Object identification in simultanagnosia: When wholes are not the sum of their parts

Abstract

We examined object identification in two simultanagnosic patients, ES and GK. We show that the patients tended to identify animate objects more accurately than inanimate objects (Experiments 1 and 4). The patients also showed relatively good identification of objects that could be recognised from their global shape, but not objects whose recognition depended on their internal detail (Experiment 2). Indeed, the presence of local segmentation cues disrupted global identification (Experiment 3). Identification was aided, though, by the presence of surface colour and texture (Experiment 4). We suggest that the patients could derive global representations of objects that served to recognise animate items. In contrast, they were impaired at coding parts-based representations for the identification of inanimate objects.     

Nouns, verbs, objects, actions, and the animate/inanimate effect

We report an aphasic patient, Z.B.L., who showed a significant advantage for verbs compared to nouns in picture-naming tests. Within the object class, he performed better on animate things than on nonliving things in picture naming as well as in an "attribute judgement task". This pattern of performance is contrary to the central prediction of a recent proposal (Bird, Howard, & Franklin, 2000), which attributes noun-verb dissociation in aphasic patients to deficits in processing certain kinds of semantic features. This model proposes that conceptual representations of verbs have a lower proportion of sensory features than do representations of nouns; the same is proposed for inanimate versus animate items within the noun category. Noun deficits are assumed to arise due to impairment for the processing of sensory features. The model predicts that if a patient is more impaired for nouns than for verbs, he will also display more difficulty with animate than with inanimate objects. Contrary to predications derived from this theory, Z.B.L. performed better with animate than inanimate nouns.     

Object category structure in response patterns of neuronal population in monkey inferior temporal cortex

Our mental representation of object categories is hierarchically organized, and our rapid and seemingly effortless categorization ability is crucial for our daily behavior. Here, we examine responses of a large number (>600) of neurons in monkey inferior temporal (IT) cortex with a large number (>1,000) of natural and artificial object images. During the recordings, the monkeys performed a passive fixation task. We found that the categorical structure of objects is represented by the pattern of activity distributed over the cell population. Animate and inanimate objects created distinguishable clusters in the population code. The global category of animate objects was divided into bodies, hands, and faces. Faces were divided into primate and nonprimate faces, and the primate-face group was divided into human and monkey faces. Bodies of human, birds, and four-limb animals clustered together, whereas lower animals such as fish, reptile, and insects made another cluster. Thus the cluster analysis showed that IT population responses reconstruct a large part of our intuitive category structure, including the global division into animate and inanimate objects, and further hierarchical subdivisions of animate objects. The representation of categories was distributed in several respects, e.g., the similarity of response patterns to stimuli within a category was maintained by both the cells that maximally responded to the category and the cells that responded weakly to the category. These results advance our understanding of the nature of the IT neural code, suggesting an inherently categorical representation that comprises a range of categories including the amply investigated face category.     

A tale of two agnosias: Distinctions between form and integrative agnosia

The performance of two patients with visual agnosia was compared across a number of tests examining visual processing. The patients were distinguished by having dorsal and medial ventral extrastriate lesions. While inanimate objects were disadvantaged for the patient with a dorsal extrastriate lesion, animate items are disadvantaged for the patient with the medial ventral extrastriate lesion. The patients also showed contrasting patterns of performance on the Navon Test: The patient with a dorsal extrastriate lesion demonstrated a local bias while the patient with a medial ventral extrastriate lesion had a global bias. We propose that the dorsal and medial ventral visual pathways may be characterized at an extrastriate level by differences in local relative to more global visual processing and that this can link to visually based category-specific deficits in processing.     

