Two systems for colour-naming defects: verbal disconnection vs colour imagery disorder

No clear evidence of a difference between individuals who self-report an absence of auditory imagery and typical imagers on auditory imagery tasks

Aphantasia is characterised by the inability to create mental images in one's mind. Studies investigating impairments in imagery typically focus on the visual domain. However, it is possible to generate many different forms of imagery including imagined auditory, kinesthetic, tactile, motor, taste and other experiences. Recent studies show that individuals with aphantasia report a lack of imagery in modalities, other than vision, including audition. However, to date, no research has examined whether these reductions in self-reported auditory imagery are associated with decrements in tasks that require auditory imagery. Understanding the extent to which visual and auditory imagery deficits co-occur can help to better characterise the core deficits of aphantasia and provide an alternative perspective on theoretical debates on the extent to which imagery draws on modality-specific or modality-general processes. In the current study, individuals that self-identified as being aphantasic and matched control participants with typical imagery performed two tasks: a musical pitch-based imagery and voice-based categorisation task. The majority of participants with aphantasia self-reported significant deficits in both auditory and visual imagery. However, we did not find a concomitant decrease in performance on tasks which require auditory imagery, either in the full sample or only when considering those participants that reported significant deficits in both domains. These findings are discussed in relation to the mechanisms that might obscure observation of imagery deficits in auditory imagery tasks in people that report reduced auditory imagery.

Visual imagery deficits in posterior cortical atrophy

Visual imagery has a close overlapping relationship with visual perception. Posterior cortical atrophy (PCA) is a neurodegenerative syndrome marked by early impairments in visuospatial processing and visual object recognition. We asked whether PCA would therefore also be marked by deficits in visual imagery, tested using objective forced-choice questionnaires, and whether imagery deficits would be selective for certain properties. We recruited four patients with PCA and a patient with integrative visual agnosia due to bilateral occipitotemporal strokes for comparison. We administered a test battery probing imagery for object shape, size, colour lightness, hue, upper-case letters, lower-case letters, word shape, letter construction, and faces. All subjects showed significant impairments in visual imagery, with imagery for lower-case letters most likely to be spared. We conclude that PCA subjects can show severe deficits in visual imagery. Further work is needed to establish how frequently this occurs and how early it can be found.

Identification of candidate genes for developmental colour agnosia in a single unique family

Colour agnosia is a disorder that impairs colour knowledge (naming, recognition) despite intact colour perception. Previously, we have identified the first and only-known family with hereditary developmental colour agnosia. The aim of the current study was to explore genomic regions and candidate genes that potentially cause this trait in this family. For three family members with developmental colour agnosia and three unaffected family members CGH-array analysis and exome sequencing was performed, and linkage analysis was carried out using DominantMapper, resulting in the identification of 19 cosegregating chromosomal regions. Whole exome sequencing resulted in 11 rare coding variants present in all affected family members with developmental colour agnosia and absent in unaffected members. These variants affected genes that have been implicated in neural processes and functions (CACNA2D4, DDX25, GRINA, MYO15A) or that have an indirect link to brain function, development or disease (MAML2, STAU1, TMED3, RABEPK), and a remaining group lacking brain expression or involved in non-neural traits (DEPDC7, OR1J1, OR8D4). Although this is an explorative study, the small set of candidate genes that could serve as a starting point for unravelling mechanisms of higher level cognitive functions and cortical specialization, and disorders therein such as developmental colour agnosia.

Predictive processing and perception: What does imagining have to do with it?

Predictive processing (PP) accounts of perception are unique not merely in that they postulate a unity between perception and imagination, but in claiming that (i) perception should be conceptualised in terms of imagination and (ii) the two involve an identity of neural implementation. This paper argues against these claims, on both conceptual and empirical grounds. Conceptually, the manner in which PP theorists link perception and imagination belies an impoverished account of imagery as cloistered from the external world in its intentionality, akin to a virtual reality, as well as endogenously generated. Yet this ignores a whole class of imagery whose intentionality is directed on the actual environment-projected mental imagery-and also ignores the fact that imagery may be triggered crossmodally in a bottom-up, stimulus-driven way. Empirically, claiming that imagery and perception share neural circuitry ignores relevant clinical results in this area. These evidence substantial perception/imagery neural dissociations, most notably in the case of aphantasia. Taken together, the arguments here suggest that PP theorists should substantially temper, if not outright abandon, their claim to a perception/imagination unity.

