Attention to 3-D shape, 3-D motion, and texture in 3-D structure from motion displays

Similar object shape representation encoded in the inferolateral occipitotemporal cortex of sighted and early blind people

We can sense an object's shape by vision or touch. Previous studies suggested that the inferolateral occipitotemporal cortex (ILOTC) implements supramodal shape representations as it responds more to seeing or touching objects than shapeless textures. However, such activation in the anterior portion of the ventral visual pathway could be due to the conceptual representation of an object or visual imagery triggered by touching an object. We addressed these possibilities by directly comparing shape and conceptual representations of objects in early blind (who lack visual experience/imagery) and sighted participants. We found that bilateral ILOTC in both groups showed stronger activation during a shape verification task than during a conceptual verification task made on the names of the same manmade objects. Moreover, the distributed activity in the ILOTC encoded shape similarity but not conceptual association among objects. Besides the ILOTC, we also found shape representation in both groups' bilateral ventral premotor cortices and intraparietal sulcus (IPS), a frontoparietal circuit relating to object grasping and haptic processing. In contrast, the conceptual verification task activated both groups' left perisylvian brain network relating to language processing and, interestingly, the cuneus in early blind participants only. The ILOTC had stronger functional connectivity to the frontoparietal circuit than to the left perisylvian network, forming a modular structure specialized in shape representation. Our results conclusively support that the ILOTC selectively implements shape representation independently of visual experience, and this unique functionality likely comes from its privileged connection to the frontoparietal haptic circuit.

Uncovering the fast, directional signal flow through the human temporal pole during semantic processing

The temporal pole (TP) plays a central role in semantic memory, yet its neural machinery is unknown. Intracerebral recordings in patients discriminating visually the gender or actions of an actor, yielded gender discrimination responses in the ventrolateral (VL) and tip (T) regions of right TP. Granger causality revealed task-specific signals travelling first forward from VL to T, under control of orbitofrontal cortex (OFC) and neighboring prefrontal cortex, and then, strongly, backwards from T to VL. Many other cortical regions provided inputs to or received outputs from both TP regions, often with longer delays, with ventral temporal afferents to VL signaling the actor's physical appearance. The TP response timing reflected more that of the connections to VL, controlled by OFC, than that of the input leads themselves. Thus, visual evidence for gender categories, collected by VL, activates category labels in T, and consequently, category features in VL, indicating a two-stage representation of semantic categories in TP.

Visual Motion Coherence Responses in Human Visual Cortex

Random dot kinematograms (RDKs) have recently been used to train subjects with cortical scotomas to perform direction of motion discrimination, partially restoring visual motion perception. To study the recovery of visual perception, it is important to understand how visual areas in normal subjects and subjects with cortical scotomas respond to RDK stimuli. Studies in normal subjects have shown that blood oxygen level-dependent (BOLD) responses in human area hV5/MT+ increase monotonically with coherence, in general agreement with electrophysiology studies in primates. However, RDK responses in prior studies were obtained while the subject was performing fixation, not a motion discrimination condition. Furthermore, BOLD responses were gauged against a baseline condition of uniform illumination or static dots, potentially decreasing the specificity of responses for the spatial integration of local motion signals (motion coherence). Here, we revisit this question starting from a baseline RDK condition of no coherence, thereby isolating the component of BOLD response due specifically to the spatial integration of local motion signals. In agreement with prior studies, we found that responses in the area hV5/MT+ of healthy subjects were monotonically increasing when subjects fixated without performing a motion discrimination task. In contrast, when subjects were performing an RDK direction of motion discrimination task, responses in the area hV5/MT+ remained flat, changing minimally, if at all, as a function of motion coherence. A similar pattern of responses was seen in the area hV5/MT+ of subjects with dense cortical scotomas performing direction of motion discrimination for RDKs presented inside the scotoma. Passive RDK presentation within the scotoma elicited no significant hV5/MT+ responses. These observations shed further light on how visual cortex responses behave as a function of motion coherence, helping to prepare the ground for future studies using these methods to study visual system recovery after injury.

Two 'what' pathways for action and object recognition

The ventral visual stream is conceived as a pathway for object recognition. However, we also recognize the actions an object can be involved in. Here, we show that action recognition critically depends on a pathway in lateral occipitotemporal cortex, partially overlapping and topographically aligned with object representations that are precursors for action recognition. By contrast, object features that are more relevant for object recognition, such as color and texture, are typically found in ventral occipitotemporal cortex. We argue that occipitotemporal cortex contains similarly organized lateral and ventral 'what' pathways for action and object recognition, respectively. This account explains a number of observed phenomena, such as the duplication of object domains and the specific representational profiles in lateral and ventral cortex.

A model integrating multiple processes of synchronization and coherence for information instantiation within a cortical area

What is the form of dynamic, e.g., sensory, information in the mammalian cortex? Information in the cortex is modeled as a coherence map of a mixed chimera state of synchronous, phasic, and disordered minicolumns. The theoretical model is built on neurophysiological evidence. Complex spatiotemporal information is instantiated through a system of interacting biological processes that generate a synchronized cortical area, a coherent aperture. Minicolumn elements are grouped in macrocolumns in an array analogous to a phased-array radar, modeled as an aperture, a "hole through which radiant energy flows." Coherence maps in a cortical area transform inputs from multiple sources into outputs to multiple targets, while reducing complexity and entropy. Coherent apertures can assume extremely large numbers of different information states as coherence maps, which can be communicated among apertures with corresponding very large bandwidths. The coherent aperture model incorporates considerable reported research, integrating five conceptually and mathematically independent processes: 1) a damped Kuramoto network model, 2) a pumped area field potential, 3) the gating of nearly coincident spikes, 4) the coherence of activity across cortical lamina, and 5) complex information formed through functions in macrocolumns. Biological processes and their interactions are described in equations and a functional circuit such that the mathematical pieces can be assembled the same way the neurophysiological ones are. The model can be conceptually convolved over the specifics of local cortical areas within and across species. A coherent aperture becomes a node in a graph of cortical areas with a corresponding distribution of information.