A tale of two agnosias: distinctions between form and integrative agnosia

The performance of two patients with visual agnosia was compared across a number of tests examining visual processing. The patients were distinguished by having dorsal and medial ventral extrastriate lesions. While inanimate objects were disadvantaged for the patient with a dorsal extrastriate lesion, animate items are disadvantaged for the patient with the medial ventral extrastriate lesion. The patients also showed contrasting patterns of performance on the Navon Test: The patient with a dorsal extrastriate lesion demonstrated a local bias while the patient with a medial ventral extrastriate lesion had a global bias. We propose that the dorsal and medial ventral visual pathways may be characterized at an extrastriate level by differences in local relative to more global visual processing and that this can link to visually based category-specific deficits in processing.     

Visual processing in patients with Frégoli syndrome

We investigated four paranoid schizophrenic patients diagnosed with Frégoli delusion, and four matched psychotic controls. Neuropsychological testing included visual and verbal recognition memory, in addition to a comparison of left and right hemispheric processing of two different classes of stimuli, animate and inanimate objects. Performance on the recognition memory test failed to discriminate between the two psychotic groups on the basis of facial recognition, however, the patients with Frégoli delusion failed to show the right hemisphere processing advantage for the animate class of stimuli found for the set of norms and also present in the psychotic control group. These results are discussed in the context of both current theories of the delusional misidentification syndromes in general, and models of facial recognition in particular.     

The representation of unseen objects in visual neglect: effects of view and object identity

We provide evidence for long-term priming based on view-specific representations of neglected stimuli. A patient with visual neglect, M.P., was asked to search for a target presented amongst other objects on a table. Subsequently recognition memory was tested for items that were identified and for items missed in search. Items that were missed were rejected more slowly than novel items in the recognition memory task, providing evidence for implicit processing (Experiment 1). Implicit memory for missed items was both item-specific (Experiment 2) and view-specific (Experiment 3), and it was eliminated when there were intervening activities lasting about 1 hour (Experiment 4). There was also an implicit memory for distractors in the search task, which was item- but not view-specific (Experiments 2 and 3) and it lasted for at least an hour, even with other intervening activities (Experiment 4). The data suggest that the representations of neglected stimuli may differ qualitatively from those of nonneglected items, with representations of neglected objects being both view-specific and vulnerable across extended retention intervals. The results support the argument that attention is needed in order to encode object representations that are robust to view transformations and temporal decay or interference.     

Visual Processing in Patients with Fregoli Syndrome

W e investigated four paranoid schizophrenic patients diagnosed with Fregoli delusion, and four matched psychotic controls. Neuropsychological testing included visual and verbal recognition memory, in addition to a comparison of left and right hemispheric processing of two different classes of stimuli, animate and inanimate objects. Performance on the recognition memory test failed to discriminate between the two psychotic groups on the basis of facial recognition, however, the patients with Fre goli delusion failed to show the right hemisphere processing advantage for the animate class of stimuli found for the set of norms and also present in the psychotic control group. These results are discussed in the context of both current theories of the delusional misidentification syndromes in general, and models of facial recognition in particular.     

A deficit in contralesional object representation associated with attentional limitations after parietal damage

Stankiewicz, Hummel, and Cooper (1998) proposed that detailed coding of part-whole relations for objects is contingent on objects being attended. We report a neuropsychological test of this assertion. We examined the effects of left-right reflection on object matching in a group of patients with parietal damage and impaired attention to the contralesional side of space (Experiment 1). The patients were poor at matching objects subject to left-right reflection, relative to identical stimuli (Experiment 2). This was not due to a lack of sensitivity to information on the contralesional side. In a subsequent study, the patients were better at matching identical whole objects at fixation than when they just received half the object in their ipsilesional field (Experiment 3). However, unlike both nonlesioned controls and control patients with frontal lesions, the parietal patients were unaffected by altering the relative spatial locations of object features in their contralesional field (Experiment 4). The basic result, of poor performance with left-right-reflected items, was also replicated using a priming rather than an explicit matching procedure (Experiment 5). These results provide confirmation that visual attention, mediated by the posterior parietal cortex, is important for generating part-whole codes that facilitate the matching of mirror-reflected objects.     

