment and complicate the interpretation of tests that use visual materials. However, information about the integrity of a patient's central visual field is often unavailable. We, therefore, designed a screening tool, the computerized visual field test (c-VFT), specifically targeted at providing easily available, but rough, information about patients' central visual field. c-VFT was tested in two samples of stroke patients. Eleven patients were tested on c-VFT and on the Esterman test. Five patients were tested on c-VFT and the Humphrey Visual Field Analyzer (HFA), central 10-2. Criterion validity of the c-VFT was investigated by calculating quadrantwise intraclass correlation for both comparisons. For the HFA comparison, we also calculated point-to-point intraclass correlation, sensitivity, and specificity. Analyses revealed moderately good correspondence between c-VFT and the Esterman test, and between c-VFT and HFA 10-2, respectively. When looking specifically at test points within one degree of visual angle apart in the two tests, intraclass correlation increased. For these points, the sensitivity of c-VFT was 0.89 and specificity was 0.97. While the c-VFT is not designed to be diagnostic nor to replace the detailed visual field analysis, this study shows that it provides a reasonable screening of the central visual field. The test can easily be used and will be made freely available to neuropsychological clinicians and researchers.

Delayed processing of global shape information is associated with weaker top-down effects in developmental prosopagnosia.

In previous studies we have shown that a group of individuals with developmental prosopagnosia (DP): (i) were impaired at recognizing objects when presented as silhouettes or fragmented forms; stimuli which place particular demands on global shape processing, (ii) that these impairments correlated with their face recognition deficit, (iii) that they showed a reduced global precedence effect in Navon's paradigm, and (iv) that the magnitude of their global precedence effect correlated with their face and object recognition performance. This pattern of deficits points towards a delay in the processing of global shape information; a delay that may weaken top-down influences on recognition performance. Here we show that the DPs show reduced real object superiority effects (faster responses to real objects than nonobjects) compared with controls. Given that real object superiority effects reflect top-down processing, these findings support the notion of impaired global shape based top-down processing in DP.

Visual crowding in pure alexia and acquired prosopagnosia.

Visual crowding is a phenomenon that impairs object recognition when the features of an object are positioned too closely together. Crowding limits recognition in normal peripheral vision and it has been suggested to be the core deficit in visual agnosia, leading to a domain-general deficit in object recognition. Using a recently developed tool, we test whether crowding is the underlying deficit in four patients with category specific agnosias: Two with pure alexia and two with acquired prosopagnosia. We expected all patients to show abnormal crowding. We find that the two patients with acquired prosopagnosia show abnormal crowding effects in foveal vision, while the pure alexic patients do not, and that this constitutes a significant dissociation. Thus, abnormal crowding cannot explain all cases of visual agnosia. Much recent work has focused on similarities between pure alexia and acquired prosopagnosia. Here we show a difference in a basic visual mechanism-visual crowding.

Topographic processing in developmental prosopagnosia: Preserved perception but impaired memory of scenes.

Anecdotal evidence suggests a relation between impaired spatial (navigational) processing and developmental prosopagnosia. To address this formally, we tested two aspects of topographic processing - that is, perception and memory of mountain landscapes shown from different viewpoints. Participants included nine individuals with developmental prosopagnosia and 18 matched controls. The group with developmental prosopagnosia had no difficulty with topographic perception, but was reliably poorer in the retention of topographic information. Additional testing revealed that this did not reflect a general deficit in visual processing or visual short-term memory. Interestingly, a classical dissociation could be demonstrated between impaired face memory and preserved topographic memory in two developmental prosopagnosics. We conclude that impairments in topographic memory tend to co-occur with developmental prosopagnosia, although the underlying functions are likely to be independent.

Confusing confusability: on the problems of using psychophysical measures of letter confusability in neuropsychological research.

The effect of letter confusability on reading has received increasing attention over the last decade. Confusability scores for individual letters, derived from older psychophysical studies, have been used to calculate summed confusability scores for whole words, and effects of this variable on normal and alexic reading have been reported. On this basis, letter confusability is now increasingly controlled for in stimulus selection. In this commentary, we try to clarify what letter confusability scores represent and discuss several problems with the way this variable has been treated in neuropsychological research. We conclude that it is premature to control for this variable when selecting stimuli in studies of reading and alexia. Although letter confusability may play a role in (impaired) reading, it remains to be determined how this measure should be calculated, and what effect it may have on word and letter identification.

From word superiority to word inferiority: visual processing of letters and words in pure alexia.

Visual processing and naming of individual letters and short words were investigated in four patients with pure alexia. To test processing at different levels, the same stimuli were studied across a naming task and a visual perception task. The normal word superiority effect was eliminated in both tasks for all patients, and this pattern was more pronounced in the more severely affected patients. The relationship between performance with single letters and words was, however, not straightforward: One patient performed within the normal range on the letter perception task, while being severely impaired in letter naming and word processing, and performance with letters and words was dissociated in all four patients, with word reading being more severely impaired than letter recognition. This suggests that the word reading deficit in pure alexia may not be reduced to an impairment in single letter perception.