Human brain activity reflecting facial attractiveness from skin reflection

Facial attraction has a great influence on our daily social interactions. Previous studies have mainly focused on the attraction from facial shape and expression. We recently found that faces with radiant skin appear to be more attractive than those with oily-shiny or matte skin. In the present study, we conducted functional magnetic resonance imaging (fMRI) and psychological experiments to determine the human brain activity that reflects facial attractiveness modulated by these skin reflection types. In the fMRI experiment, female subjects were shown successive images of unfamiliar female faces with matte, oily-shiny, or radiant skin. The subjects compared each face with the immediately preceding face in terms of attractiveness, age, and skin reflection, all based on the skin. The medial part of the orbitofrontal cortex (mOFC) was significantly more active when comparing attractiveness than when comparing skin reflection, suggesting that the mOFC is involved in processing facial attractiveness from skin reflection. In the psychological experiment, attractiveness rating was highest for radiant skin, followed by oily-shiny, and then matte skin. Comparison of the results of these experiments showed that mOFC activation level increased with attractiveness rating. These results suggest that the activation level of the mOFC reflects facial attractiveness from skin reflection.

Dynamic dot displays reveal material motion network in the human brain

There is growing research interest in the neural mechanisms underlying the recognition of material categories and properties. This research field, however, is relatively more recent and limited compared to investigations of the neural mechanisms underlying object and scene category recognition. Motion is particularly important for the perception of non-rigid materials, but the neural basis of non-rigid material motion remains unexplored. Using fMRI, we investigated which brain regions respond preferentially to material motion versus other types of motion. We introduce a new database of stimuli - dynamic dot materials - that are animations of moving dots that induce vivid percepts of various materials in motion, e.g. flapping cloth, liquid waves, wobbling jelly. Control stimuli were scrambled versions of these same animations and rigid three-dimensional rotating dots. Results showed that isolating material motion properties with dynamic dots (in contrast with other kinds of motion) activates a network of cortical regions in both ventral and dorsal visual pathways, including areas normally associated with the processing of surface properties and shape, and extending to somatosensory and premotor cortices. We suggest that such a widespread preference for material motion is due to strong associations between stimulus properties. For example viewing dots moving in a specific pattern not only elicits percepts of material motion; one perceives a flexible, non-rigid shape, identifies the object as a cloth flapping in the wind, infers the object's weight under gravity, and anticipates how it would feel to reach out and touch the material. These results are a first important step in mapping out the cortical architecture and dynamics in material-related motion processing.

Neural sources of letter and Vernier acuity

Visual acuity can be measured in many different ways, including with letters and Vernier offsets. Prior psychophysical work has suggested that the two acuities are strongly linked given that they both depend strongly on retinal eccentricity and both are similarly affected in amblyopia. Here we used high-density EEG recordings to ask whether the underlying neural sources are common as suggested by the psychophysics or distinct. To measure visual acuity for letters, we recorded evoked potentials to 3 Hz alternations between intact and scrambled text comprised of letters of varying size. To measure visual acuity for Vernier offsets, we recorded evoked potentials to 3 Hz alternations between bar gratings with and without a set of Vernier offsets. Both alternation types elicited robust activity at the 3 Hz stimulus frequency that scaled in amplitude with both letter and offset size, starting near threshold. Letter and Vernier offset responses differed in both their scalp topography and temporal dynamics. The earliest evoked responses to letters occurred on lateral occipital visual areas, predominantly over the left hemisphere. Later responses were measured at electrodes over early visual cortex, suggesting that letter structure is first extracted in second-tier extra-striate areas and that responses over early visual areas are due to feedback. Responses to Vernier offsets, by contrast, occurred first at medial occipital electrodes, with responses at later time-points being more broadly distributed—consistent with feedforward pathway mediation. The previously observed commonalities between letter and Vernier acuity may be due to common bottlenecks in early visual cortex but not because the two tasks are subserved by a common network of visual areas.

A parietal region processing numerosity of observed actions: An FMRI study

When observing others' behavior, it is important to perceive not only the identity of the observed actions (OAs), but also the number of times they were performed. Given the mounting evidence implicating posterior parietal cortex in action observation, and in particular that of manipulative actions, the aim of this study was to identify the parietal region, if any, that contributes to the processing of observed manipulative action (OMA) numerosity, using the functional magnetic resonance imaging technique. Twenty‐one right‐handed healthy volunteers performed two discrimination tasks while in the scanner, responding to video stimuli in which an actor performed manipulative actions on colored target balls that appeared four times consecutively. The subjects discriminated between two small numerosities of either OMAs (“Action” condition) or colors of balls (“Ball” condition). A significant difference between the “Action” and “Ball” conditions was observed in occipito‐temporal cortex and the putative human anterior intraparietal sulcus (phAIP) area as well as the third topographic map of numerosity‐selective neurons at the post‐central sulcus (NPC3) of the left parietal cortex. A further region of interest analysis of the group‐average data showed that at the single voxel level the latter area, more than any other parietal or occipito‐temporal numerosity map, favored numerosity of OAs. These results suggest that phAIP processes the identity of OMAs, while neighboring NPC3 likely processes the numerosity of the identified OAs.

One bad apple spoils the whole bushel: The neural basis of outlier processing

How are outliers in an otherwise homogeneous object ensemble represented by our visual system? Are outliers ignored because they are the minority? Or do outliers alter our perception of an otherwise homogeneous ensemble? We have previously demonstrated ensemble representation in human anterior-medial ventral visual cortex (overlapping the scene-selective parahippocampal place area; PPA). In this study we investigated how outliers impact object-ensemble representation in this human brain region as well as visual representation throughout posterior brain regions. We presented a homogeneous ensemble followed by an ensemble containing either identical elements or a majority of identical elements with a few outliers. Human participants ignored the outliers and made a same/different judgment between the two ensembles. In PPA, fMRI adaptation was observed when the outliers in the second ensemble matched the items in the first, even though the majority of the elements in the second ensemble were distinct from those in the first; conversely, release from fMRI adaptation was observed when the outliers in the second ensemble were distinct from the items in the first, even though the majority of the elements in the second ensemble were identical to those in the first. A similarly robust outlier effect was also found in other brain regions, including a shape-processing region in lateral occipital cortex (LO) and task-processing fronto-parietal regions. These brain regions likely work in concert to flag the presence of outliers during visual perception and then weigh the outliers appropriately in subsequent behavioral decisions. To our knowledge, this is the first time the neural mechanisms involved in outlier processing have been systematically documented in the human brain. Such an outlier effect could well provide the neural basis mediating our perceptual experience in situations like "one bad apple spoils the whole bushel".

