Effects of structural similarity on neural substrates for object recognition

Semantic interference and its control: A functional neuroimaging and connectivity study

During picture naming, the ease with which humans generate words is dependent upon the context in which they are named. For instances, naming previously presented items results in facilitation. Instead, naming a picture semantically related to previous items displays persistent interference effects (i.e., cumulative semantic interference, CSI). The neural correlates of CSI are still unclear and it is a matter of debate whether semantic control, or cognitive control more in general, is necessary for the resolution of CSI. We carried out an event-related fMRI experiment to assess the neural underpinnings of the CSI effect and the involvement and nature of semantic control. Both left inferior frontal gyrus (LIFG) and the left caudate nucleus (LCN) showed a linear increase of BOLD response positively associated with the consecutive number of presentations of semantically related pictures independently of task-load. The generalized psychophysiological interaction analysis showed that LIFG demonstrated a quantitative neural connectivity difference with the left supramarginal and angular gyri for increases of task-load and with the fusiform gyri for linear CSI increases. Furthermore, seed-to-voxel functional connectivity showed that LIFG activity coupled with different regions involved in cognitive control and lexicosemantic processing when semantic interference was elicited to a minimum or maximum degree. Our results are consistent with the lexical-competitive nature of the CSI effect, and we provide novel evidence that semantic control lies upon a more general cognitive control network (i.e., LIFG and LCN) responsible for resolving interference between competing semantically related items through connectivity with different brain areas in order to guarantee the correct response. Hum Brain Mapp 37:4179-4196, 2016. © 2016 Wiley Periodicals, Inc.

Cross-cultural differences in the neural correlates of specific and general recognition

Research suggests that culture influences how people perceive the world, which extends to memory specificity, or how much perceptual detail is remembered. The present study investigated cross-cultural differences (Americans vs East Asians) at the time of encoding in the neural correlates of specific versus general memory formation. Participants encoded photos of everyday items in the scanner and 48 h later completed a surprise recognition test. The recognition test consisted of same (i.e., previously seen in scanner), similar (i.e., same name, different features), or new photos (i.e., items not previously seen in scanner). For Americans compared to East Asians, we predicted greater activation in the hippocampus and right fusiform for specific memory at recognition, as these regions were implicated previously in encoding perceptual details. Results revealed that East Asians activated the left fusiform and left hippocampus more than Americans for specific versus general memory. Follow-up analyses ruled out alternative explanations of retrieval difficulty and familiarity for this pattern of cross-cultural differences at encoding. Results overall suggest that culture should be considered as another individual difference that affects memory specificity and modulates neural regions underlying these processes.

Typical and atypical neurodevelopment for face specialization: an FMRI study

Individuals with autism spectrum disorder (ASD) and their relatives process faces differently from typically developed (TD) individuals. In an fMRI face-viewing task, TD and undiagnosed sibling (SIB) children (5-18 years) showed face specialization in the right amygdala and ventromedial prefrontal cortex, with left fusiform and right amygdala face specialization increasing with age in TD subjects. SIBs showed extensive antero-medial temporal lobe activation for faces that was not present in any other group, suggesting a potential compensatory mechanism. In ASD, face specialization was minimal but increased with age in the right fusiform and decreased with age in the left amygdala, suggesting atypical development of a frontal-amygdala-fusiform system which is strongly linked to detecting salience and processing facial information.

Structural Similarity Exerts Opposing Effects on Perceptual Differentiation and Categorization: An fMRI Study

We manipulated the degree of structural similarity between objects that had to be matched either according to whether they represented the same object (perceptual matching) or belonged to the same category (conceptual matching). Behaviorally, performance improved as a linear function of increased structural similarity during conceptual matching but deteriorated as a linear function of increased structural similarity during perceptual matching. These effects were mirrored in fMRI recordings where activation in several ventral posterior areas exhibited a similar interaction between match type and structural similarity. Our findings provide direct support for the notion that structural similarity exerts opposing effects on classification depending on whether objects are to be perceptually differentiated or categorized—a notion that has been based on rather circumstantial evidence. In particular, the finding that structural similarity plays a major role in categorization of instances according to taxonomy challenges the view that the organization of superordinate categories is not driven by shared structural features.

