Incremental learning of perceptual and conceptual representations and the puzzle of neural repetition suppression

Incremental learning models of long-term perceptual and conceptual knowledge hold that neural representations are gradually acquired over many individual experiences via Hebbian-like activity-dependent synaptic plasticity across cortical connections of the brain. In such models, variation in task relevance of information, anatomic constraints, and the statistics of sensory inputs and motor outputs lead to qualitative alterations in the nature of representations that are acquired. Here, the proposal that behavioral repetition priming and neural repetition suppression effects are empirical markers of incremental learning in the cortex is discussed, and research results that both support and challenge this position are reviewed. Discussion is focused on a recent fMRI-adaptation study from our laboratory that shows decoupling of experience-dependent changes in neural tuning, priming, and repetition suppression, with representational changes that appear to work counter to the explicit task demands. Finally, critical experiments that may help to clarify and resolve current challenges are outlined.     

Neural correlates of viewing paintings: Evidence from a quantitative meta-analysis of functional magnetic resonance imaging data

Many studies involving functional magnetic resonance imaging (fMRI) have exposed participants to paintings under varying task demands. To isolate neural systems that are activated reliably across fMRI studies in response to viewing paintings regardless of variation in task demands, a quantitative meta-analysis of fifteen experiments using the activation likelihood estimation (ALE) method was conducted. As predicted, viewing paintings was correlated with activation in a distributed system including the occipital lobes, temporal lobe structures in the ventral stream involved in object (fusiform gyrus) and scene (parahippocampal gyrus) perception, and the anterior insula—a key structure in experience of emotion. In addition, we also observed activation in the posterior cingulate cortex bilaterally—part of the brain’s default network. These results suggest that viewing paintings engages not only systems involved in visual representation and object recognition, but also structures underlying emotions and internalized cognitions.     

From Fragments to Geometric Shape: Changes in Visual Object Recognition Between 18 and 24 Months

ABSTRACT— Visual object recognition is foundational to processes of categorization, tool use, and real-world problem solving. Despite considerable effort across many disciplines and many specific advances, there is no comprehensive or well-accepted account of this ability. Moreover, none of the extant approaches consider how human object recognition develops. New evidence indicates a period of rapid change in toddlers' visual object recognition between 18 and 24 months that is related to the learning of object names and to goal-directed action. Children appear to shift from recognition based on piecemeal fragments to recognition based on geometric representations of three-dimensional shape. These findings may lead to a more unified understanding of the processes that make human object recognition as impressive as it is.     

Hierarchies, similarity, and interactivity in object recognition: "category-specific" neuropsychological deficits.

Category-specific impairments of object recognition and naming are among the most intriguing disorders in neuropsychology, affecting the retrieval of knowledge about either living or nonliving things. They can give us insight into the nature of our representations of objects: Have we evolved different neural systems for recognizing different categories of object? What kinds of knowledge are important for recognizing particular objects? How does visual similarity within a category influence object recognition and representation? What is the nature of our semantic knowledge about different objects? We review the evidence on category-specific impairments, arguing that deficits even for one class of object (e.g., living things) cannot be accounted for in terms of a single information processing disorder across all patients; problems arise at contrasting loci in different patients. The same apparent pattern of impairment can be produced by damage to different loci. According to a new processing framework for object recognition and naming, the hierarchical interactive theory (HIT), we have a hierarchy of highly interactive stored representations. HIT explains the variety of patients in terms of (1) lesions at different levels of processing and (2) different forms of stored knowledge used both for particular tasks and for particular categories of object.     

自我面孔识别的神经机制：基于fMRI研究的ALE元分析

自我面孔识别反映了个体通过自我与他人的区分识别出自我面孔的过程。本文采用ALE元分析的方法, 对自我面孔识别的fMRI研究进行系统的定量分析, 探究自我面孔识别的神经基础。结果显示, 自我面孔识别的关键脑区包括顶上小叶、额中回、额下回、脑岛、梭状回、楔前叶和枕叶皮层。另外, 自我面孔识别可能包括两个层面的加工过程：知觉层面的加工整合过程以及由知觉引发的评价和情绪反应过程。知觉加工整合涵盖了自我面孔识别的各个加工阶段, 主要涉及枕叶、梭状回和楔前叶的功能; 而评价加工及情绪反应过程则发生在自我面孔识别的中晚期, 主要涉及顶上小叶、额中回、额下回及脑岛的功能。未来研究可结合时间和空间数据并关注脑区间的协同功能, 考察与内感受的神经关联, 开展临床研究并探索威胁信息的影响机制。     