Temporal integration in the perception and discrimination of solid shape

Two experiments evaluated the importance of temporal integration for the perception and discrimination of solid object shape. In Experiment 1, observers anorthoscopically viewed moving or stationary cast shadows of naturally shaped solid objects (bell peppers, Capsicum annuum) through narrow (4-mm wide) slits. At any given moment, observers could only see a very small portion of the overall object shape (generally less than 10%). The results showed that the observers' discrimination performance for the moving cast shadows was much higher than that obtained for the stationary shadows, demonstrating the ability to temporally integrate the piecemeal momentary information about shape that was available through the narrow apertures. In a second experiment, estimates of the strength of the observers' impressions of solid shapes rotating in depth were obtained as well as discrimination accuracies; perceptions of the original moving condition were compared with a new condition where the frames of the apparent motion sequences depicting solid objects in continuous motion (behind the slits) were randomly scrambled. The observers perceived the anorthoscopic displays as depicting solid objects rotating in depth, but only in the continuous motion condition. Interestingly, the discrimination performance in the scrambled condition remained relatively high-observers were still able to integrate information across the multiple scrambled frames in order to produce discrimination performance that was significantly higher than that obtained in the stationary shadow condition. This study was the first to thoroughly evaluate whether and to what extent human observers can effectively discriminate and perceive solid object shape anorthoscopically.

Predicting how color and shape combine in the human visual system to direct attention

Objects in a scene can be distinct from one another along a multitude of visual attributes, such as color and shape, and the more distinct an object is from its surroundings, the easier it is to find it. However, exactly how this distinctiveness advantage arises in vision is not well understood. Here we studied whether and how visual distinctiveness along different visual attributes (color and shape, assessed in four experiments) combine to determine an object’s overall distinctiveness in a scene. Unidimensional distinctiveness scores were used to predict performance in six separate experiments where a target object differed from distractor objects along both color and shape. Results showed that there is mathematical law determining overall distinctiveness as the simple sum of the distinctiveness scores along each visual attribute. Thus, the brain must compute distinctiveness scores independently for each visual attribute before summing them into the overall score that directs human attention.

Representation of shape, space, and attention in monkey cortex

Attentional deficits are core to numerous developmental, neurological, and psychiatric disorders. At the single-cell level, much knowledge has been garnered from studies of shape and spatial properties, as well as from numerous demonstrations of attentional modulation of those properties. Despite this wealth of knowledge of single-cell responses across many brain regions, little is known about how these cellular characteristics relate to population level representations and how such representations relate to behavior; in particular, how these cellular responses relate to the representation of shape, space, and attention, and how these representations differ across cortical areas and streams. Here we will emphasize the role of population coding as a missing link for connecting single-cell properties with behavior. Using a data-driven intrinsic approach to population decoding, we show that both 'what' and 'where' cortical visual streams encode shape, space, and attention, yet demonstrate striking differences in these representations. We suggest that both pathways fully process shape and space, but that differences in representation may arise due to their differing functions and input and output constraints. Moreover, differences in the effects of attention on shape and spatial population representations in the two visual streams suggest two distinct strategies: in a ventral area, attention or task demands modulate the population representations themselves (perhaps to expand or enhance one part at the expense of other parts) while in a dorsal area, at a population representation level, attention effects are weak and nearly non-existent, perhaps in order to maintain veridical representations needed for visuomotor control. We show that an intrinsic approach, as opposed to theory-driven and labeled approaches, is useful for understanding how representations develop and differ across brain regions. Most importantly, these approaches help link cellular properties more tightly with behavior, a much-needed step to better understand and interpret cellular findings and key to providing insights to improve interventions in human disorders.

Areal differences in depth cue integration between monkey and human

Electrophysiological evidence suggested primarily the involvement of the middle temporal (MT) area in depth cue integration in macaques, as opposed to human imaging data pinpointing area V3B/kinetic occipital area (V3B/KO). To clarify this conundrum, we decoded monkey functional MRI (fMRI) responses evoked by stimuli signaling near or far depths defined by binocular disparity, relative motion, and their combination, and we compared results with those from an identical experiment previously performed in humans. Responses in macaque area MT are more discriminable when two cues concurrently signal depth, and information provided by one cue is diagnostic of depth indicated by the other. This suggests that monkey area MT computes fusion of disparity and motion depth signals, exactly as shown for human area V3B/KO. Hence, these data reconcile previously reported discrepancies between depth processing in human and monkey by showing the involvement of the dorsal stream in depth cue integration using the same technique, despite the engagement of different regions.

In everyday life, we interact with a three-dimensional world that we perceive via our two-dimensional retinas. Our brain can reconstruct the third dimension from these flat retinal images using multiple sources of visual information, or cues. The horizontal displacement of the two retinal images, known as binocular disparity, and the relative motion between different objects are two important depth cues. However, to make the most of the information provided by each cue, our brains must efficiently integrate across them. To examine this process, we used neuroimaging in monkeys to record brain responses evoked by stimuli signaling depths defined by either binocular disparity or relative motion in isolation, and also when the two cues are combined congruently or incongruently. We found that cortical area MT in monkeys is involved in the fusion of these two particular depth cues, in contrast to previous human imaging data that pinpoint a more posterior cortical area, V3B/KO. Our findings support the existence of depth cue integration mechanisms in primates; however, this fusion appears to be computed in slightly different areas in humans and monkeys.

The role of putative human anterior intraparietal sulcus area in observed manipulative action discrimination

INTRODUCTION

Although it has become widely accepted that the action observation network (AON) includes three levels (occipito-temporal, parietal and premotor), little is known concerning the specific role of these levels within perceptual tasks probing action observation. Recent single cell studies suggest that the parietal level carries the information required to discriminate between two-alternative observed actions, but do not exclude possible contributions from the other two levels.

METHODS

Two functional magnetic resonance imaging experiments used a task-based attentional modulation paradigm in which subjects viewed videos of an actor performing a manipulative action on a coloured object, and discriminated between either two observed manipulative actions, two actors or two colours.

RESULTS

Both experiments demonstrated that relative to actor and colour discrimination, discrimination between observed manipulative actions involved the putative human anterior intraparietal sulcus (phAIP) area in parietal cortex. In one experiment, where the observed actions also differed with regard to effectors, premotor cortex was also specifically recruited.

CONCLUSIONS

Our results highlight the primary role of parietal cortex in discriminating between two-alternative observed manipulative actions, consistent with the view that this level plays a major role in representing the identity of an observed action.