A systematic review and narrative synthesis of mental imagery tasks in people with an intellectual disability: Implications for psychological therapies

Mental imagery is recognised for its role in both psychological distress and wellbeing, with mental imagery techniques increasingly being incorporated into psychological interventions. In this systematic review and narrative synthesis (PROSPERO 2021: CRD42021240930), we identify and evaluate the evidence base for the phenomenon and phenomenology of mental imagery in people with intellectual disabilities, to ascertain the applicability of such interventions for this population. Electronic searches of nine databases and grey literature identified relevant publications. Two reviewers independently assessed titles and abstracts of retrieved records (n = 8609) and full-text articles (n = 101) against eligibility criteria. Data were extracted and quality appraised. Forty-onepapers met our eligibility criteria. The quality and designs were variable. Mental imagery was facilitated through ensuring participants understood tasks, providing opportunity to rehearse tasks (including using concrete prompts) and using scaffolding to help participants elaborate their responses. People with intellectual disabilities can engage with mental imagery, with appropriate adaptations, although the associated phenomenology has not been thoroughly investigated. Mental imagery interventions may be useful for people with intellectual disabilities with appropriate modifications.

The persistence of remote visual semantic memory following ocular blindness

Subjects with complete ocular blindness in both eyes provide a unique opportunity to study the long-term durability of visual semantic memory. In this cross-sectional study we recruited eleven subjects who had acquired blindness for between 1 and 36 years. For comparison, we studied four subjects with congenital blindness and seventeen age- and sex-matched sighted control subjects. We administered ten forced-choice questionnaires that probed one auditory category and four visual categories, namely object shape and size; object hue and lightness; word and letter shape; and the shape and features of famous faces. Subjects with congenital blindness performed worse than controls on all visual categories, but nevertheless performed better than chance on object structure or colour, suggesting that the answers to some questions about visual properties can be derived from haptic or non-visual semantic information. Subjects with acquired blindness performed similarly to controls on all categories except for facial memory, particularly for facial features. We conclude that there is a substantial "permastore" of visual semantic memory but that facial memories are less durable, perhaps indicating that they are either less over-learned or more dependent on visual representations than other forms of visual object information.

Neural bases of color-specific semantic loss: Two cases of object-color knowledge impairment

Human color processing includes perception, naming, and knowledge of colors. These facets are dissociable from each other and appear to have discrete neuronal bases. Here, we present two cases with loss of object color knowledge but spared color perception and knowledge of object other than color. Case 1, a stroke patient with lesions in the left medial occipitotemporal lobe, is impaired in associating colors or color names with objects or object names. However, he demonstrated good color perception and well-preserved knowledge of object form, size, and functions. Case 2, another stroke patient with a lesion in the left fusiform and lingual gyri, showed anomia for colors and slight impairment in object color knowledge. Case 1 is the first subject to have complete loss of object color knowledge, including the verbal association between object and color names without impairment in object knowledge about perceptual properties other than color. These results indicate that color and object processing is comprised of numerous dissociable features with distinct neuronal bases. Further, they provide evidence supporting the critical role played by the left medial occipitotemporal region in color knowledge.

Towards Strong Inference in Research on Embodiment - Possibilities and Limitations of Causal Paradigms

A central question in the cognitive sciences is which role embodiment plays for high-level cognitive functions, such as conceptual processing. Here, we propose that one reason why progress regarding this question has been slow is a lacking focus on what Platt (1964) called “strong inference”. Strong inference is possible when results from an experimental paradigm are not merely consistent with a hypothesis, but they provide decisive evidence for one particular hypothesis compared to competing hypotheses. We discuss how causal paradigms, which test the functional relevance of sensory-motor processes for high-level cognitive functions, can move the field forward. In particular, we explore how congenital sensory-motor disorders, acquired sensory-motor deficits, and interference paradigms with healthy participants can be utilized as an opportunity to better understand the role of sensory experience in conceptual processing. Whereas all three approaches can bring about valuable insights, we highlight that the study of congenitally and acquired sensorimotor disorders is particularly effective in the case of conceptual domains with strong unimodal basis (e.g., colors), whereas interference paradigms with healthy participants have a broader application, avoid many of the practical and interpretational limitations of patient studies, and allow a systematic and step-wise progressive inference approach to causal mechanisms.

Color vision

Color is a fundamental aspect of normal visual experience. This chapter provides an overview of the role of color in human behavior, a survey of current knowledge regarding the genetic, retinal, and neural mechanisms that enable color vision, and a review of inherited and acquired defects of color vision including a discussion of diagnostic tests.

What Cognitive Neurology Teaches Us about Our Experience of Color

Color provides valuable information about the environment, yet the exact mechanisms explaining how colors appear to us remain poorly understood. Retinal signals are processed in the visual cortex through high-level mechanisms that link color perception with top-down expectations and knowledge. Here, we review the neuroimaging evidence about color processing in the brain, and how it is affected by acquired brain lesions in humans. Evidence from patients with brain-damage suggests that high-level color processing may be divided into at least three modules: perceptual color experience, color naming, and color knowledge. These modules appear to be functionally independent but richly interconnected, and serve as cortical relays linking sensory and semantic information, with the final goal of directing object-related behavior. We argue that the relations between colors and their objects are key mechanisms to understand high-level color processing.