Evidence for a Classical Dissociation between Face and Object Recognition in Developmental Prosopagnosia.

It is still a matter of debate whether developmental prosopagnosia is a disorder selective to faces or whether object recognition is also affected. In a previous study, based on a small sample of developmental prosopagnosics (DPs; N = 10), we found impairments in both domains although the difficulties were most pronounced for faces. Importantly, impairments with faces and objects were systematically related. We suggested that that the seemingly disproportional impairment for faces in DP was likely to reflect differences between stimulus categories in visual similarity. Here, we aimed to replicate these findings in a larger, independent sample of DPs (N = 21) using the same experimental paradigms. Contrary to our previous results, we found no disproportional effect of visual similarity on performance with faces or objects in the new DP group when compared to controls (N = 21). The new DP group performed within the control range, and significantly better than the old DP-group, on sensitive and demanding object recognition tasks, and we can demonstrate a classical dissociation between face and object recognition at the group level. These findings are perhaps the strongest evidence yet presented for a face-specific deficit in developmental prosopagnosia.

Cognitive Functioning and Assessment in Adults with Cerebral Palsy: A Scoping Review.

In this scoping review, we summarize the current knowledge of cognitive functioning in adults with cerebral palsy (CP), and identify the neuropsychological tests typically used in this population. 39 studies from the period January 1990 - August 2023 were included in the review, and they differ widely in their aims and approach to studying cognition. Very few studies have cognitive assessment as their core aim and use a neuropsychological test battery. The included studies show great variability in reported intelligence and cognitive functioning in adults with CP, and cognitive deficits have been reported in all cognitive domains. Most of the studies suffer from methodological limitations, and there is ample room for improvement within the field. We conclude by suggesting a number of recommendations that may contribute to increasing our understanding of cognitive impairments in adults with CP.

Disentangling developmental prosopagnosia: A scoping review of terms, tools and topics.

The goal of this preregistered scoping review is to create an overview of the research on developmental prosopagnosia (DP). Through analysis of all empirical studies of DP in adults, we investigate 1) how DP is conceptualized and defined, 2) how individuals are classified with DP and 3) which aspects of DP are investigated in the literature. We reviewed 224 peer-reviewed studies of DP. Our analysis of the literature reveals that while DP is predominantly defined as a lifelong face recognition impairment in the absence of acquired brain injury and intellectual/cognitive problems, there is far from consensus on the specifics of the definition with some studies emphasizing e.g., deficits in face perception, discrimination and/or matching as core characteristics of DP. These differences in DP definitions is further reflected in the vast heterogeneity in classification procedures. Only about half of the included studies explicitly state how they classify individuals with DP, and these studies adopt 40 different assessment tools. The two most frequently studied aspects of DP are the role of holistic processing and the specificity of face processing, and alongside a substantial body of neuroimaging studies of DP, this paints a picture of a research field whose scientific interests and aims are rooted in cognitive neuropsychology and neuroscience. We argue that these roots - alongside the heterogeneity in DP definition and classification - may have limited the scope and interest of DP research unnecessarily, and we point to new avenues of research for the field.

Rehabilitation of pure alexia: a review.

Acquired reading problems caused by brain injury (alexia) are common, either as a part of an aphasic syndrome, or as an isolated symptom. In pure alexia, reading is impaired while other language functions, including writing, are spared. Being in many ways a simple syndrome, one would think that pure alexia was an easy target for rehabilitation efforts. We review the literature on rehabilitation of pure alexia from 1990 to the present, and find that patients differ widely on several dimensions, such as alexia severity and associated deficits. Many patients reported to have pure alexia in the reviewed studies, have associated deficits such as agraphia or aphasia and thus do not strictly conform to the diagnosis. Few studies report clear and generalisable effects of training, none report control data, and in many cases the reported findings are not supported by statistics. We can, however, tentatively conclude that Multiple Oral Re-reading techniques may have some effect in mild pure alexia where diminished reading speed is the main problem, while Tacile-Kinesthetic training may improve letter identification in more severe cases of alexia. There is, however, still a great need for well-designed and controlled studies of rehabilitation of pure alexia.

Using representational similarity analysis to reveal category and process specificity in visual object recognition.