Rapid and specific processing of person-related information in human anterior temporal lobe

The anterior temporal lobe (ATL), located at the tip of the human temporal lobes, has been heavily implicated in semantic processing by neuropsychological and functional imaging studies. These techniques have revealed a hemispheric specialization of ATL, but little about the time scale on which it operates. Here we show that ATL is specifically activated in intracerebral recordings when subjects discriminate the gender of an actor presented in a static frame followed by a video. ATL recording sites respond briefly (100 ms duration) to the visual static presentation of an actor in a task-, but not in a stimulus-duration-dependent way. Their response latencies correlate with subjects' reaction times, as do their activity levels, but oppositely in the two hemispheres operating in a push-pull fashion. Comparison of ATL time courses with those of more posterior, less specific regions emphasizes the role of inhibitory operations sculpting the fast ATL responses underlying semantic processing.

Neural Mechanisms of Material Perception: Quest on Shitsukan

In recent years, a growing body of research has addressed the nature and mechanism of material perception. Material perception entails perceiving and recognizing a material, surface quality or internal state of an object based on sensory stimuli such as visual, tactile, and/or auditory sensations. This process is ongoing in every aspect of daily life. We can, for example, easily distinguish whether an object is made of wood or metal, or whether a surface is rough or smooth. Judging whether the ground is wet or dry or whether a fish is fresh also involves material perception. Information obtained through material perception can be used to govern actions toward objects and to make decisions about whether to approach an object or avoid it. Because the physical processes leading to sensory signals related to material perception is complicated, it has been difficult to manipulate experimental stimuli in a rigorous manner. However, that situation is now changing thanks to advances in technology and knowledge in related fields. In this article, we will review what is currently known about the neural mechanisms responsible for material perception. We will show that cortical areas in the ventral visual pathway are strongly involved in material perception. Our main focus is on vision, but every sensory modality is involved in material perception. Information obtained through different sensory modalities is closely linked in material perception. Such cross-modal processing is another important feature of material perception, and will also be covered in this review.

Towards a unified perspective of object shape and motion processing in human dorsal cortex

Although object-related areas were discovered in human parietal cortex a decade ago, surprisingly little is known about the nature and purpose of these representations, and how they differ from those in the ventral processing stream. In this article, we review evidence for the unique contribution of object areas of dorsal cortex to three-dimensional (3-D) shape representation, the localization of objects in space, and in guiding reaching and grasping actions. We also highlight the role of dorsal cortex in form-motion interaction and spatiotemporal integration, possible functional relationships between 3-D shape and motion processing, and how these processes operate together in the service of supporting goal-directed actions with objects. Fundamental differences between the nature of object representations in the dorsal versus ventral processing streams are considered, with an emphasis on how and why dorsal cortex supports veridical (rather than invariant) representations of objects to guide goal-directed hand actions in dynamic visual environments.

Cortical responses to shape-from-motion stimuli in the infant

Our ability to extract three-dimensional (3-D) object structure from motion-carried information is a basic visual capacity that is fundamental to object perception. Despite a rich body of behavioral work demonstrating that infants are sensitive to motion-carried information from the early months of life, little is known about the cortical networks that support infants' use of motion-carried information to extract 3-D object structure. This study assessed patterns of cortical activation in infants aged 4 to 6 months as they viewed two types of visual stimuli: (a) shape-from-motion (SFM) displays, where coherent motion of randomly distributed dots gave rise to the percept of 3-D shape and (b) random motion (RM) displays, where dots' motions lacked a coherent structure and gave rise to the percept of randomly moving dots. Functional near-infrared spectroscopy was used to assess activation in occipital, inferior parietal, and posterior temporal cortex. The optical imaging data revealed differential responding to SFM and RM in lower level object processing areas than typically observed in the adult. Possible explanations for this pattern of results are considered.

How Evolution Constrains Human Numerical Concepts

The types of cognitive and neural mechanisms available to children for making concepts depend on the problems their brains evolved to solve over the past millions of years. Comparative research on numerical cognition with humans and nonhuman primates has revealed a system for quantity representation that lays the foundation for quantitative development. Nonhuman primates in particular share many human abilities to compute quantities, and are likely to exhibit evolutionary continuity with humans. While humans conceive of quantity in ways that are similar to other primates, they are unique in their capacity for symbolic counting and logic. These uniquely human constructs interact with primitive systems of numerical reasoning. In this article, I discuss how evolution shapes human numerical concepts through evolutionary constraints on human object-based perception and cognition, neural homologies among primates, and interactions between uniquely human concepts and primitive logic.

Neural representation of geometry and surface properties in object and scene perception

Multiple cortical regions are crucial for perceiving the visual world, yet the processes shaping representations in these regions are unclear. To address this issue, we must elucidate how perceptual features shape representations of the environment. Here, we explore how the weighting of different visual features affects neural representations of objects and scenes, focusing on the scene-selective parahippocampal place area (PPA), but additionally including the retrosplenial complex (RSC), occipital place area (OPA), lateral occipital (LO) area, fusiform face area (FFA) and occipital face area (OFA). Across three experiments, we examined functional magnetic resonance imaging (fMRI) activity while human observers viewed scenes and objects that varied in geometry (shape/layout) and surface properties (texture/material). Interestingly, we found equal sensitivity in the PPA for these properties within a scene, revealing that spatial-selectivity alone does not drive activation within this cortical region. We also observed sensitivity to object texture in PPA, but not to the same degree as scene texture, and representations in PPA varied when objects were placed within scenes. We conclude that PPA may process surface properties in a domain-specific manner, and that the processing of scene texture and geometry is equally-weighted in PPA and may be mediated by similar underlying neuronal mechanisms.

Spatio-temporal dynamics of attentional selection stages during multiple object tracking

Subjects can visually track several moving items simultaneously, a fact that is difficult to explain by classical attention models. Previous work revealed that building a global shape based on the spatial position of the tracked items improves performance. Here we investigated the involved neural processes and the role of attention. A task-irrelevant probe stimulus was presented during multiple objects tracking at a fixed spatial location. Depending on the tracked item's trajectories the probe appeared either outside, inside, or on the edge of aforementioned global shape. Event-related potentials to the probe stimulus revealed two subsequent stages of attentional selection during multiple object tracking. After 100ms attention was deployed on the edge/boundary of the figure formed by the tracked items. In the following 80ms, attention spread from the outline to the full figure. These findings clarify the eminent contribution of attentional mechanisms in multiple objects tracking.