Probing the visual representation of faces with adaptation: A view from the other side of the mean

Sensory adaptation and visual aftereffects have long given insight into the neural codes underlying basic dimensions of visual perception. Recently discovered perceptual adaptation effects for complex shapes like faces can offer similar insight into high-level visual representations. In the experiments reported here, we demonstrated first that face adaptation transfers across a substantial change in viewpoint and that this transfer occurs via processes unlikely to be specific to faces. Next, we probed the visual codes underlying face recognition using face morphs that varied selectively in reflectance or shape. Adaptation to these morphs affected the perception of "opposite" faces both from the same viewpoint and from a different viewpoint. These results are consistent with high-level face representations that pool local shape and reflectance patterns into configurations that specify facial appearance over a range of three-dimensional viewpoints. These findings have implications for computational models of face recognition and for competing neural theories of face and object recognition.     

Decoding overlapping memories in the medial temporal lobes using high-resolution fMRI

The hippocampus is proposed to process overlapping episodes as discrete memory traces, although direct evidence for this in human episodic memory is scarce. Using green-screen technology we created four highly overlapping movies of everyday events. Participants were scanned using high-resolution fMRI while recalling the movies. Multivariate pattern analysis revealed that the hippocampus supported distinct representations of each memory, while neighboring regions did not, demonstrating that the human hippocampus maintains unique pattern-separated memory traces even when memories are highly overlapping. The hippocampus also contained representations of spatial contexts that were shared across different memories, consistent with a specialized role in processing space.     

愉快面孔识别优势及其认知神经机制

愉快面孔识别优势表现为被试对高兴面孔比对其他情绪面孔的识别正确率更高、反应时更短。大量研究以简笔画和面孔图片为材料, 在情绪分类任务和视觉搜索任务中均发现这一优势。该优势存在诊断性价值假说、情绪独特性假说和出现频率假说三种不同的理论解释。近年来, 研究者采用ERP技术发现这一优势形成于反应选择阶段, 但其起始阶段尚无一致结论。未来可借助fMRI技术进一步研究其认知神经机制。     

Distinct mechanisms for the representation of moving and static objects

The visual system has been suggested to integrate different views of an object in motion. We investigated differences in the way moving and static objects are represented by testing for priming effects to previously seen ("known") and novel object views. We showed priming effects for moving objects across image changes (e.g., mirror reversals, changes in size, and changes in polarity) but not over temporal delays. The opposite pattern of results was observed for objects presented statically; that is, static objects were primed over temporal delays but not across image changes. These results suggest that representations for moving objects are: (1) updated continuously across image changes, whereas static object representations generalize only across similar images, and (2) more short-lived than static object representations. These results suggest two distinct representational mechanisms: a static object mechanism rather spatially refined and permanent, possibly suited for visual recognition, and a motion-based object mechanism more temporary and less spatially refined, possibly suited for visual guidance of motor actions.     

Combining disparate views of objects: Viewpoint costs are reduced by stereopsis

An issue of central concern in the object recognition literature is whether changes in the viewpoint from which an object is depicted produces systematic costs in performance, or whether performance is (largely) unaffected by such changes. This issue has generated a vigorous and lengthy debate because viewpoint-dependent or viewpoint-independent performance has been seen as a reflection of the underlying object representations. The current experiment shows that the effect of viewpoint differences between objects is strongly affected by whether or not they are depicted with stereoscopic depth, a result that is predicted by neither of the main approaches to object recognition. Instead, it is proposed that viewpoint costs in object recognition experiments are a function of the extent to which the information a subject is provided with generalizes across views, without this holding any necessary implications for the nature of the underlying object representations.     

Distinct pattern separation related transfer functions in human CA3/dentate and CA1 revealed using high-resolution fMRI and variable mnemonic similarity

Producing and maintaining distinct (orthogonal) neural representations for similar events is critical to avoiding interference in long-term memory. Recently, our laboratory provided the first evidence for separation-like signals in the human CA3/dentate. Here, we extended this by parametrically varying the change in input (similarity) while monitoring CA1 and CA3/dentate for separation and completion-like signals using high-resolution fMRI. In the CA1, activity varied in a graded fashion in response to increases in the change in input. In contrast, the CA3/dentate showed a stepwise transfer function that was highly sensitive to small changes in input.     