Mental imagery of gravitational motion

There is considerable evidence that gravitational acceleration is taken into account in the interaction with falling targets through an internal model of Earth gravity. Here we asked whether this internal model is accessed also when target motion is imagined rather than real. In the main experiments, naïve participants grasped an imaginary ball, threw it against the ceiling, and caught it on rebound. In different blocks of trials, they had to imagine that the ball moved under terrestrial gravity (1g condition) or under microgravity (0g) as during a space flight. We measured the speed and timing of the throwing and catching actions, and plotted ball flight duration versus throwing speed. Best-fitting duration-speed curves estimate the laws of ball motion implicit in the participant's performance. Surprisingly, we found duration-speed curves compatible with 0g for both the imaginary 0g condition and the imaginary 1g condition, despite the familiarity with Earth gravity effects and the added realism of performing the throwing and catching actions. In a control experiment, naïve participants were asked to throw the imaginary ball vertically upwards at different heights, without hitting the ceiling, and to catch it on its way down. All participants overestimated ball flight durations relative to the durations predicted by the effects of Earth gravity. Overall, the results indicate that mental imagery of motion does not have access to the internal model of Earth gravity, but resorts to a simulation of visual motion. Because visual processing of accelerating/decelerating motion is poor, visual imagery of motion at constant speed or slowly varying speed appears to be the preferred mode to perform the tasks.

Unconscious Imagination and the Mental Imagery Debate

Traditionally, philosophers have appealed to the phenomenological similarity between visual experience and visual imagery to support the hypothesis that there is significant overlap between the perceptual and imaginative domains. The current evidence, however, is inconclusive: while evidence from transcranial brain stimulation seems to support this conclusion, neurophysiological evidence from brain lesion studies (e.g., from patients with brain lesions resulting in a loss of mental imagery but not a corresponding loss of perception and vice versa) indicates that there are functional and anatomical dissociations between mental imagery and perception. Assuming that the mental imagery and perception do not overlap, at least, to the extent traditionally assumed, then the question arises as to what exactly mental imagery is and whether it parallels perception by proceeding via several functionally distinct mechanisms. In this review, we argue that even though there may not be a shared mechanism underlying vision for perception and conscious imagery, there is an overlap between the mechanisms underlying vision for action and unconscious visual imagery. On the basis of these findings, we propose a modification of Kosslyn's model of imagery that accommodates unconscious imagination and explore possible explanations of the quasi-pictorial phenomenology of conscious visual imagery in light of the fact that its underlying neural substrates and mechanisms typically are distinct from those of visual experience.

The impact of ageing and gender on visual mental imagery processes: A study of performance on tasks from the Complete Visual Mental Imagery Battery (CVMIB)

In this study we aim to evaluate the impact of ageing and gender on different visual mental imagery processes. Two hundred and fifty-one participants (130 women and 121 men; age range = 18-77 years) were given an extensive neuropsychological battery including tasks probing the generation, maintenance, inspection, and transformation of visual mental images (Complete Visual Mental Imagery Battery, CVMIB). Our results show that all mental imagery processes with the exception of the maintenance are affected by ageing, suggesting that other deficits, such as working memory deficits, could account for this effect. However, the analysis of the transformation process, investigated in terms of mental rotation and mental folding skills, shows a steeper decline in mental rotation, suggesting that age could affect rigid transformations of objects and spare non-rigid transformations. Our study also adds to previous ones in showing gender differences favoring men across the lifespan in the transformation process, and, interestingly, it shows a steeper decline in men than in women in inspecting mental images, which could partially account for the mixed results about the effect of ageing on this specific process. We also discuss the possibility to introduce the CVMIB in clinical assessment in the context of theoretical models of mental imagery.

Flexible information coding in human auditory cortex during perception, imagery, and STM of complex sounds

Auditory cortex is the first cortical region of the human brain to process sounds. However, it has recently been shown that its neurons also fire in the absence of direct sensory input, during memory maintenance and imagery. This has commonly been taken to reflect neural coding of the same acoustic information as during the perception of sound. However, the results of the current study suggest that the type of information encoded in auditory cortex is highly flexible. During perception and memory maintenance, neural activity patterns are stimulus specific, reflecting individual sound properties. Auditory imagery of the same sounds evokes similar overall activity in auditory cortex as perception. However, during imagery abstracted, categorical information is encoded in the neural patterns, particularly when individuals are experiencing more vivid imagery. This highlights the necessity to move beyond traditional "brain mapping" inference in human neuroimaging, which assumes common regional activation implies similar mental representations.

