Perceptual Grouping and Visual Enumeration

We used lateralized Event-Related Potential (ERP) measures – the N2pc and CDA/SPCN components – to assess the role of grouping by target similarity during enumeration. Participants saw a variable number (0, 1, 2 or 3) of same- or differently-colored targets presented among homogeneous distracters, and performed an enumeration task. Results showed that the N2pc, but not the CDA, was larger for multiple targets of identical color relative to targets of different colors. The findings are interpreted in terms of the effects of grouping on early versus late stages of multiple object processing. Within this framework, they reveal that grouping has an effect on early individuation mechanisms, while later processing mechanisms are less prone to such an influence.Psycholog

The neural mechanisms for the recognition of face identity in humans

Every day we encounter dozens of people, and in order to interact with them appropriately we need to recognize their identity. The face is a crucial source of information to recognize a person’s identity. However, recognizing the identity of a face is challenging because it requires distinguishing between very similar images (e.g., the front views of two different faces) while categorizing very different images (e.g., a front view and a profile) as the same person. Neuroimaging has the whole-brain coverage needed to investigate where representations of face identity are encoded, but it is limited in terms of spatial and temporal resolution. In this article, we review recent neuroimaging research that attempted to investigate the representation of face identity, the challenges it faces, and the proposed solutions, to conclude that given the current state of the evidence the right anterior temporal lobe is the most promising candidate region for the representation of face identity

Representation of Grammatical Categories of Words in the Brain

We report the performance of a patient who, as a consequence of left frontal and temporoparietal strokes, makes far more errors on nouns than on verbs in spoken output tasks, but makes far more errors on verbs than on nouns in written input tasks. This double dissociation within a single patient with respect to grammatical category provides evidence for the hypothesis that phonological and orthographic representations of nouns and verbs are processed by independent neural mechanisms. Furthermore, the opposite dissociation in the verbal output modality, an advantage for nouns over verbs in spoken tasks, by a different patient using the same stimuli has also been reported (Caramazza & Hillis, 1991). This double dissociation across patients on the same task indicates that results cannot be ascribed to "greater difficulty" with one type of stimulus, and provides further evidence for the view that grammatical category information is an important organizational principle of lexical knowledge in the brain.Psycholog

Brain Regions That Represent Amodal Conceptual Knowledge

To what extent do the brain regions implicated in semantic processing contribute to the representation of amodal conceptual content rather than modality-specific mechanisms or mechanisms of semantic access and manipulation? Here, we propose that a brain region can be considered to represent amodal conceptual object knowledge if it is supramodal and plays a role in distinguishing among the conceptual representations of different objects. In an fMRI study, human participants made category typicality judgments about pictured objects or their names drawn from five different categories. Crossmodal multivariate pattern analysis revealed a network of six left-lateralized regions largely outside of category-selective visual cortex that showed a supramodal representation of object categories. These were located in the posterior middle/inferior temporal gyrus (pMTG/ITG), angular gyrus, ventral temporal cortex, posterior cingulate/precuneus (PC), and lateral and dorsomedial prefrontal cortex. Representational similarity analysis within these regions determined that the similarity between category-specific patterns of neural activity in the pMTG/ITG and the PC was consistent with the semantic similarity between these categories. This finding supports the PC and pMTG/ITG as candidate regions for the amodal representation of the conceptual properties of objects.Psycholog

What Body Parts Reveal About the Organization of the Brain

In this issue of Neuron, Orlov et al. show that the human occipitotemporal cortex contains regions responding preferentially to body part categories, such as upper limbs (hand, elbow), torsos, or lower faces (mouth, chin). This organization may reflect differences in the connectivity of these regions with other brain regions, to support the efficient processing of the different types of information different body parts provide.Psycholog