Functional correlates of preserved naming performance in amnestic Mild Cognitive Impairment

Naming abilities are typically preserved in amnestic Mild Cognitive Impairment (aMCI), a condition associated with increased risk of progression to Alzheimer's disease (AD). We compared the functional correlates of covert picture naming and word reading between a group of aMCI subjects and matched controls. Unimpaired picture naming performance was associated with more extensive activations, in particular involving the parietal lobes, in the aMCI group. In addition, in the condition associated with higher processing demands (blocks of categorically homogeneous items, living items), increased activity was observed in the aMCI group, in particular in the left fusiform gyrus. Graph analysis provided further evidence of increased modularity and reduced integration for the homogenous sets in the aMCI group. The functional modifications associated with preserved performance may reflect, in the case of more demanding tasks, compensatory mechanisms for the subclinical involvement of semantic processing areas by AD pathology.

Process and domain specificity in regions engaged for face processing: an fMRI study of perceptual differentiation

The degree to which face-specific brain regions are specialized for different kinds of perceptual processing is debated. This study parametrically varied demands on featural, first-order configural, or second-order configural processing of faces and houses in a perceptual matching task to determine the extent to which the process of perceptual differentiation was selective for faces regardless of processing type (domain-specific account), specialized for specific types of perceptual processing regardless of category (process-specific account), engaged in category-optimized processing (i.e., configural face processing or featural house processing), or reflected generalized perceptual differentiation (i.e., differentiation that crosses category and processing type boundaries). ROIs were identified in a separate localizer run or with a similarity regressor in the face-matching runs. The predominant principle accounting for fMRI signal modulation in most regions was generalized perceptual differentiation. Nearly all regions showed perceptual differentiation for both faces and houses for more than one processing type, even if the region was identified as face-preferential in the localizer run. Consistent with process specificity, some regions showed perceptual differentiation for first-order processing of faces and houses (right fusiform face area and occipito-temporal cortex and right lateral occipital complex), but not for featural or second-order processing. Somewhat consistent with domain specificity, the right inferior frontal gyrus showed perceptual differentiation only for faces in the featural matching task. The present findings demonstrate that the majority of regions involved in perceptual differentiation of faces are also involved in differentiation of other visually homogenous categories.

Semantic category effects modulate visual priming in neglect patients

Previous studies indicate that extinguished stimuli can still be unconsciously processed, leading to implicit priming effects. Here we investigated whether these implicit effects might be modulated by the semantic nature of the stimuli. Five neglect patients and ten controls performed an identification task of items belonging to living and non-living categories. In the study phase photographs of animals and artifacts were presented either to the left visual field (LVF) or to the right visual field (RVF). In the identification phase, each stimulus was displayed centrally and was revealed in a sequence of frames where the item was represented by an increasingly less and less filtered image up to a complete version. The results showed that lateralized stimuli differentially affected controls' and neglect patients' memory retrieval. In controls memory traces from the study phase served as efficient primes, thereby reducing the amount of information necessary for the identification of both stimulus categories. Moreover, hemispheric differences emerged with an advantage of the RVF/left hemisphere for artifact items, while no difference was found for living things. Neglect patients showed a priming effect for artifact items presented either to the RVF/left hemisphere or LVF/right hemisphere, as well as for living items presented to the RVF/left hemisphere, but not for living items presented to the LVF/right hemisphere. The priming effect observed for extinguished artifacts is consistent with the evidence of the existence of a specific mechanism destined to analyze, in an automatic and implicit fashion, motor-relevant information of manipulable objects and tools, which are important for identification process. Results are discussed in relation to current models of organization of conceptual knowledge within the framework of different processes performed by the two hemispheres.

Testing for the dual-route cascade reading model in the brain: an fMRI effective connectivity account of an efficient reading style

Neuropsychological data about the forms of acquired reading impairment provide a strong basis for the theoretical framework of the dual-route cascade (DRC) model which is predictive of reading performance. However, lesions are often extensive and heterogeneous, thus making it difficult to establish precise functional anatomical correlates. Here, we provide a connective neural account in the aim of accommodating the main principles of the DRC framework and to make predictions on reading skill. We located prominent reading areas using fMRI and applied structural equation modeling to pinpoint distinct neural pathways. Functionality of regions together with neural network dissociations between words and pseudowords corroborate the existing neuroanatomical view on the DRC and provide a novel outlook on the sub-regions involved. In a similar vein, congruent (or incongruent) reliance of pathways, that is reliance on the word (or pseudoword) pathway during word reading and on the pseudoword (or word) pathway during pseudoword reading predicted good (or poor) reading performance as assessed by out-of-magnet reading tests. Finally, inter-individual analysis unraveled an efficient reading style mirroring pathway reliance as a function of the fingerprint of the stimulus to be read, suggesting an optimal pattern of cerebral information trafficking which leads to high reading performance.