Autonomic nervous system correlates in movement observation and motor imagery

The purpose of the current article is to provide a comprehensive overview of the literature offering a better understanding of the autonomic nervous system (ANS) correlates in motor imagery (MI) and movement observation. These are two high brain functions involving sensori-motor coupling, mediated by memory systems. How observing or mentally rehearsing a movement affect ANS activity has not been extensively investigated. The links between cognitive functions and ANS responses are not so obvious. We will first describe the organization of the ANS whose main purposes are controlling vital functions by maintaining the homeostasis of the organism and providing adaptive responses when changes occur either in the external or internal milieu. We will then review how scientific knowledge evolved, thus integrating recent findings related to ANS functioning, and show how these are linked to mental functions. In turn, we will describe how movement observation or MI may elicit physiological responses at the peripheral level of the autonomic effectors, thus eliciting autonomic correlates to cognitive activity. Key features of this paper are to draw a step-by step progression from the understanding of ANS physiology to its relationships with high mental processes such as movement observation or MI. We will further provide evidence that mental processes are co-programmed both at the somatic and autonomic levels of the central nervous system (CNS). We will thus detail how peripheral physiological responses may be analyzed to provide objective evidence that MI is actually performed. The main perspective is thus to consider that, during movement observation and MI, ANS activity is an objective witness of mental processes.

The color "fruit": object memories defined by color

Most fruits and other highly color-diagnostic objects have color as a central aspect of their identity, which can facilitate detection and visual recognition. It has been theorized that there may be a large amount of overlap between the neural representations of these objects and processing involved in color perception. In accordance with this theory we sought to determine if the recognition of highly color diagnostic fruit objects could be facilitated by the visual presentation of their known color associates. In two experiments we show that color associate priming is possible, but contingent upon multiple factors. Color priming was found to be maximally effective for the most highly color diagnostic fruits, when low spatial-frequency information was present in the image, and when determination of the object's specific identity, not merely its category, was required. These data illustrate the importance of color for determining the identity of certain objects, and support the theory that object knowledge involves sensory specific systems.

Assessing mental imagery in clinical psychology: a review of imagery measures and a guiding framework

Mental imagery is an under-explored field in clinical psychology research but presents a topic of potential interest and relevance across many clinical disorders, including social phobia, schizophrenia, depression, and post-traumatic stress disorder. There is currently a lack of a guiding framework from which clinicians may select the domains or associated measures most likely to be of appropriate use in mental imagery research. We adopt an interdisciplinary approach and present a review of studies across experimental psychology and clinical psychology in order to highlight the key domains and measures most likely to be of relevance. This includes a consideration of methods for experimentally assessing the generation, maintenance, inspection and transformation of mental images; as well as subjective measures of characteristics such as image vividness and clarity. We present a guiding framework in which we propose that cognitive, subjective and clinical aspects of imagery should be explored in future research. The guiding framework aims to assist researchers in the selection of measures for assessing those aspects of mental imagery that are of most relevance to clinical psychology. We propose that a greater understanding of the role of mental imagery in clinical disorders will help drive forward advances in both theory and treatment.

Vivid visual mental imagery in the absence of the primary visual cortex

The role of the primary visual cortex in visual mental imagery has provided significant debate in the imagery literature. Functional neuroimaging studies show considerable variation depending on task and technique. Patient studies can be difficult to interpret due to the diverse nature of cortical damage. The type of cortical damage in patient SBR is exceedingly rare as it is restricted to the gray matter of the calcarine sulcus. In this study, we show that in spite of his near-complete cortical blindness, SBR exhibits vivid visual mental imagery both behaviorally and when measured with functional magnetic resonance imaging. The pattern of cortical activation to visual mental imagery in SBR is indistinguishable from individual sighted subjects, in contrast to the visual perceptual responses, which are greatly attenuated.

Colour, face, and visuospatial imagery abilities in low-vision individuals with visual field deficits

This study investigates to what extent visual perception integrity is necessary for visual mental imagery. Sixteen low-vision participants with severe peripheral visual field loss, 16 with severe central field loss, 6 left brain-damaged patients with right homonymous hemianopia, 6 right brain-damaged patients with left homonymous hemianopia, and 16 normally sighted controls performed perceptual and imagery tasks using colours, faces, and spatial relationships. Results showed that (a) the perceptual and mental image>ry disorders vary according to the type of visual field loss, (b) hemianopics had no more difficulties imagining spatial stimuli in their contralesional hemispace than in their ipsilesional one, and (c) the only hemianopic participant to have perceptual and mental imagery impairments suffered from attentional deficits. Results suggest that (a) visual memory is not definitively established, but rather needs perceptual practice to be maintained, and (b) that visual mental imagery may involve some of the attentional-exploratory mechanisms that are employed in visual behaviour.