Universal and uniquely human factors in spontaneous number perception

A capacity for nonverbal numerical estimation is widespread among humans and animals. However, it is currently unclear whether numerical percepts are spontaneously extracted from the environment and whether nonverbal perception is influenced by human exposure to formal mathematics. We tested US adults and children, non-human primates, and numerate and innumerate Tsimane' adults on a quantity task in which they could choose to categorize sets of dots on the basis of number alone, surface area alone or a combination of the two. Despite differences in age, species and education, subjects are universally biased to base their judgments on number as opposed to the alternatives. Numerical biases are uniquely enhanced in humans compared to non-human primates, and correlated with degree of mathematics experience in both the US and Tsimane' groups. We conclude that humans universally and spontaneously extract numerical information, and that human nonverbal numerical perception is enhanced by symbolic numeracy.

Aesthetics by Numbers: Links between Perceived Texture Qualities and Computed Visual Texture Properties

Our world is filled with texture. For the human visual system, this is an important source of information for assessing environmental and material properties. Indeed-and presumably for this reason-the human visual system has regions dedicated to processing textures. Despite their abundance and apparent relevance, only recently the relationships between texture features and high-level judgments have captured the interest of mainstream science, despite long-standing indications for such relationships. In this study, we explore such relationships, as these might be used to predict perceived texture qualities. This is relevant, not only from a psychological/neuroscience perspective, but also for more applied fields such as design, architecture, and the visual arts. In two separate experiments, observers judged various qualities of visual textures such as beauty, roughness, naturalness, elegance, and complexity. Based on factor analysis, we find that in both experiments, ~75% of the variability in the judgments could be explained by a two-dimensional space, with axes that are closely aligned to the beauty and roughness judgments. That a two-dimensional judgment space suffices to capture most of the variability in the perceived texture qualities suggests that observers use a relatively limited set of internal scales on which to base various judgments, including aesthetic ones. Finally, for both of these judgments, we determined the relationship with a large number of texture features computed for each of the texture stimuli. We find that the presence of lower spatial frequencies, oblique orientations, higher intensity variation, higher saturation, and redness correlates with higher beauty ratings. Features that captured image intensity and uniformity correlated with roughness ratings. Therefore, a number of computational texture features are predictive of these judgments. This suggests that perceived texture qualities-including the aesthetic appreciation-are sufficiently universal to be predicted-with reasonable accuracy-based on the computed feature content of the textures.

Demonstrations of Spatiotemporal Integration and what they Tell us about the Visual System

Five sets of displays are presented on the journal website to be viewed in conjunction with the text. We concentrate on the factors that give rise to the integration and disruption of the direction of apparent motion in two-dimensional and three-dimensional space. In the first set of displays we examine what factors contribute to the integration and disruption of apparent motion in the Ramachandran/Anstis clustered bistable quartets. In the second set we examine what factors give rise to the perception of the direction of motion in rotating two-dimensional wheels and dots. In the third and fourth sets we examine how the depth cues of shading and disparity contribute to the perception of apparent motion of opaque displays, and to the perception of rotating unoccluded displays, respectively. In the fifth set we examine how the depth cue of motion parallax influences the perception of apparent motion. Throughout, we make inferences about the roles which various parallel pathways and cortical areas play in the perceptions produced by the displays shown.

Dorsal and ventral stream contributions to form-from-motion perception in a patient with form-from motion deficit: a case report

The main model of visual processing in primates proposes an anatomo-functional distinction between the dorsal stream, specialized in spatio-temporal information, and the ventral stream, processing essentially form information. However, these two pathways also communicate to share much visual information. These dorso-ventral interactions have been studied using form-from-motion (FfM) stimuli, revealing that FfM perception first activates dorsal regions (e.g., MT+/V5), followed by successive activations of ventral regions (e.g., LOC). However, relatively little is known about the implications of focal brain damage of visual areas on these dorso-ventral interactions. In the present case report, we investigated the dynamics of dorsal and ventral activations related to FfM perception (using topographical ERP analysis and electrical source imaging) in a patient suffering from a deficit in FfM perception due to right extrastriate brain damage in the ventral stream. Despite the patient's FfM impairment, both successful (observed for the highest level of FfM signal) and absent/failed FfM perception evoked the same temporal sequence of three processing states observed previously in healthy subjects. During the first period, brain source localization revealed cortical activations along the dorsal stream, currently associated with preserved elementary motion processing. During the latter two periods, the patterns of activity differed from normal subjects: activations were observed in the ventral stream (as reported for normal subjects), but also in the dorsal pathway, with the strongest and most sustained activity localized in the parieto-occipital regions. On the other hand, absent/failed FfM perception was characterized by weaker brain activity, restricted to the more lateral regions. This study shows that in the present case report, successful FfM perception, while following the same temporal sequence of processing steps as in normal subjects, evoked different patterns of brain activity. By revealing a brain circuit involving the most rostral part of the dorsal pathway, this study provides further support for neuro-imaging studies and brain lesion investigations that have suggested the existence of different brain circuits associated with different profiles of interaction between the dorsal and the ventral streams.

What is the Bandwidth of Perceptual Experience?

Although our subjective impression is of a richly detailed visual world, numerous empirical results suggest that the amount of visual information observers can perceive and remember at any given moment is limited. How can our subjective impressions be reconciled with these objective observations? Here, we answer this question by arguing that, although we see more than the handful of objects, claimed by prominent models of visual attention and working memory, we still see far less than we think we do. Taken together, we argue that these considerations resolve the apparent conflict between our subjective impressions and empirical data on visual capacity, while also illuminating the nature of the representations underlying perceptual experience.

The neural representation of objects formed through the spatiotemporal integration of visual transients

Oftentimes, objects are only partially and transiently visible as parts of them become occluded during observer or object motion. The visual system can integrate such object fragments across space and time into perceptual wholes or spatiotemporal objects. This integrative and dynamic process may involve both ventral and dorsal visual processing pathways, along which shape and spatial representations are thought to arise. We measured fMRI BOLD response to spatiotemporal objects and used multi-voxel pattern analysis (MVPA) to decode shape information across 20 topographic regions of visual cortex. Object identity could be decoded throughout visual cortex, including intermediate (V3A, V3B, hV4, LO1-2,) and dorsal (TO1-2, and IPS0-1) visual areas. Shape-specific information, therefore, may not be limited to early and ventral visual areas, particularly when it is dynamic and must be integrated. Contrary to the classic view that the representation of objects is the purview of the ventral stream, intermediate and dorsal areas may play a distinct and critical role in the construction of object representations across space and time.