如何利用开源工具分析fMRI数据：基于多体素模式的有监督机器学习算法介绍

摘要：目前,多体素模式分析（MVPA）日渐普遍地应用于脑影像研究。近些年,机器学习的模式分类等算法在MVPA方法中被广泛应用,因其具有能够抽取高维数据模式,提高数据利用率的优点。其中一种典型的应用是利用解码的思想来解决神经表征问题,本文主要介绍了利用基于Python语言的工具库中有监督学习算法分析数据的过程。除介绍Nilearn结合Scikit-learn分析数据的步骤外,还比较不同算法的效率,为算法的选择及参数设备提供具体参考。     

Neural correlates of successful and unsuccessful verbal memory encoding

Recent neuroimaging studies suggest that episodic memory encoding involves a network of neocortical structures which may act interdependently with medial temporal lobe (mTL) structures to promote the formation of durable memories, and that activation in certain structures is modulated according to task performance. Functional magnetic resonance imaging (fMRI) was used to determine the neural structures recruited during a verbal episodic encoding task and to examine the relationship between activation during encoding and subsequent recognition memory performance across subjects. Our results show performance-correlated activation during encoding both in neocortical and medial temporal structures. Neocortical activations associated with later successful and unsuccessful recognition memory were found to differ not only in magnitude, but also in hemispheric laterality. These performance-related hemispheric effects, which have not been previously reported, may correspond to between-subject differences in encoding strategy.     

Neural adaptation across viewpoint and exemplar in fusiform cortex

The visual system has the remarkable ability to generalize across different viewpoints and exemplars to recognize abstract categories of objects, and to discriminate between different viewpoints and exemplars to recognize specific instances of particular objects. Behavioral experiments indicate the critical role of the right hemisphere in specific-viewpoint and -exemplar visual form processing and the left hemisphere in abstract-viewpoint and -exemplar visual form processing. Neuroimaging studies indicate the role of fusiform cortex in these processes, however results conflict in their support of the behavioral findings. We investigated this inconsistency in the present study by examining adaptation across viewpoint and exemplar changes in the functionally defined fusiform face area (FFA) and in fusiform regions exhibiting adaptation. Subjects were adapted to particular views of common objects and then tested with objects appearing in four critical conditions: same-exemplar, same-viewpoint adapted, same-exemplar, different-viewpoint adapted, different-exemplar adapted, and not adapted. In line with previous results, the FFA demonstrated a release from neural adaptation for repeated different viewpoints and exemplars of an object. In contrast to previous work, a (non-FFA) right medial fusiform area also demonstrated a release from neural adaptation for repeated different viewpoints and exemplars of an object. Finally, a left lateral fusiform area demonstrated neural adaptation for repeated different viewpoints, but not exemplars, of an object. Test-phase task demands did not affect adaptation in these regions. Together, results suggest that dissociable neural subsystems in fusiform cortex support the specific identification of a particular object and the abstract recognition of that object observed from a different viewpoint. In addition, results suggest that areas within fusiform cortex do not support abstract recognition of different exemplars of objects within a category.     

Distinct patterns of viewpoint-dependent BOLD activity during common-object recognition and mental rotation

A fundamental but unanswered question about the human visual system concerns the way in which misoriented objects are recognized. One hypothesis maintains that representations of incoming stimuli are transformed via parietally based spatial normalization mechanisms (eg mental rotation) to match view-specific representations in long-term memory. Using fMRI, we tested this hypothesis by directly comparing patterns of brain activity evoked during classic mental rotation and misoriented object recognition involving everyday objects. BOLD activity increased systematically with stimulus rotation within the ventral visual stream during object recognition and within the dorsal visual stream during mental rotation. More specifically, viewpoint-dependent activity was significantly greater in the right superior parietal lobule during mental rotation than during object recognition. In contrast, viewpoint-dependent activity was significantly greater in the right fusiform gyrus during object recognition than during mental rotation. In addition to these differences in viewpoint-dependent activity, object recognition and mental rotation produced distinct patterns of brain activity, independent of stimulus rotation: object recognition resulted in greater overall activity within ventral stream visual areas and mental rotation resulted in greater overall activity within dorsal stream visual areas. The present results are inconsistent with the hypothesis that misoriented object recognition is mediated by structures within the parietal lobe that are known to be involved in mental rotation.     