A deficit in contralesional object representation associated with attentional limitations after parietal damage

Stankiewicz, Hummel, and Cooper (1998) proposed that detailed coding of part–whole relations for objects is contingent on objects being attended. We report a neuropsychological test of this assertion. We examined the effects of left–right reflection on object matching in a group of patients with parietal damage and impaired attention to the contralesional side of space (Experiment 1). The patients were poor at matching objects subject to left–right reflection, relative to identical stimuli (Experiment 2). This was not due to a lack of sensitivity to information on the contralesional side. In a subsequent study, the patients were better at matching identical whole objects at fixation than when they just received half the object in their ipsilesional field (Experiment 3). However, unlike both nonlesioned controls and control patients with frontal lesions, the parietal patients were unaffected by altering the relative spatial locations of object features in their contralesional field (Experiment 4). The basic result, of poor performance with left–right-reflected items, was also replicated using a priming rather than an explicit matching procedure (Experiment 5). These results provide confirmation that visual attention, mediated by the posterior parietal cortex, is important for generating part–whole codes that facilitate the matching of mirror-reflected objects.     

Nouns,verbs, objects,actions, and the animate/inanimate effect

We report an aphasic patient, Z.B.L., who showed a significant advantage for verbs compared to nouns in picture-naming tests. Within the object class, he performed better on animate things than on nonliving things in picture naming as well as in an “attribute judgement task”. This pattern of performance is contrary to the central prediction of a recent proposal (Bird, Howard, & Franklin, 2000 Bird, H., Howard, D. and Franklin, S. 2000. Why is a verb like an inanimate object? Grammatical category and semantic category deficits. Brain and Language, 72: 246–309. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]), which attributes noun–verb dissociation in aphasic patients to deficits in processing certain kinds of semantic features. This model proposes that conceptual representations of verbs have a lower proportion of sensory features than do representations of nouns; the same is proposed for inanimate versus animate items within the noun category. Noun deficits are assumed to arise due to impairment for the processing of sensory features. The model predicts that if a patient is more impaired for nouns than for verbs, he will also display more difficulty with animate than with inanimate objects. Contrary to predications derived from this theory, Z.B.L. performed better with animate than inanimate nouns.     

Core knowledge of object,number, and geometry: A comparative and neural approach

Studies on the ontogenetic origins of human knowledge provide evidence for a small set of separable systems of core knowledge dealing with the representation of inanimate and animate objects, number, and geometry. Because core knowledge systems are evolutionarily ancient, they can be investigated from a comparative perspective, making use of various animal models. In this review, I discuss evidence showing precocious abilities in nonhuman species to represent (a) objects that move partly or fully out of view and their basic mechanical properties such as solidity, (b) the cardinal and ordinal/sequential aspects of numerical cognition and rudimentary arithmetic with small numerosities, and (c) the geometrical relationships among extended surfaces in the surrounding layout. Controlled rearing studies suggest that the abilities associated with core knowledge systems of objects, number, and geometry are observed in animals in the absence (or with very reduced) experience, supporting a nativistic foundation of such cognitive mechanisms. Animal models also promise a fresh approach to the issue of the neurobiological and genetic mechanisms underlying the expression of core knowledge systems.     

Cortical neurons combine visual cues about self-movement

Visual cues about self-movement are derived from the patterns of optic flow and the relative motion of discrete objects. We recorded dorsal medial superior temporal (MSTd) cortical neurons in monkeys that held centered visual fixation while viewing optic flow and object motion stimuli simulating the self-movement cues seen during translation on a circular path. Twenty stimulus configurations presented naturalistic combinations of optic flow with superimposed objects that simulated either earth-fixed landmark objects or independently moving animate objects. Landmarks and animate objects yield the same response interactions with optic flow; mainly additive effects, with a substantial number of sub- and super-additive responses. Sub- and super-additive interactions reflect each neuron’s local and global motion sensitivities: Local motion sensitivity is based on the spatial arrangement of directions created by object motion and the surrounding optic flow. Global motion sensitivity is based on the temporal sequence of self-movement headings that define a simulated path through the environment. We conclude that MST neurons’ spatio-temporal response properties combine object motion and optic flow cues to represent self-movement in diverse, naturalistic circumstances.     