Category-specificity in visual object recognition

Are all categories of objects recognized in the same manner visually? Evidence from neuropsychology suggests they are not: some brain damaged patients are more impaired in recognizing natural objects than artefacts whereas others show the opposite impairment. Category-effects have also been demonstrated in neurologically intact subjects, but the findings are contradictory and there is no agreement as to why category-effects arise. This article presents a pre-semantic account of category-effects (PACE) in visual object recognition. PACE assumes two processing stages: shape configuration (the binding of shape elements into elaborate shape descriptions) and selection (among competing representations in visual long-term memory), which are held to be differentially affected by the structural similarity between objects. Drawing on evidence from clinical studies, experimental studies with neurologically intact subjects and functional imaging studies, it is argued that PACE can account for category-effects at both behavioural and neural levels in patients and neurologically intact subjects. The theory also accounts for the way in which category-effects are affected by different task parameters (the degree of perceptual differentiation called for), stimulus characteristics (whether stimuli are presented as silhouettes, full line-drawings, or fragmented forms), stimulus presentation (stimulus exposure duration and position) as well as interactions between these parameters.

Mid-fusiform activation during object discrimination reflects the process of differentiating structural descriptions

The present study explored constraints on mid-fusiform activation during object discrimination. In three experiments, participants performed a matching task on simple line configurations, nameable objects, three dimensional (3-D) shapes, and colors. Significant bilateral mid-fusiform activation emerged when participants matched objects and 3-D shapes, as compared to when they matched two-dimensional (2-D) line configurations and colors, indicating that the mid-fusiform is engaged more strongly for processing structural descriptions (e.g., comparing 3-D volumetric shape) than perceptual descriptions (e.g., comparing 2-D or color information). In two of the experiments, the same mid-fusiform regions were also modulated by the degree of structural similarity between stimuli, implicating a role for the mid-fusiform in fine differentiation of similar visual object representations. Importantly, however, this process of fine differentiation occurred at the level of structural, but not perceptual, descriptions. Moreover, mid-fusiform activity was more robust when participants matched shape compared to color information using the identical stimuli, indicating that activity in the mid-fusiform gyrus is not driven by specific stimulus properties, but rather by the process of distinguishing stimuli based on shape information. Taken together, these findings further clarify the nature of object processing in the mid-fusiform gyrus. This region is engaged specifically in structural differentiation, a critical component process of object recognition and categorization.

The influence of colour and sound on neuronal activation during visual object naming

This paper investigates how neuronal activation for naming photographs of objects is influenced by the addition of appropriate colour or sound. Behaviourally, both colour and sound are known to facilitate object recognition from visual form. However, previous functional imaging studies have shown inconsistent effects. For example, the addition of appropriate colour has been shown to reduce antero-medial temporal activation whereas the addition of sound has been shown to increase posterior superior temporal activation. Here we compared the effect of adding colour or sound cues in the same experiment. We found that the addition of either the appropriate colour or sound increased activation for naming photographs of objects in bilateral occipital regions and the right anterior fusiform. Moreover, the addition of colour reduced left antero-medial temporal activation but this effect was not observed for the addition of object sound. We propose that activation in bilateral occipital and right fusiform areas precedes the integration of visual form with either its colour or associated sound. In contrast, left antero-medial temporal activation is reduced because object recognition is facilitated after colour and form have been integrated.

Negative priming in naming of categorically related objects: an fMRI study

Ignoring an object slows subsequent naming responses to it, a phenomenon known as negative priming (NP). A central issue in NP research concerns the level of representation at which the effect occurs. As object naming is typically considered to involve access to abstract semantic representations, Tipper 1985 proposed that the NP effect occurred at this level of processing, and other researchers supported this proposal by demonstrating a similar result with categorically related objects (e.g., Allport et al., 1985; Murray, 1995), an effect referred to as semantic NP. However, objects within categories share more physical or structural features than objects from different categories. Consequently, the NP effect observed with categorically related objects might occur at a structural rather than semantic level of representation. We used event related fMRI interleaving overt object naming and image acquisition to demonstrate for the first time that the semantic NP effect activates the left posterior-mid fusiform and insular-opercular cortices. Moreover, both naming latencies and left posterior-mid fusiform cortex responses were influenced by the structural similarity of prime-probe object pairings in the categorically related condition, increasing with the number of shared features. None of the cerebral regions activated in a previous fMRI study of the identity NP effect (de Zubicaray et al., 2006) showed similar activation during semantic NP, including the left anterolateral temporal cortex, a region considered critical for semantic processing. The results suggest that the identity and semantic NP effects differ with respect to their neural mechanisms, and the label "semantic NP" might be a misnomer. We conclude that the effect is most likely the result of competition between structurally similar category exemplars that determines the efficiency of object name retrieval.

