Rigid And Nonrigid Objects In Canonical And Noncanonical Views: Hemisphere-Specific Effects On Object Identification

The effects of changes in object location on object identity detection: A simultaneous EEG-fMRI study

Object identity and location are bound together to form a unique integration that is maintained and processed in visual working memory (VWM). Changes in task-irrelevant object location have been shown to impair the retrieval of memorial representations and the detection of object identity changes. However, the neural correlates of this cognitive process remain largely unknown. In the present study, we aim to investigate the underlying brain activation during object color change detection and the modulatory effects of changes in object location and VWM load. To this end we used simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) recordings, which can reveal the neural activity with both high temporal and high spatial resolution. Subjects responded faster and with greater accuracy in the repeated compared to the changed object location condition, when a higher VWM load was utilized. These results support the spatial congruency advantage theory and suggest that it is more pronounced with higher VWM load. Furthermore, the spatial congruency effect was associated with larger posterior N1 activity, greater activation of the right inferior frontal gyrus (IFG) and less suppression of the right supramarginal gyrus (SMG), when object location was repeated compared to when it was changed. The ERP-fMRI integrative analysis demonstrated that the object location discrimination-related N1 component is generated in the right SMG.

Hemispheric lateralization in top-down attention during spatial relation processing: a Granger causal model approach

Magnetoencephalography was recorded during a matching-to-sample plus cueing paradigm, in which participants judged the occurrence of changes in either categorical (CAT) or coordinate (COO) spatial relations. Previously, parietal and frontal lobes were identified as key areas in processing spatial relations and it was shown that each hemisphere was differently involved and modulated by the scope of the attention window (e.g. a large and small cue). In this study, Granger analysis highlighted the patterns of causality among involved brain areas--the direction of information transfer ran from the frontal to the visual cortex in the right hemisphere, whereas it ran in the opposite direction in the left side. Thus, the right frontal area seems to exert top-down influence, supporting the idea that, in this task, top-down signals are selectively related to the right side. Additionally, for CAT change preceded by a small cue, the right frontal gyrus was not involved in the information transfer, indicating a selective specialization of the left hemisphere for this condition. The present findings strengthen the conclusion of the presence of a remarkable hemispheric specialization for spatial relation processing and illustrate the complex interactions between the lateralized parts of the neural network. Moreover, they illustrate how focusing attention over large or small regions of the visual field engages these lateralized networks differently, particularly in the frontal regions of each hemisphere, consistent with the theory that spatial relation judgements require a fronto-parietal network in the left hemisphere for categorical relations and on the right hemisphere for coordinate spatial processing.

Testing the reliability of hands and ears as biometrics: the importance of viewpoint

Two experiments are presented to explore the limits when matching a sample to a suspect utilising the hand as a novel biometric. The results of Experiment 1 revealed that novice participants were able to match hands at above-chance levels as viewpoint changed. Notably, a moderate change in viewpoint had no notable effect, but a more substantial change in viewpoint affected performance significantly. Importantly, the impact of viewpoint when matching hands was smaller than that when matching ears in a control condition. This was consistent with the suggestion that the flexibility of the hand may have minimised the negative impact of a sub-optimal view. The results of Experiment 2 confirmed that training via a 10-min expert video was sufficient to reduce the impact of viewpoint in the most difficult case but not to remove it entirely. The implications of these results were discussed in terms of the theoretical importance of function when considering the canonical view and in terms of the applied value of the hand as a reliable biometric across viewing conditions.