Tripartite Organization of the Ventral Stream by Animacy and Object Size

Occipito-temporal cortex is known to house visual object representations, but the organization of the neural activation patterns along this cortex is still being discovered. Here we found a systematic, large-scale structure in the neural responses related to the interaction between two major cognitive dimensions of object representation: animacy and real-world size. Neural responses were measured with functional magnetic resonance imaging while human observers viewed images of big and small animals and big and small objects. We found that real-world size drives differential responses only in the object domain, not the animate domain, yielding a tripartite distinction in the space of object representation. Specifically, cortical zones with distinct response preferences for big objects, all animals, and small objects, are arranged in a spoked organization around the occipital pole, along a single ventromedial, to lateral, to dorsomedial axis. The preference zones are duplicated on the ventral and lateral surface of the brain. Such a duplication indicates that a yet unknown higher-order division of labor separates object processing into two substreams of the ventral visual pathway. Broadly, we suggest that these large-scale neural divisions reflect the major joints in the representational structure of objects and thus place informative constraints on the nature of the underlying cognitive architecture.Psycholog

Tuning Curves for Movement Direction in the Human Visuomotor System

Neurons in macaque primary motor cortex (M1) are broadly tuned to arm movement direction. Recent evidence suggests that human M1 contains directionally tuned neurons, but it is unclear which other areas are part of the network coding movement direction and what characterizes the responses of neuronal populations in those areas. Such information would be highly relevant for the implementation of brain–computer interfaces (BCIs) in paralyzed patients. We used functional magnetic resonance imaging adaptation to identify which areas of the human brain show directional selectivity and the degree to which these areas are affected by the type of motor act (to press vs to grasp). After adapting participants to one particular hand movement direction, we measured the release from adaptation during occasional test trials, parametrically varying the angular difference between adaptation and test direction. We identified multiple areas broadly tuned to movement direction, including M1, dorsal premotor cortex, intraparietal sulcus, and the parietal reach region. Within these areas, we observed a gradient of directional selectivity, with highest directional selectivity in the right parietal reach region, for both right- and left-hand movements. Moreover, directional selectivity was modulated by the type of motor act to varying degrees, with the largest effect in M1 and the smallest modulation in the parietal reach region. These data provide an important extension of our knowledge about directional tuning in the human brain. Furthermore, our results suggest that the parietal reach region might be an ideal candidate for the implementation of BCI in paralyzed patients.Psycholog

Temporal Brain Dynamics of Multiple Object Processing: The Flexibility of Individuation

The ability to process concurrently multiple visual objects is fundamental for a coherent perception of the world. A core component of this ability is the simultaneous individuation of multiple objects. Many studies have addressed the mechanism of object individuation but it remains unknown whether the visual system mandatorily individuates all relevant elements in the visual field, or whether object indexing depends on task demands. We used a neural measure of visual selection, the N2pc component, to evaluate the flexibility of multiple object individuation. In three ERP experiments, participants saw a variable number of target elements among homogenous distracters and performed either an enumeration task (Experiment 1) or a detection task, reporting whether at least one (Experiment 2) or a specified number of target elements (Experiment 3) was present. While in the enumeration task the N2pc response increased as a function of the number of targets, no such modulation was found in Experiment 2, indicating that individuation of multiple targets is not mandatory. However, a modulation of the N2pc similar to the enumeration task was visible in Experiment 3, further highlighting that object individuation is a flexible mechanism that binds indexes to object properties and locations as needed for further object processing.Psycholog

Orthographic and Phonological Effects in the Picture–word Interference Paradigm: Evidence From a Logographic Language

One important finding with the picture–word interference paradigm is that picture-naming performance is facilitated by the presentation of a distractor (e.g., CAP) formally related to the picture name (e.g., “cat”). In two picture-naming experiments we investigated the nature of such form facilitation effect with Mandarin Chinese, separating the effects of phonology and orthography. Significant facilitation effects were observed both when distractors were only orthographically or only phonologically related to the targets. The orthographic effect was overall stronger than the phonological effect. These findings suggest that the classic form facilitation effect in picture–word interference is a mixed effect with multiple loci: it cannot be attributed merely to the nonlexical activation of the target phonological segments from the visual input of the distractor. It seems instead that orthographically only related distractors facilitate the lexical selection process of picture naming, and phonologically only related distractors facilitate the retrieval of target phonological segments.Psycholog