Look but don't touch: Visual cues to surface structure drive somatosensory cortex

When planning interactions with nearby objects, our brain uses visual information to estimate shape, material composition, and surface structure before we come into contact with them. Here we analyse brain activations elicited by different types of visual appearance, measuring fMRI responses to objects that are glossy, matte, rough, or textured. In addition to activation in visual areas, we found that fMRI responses are evoked in the secondary somatosensory area (S2) when looking at glossy and rough surfaces. This activity could be reliably discriminated on the basis of tactile-related visual properties (gloss, rough, and matte), but importantly, other visual properties (i.e., coloured texture) did not substantially change fMRI activity. The activity could not be solely due to tactile imagination, as asking explicitly to imagine such surface properties did not lead to the same results. These findings suggest that visual cues to an object's surface properties evoke activity in neural circuits associated with tactile stimulation. This activation may reflect the a-priori probability of the physics of the interaction (i.e., the expectation of upcoming friction) that can be used to plan finger placement and grasp force.

Distinct cognitive mechanisms involved in the processing of single objects and object ensembles

Behavioral research has demonstrated that the shape and texture of single objects can be processed independently. Similarly, neuroimaging results have shown that an object's shape and texture are processed in distinct brain regions with shape in the lateral occipital area and texture in parahippocampal cortex. Meanwhile, objects are not always seen in isolation and are often grouped together as an ensemble. We recently showed that the processing of ensembles also involves parahippocampal cortex and that the shape and texture of ensemble elements are processed together within this region. These neural data suggest that the independence seen between shape and texture in single-object perception would not be observed in object-ensemble perception. Here we tested this prediction by examining whether observers could attend to the shape of ensemble elements while ignoring changes in an unattended texture feature and vice versa. Across six behavioral experiments, we replicated previous findings of independence between shape and texture in single-object perception. In contrast, we observed that changes in an unattended ensemble feature negatively impacted the processing of an attended ensemble feature only when ensemble features were attended globally. When they were attended locally, thereby making ensemble processing similar to single-object processing, interference was abolished. Overall, these findings confirm previous neuroimaging results and suggest that distinct cognitive mechanisms may be involved in single-object and object-ensemble perception. Additionally, they show that the scope of visual attention plays a critical role in determining which type of object processing (ensemble or single object) is engaged by the visual system.

Lateral and Medial Ventral Occipitotemporal Regions Interact During the Recognition of Images Revealed from Noise

Several studies suggest different functional roles for the medial and the lateral sections of the ventral visual cortex in object recognition. Texture and surface information is processed in medial sections, while shape information is processed in lateral sections. This begs the question whether and how these functionally specialized sections interact with each other and with early visual cortex to facilitate object recognition. In the current research, we set out to answer this question. In an fMRI study, 13 subjects viewed and recognized images of objects and animals that were gradually revealed from noise while their brains were being scanned. We applied dynamic causal modeling (DCM)-a method to characterize network interactions-to determine the modulatory effect of object recognition on a network comprising the primary visual cortex (V1), the lingual gyrus (LG) in medial ventral cortex and the lateral occipital cortex (LO). We found that object recognition modulated the bilateral connectivity between LG and LO. Moreover, the feed-forward connectivity from V1 to LG and LO was modulated, while there was no evidence for feedback from these regions to V1 during object recognition. In particular, the interaction between medial and lateral areas supports a framework in which visual recognition of objects is achieved by networked regions that integrate information on image statistics, scene content and shape-rather than by a single categorically specialized region-within the ventral visual cortex.

Human visual cortical responses to specular and matte motion flows

Determining the compositional properties of surfaces in the environment is an important visual capacity. One such property is specular reflectance, which encompasses the range from matte to shiny surfaces. Visual estimation of specular reflectance can be informed by characteristic motion profiles; a surface with a specular reflectance that is difficult to determine while static can be confidently disambiguated when set in motion. Here, we used fMRI to trace the sensitivity of human visual cortex to such motion cues, both with and without photometric cues to specular reflectance. Participants viewed rotating blob-like objects that were rendered as images (photometric) or dots (kinematic) with either matte-consistent or shiny-consistent specular reflectance profiles. We were unable to identify any areas in low and mid-level human visual cortex that responded preferentially to surface specular reflectance from motion. However, univariate and multivariate analyses identified several visual areas; V1, V2, V3, V3A/B, and hMT+, capable of differentiating shiny from matte surface flows. These results indicate that the machinery for extracting kinematic cues is present in human visual cortex, but the areas involved in integrating such information with the photometric cues necessary for surface specular reflectance remain unclear.

Cortical activation associated with determination of depth order during transparent motion perception: A normalized integrative fMRI-MEG study

When visual patterns drifting in different directions and/or at different speeds are superimposed on the same plane, observers perceive transparent surfaces on planes of different depths. This phenomenon is known as transparent motion perception. In this study, cortical activities were measured using functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) to reveal the cortical dynamics associated with determination of depth order during transparent motion perception. In addition, offline eye movement measurements were performed to determine the latencies of the start of both pursuit eye movements and depth attention that are important in determination of the depth order. MEG and fMRI data were analyzed by a normalized integrative fMRI-MEG method that enables reconstruction of time-varying dipole moments of activated regions from MEG signals. Statistical analysis of fMRI data was performed to identify activated regions. The activated regions were used as spatial constraints for the reconstruction using the integrative fMRI-MEG method. We focused on the period between latencies (216-405 ms) determined by eye movement experiment, which are related to determination of the depth order. The results of integrative analysis revealed that significant neural activities were observed in the visual association area, the human middle temporal area, the intraparietal sulcus, the lateral occipital cortex, and the anterior cingulate cortex between 216 and 405 ms. These results suggest that initial eye movement and accompanying cortical activations during focused duration play an important role in determining the depth order during transparent motion perception.