Focusing narrowly or broadly attention when judging categorical and coordinate spatial relations: a MEG study

We measured activity in the dorsal system of the human cortex with magnetoencephalography (MEG) during a matching-to-sample plus cueing paradigm, where participants judged the occurrence of changes in either categorical or coordinate spatial relations (e.g., exchanges of left versus right positions or changes in the relative distances) between images of pairs of animals. The attention window was primed in each trial to be either small or large by using cues that immediately preceded the matching image. In this manner, we could assess the modulatory effects of the scope of attention on the activity of the dorsal system of the human cortex during spatial relations processing. The MEG measurements revealed that large spatial cues yielded greater activations and longer peak latencies in the right inferior parietal lobe for coordinate trials, whereas small cues yielded greater activations and longer peak latencies in the left inferior parietal lobe for categorical trials. The activity in the superior parietal lobe, middle frontal gyrus, and visual cortex, was also modulated by the size of the spatial cues and by the type of spatial relation change. The present results support the theory that the lateralization of each kind of spatial processing hinges on differences in the sizes of regions of space attended to by the two hemispheres. In addition, the present findings are inconsistent with the idea of a right-hemispheric dominance for all kinds of challenging spatial tasks, since response times and accuracy rates showed that the categorical spatial relation task was more difficult than the coordinate task and the cortical activations were overall greater in the left hemisphere than in the right hemisphere.

Imitation of a bimanual task in preschool- and school-age children: a hierarchical construction

The present study examined the development of bimanual interaction during the imitation of a live demonstration. To this end, children of five different age groups observed an adult model performing in an object manipulation task consisting to open a box with one hand, taking out an object with the other hand, and closing the box again, before they were asked to imitate this motor task under different imitation conditions. The children's responses were videotaped, coded in dichotomous data, and then transformed in percentage scores. The main results showed that all children were able to imitate/attain the goal of the task. However, differences were observed for the different imitation conditions, which were also reflected in some age effects, while hand dominance was a strong constraint on imitation. Also, practice did not seem to increase the likelihood of model imitation. These findings confirm that imitation is a reconstruction mechanism hierarchically organized.

Lateralized effects of categorical and coordinate spatial processing of component parts on the recognition of 3D non-nameable objects

Participants performed two object-matching tasks for novel, non-nameable objects consisting of geons. For each original stimulus, two transformations were applied to create comparison stimuli. In the categorical transformation, a geon connected to geon A was moved to geon B. In the coordinate transformation, a geon connected to geon A was moved to a different position on geon A. The Categorical task consisted of the original and the categorically transformed objects. The Coordinate task consisted of the original and the coordinately transformed objects. The original object was presented to the central visual field, followed by a comparison object presented to the right or left visual half-fields (RVF and LVF). The results showed an RVF advantage for the Categorical task and an LVF advantage for the Coordinate task. The possibility that categorical and coordinate spatial processing subsystems would be basic computational elements for between- and within-category object recognition was discussed.

Knowing where but not what: impaired thematic roles and spatial language

We describe case J.P. who, following a left inferior frontal lesion, made frequent role confusions in comprehension and production (e.g., saying "The boy kicks the girl" for a picture showing a girl kicking a boy). J.P.'s preserved ability to judge the grammaticality of sentences rules out a syntactic deficit as the primary cause of the role confusions. Thematic role assignment is also required with spatial prepositions such as in or above, and J.P.'s thematic role assignment was also severely impaired with spatial prepositions. We capitalized on prior linguistic analyses and behavioural studies to design accurate tests of the semantics of spatial terms, spatial relations, and critical features of objects. Fine-grain semantic tests revealed that the semantics of spatial terms and objects was intact. We hypothesize that J.P.'s role confusions reflected a failure to integrate objects within semantic representations that define the thematic roles. Our data suggest that properties of objects and thematic roles are specified by distinct semantic processes, which have different brain localizations. J.P.'s lesion further suggests that left inferior frontal regions are critical in thematic role assignment, thus contributing to the understanding of the linguistic functions of these regions.