Disorders of color and object recognition: syndromes of the ventral occipitotemporal pathway

Although lesions of the striate cortex are associated with hemifield defects, lesions of the inferior and medial occipitotemporal cortex often are associated with disorders of more high-level and complex visual processing. These disorders of the ventral processing stream can be considered as impairing the perception of color and recognition of objects, in contrast to the problems with motion and spatial localization seen with lesions of the dorsal occipitoparietal stream. Dysfunction in the ventral stream leads to the prototypic syndromes of achromatopsia, general visual agnosia, prosopagnosia, alexia without agraphia, and some forms of topographagnosia. Most of these are not single entities but families of disorders in which dysfunction in different cognitive and perceptual processes can lead to the same symptom. Continuum Lifelong Learning Neurol 2010;16(4):111-127.

[Presentation of an assessment battery for visual mental imagery and visual perception]

INTRODUCTION

The relationship between visual perception and visual mental imagery are at the center of a lively theoretical debate between those postulating common neurocognitive processes between perception and imagery and those who emphasize the differences between these two entities. Neuropsychology can make an important contribution to this debate, by assessing associations and dissociations between perceptual and imaginal deficits in patients with brain damage. However, currently there is no standardized test battery available for such assessments.

MATERIAL AND METHODS

Here we present a battery of paper-and-pencil tests assessing different domains of visual mental imagery and visual perception abilities: object form and color, animals, orthographic material, numbers, faces, and space. We also explored the effects of age, educational level and gender on performance on a group of 103 participants free of neurological damage.

RESULTS

The battery includes two parts: one composed of 14 tests assessing mental imagery and the second part composed of eight tests assessing the abilities of visual perception. We calculated the correlations between the tests, and found that, with the exception of orthographic material, there were generally poor correlations between imagery and perceptual tests.

CONCLUSION

This result seems inconsistent with hypotheses postulating a strict correspondence between perceptual and imagery abilities.

Semantic elaboration in auditory and visual spatial memory

The aim of this study was to investigate the hypothesis that semantic information facilitates auditory and visual spatial learning and memory. An auditory spatial task was administered, whereby healthy participants were placed in the center of a semi-circle that contained an array of speakers where the locations of nameable and non-nameable sounds were learned. In the visual spatial task, locations of pictures of abstract art intermixed with nameable objects were learned by presenting these items in specific locations on a computer screen. Participants took part in both the auditory and visual spatial tasks, which were counterbalanced for order and were learned at the same rate. Results showed that learning and memory for the spatial locations of nameable sounds and pictures was significantly better than for non-nameable stimuli. Interestingly, there was a cross-modal learning effect such that the auditory task facilitated learning of the visual task and vice versa. In conclusion, our results support the hypotheses that the semantic representation of items, as well as the presentation of items in different modalities, facilitate spatial learning and memory.

To know what it is for, but not how it is: semantic dissociations in a case of visual agnosia

We report the case of a woman who displayed impaired object recognition following a severe head injury. Her elementary visual functions were substantially preserved, allowing her a coherent percept. On the other hand, she was impaired in accessing stored knowledge from both visual and verbal input. In particular, she showed a dramatic dissociation between fully preserved access to functional knowledge, and severely impaired access to perceptual knowledge so that she could describe what objects are for, but not how they are. Our findings from this case suggest that different categories of object knowledge are represented independently in separate units within the semantic system.

A common neural substrate for perceiving and knowing about color

Functional neuroimaging research has demonstrated that retrieving information about object-associated colors activates the left fusiform gyrus in posterior temporal cortex. Although regions near the fusiform have previously been implicated in color perception, it remains unclear whether color knowledge retrieval actually activates the color perception system. Evidence to this effect would be particularly strong if color perception cortex was activated by color knowledge retrieval triggered strictly with linguistic stimuli. To address this question, subjects performed two tasks while undergoing fMRI. First, subjects performed a property verification task using only words to assess conceptual knowledge. On each trial, subjects verified whether a named color or motor property was true of a named object (e.g., TAXI-yellow, HAIR-combed). Next, subjects performed a color perception task. A region of the left fusiform gyrus that was highly responsive during color perception also showed greater activity for retrieving color than motor property knowledge. These data provide the first evidence for a direct overlap in the neural bases of color perception and stored information about object-associated color, and they significantly add to accumulating evidence that conceptual knowledge is grounded in the brain's modality-specific systems.