Object processing in the infant: lessons from neuroscience

Object identification is a fundamental cognitive capacity that forms the basis for complex thought and behavior. The adult cortex is organized into functionally distinct visual object-processing pathways that mediate this ability. Insights into the origin of these pathways have begun to emerge through the use of neuroimaging techniques with infant populations. The outcome of this work supports the view that, from the early days of life, object-processing pathways are organized in a way that resembles that of the adult. At the same time, theoretically important changes in patterns of cortical activation are observed during the first year. These findings lead to a new understanding of the cognitive and neural architecture in infants that supports their emerging object-processing capacities.

fNIRS in the developmental sciences

With the introduction of functional near-infrared spectroscopy (fNIRS) into the experimental setting, developmental scientists have, for the first time, the capacity to investigate the functional activation of the infant brain in awake, engaged participants. The advantages of fNIRS clearly outweigh the limitations, and a description of how this technology is implemented in infant populations is provided. Most fNIRS research falls into one of three content domains: object processing, processing of biologically and socially relevant information, and language development. Within these domains, there are ongoing debates about the origins and development of human knowledge, making early neuroimaging particularly advantageous. The use of fNIRS has allowed investigators to begin to identify the localization of early object, social, and linguistic knowledge in the immature brain and the ways in which this changes with time and experience. In addition, there is a small but growing body of research that provides insight into the neural mechanisms that support and facilitate learning during the first year of life. At the same time, as with any emerging field, there are limitations to the conclusions that can be drawn on the basis of current findings. We offer suggestions as to how to optimize the use of this technology to answer questions of theoretical and practical importance to developmental scientists.

Functional Reorganization of the Visual Dorsal Stream as Probed by 3-D Visual Coherence in Williams Syndrome

Object and depth perception from motion cues involves the recruitment of visual dorsal stream brain areas. In 3-D structure-from-motion (SFM) perception, motion and depth information are first extracted in this visual stream to allow object categorization, which is in turn mediated by the ventral visual stream. Such interplay justifies the use of SFM paradigms to understand dorsal–ventral integration of visual information. The nature of such processing is particularly interesting to be investigated in a neurological model of cognitive dissociation between dorsal (impaired) and ventral stream (relatively preserved) processing, Williams syndrome (WS). In the current fMRI study, we assessed dorsal versus ventral stream processing by using a performance-matched 3-D SFM object categorization task. We found evidence for substantial reorganization of the dorsal stream in WS as assessed by whole-brain ANOVA random effects analysis, with subtle differences in ventral activation. Dorsal reorganization was expressed by larger medial recruitment in WS (cuneus, precuneus, and retrosplenial cortex) in contrast with controls, which showed the expected dorsolateral pattern (caudal intraparietal sulcus and lateral occipital cortex). In summary, we found a substantial reorganization of dorsal stream regions in WS in response to simple visual categories and 3-D SFM perception, with less affected ventral stream. Our results corroborate the existence of a medial dorsal pathway that provides the substrate for information rerouting and reorganization in the presence of lateral dorsal stream vulnerability. This interpretation is consistent with recent findings suggesting parallel routing of information in medial and lateral parts of dorsal stream.

What you see depends on what you saw, and what else you saw: the interactions between motion priming and object priming

Both visual object priming and motion priming have been reported independently, but the interactions between the two are still largely unexplored. Here we investigated this question using a novel type of SFM stimuli, 3-D helixes, and found that the motion direction perception of an ambiguous helix can be biased by the motion direction of a preceding SFM stimulus - a classic motion priming effect. However, the effectiveness of motion priming depends on object priming: a neutral object priming produced a weak motion priming, a congruent object priming led to a strong motion priming, and critically, an incongruent object priming abolished and overpowered the motion priming. In contrast, object priming alone (in the absence of motion overlap) had little effects biasing motion perception. Taken together, these results suggest that there exists an integrated neural representation of motion and structure of 3-D SFM stimuli, and motion priming of 3-D SFM stimuli might happen at an intermediate stage between MT/V5 (which is not shape selective) and LO (lateral occipital, which is not motion selective). This novel type of stimuli, 3-D helixes, along with the prime-target paradigm, thus might offer a unique tool to examine neural bases underlying the perception of 3-D SFM stimuli and perceptual priming.

Cortical activation to object shape and speed of motion during the first year

A great deal is known about the functional organization of cortical networks that mediate visual object processing in the adult. The current research is part of a growing effort to identify the functional maturation of these pathways in the developing brain. The current research used near-infrared spectroscopy to investigate functional activation of the infant cortex during the processing of featural information (shape) and spatiotemporal information (speed of motion) during the first year of life. Our investigation focused on two areas that were implicated in previous studies: anterior temporal cortex and posterior parietal cortex. Neuroimaging data were collected with 207 infants across three age groups: 3-6 months (Experiment 1), 7-8 months (Experiment 2), and 10-12 months (Experiments 3 and 4). The neuroimaging data revealed age-related changes in patterns of activation to shape and speed information, mostly involving posterior parietal areas, some of which were predicted and others that were not. We suggest that these changes reflect age-related differences in the perceptual and/or cognitive processes engaged during the task.

Perceptual adaptation to structure-from-motion depends on the size of adaptor and probe objects, but not on the similarity of their shapes

Perceptual adaptation destabilizes the phenomenal appearance of multistable visual displays. Prolonged dominance of a perceptual state fatigues the associated neural population, lowering the likelihood of renewed perception of the same appearance (Nawrot & Blake in Perception & Psychophysics, 49, 230-44, 1991). Here, we used a selective adaptation paradigm to investigate perceptual adaptation for the illusory rotation of ambiguous structure-from-motion (SFM) displays. Specifically, we generated SFM objects with different three-dimensional shapes and presented them in random order, separating successive objects by brief blank periods, which included a mask. To assess the specificity of perceptual adaptation to the shape of SFM objects, we established the probability that a perceived direction of rotation persisted between successive objects of similar or dissimilar shape. We found that the strength of negative aftereffects depended on the volume, but not the shape, of adaptor and probe objects. More voluminous objects were both more effective as adaptor objects and more sensitive as probe objects. Surprisingly, we found these volume effects to be completely independent, since any relationship between two shapes (such as overlap between volumes, similarity of shape, or similarity of velocity profiles) failed to modulate the negative aftereffect. This pattern of results was the opposite of that observed for sensory memory of SFM objects, which reflects similarity between objects, but not volume of individual objects (Pastukhov et al. in Attention, Perception & Psychophysics, 75, 1215-1229, 2013). The disparate specificities of perceptual adaptation and sensory memory for identical SFM objects suggest that the two aftereffects engage distinct neural representations, consistent with recent brain imaging results (Schwiedrzik et al. in Cerebral Cortex, 2012).