Fast perceptual priming in the left and right hemispheres

Visual field differences in fast perceptual priming of possible and impossible object decisions were investigated in a go/no-go task. Each participant (n = 74) was tested in two blocks of trials, each block containing 128 combinations of same-field and cross-field presentations of prime (blank) and target stimuli. The results indicate that fast perceptual priming of object decisions recruits processes that involve both cerebral hemispheres, independent of pre-existing representation. The priming effect was larger for possible than for impossible objects, but fast perceptual priming of object-decisions was demonstrated for both possible and impossible objects, in terms of both reaction times and accuracy. Left-hemisphere specific priming for impossible stimuli may be due to a left hemisphere encoding advantage for impossible parts, consistent with a structural description account.

Neural representations of perceived bodily actions using a categorical frame of reference

In object-centered, or categorical, visual representations of an agent's actions, the spatial positions of (parts of) the body action are defined with respect to the principal axis of the agent, rather than in relation to the observer. Some cells in the superior temporal sulcus (STS) of the macaque monkey have been reported to use such a categorical frame of reference to code for bodily postures and actions, but their small numbers prevented a detailed investigation. Here we report for the first time that anterior sites in the STS contain a relatively large number of cells that use an object-centered frame of reference to code for animate objects and their actions. We further show that these cells are selectively responsive to much more restricted sections of an action trajectory than previously thought, and that they generalize over highly unusual, hitherto untested, orientations (such as upside-down walking). Quite remarkably, some cells coded for the position of a body part not only with respect to the object's body structure, but also with respect to objects in the immediate surrounding, such as the supporting substrate the agent was standing on. We illustrate these properties using three cell populations: one responding to rotations of the upper body with respect to the lower body, one responding to forward or backward walking actions, and one responding to flexions of the knees. We discuss a possible role for the object-centered STS cell populations in representing the abstract object structure of flexible, animate objects, which could enable their recognition even when presented in highly unusual poses. We further discuss their possible role in representing goal-directed or intentional actions, and in imitation.

Prefrontal cortex hemispheric specialization for categorical and coordinate visual spatial memory

During visual spatial perception of multiple items, the left hemisphere has been shown to preferentially process categorical spatial relationships while the right hemisphere has been shown to preferentially process coordinate spatial relationships. We hypothesized that this hemispheric processing distinction would be reflected in the prefrontal cortex during categorical and coordinate visual spatial memory, and tested this hypothesis using functional magnetic resonance imaging (fMRI). During encoding, abstract shapes were presented in the left or right hemifield in addition to a dot at a variable distance from the shape (with some dots on the shape); participants were instructed to remember the position of each dot relative to the shape. During categorical memory retrieval, each shape was presented centrally and participants responded whether the previously corresponding dot was 'on' or 'off' of the shape. During coordinate memory retrieval, each shape was presented centrally and participants responded whether the previously corresponding dot was 'near' or 'far' from the shape (relative to a reference distance). Consistent with our hypothesis, a region in the left prefrontal cortex (BA10) was preferentially associated with categorical visual spatial memory and a region in the right prefrontal cortex (BA9/10) was preferentially associated with coordinate visual spatial memory. These results have direct implications for interpreting previous findings that the left prefrontal cortex is associated with source memory, as this cognitive process is categorical in nature, and the right prefrontal cortex is associated with item memory, as this process depends on the precise spatial relations among item features or components.

Constructional apraxia after left or right unilateral stroke

The present study re-assesses the question whether deficits, after brain damage, in constructional tasks can be partitioned in different types of disorders of spatial cognition. Based on a current cognitive neuroscience account, originally proposed by Kosslyn [Kosslyn, S. M. (1987). Seeing and imagining in the cerebral hemispheres: A computational approach. Psychological Review, 94, 148-175], that posits two complementary lateralized systems for the encoding of (categorical and coordinate) spatial relations, it is here proposed that two qualitatively different types of "constructional apraxia" can occur and that the nature of the constructional impairment after unilateral lesions closely reflects the loss of lateralized components for the perceptual processing of differing types of spatial relations. New evidence is presented, based on the study of two groups of patients with unilateral posterior brain lesions, which supports such a bipartition of constructional apraxia. In addition, past evidence is reviewed in the light of this new cognitive neuroscience account.