Lateralization of ventral fins use during object exploration in the blue gourami (Trichogaster trichopterus)

Blue gourami fish have a pair of modified ventral fins that are used to obtain tactile information about surrounding objects. Use of ventral fins by blue gourami was investigated during initial exploration of novel objects. When exposed to a sequence of novel plastic objects, varying in shape and colour, the blue gourami showed preferential use of the left fin during initial contacts. Laterality apparently depends on the nature of the stimulus: Fish exposed to a randomized series of natural objects showed preferential use of the left fin for inanimate mineral objects, but no asymmetry was apparent for investigating animate objects. This would suggest that some form of 'handedness' may have been present prior to the appearance of tetrapods. On the other hand, measurements of fish monocular viewing revealed that the fin use was strongly associated with preferential use of the ipsilateral eye before the touching of the stimulus took place, thus, suggesting that the asymmetry in fin use may also be related to lateralization of the visual system.     

The role of action representations in visual object recognition

It is typically assumed that perception for action and object recognition are subserved by functionally and neuroanatomically distinct processing streams in the brain. However, recent evidence challenges this classical view and suggests an interaction between both visual processing streams. While previous studies showed an influence of object perception on action-related tasks, we investigated whether action representations facilitate visual object recognition. In order to address this question, two briefly displayed masked objects were sequentially presented, either affording congruent or incongruent motor interactions. We found superior naming accuracy for object pairs with congruent as compared to incongruent motor interactions (Experiment 1). This action priming effect indicates that action representations can facilitate object recognition. We further investigated the nature of the representations underlying this action priming effect. The effect was absent when the prime stimulus was presented as a word (Experiment 2). Thus, the action priming effect seems to rely on action representations specified by visual object information. Our findings suggest that processes of object-directed action influence object recognition.     

Local capture in Balint's syndrome: effects of grouping and item familiarity

We assessed the factors contributing to local capture in G.K., a patient with Balint's syndrome. G.K. found it difficult to identify the global shape of a compound stimulus, and his poor identification of the global shape was not resolved by introducing familiar local stimuli that were either from the same category as the global target but not tied to a response (Experiment 1) or that belonged to a different category to the target (Experiment 2). Effects of item familiarity were tested by examining local capture from Hebrew letters on compound English letters. Prior to training with the Hebrew letters, G.K. was able to identify the global compounds (Experiment 3a). In contrast, after training with the letters, there was a significant increase in local capture (Experiment 3b). Two additional experiments examined effects of local grouping. Local capture was reduced when the local elements were rectangles or ellipses and grouped by closure of local elements (Experiment 4). Global discrimination also improved when local items were unfamiliar rectangular figure eights (Experiment 5a). However, these grouping effects were counteracted by effects of familiarity when the local elements were changed slightly to become familiar number eights (Experiment 5b). The data suggest that familiar local items are likely to capture spatial attention, whilst grouping by closure between local elements can help global shapes compete for spatial attention with local elements in such patients. The impairment in global perception in Balint's syndrome is not all-or-none but graded according to the factors influencing local capture.     