Feature integration and object representations along the dorsal stream visual hierarchy

The visual system is split into two processing streams: a ventral stream that receives color and form information and a dorsal stream that receives motion information. Each stream processes that information hierarchically, with each stage building upon the previous. In the ventral stream this leads to the formation of object representations that ultimately allow for object recognition regardless of changes in the surrounding environment. In the dorsal stream, this hierarchical processing has classically been thought to lead to the computation of complex motion in three dimensions. However, there is evidence to suggest that there is integration of both dorsal and ventral stream information into motion computation processes, giving rise to intermediate object representations, which facilitate object selection and decision making mechanisms in the dorsal stream. First we review the hierarchical processing of motion along the dorsal stream and the building up of object representations along the ventral stream. Then we discuss recent work on the integration of ventral and dorsal stream features that lead to intermediate object representations in the dorsal stream. Finally we propose a framework describing how and at what stage different features are integrated into dorsal visual stream object representations. Determining the integration of features along the dorsal stream is necessary to understand not only how the dorsal stream builds up an object representation but also which computations are performed on object representations instead of local features.

The transition in the ventral stream from feature to real-world entity representations

We propose that the ventral visual pathway of human and non-human primates is organized into three levels: (1) ventral retinotopic cortex including what is known as TEO in the monkey but corresponds to V4A and PITd/v, and the phPIT cluster in humans, (2) area TE in the monkey and its homolog LOC and neighboring fusiform regions, and more speculatively, (3) TGv in the monkey and its possible human equivalent, the temporal pole. We attribute to these levels the visual representations of features, partial real-world entities (RWEs), and known, complete RWEs, respectively. Furthermore, we propose that the middle level, TE and its homolog, is organized into three parallel substreams, lower bank STS, dorsal convexity of TE, and ventral convexity of TE, as are their corresponding human regions. These presumably process shape in depth, 2D shape and material properties, respectively, to construct RWE representations.

The Impact of Density and Ratio on Object-Ensemble Representation in Human Anterior-Medial Ventral Visual Cortex

Behavioral research has demonstrated that observers can extract summary statistics from ensembles of multiple objects. We recently showed that a region of anterior-medial ventral visual cortex, overlapping largely with the scene-sensitive parahippocampal place area (PPA), participates in object-ensemble representation. Here we investigated the encoding of ensemble density in this brain region using fMRI-adaptation. In Experiment 1, we varied density by changing the spacing between objects and found no sensitivity in PPA to such density changes. Thus, density may not be encoded in PPA, possibly because object spacing is not perceived as an intrinsic ensemble property. In Experiment 2, we varied relative density by changing the ratio of 2 types of objects comprising an ensemble, and observed significant sensitivity in PPA to such ratio change. Although colorful ensembles were shown in Experiment 2, Experiment 3 demonstrated that sensitivity to object ratio change was not driven mainly by a change in the ratio of colors. Thus, while anterior-medial ventral visual cortex is insensitive to density (object spacing) changes, it does code relative density (object ratio) within an ensemble. Object-ensemble processing in this region may thus depend on high-level visual information, such as object ratio, rather than low-level information, such as spacing/spatial frequency.

Cortical responses to optic flow and motion contrast across patterns and speeds

Motion provides animals with fast and robust cues for navigation and object detection. In the first case, stereotyped patterns of optic flow inform a moving observer about the direction and speed of its own movement. In the case of object detection, regional differences in motion allow for the segmentation of figures from their background, even in the absence of color or shading cues. Previous research has investigated human electrophysiological responses to global motion across speeds, but only focused upon one type of optic flow pattern. Here, we compared steady-state visual evoked potential (SSVEP) responses across patterns and speeds, both for optic flow and for motion-defined figure patterns, to assess the extent to which the processes are pattern-general or pattern-specific. For optic flow, pattern and speed effects on response amplitudes varied substantially across channels, suggesting pattern-specific processing at slow speeds and pattern-general activity at fast speeds. Responses for coherence- and direction-defined figures were comparatively more uniform, with similar response profiles and spatial distributions. Self- and object-motion patterns activate some of the same circuits, but these data suggest differential sensitivity: not only across the two classes of motion, but also across the patterns within each class, and across speeds. Thus, the results demonstrate that cortical processing of global motion is complex and activates a distributed network.

Representation of the material properties of objects in the visual cortex of nonhuman primates

Information about the material from which objects are made provide rich and useful clues that enable us to categorize and identify those objects, know their state (e.g., ripeness of fruits), and properly act on them. However, despite its importance, little is known about the neural processes that underlie material perception in nonhuman primates. Here we conducted an fMRI experiment in awake macaque monkeys to explore how information about various real-world materials is represented in the visual areas of monkeys, how these neural representations correlate with perceptual material properties, and how they correspond to those in human visual areas that have been studied previously. Using a machine-learning technique, the representation in each visual area was read out from multivoxel patterns of regional activity elicited in response to images of nine real-world material categories (metal, wood, fur, etc.). The congruence of the neural representations with either a measure of low-level image properties, such as spatial frequency content, or with the visuotactile properties of materials, such as roughness, hardness, and warmness, were tested. We show that monkey V1 shares a common representation with human early visual areas reflecting low-level image properties. By contrast, monkey V4 and the posterior inferior temporal cortex represent the visuotactile properties of material, as in human ventral higher visual areas, although there were some interspecies differences in the representational structures. We suggest that, in monkeys, V4 and the posterior inferior temporal cortex are important stages for constructing information about the material properties of objects from their low-level image features.

The representation of material categories in the brain

Using textures mapped onto virtual nonsense objects, it has recently been shown that early visual cortex plays an important role in processing material properties. Here, we examined brain activation to photographs of materials, consisting of wood, stone, metal and fabric surfaces. These photographs were close-ups in the sense that the materials filled the image. In the first experiment, observers categorized the material in each image (i.e., wood, stone, metal, or fabric), while in an fMRI-scanner. We predicted the assigned material category using the obtained voxel patterns using a linear classifier. Region-of-interest and whole-brain analyses demonstrated material coding in the early visual regions, with lower accuracies for more anterior regions. There was little evidence for material coding in other brain regions. In the second experiment, we used an adaptation paradigm to reveal additional brain areas involved in the perception of material categories. Participants viewed images of wood, stone, metal, and fabric, presented in blocks with images of either different material categories (no adaptation) or images of different samples from the same material category (material adaptation). To measure baseline activation, blocks with the same material sample were presented (baseline adaptation). Material adaptation effects were found mainly in the parahippocampal gyrus, in agreement with fMRI-studies of texture perception. Our findings suggest that the parahippocampal gyrus, early visual cortex, and possibly the supramarginal gyrus are involved in the perception of material categories, but in different ways. The different outcomes from the two studies are likely due to inherent differences between the two paradigms. A third experiment suggested, based on anatomical overlap between activations, that spatial frequency information is important for within-category material discrimination.