Cross-condition comparisons on neurodevelopmental conditions are central in neurodiversity research. In the realm of visual perception, the performance of participants with different category-specific disorders such as developmental prosopagnosia (problems with faces) and dyslexia (problems with words) have contributed to understanding of perceptual processes involved in word and face recognition. Alterations in face and word recognition are present in several neurodiverse populations, and improved knowledge about their relationship may increase our understanding of this variability of impairment. The present study investigates organizing principles of visual object processing and their implications for developmental disorders of recognition. Some accounts suggest that distinct mechanisms are responsible for recognizing objects of different categories, while others propose that categories share or even compete for cortical resources. We took an individual differences approach to estimate the relationship between abilities in recognition. Neurotypical participants (N = 97 after outlier exclusion) performed a match-to-sample task with faces, houses, and pseudowords. Either individual features or feature configurations were manipulated. To estimate the separability of visual recognition mechanisms, we used representational similarity analysis (RSA) where correlational matrices for accuracy were compared to predicted data patterns. Recognition abilities separated into face recognition on one hand and house/pseudoword recognition on the other, indicating that face recognition may rely on relatively selective mechanisms in neurotypicals. We also found evidence for a general visual object recognition mechanism, while some combinations of category (faces, houses, words) and processing type (featural, configural) likely rely on additional mechanisms. Developmental conditions may therefore reflect combinations of impaired and intact aspects of specific and general visual object recognition mechanisms, where featural and configural processes for one object category separate from the featural or configural processing of another. More generally, RSA is a promising approach for advancing understanding of neurodiversity, including shared aspects and distinctions between neurodevelopmental conditions of visual recognition.

The face inversion effect or the face upright effect?

The face inversion effect (FIE) refers to the observation that presenting stimuli upside-down impairs the processing of faces disproportionally more than other mono-oriented objects. This has been taken as evidence that processing of faces and objects differ qualitatively. However, nearly all FIE studies are based on comparing individuation of upright faces, which most people are rather good at, with individuation of objects most people are much less familiar with individuating (e.g., radios and airplanes). Consequently, the FIE may mainly reflect differences between categories in how they are processed prior to inversion, with within-category discrimination of upright faces being a much more familiar task than within-category discrimination among members belonging to other object classes. We tested this hypothesis by comparing inversion effects for faces and objects using object recognition tasks that do not require within-category discrimination (object decision and old/new recognition memory tasks). In all tasks (seven with objects and two with faces) we find credible inversion effects, but in no instance were these effects significantly larger for faces than for objects. This suggests that the FIE can be a product of familiarity with the type of identification process required in the upright conditions rather than some process that is selectively affected for faces when stimuli are inverted.

The Danish Version of the 20-Item Prosopagnosia Index (PI20): Translation, Validation and a Link to Face Perception.

Developmental prosopagnosia (DP) is a neurodevelopmental condition characterized by face recognition problems. Psychometrically sound self-report measures of face recognition problems are important tools in classification of DP. A widely used measure of such problems is the 20-item prosopagnosia index (PI20). Here, we present a Danish translation of the PI20 (PI20DK). We administered the PI20DK alongside three objective measures of face and object processing performance to 119 participants to validate the PI20DK. Further, we assess the underlying factor structure of the PI20DK. Finally, as the first study in the field, we investigate the association between self-reported face recognition ability and face perception performance. The project was preregistered prior to data collection. The results suggest excellent convergent validity, discriminant validity and internal consistency for the PI20DK. A confirmatory factor analysis, however, indicates a suboptimal fit of the PI20DK to a one factor solution. An investigation of the association between the PI20DK and face perception suggests that the poor fit may reflect that the PI20DK measures problems with face recognition in general and not specifically face memory problems.

Systematic evaluation of high-level visual deficits and lesions in posterior cerebral artery stroke.

Knowledge about the consequences of stroke on high-level vision comes primarily from single case studies of patients selected based on their behavioural profiles, typically patients with specific stroke syndromes like pure alexia or prosopagnosia. There are, however, no systematic, detailed, large-scale evaluations of the more typical clinical behavioural and lesion profiles of impairments in high-level vision after posterior cerebral artery stroke. We present behavioural and lesion data from the Back of the Brain project, to date the largest (N = 64) and most detailed examination of patients with cortical posterior cerebral artery strokes selected based on lesion location. The aim of the current study was to relate behavioural performance with faces, objects and written words to lesion data through two complementary analyses: (i) a multivariate multiple regression analysis to establish the relationships between lesion volume, lesion laterality and the presence of a bilateral lesion with performance and (ii) a voxel-based correlational methodology analysis to establish whether there are distinct or separate regions within the posterior cerebral artery territory that underpin the visual processing of words, faces and objects. Behaviourally, most patients showed more general deficits in high-level vision (n = 22) or no deficits at all (n = 21). Category-selective deficits were rare (n = 6) and were only found for words. Overall, total lesion volume was most strongly related to performance across all three domains. While behavioural impairments in all domains were observed following unilateral left and right as well as bilateral lesions, the regions most strongly related to performance mainly confirmed the pattern reported in more selective cases. For words, these included a left hemisphere cluster extending from the occipital pole along the fusiform and lingual gyri; for objects, bilateral clusters which overlapped with the word cluster in the left occipital lobe. Face performance mainly correlated with a right hemisphere cluster within the white matter, partly overlapping with the object cluster. While the findings provide partial support for the relative laterality of posterior brain regions supporting reading and face processing, the results also suggest that both hemispheres are involved in the visual processing of faces, words and objects.