The representation of object concepts in the brain

Evidence from functional neuroimaging of the human brain indicates that information about salient properties of an object-such as what it looks like, how it moves, and how it is used-is stored in sensory and motor systems active when that information was acquired. As a result, object concepts belonging to different categories like animals and tools are represented in partially distinct, sensory- and motor property-based neural networks. This suggests that object concepts are not explicitly represented, but rather emerge from weighted activity within property-based brain regions. However, some property-based regions seem to show a categorical organization, thus providing evidence consistent with category-based, domain-specific formulations as well.

Vividness of mental imagery: individual variability can be measured objectively

When asked to imagine a visual scene, such as an ant crawling on a checkered table cloth toward a jar of jelly, individuals subjectively report different vividness in their mental visualization. We show that reported vividness can be correlated with two objective measures: the early visual cortex activity relative to the whole brain activity measured by functional magnetic resonance imaging (fMRI) and the performance on a novel psychophysical task. These results show that individual differences in the vividness of mental imagery are quantifiable even in the absence of subjective report.

A familial factor in the development of colour agnosia

An important aspect of research into the link between genes and behaviour concerns the identification of familial determination. There is evidence for familial factors in selective deficits, such as developmental dyslexia and developmental prosopagnosia. Colour agnosia concerns a selective neuropsychological condition in which colour perception is intact, while the identification and naming of colour is disrupted. We recently demonstrated that this deficit can occur as a developmental deficit. Here, we show that there is a familial factor in the development of colour agnosia by reporting the colour processing abilities of the mother and the daughters of a man with developmental colour agnosia.

Colour knowledge in semantic dementia: It is not all black and white

In three experiments we assessed the colour knowledge of patients with semantic dementia, a neuro-degenerative condition that gradually erodes conceptual knowledge. In Experiment 1, the patients' colour naming performance correlated strongly with their object naming for frequency-matched items, with no patient showing better-than-expected naming of colours relative to objects. In Experiment 2, where patients were asked to colour black-and-white line drawings of common objects, all patients were impaired relative to controls, and performance correlated strongly with degree of semantic deficit. The fact that patients often erroneously selected green for fruits or vegetables, and brown for animals, suggests some preservation of general knowledge about the colours that typify a given domain. In Experiment 3, patients were given pairs of identical line drawings of familiar animals, fruits and vegetables--one of each pair coloured correctly, and one incorrectly--and were asked to choose the correct one. When the target's colour was characteristic of the domain, patients scored well; but when the distractor had a typical hue and the target's colour was unusual (e.g. a green versus an orange carrot), performance was far poorer. The results are discussed with reference to alternative theories about the neural basis of conceptual knowledge.

Evidence from two genetic syndromes for the independence of spatial and visual working memory

This study aimed at investigating the possible dissociation between visual-object and visual-spatial working memory (WM) in individuals with Williams syndrome (WS) and Down syndrome (DS). Four study groups were included: WS group (10 males, 5 females) with a mean chronological age (CA) of 19 years 8 months (SD 6y 1mo) and a mean mental age (MA)of 6 years 11 months (SD 1y 5mo); WS comparison group (7 males, 8 females) comprised of typically developing children with a mean CA of 6 years 10 months (SD 10mo) and a mean MA of 6 years 11 months (SD 8mo)matched as a group with the participants with WS on the basis of mental age; DS group (11 males, 7 females) with a mean CA of 15 years 10 months (SD 5y 8mo) and a mean MA of 5 years 2 months (SD 8mo); and DS comparison group (10 males, 8 females) with a mean CA of 5 years and 1 month (SD 7mo)and a mean MA of 5 years 2 months (SD 8mo) selected to match the DS group on the basis of mental age. They were all administered tests that explored visual perception (Visual Perception Test - Subtest 4 and Line Orientation tests), visual imagery (imaging the colour of objects and the tail length of well-known animals), spatial imagery (mental rotation of visually presented or verbally evoked objects), and WM for visual-object and visual-spatial information. Individuals with WS exhibited specific difficulties in the visual-spatial, but not the visual-object, WM task. Instead, people with DS showed reduced performance in both tests. However, whereas the observed deficit in individuals with DS persisted when perceptual abilities were taken into account, the deficit in individuals with DS was compensated when their scores were adjusted for performance on perceptual tasks. These results support the hypothesis of a dissociation within the sketch-pad slave system in the WM model and reinforce the view of intellectual disability as a non-unitary condition.