Age and culture modulate object processing and object-scene binding in the ventral visual area

Behavioral differences in the visual processing of objects and backgrounds as a function of cultural group are well documented. Recent neuroimaging evidence also points to cultural differences in neural activation patterns. Compared with East Asians, Westerners' visual processing is more object focused, and they activate neural structures that reflect this bias for objects. In a recent adaptation study, East Asian older adults showed an absence of an object-processing area but normal adaptation for background areas. In the present study, 75 young and old adults (half East Asian and half Western) were tested in an fMR-adaptation study to examine differences in object and background processing as well as object-background binding. We found equivalent background processing in the parahippocampal gyrus in all four groups, diminished binding processes in the hippocampus in elderly East Asians and Westerners, and diminished object processing in elderly versus young adults in the lateral occipital complex. Moreover, elderly East Asians showed significantly less adaptation response in the object areas than did elderly Westerners. These findings demonstrate the malleability of perceptual processes as a result of differences in cohort-specific experiences or in cultural exposure over time.

Cultural differences in neural function associated with object processing

Behavioral research suggests that Westerners focus more on objects, whereas East Asians attend more to relationships and contexts. We evaluated the neural basis for these cultural differences in an event-related fMRI study. East Asian and American participants incidentally encoded pictures of (1) a target object alone, (2) a background scene with no discernable target object, and (3) a distinct target object against a meaningful background. Americans, relative to East Asians, activated more regions implicated in object processing, including bilateral middle temporal gyrus, left superior parietal/angular gyrus, and right superior temporal/supramarginal gyrus. In contrast to the cultural differences in object-processing areas, few differences emerged in background-processing regions. These results suggest that cultural experiences subtly direct neuralactivity, particularly for focal objects, at an early stage of scene encoding.

fMRI correlates of cortical specialization and generalization for letter processing

The present study used functional magnetic resonance imaging to examine cortical specialization for letter processing. We assessed whether brain regions that were involved in letter processing exhibited domain-specific and/or mandatory responses, following Fodor's definition of properties of modular systems (Fodor, J.A., 1983. The Modularity of Mind. The MIT Press, Cambridge, MA.). Domain-specificity was operationalized as selective, or exclusive, activation for letters relative to object and visual noise processing and a baseline fixation task. Mandatory processing was operationalized as selective activation for letters during both a silent naming and a perceptual matching task. In addition to these operational definitions, other operational definitions of selectivity for letter processing discussed by [Pernet, C., Celsis, P., Demonet, J., 2005. Selective response to letter categorization within the left fusiform gyrus. NeuroImage 28, 738-744] were applied to the data. Although the left fusiform gyrus showed a specialized response to letters using the definition of selectivity put forth by [Pernet, C., Celsis, P., Demonet, J., 2005. Selective response to letter categorization within the left fusiform gyrus. NeuroImage 28, 738-744], this region did not exhibit specialization for letters according to our more conservative definition of selectivity. Instead, this region showed equivalent activation by letters and objects in both the naming and matching tasks. Hence, the left fusiform gyrus does not exhibit domain-specific or mandatory processing but may reflect a shared input system for both stimulus types. The left insula and some portions of the left inferior parietal lobule, however, did show a domain-specific response for letter naming but not for letter matching. These regions likely subserve some linguistically oriented cognitive process that is unique to letters, such as grapheme-to-phoneme translation or retrieval of phonological codes for letter names. Hence, cortical specialization for letters emerged in the naming task in some peri-sylvian language related cortices, but not in occipito-temporal cortex. Given that the domain-specific response for letters in left peri-sylvian regions was only present in the naming task, these regions do not process letters in a mandatory fashion, but are instead modulated by the linguistic nature of the task.