Neural representations of faces and limbs neighbor in human high-level visual cortex: evidence for a new organization principle

Neurophysiology and optical imaging studies in monkeys and functional magnetic resonance imaging (fMRI) studies in both monkeys and humans have localized clustered neural responses in inferotemporal cortex selective for images of biologically relevant categories, such as faces and limbs. Using higher resolution (1.5 mm voxels) fMRI scanning methods than past studies (3–5 mm voxels), we recently reported a network of multiple face- and limb-selective regions that neighbor one another in human ventral temporal cortex (Weiner and Grill-Spector, Neuroimage, 52(4):1559–1573, 2010) and lateral occipitotemporal cortex (Weiner and Grill-Spector, Neuroimage, 56(4):2183–2199, 2011). Here, we expand on three basic organization principles of high-level visual cortex revealed by these findings: (1) consistency in the anatomical location of functional regions, (2) preserved spatial relationship among functional regions, and (3) a topographic organization of face- and limb-selective regions in adjacent and alternating clusters. We highlight the implications of this structure in comparing functional brain organization between typical and atypical populations. We conclude with a new model of high-level visual cortex consisting of ventral, lateral, and dorsal components, where multimodal processing related to vision, action, haptics, and language converges in the lateral pathway.     

Mechanisms and neural basis of object and pattern recognition: a study with chess experts

Comparing experts with novices offers unique insights into the functioning of cognition, based on the maximization of individual differences. Here we used this expertise approach to disentangle the mechanisms and neural basis behind two processes that contribute to everyday expertise: object and pattern recognition. We compared chess experts and novices performing chess-related and -unrelated (visual) search tasks. As expected, the superiority of experts was limited to the chess-specific task, as there were no differences in a control task that used the same chess stimuli but did not require chess-specific recognition. The analysis of eye movements showed that experts immediately and exclusively focused on the relevant aspects in the chess task, whereas novices also examined irrelevant aspects. With random chess positions, when pattern knowledge could not be used to guide perception, experts nevertheless maintained an advantage. Experts' superior domain-specific parafoveal vision, a consequence of their knowledge about individual domain-specific symbols, enabled improved object recognition. Functional magnetic resonance imaging corroborated this differentiation between object and pattern recognition and showed that chess-specific object recognition was accompanied by bilateral activation of the occipitotemporal junction, whereas chess-specific pattern recognition was related to bilateral activations in the middle part of the collateral sulci. Using the expertise approach together with carefully chosen controls and multiple dependent measures, we identified object and pattern recognition as two essential cognitive processes in expert visual cognition, which may also help to explain the mechanisms of everyday perception.     

The role of object recognition in young infants' object segregation

Needham's (2001, this issue) new results confirm that young infants draw on experientially derived representations in resolving individuation ambiguities due to shared boundaries between adjacent objects. They extend previous findings in a surprising way: The memory representations that infants draw upon have bound together information about shape, color, and pattern. Our commentary on these important results draws a distinction between two senses of "recognition" and asks in which sense object recognition contributes to object individuation in these experiments.     

Evidence for individual face discrimination in non-face selective areas of the visual cortex in acquired prosopagnosia

Two areas in the human occipito-temporal cortex respond preferentially to faces: 'the fusiform face area' ('FFA') and the 'occipital face area' ('OFA'). However, it is unclear whether these areas have an exclusive role in processing faces, or if sub-maximal responses in other visual areas such as the lateral occipital complex (LOC) are also involved. To clarify this issue, we tested a brain-damaged patient (PS) presenting a face-selective impairment with functional magnetic resonance imaging (fMRI). The right hemisphere lesion of the prosopagnosic patient encompasses the 'OFA' but preserves the 'FFA' and LOC. Using fMRI-adaptation, we found a larger response to different faces than repeated faces in the ventral part of the LOC both for normals and the patient, next to her right hemisphere lesion. This observation indicates that following prosopagnosia, areas that do not respond preferentially to faces such as the ventral part of the LOC (vLOC) may still be recruited to subtend residual perception of individual faces.