Neurocognitive correlates of socioeconomic status in kindergarten children

Socioeconomic status (SES) is strongly associated with cognitive ability and achievement during childhood and beyond. Little is known about the developmental relationships between SES and specific brain systems or their associated cognitive functions. In this study we assessed neurocognitive functioning of kindergarteners from different socioeconomic backgrounds, using tasks drawn from the cognitive neuroscience literature in order to determine how childhood SES predicts the normal variance in performance across different neurocognitive systems. Five neurocognitive systems were examined: the occipitotemporal/visual cognition system, the parietal/spatial cognition system, the medial temporal/memory system, the left perisylvian/language system, and the prefrontal/executive system. SES was disproportionately associated with the last two, with low SES children performing worse than middle SES children on most measures of these systems. Relations among language, executive function, SES and specific aspects of early childhood experience were explored, revealing intercorrelations and a seemingly predominant role of individual differences in language ability involved in SES associations with executive function.

Writing through the phonological buffer: a case of progressive writing disorder

A progressively dysgraphic patient is described, whose deficit involved, at different stages, the post-allographic, the allographic and the orthographic representation of words. The patient's roughly comparable difficulties in oral and written spelling and in dictation by composition, as the disease progressed, showed that the damage was no longer limited to output mechanisms but also involved more central processes. The nature of the errors (phonologically based), their identical distributions for words and non-words, the inability to write under articulatory suppression, the normal repetition and the impairment in reading and lexical decision suggest that the patient cannot rely on the orthographic representation of words and instead makes use of a phonological representation by spelling through the phonological buffer.

Progressive impairment of constructional abilities: a visuospatial sketchpad deficit?

The case of a patient, PC, with an impairment of constructional abilities due to a progressive degenerative disease is described. Ideomotor apraxia was also present. PC showed difficulties in all tasks requiring a "manipulation" of a visual model or requiring a visual model to address a specific movement or a choice among alternatives. The spatial component of mental imagery was also severely impaired. The conclusion was that the patient presented a deficit of the rehearsal component of the visuospatial sketchpad (VSSP). This produced an impairment of spatial learning, but spatial retrograde memory was preserved, as well as object recognition. The most prominent sites of atrophy were located in the parietal lobe bilaterally. A 3-year follow-up is reported, showing a progressive impairment of verbal abilities.

Is autotopoagnosia real? EC says yes. A case study

We report a case of pure autotopagnosia (AT) following a left subcortical vascular accident. The absence of any language disorder, general mental deterioration or other cognitive impairments in this patient allowed an in-depth study of AT. Several tests of body representation and object and animal representation, as well as tests assessing semantic skills were administered to verify current interpretations of AT. Results showed a clear-cut dissociation between defective performances in body representation tests and normal performances on tests involving other kinds of stimuli. The patient's performances were particularly defective on tests relying on visuo-spatial body representation, but her semantic and linguistic knowledge seemed to be spared. This dissociation between different aspects of body representation supports Sirigu et al.'s hypothesis that multiple, partially independent systems are involved in body knowledge. In agreement with this hypothesis, in the present patient AT seems be due to a deficit in a system that processes the structural properties and relative position of single body parts. The present results, reporting the first observation of a subject not affected by any cognitive impairment other than AT, strongly support the existence of a system specifically devoted to body representation.

Visually- and motor-based knowledge of letters: evidence from a pure alexic patient

We describe a patient, VSB, whose reading was impaired as a consequence of a left temporal-parietal lesion, whereas writing was relatively preserved. At variance with other pure alexic patients described in the literature, VSB claimed to have become unable to mentally visualise letters and words. Indeed, his performance on a series of tests tapping visual mental imagery for orthographic material was severely impaired. However, performance on the same tests was dramatically ameliorated by allowing VSB to trace each item with his finger. Visual mental imagery for non-orthographic items was comparatively spared. The pattern of dissociation shown by VSB between impaired visual mental imagery and relatively preserved motor-based knowledge for orthographic material lends support to the view that separate codes, respectively based on visual appearance and on motor engrams, may be used to access knowledge of the visual form of letters and words.

The relationship between visual perception and visual mental imagery: a reappraisal of the neuropsychological evidence

Visual perception and visual mental imagery, the faculty whereby we can revisualise a visual item from memory, have often been regarded as cognitive functions subserved by common mechanisms. Thus, the leading cognitive model of visual mental imagery holds that visual perception and visual imagery share a number of mental operations, and rely upon common neural structures, including early visual cortices. In particular, a single visual buffer would be used "bottom-up" to display visual percepts and "top-down" to display internally generated images. The proposed neural substrate for this buffer consists of some cortical visual areas organised retinotopically, that is, the striate and extrastriate occipital areas. Empirical support for this model came from the report of brain-damaged patients showing an imagery deficit which parallels a perceptual impairment in the same cognitive domain. However, recent reports of patients showing double dissociations between perception and imagery abilities challenged the perception-imagery equivalence hypothesis from the functional point of view. From the anatomical point of view, the available evidence suggests that occipital damage is neither necessary nor sufficient to produce imagery deficits. On the other hand, extensive left temporal damage often accompanies imagery deficits for object form or colour. Thus, visual mental imagery abilities might require the integrity of brain areas related to vision, but at an higher level of integration than previously proposed.