Shape configuration and category-specificity

We examined the neural correlates of visual shape configuration, the binding of local shape characteristics into wholistic object descriptions, by comparing the regional cerebral blood flow associated with recognition of outline drawings and fragmented drawings. We found no areas that responded more to fragmented drawings than to outline drawings even though fragmentation had a clear impact on recognition performance. Instead, a region extending from the inferior occipital gyri to the middle parts of the fusiform gyri was activated during shape configuration of both outline drawings and fragmented drawings. We also examined whether fragmentation had different impact on the recognition of natural objects and artefacts and found that recognition of artefacts was more affected by fragmentation than recognition of natural objects. Thus, the usual finding of an advantage for artefacts in difficult object decision tasks, which is also found in the present experiments with outlines, is reversed when the stimuli are fragmented. This interaction between category (natural versus artefacts) and stimulus type (outlines versus fragmented forms) is in accordance with predictions derived from a recent account of category-specificity and lends support to the notion that category-specific impairments can occur for both natural objects and artefacts following damage to pre-semantic stages in visual object recognition. The implications of the present findings are discussed in relation to theories of perceptual organization, visual object recognition and category-specificity.

Fusiform Activation to Animals is Driven by the Process, Not the Stimulus

Previous studies have found that the lateral posterior fusiform gyri respond more robustly to pictures of animals than pictures of manmade objects and suggested that these regions encode the visual properties characteristic of animals. We suggest that such effects actually reflect processing demands arising when items with similar representations must be finely discriminated. In a positron emission tomography (PET) study of category verification with colored photographs of animals and vehicles, there was robust animal-specific activation in the lateral posterior fusiform gyri when stimuli were categorized at an intermediate level of specificity (e.g., dog or car). However, when the same photographs were categorized at a more specific level (e.g., Labrador or BMW), these regions responded equally strongly to animals and vehicles. We conclude that the lateral posterior fusiform does not encode domain-specific representations of animals or visual properties characteristic of animals. Instead, these regions are strongly activated whenever an item must be discriminated from many close visual or semantic competitors. Apparent category effects arise because, at an intermediate level of specificity, animals have more visual and semantic competitors than do artifacts.

Involvement of right piriform cortex in olfactory familiarity judgments

Previous studies have shown activation of right orbitofrontal cortex during judgments of odor familiarity. In the present study, we sought to extend our knowledge about the neural circuits involved in such a task by exploring the involvement of the right prefrontal areas and limbic/primary olfactory structures. Fourteen right-handed male subjects were tested using fMRI with a single functional run of two olfactory conditions (odor detection and familiarity judgments). Each condition included three epochs. During the familiarity condition, subjects rated whether odors were familiar or unfamiliar. During the detection condition, participants decided if odors were present. When contrasting the familiarity with the detection conditions, activated areas were found mainly in the right piriform cortex (PC) and hippocampus, the left inferior frontal gyrus and amygdala, and bilaterally in the mid-fusiform gyrus. Further analyses demonstrated that the right PC was more strongly activated than the left PC. This result supports the notion that the right PC is preferentially involved in judgments of odor familiarity.

Developmental shifts in cortical loci for face and object recognition

Information on normal functional organization and development of the ventral processing stream in 5- to 11-year-old children is minimal. The present fMRI study identified neural correlates for face and object processing in children aged 5-8 and 9-11 years, with data from a similar adult study used for comparison. All age groups showed face-preferential activation in the ventral processing stream, but adults and children aged 9-11 years showed face-preferential loci near the classically defined fusiform face area, whereas children aged 5-8 years showed this activation in the posterior ventral processing stream. In addition, the degree of category-selectivity in other brain regions increased with age. Collectively, these developmental changes may reflect fine-tuning in visual recognition processes based on learning and experience.

Cortical regions associated with different aspects of object recognition performance

In the present object recognition study, we examined the relationship between brain activation and four behavioral measures: error rate, reaction time, observer sensitivity, and response bias. Subjects perceptually matched object pairs in which structural similarity (SS), an index of structural differentiation, and exposure duration (DUR), an index of task difficulty, were manipulated. The SS manipulation affected the fMRI signal in the left anterior fusiform and parietal cortices, which in turn reflected a bias to respond same. Conversely, an SS-modulated fMRI signal in the right middle frontal gyrus reflected a bias to respond different. The DUR manipulation affected the fMRI signal in occipital and posterior fusiform regions, which in turn reflected greater sensitivity, longer reaction times, and greater accuracy. These findings demonstrate that the regions most strongly implicated in processing object shape (SS-modulated regions) are associated with response bias, whereas regions that are not directly involved in shape processing are associated with successful recognition performance.