Local capture in Balint's syndrome: Effects of grouping and item familiarity

We assessed the factors contributing to local capture in G.K., a patient with Balint's syndrome. G.K. found it difficult to identify the global shape of a compound stimulus, and his poor identification of the global shape was not resolved by introducing familiar local stimuli that were either from the same category as the global target but not tied to a response (Experiment 1) or that belonged to a different category to the target (Experiment 2). Effects of item familiarity were tested by examining local capture from Hebrew letters on compound English letters. Prior to training with the Hebrew letters, G.K. was able to identify the global compounds (Experiment 3a). In contrast, after training with the letters, there was a significant increase in local capture (Experiment 3b). Two additional experiments examined effects of local grouping. Local capture was reduced when the local elements were rectangles or ellipses and grouped by closure of local elements (Experiment 4). Global discrimination also improved when local items were unfamiliar rectangular figure eights (Experiment 5a). However, these grouping effects were counteracted by effects of familiarity when the local elements were changed slightly to become familiar number eights (Experiment 5b). The data suggest that familiar local items are likely to capture spatial attention, whilst grouping by closure between local elements can help global shapes compete for spatial attention with local elements in such patients. The impairment in global perception in Balint's syndrome is not all-or-none but graded according to the factors influencing local capture.     

Age and binding within-dimension features in visual short-term memory

Older adults have difficulties in binding information in long-term memory (e.g. objects with colours). The effect of age on visual short-term memory (VSTM) binding is less well understood. Recent evidence has suggested that older adults' VSTM for colours bound to shapes or for locations bound in configural representations may be preserved. In two experiments we investigated whether this lack of an age effect on VSTM for bound features can be reproduced when features are drawn from the same dimension (i.e. colour-colour binding) and when spatial clues are not available. Younger and older adults were presented with two sequential arrays of unicoloured or bicoloured objects and their accuracy in detecting changes between arrays was used as the measure of memory performance. Memory was assessed using a change detection paradigm for unicoloured objects and for bicoloured objects with changes in colour conjunctions (i.e. colours swapping between objects) or with changes in non-conjunctive colours (i.e. colours replacing colours in the study array). Both young and older adults were less accurate at remembering objects defined by colour conjunctions than unicoloured objects or objects composed of two non-conjunctive colours (Experiment 1). Increasing task demands in terms of memory and perceptual load had no greater effect on the older than the younger adults (Experiment 2). We suggest (1) that colours were not integrated into single units in VSTM; (2) that remembering the binding between colours has a cost; and (3) that neither of these effects are age-dependent.     

Implicit Location Encoding Via Stored Representations Of Familiar Objects: Neuropsychological Evidence

We report data on the visual localisation ability of a patient with Balint's syndrome, GK. We show that, with relatively long exposures of displays, GK is better able to judge the spatial relations between separate objects (a “between-object judgement”) than the spatial relations between a part and a whole object (a “within-object judgement”) (Experiments 1–3). This dissociation occurred even when the same stimulus was used for both judgements, and the task instructions biased GK to parse the stimulus as either a single or as two separate objects (Experiments 2 and 6). However, when he could use a stored representation to make a within-object judgement, then performance was better than on a comparable spatial judgement of the relations between two separate objects (Experiments 4–7). The data demonstrate that stored representations of objects can support the spatial coding of parts to perceptual wholes. In the absence of stored representations, part-whole relations must be explicitly coded by attention, a process that is impaired in this patient.     

Implicit location encoding via stored representations of familiar objects: neuropsychological evidence

We report data on the visual localisation ability of a patient with Balint's syndrome, GK. We show that, with relatively long exposures of displays, GK is better able to judge the spatial relations between separate objects (a "between-object judgement") than the spatial relations between a part and a whole object (a "within-object judgement") (Experiments 1-3). This dissociation occurred even when the same stimulus was used for both judgements, and the task instructions biased GK to parse the stimulus as either a single or as two separate objects (Experiments 2 and 6). However, when he could use a stored representation to make a within-object judgement, then performance was better than on a comparable spatial judgement of the relations between two separate objects (Experiments 4-7). The data demonstrate that stored representations of objects can support the spatial coding of parts to perceptual wholes. In the absence of stored representations, part-whole relations must be explicitly coded by attention, a process that is impaired in this patient.