Large, colorful, or noisy? Attribute- and modality-specific activations during retrieval of perceptual attribute knowledge

Position emission tomography was used to investigate whether retrieval of perceptual knowledge from long-term memory activates unique cortical regions associated with the modality and/or attribute type retrieved. Knowledge about the typical color, size, and sound of common objects and animals was probed, in response to written words naming the objects. Relative to a nonsemantic control task, all the attribute judgments activated similar left temporal and frontal regions. Visual (color, size) knowledge selectively activated the right posterior inferior temporal (PIT) cortex, whereas sound judgments elicited selective activation in the left posterior superior temporal gyrus and the adjacent parietal cortex. All of the attribute judgments activated a left PIT region, but color retrieval generated more activation in this area. Size judgments activated the right medial parietal cortex. These results indicate that the retrieval of perceptual semantic information activates not only a general semantic network, but also cortical areas specialized for the modality and attribute type of the knowledge retrieved.

The functional anatomy of the McCollough contingent colour after-effect

We report two functional magnetic resonance imaging (fMRI) experiments which reveal a cortical network activated when perceiving coloured grids, and experiencing the McCollough effect (ME). Our results show that perception of red-black and green-black grids activate the right fusiform gyrus (area V4) plus the left and right lingual gyri, right striate cortex (V1) and left insula. The ME activated the left anterior fusiform gyrus as well as the ventrolateral prefrontal cortex, and in common with colour perception, the left insula. These data confirm the critical role of the fusiform gyrus in actual and illusory colour perception as well as revealing localized frontal cortical activation associated with the ME, which would suggest that a 'top-down' mechanism is implicated in this illusion.

Cortical regions associated with perceiving, naming, and knowing about colors

Positron emission tomography (PET) was used to investigate whether retrieving information about a specific object attribute requires reactivation of brain areas that mediate perception of that attribute. During separate PET scans, subjects passively viewed colored and equiluminant gray-scale Mondrians, named colored and achromatic objects, named the color of colored objects, and generated color names associated with achromatic objects. Color perception was associated with activations in the lingual and fusiform gyri of the occipital lobes, consistent with previous neuroimaging and human lesion studies. Retrieving information about object color (generating color names for achromatic objects relative to naming achromatic objects) activated the left inferior temporal, left frontal, and left posterior parietal cortices, replicating previous findings from this laboratory. When subjects generated color names for achromatic objects relative to the low-level baseline of viewing gray-scale Mondrians, additional activations in the left fusiform/lateral occipital region were detected. However, these activations were lateral to the occipital regions associated with color perception and identical to occipital regions activated when subjects simply named achromatic objects relative to the same low-level baseline. This suggests that the occipital activations associated with retrieving color information were due to the perception of object form rather than to the top-down influence of brain areas that mediate color perception. Taken together, these results indicate that retrieving previously acquired information about an object's typical color does not require reactivation of brain regions that subserve color perception.

Hue memory and discrimination in young children

As first remarked by Charles Darwin (1877), very young children frequently have difficulty when naming or choosing colors. To investigate the cause of this difficulty, we have tested preschoolers (mean age = 4.1) for hue discrimination and hue memory and compared their results with those of preadolescents (mean age = 9.6) and young adults (mean age = 25.8). The tests were designed to minimize the influence of verbal coding on the results. We find that preschoolers are as good as the two older groups in hue discrimination. However, in visual hue memory, they are significantly poorer. The 3-fold increased errors they make, relative to preadolescents and young adults, may be related to the development of visual hue categories and the integration of verbal and visual processes. However, such errors cannot explain why young children often experience extreme difficulty in color naming.

The functional anatomy of imagining and perceiving colour

We report two functional magnetic resonance imaging experiments which reveal similarities and differences between perceptual and imaginal networks within the single visual submodality of colour. The first experiment contrasted viewing of a coloured and grey-scale Mondrian display, while the second contrasted a relative colour judgement with a spatial task and required the generation of mental images. Our results show that colour perception activates the posterior fusiform gyrus bilaterally (area V4), plus right-sided anterior fusiform and lingual gyri, striate cortex (area V1), and the left and right insula. Colour imagery activated right anterior fusiform gyrus, left insula, right hippocampus and parahippocampal gyrus, but not V4 or V1. The findings reconcile neurological case studies suggesting a double dissociation between deficits in colour imagery and perception and point to anterior fusiform, parahippocampal gyri and hippocampus as the location for stored representations of coloured objects.