Shape coding in occipito-temporal cortex relies on object silhouette, curvature, and medial axis.

Object recognition relies on different transformations of the retinal input, carried out by the visual system, that range from local contrast to object shape and category. While some of those transformations are thought to occur at specific stages of the visual hierarchy, the features they represent are correlated (e.g., object shape and identity) and selectivity for the same feature overlaps in many brain regions. This may be explained either by collinearity across representations or may instead reflect the coding of multiple dimensions by the same cortical population. Moreover, orthogonal and shared components may differently impact distinctive stages of the visual hierarchy. We recorded functional MRI activity while participants passively attended to object images and employed a statistical approach that partitioned orthogonal and shared object representations to reveal their relative impact on brain processing. Orthogonal shape representations (silhouette, curvature, and medial axis) independently explained distinct and overlapping clusters of selectivity in the occitotemporal and parietal cortex. Moreover, we show that the relevance of shared representations linearly increases moving from posterior to anterior regions. These results indicate that the visual cortex encodes shared relations between different features in a topographic fashion and that object shape is encoded along different dimensions, each representing orthogonal features.NEW & NOTEWORTHY There are several possible ways of characterizing the shape of an object. Which shape description better describes our brain responses while we passively perceive objects? Here, we employed three competing shape models to explain brain representations when viewing real objects. We found that object shape is encoded in a multidimensional fashion and thus defined by the interaction of multiple features.

The relative contribution of shape and colour to object memory.

The current studies examined the relative contribution of shape and colour in object representations in memory. A great deal of evidence points to the significance of shape in object recognition, with the role of colour being instrumental under certain circumstances. A key but yet unanswered question concerns the contribution of colour relative to shape in mediating retrieval of object representations from memory. Two experiments (N=80) used a new method to probe episodic memory for objects and revealed the relative contribution of colour and shape in recognition memory. Participants viewed pictures of objects from different categories, presented one at a time. During a practice phase, participants performed yes/no recognition with some of the studied objects and their distractors. Unpractised objects shared shape only (Rp-Shape), colour only (Rp-Colour), shape and colour (Rp-Both), or neither shape nor colour (Rp-Neither), with the practised objects. Interference effects in memory between practised and unpractised items were revealed in the forgetting of related unpractised items - retrieval-induced forgetting. Retrieval-induced forgetting was consistently significant for Rp-Shape and Rp-Colour objects. These findings provide converging evidence that colour is an automatically encoded object property, and present new evidence that both shape and colour act simultaneously and effectively to drive retrieval of objects from long-term memory.

Representation of object's shape by multiple electric images in electrolocation.

Weakly electric fish generate an electric field by discharging an electric organ located on the tail region. An object near the fish modulates the self-generated electric field. The modulated field enables the fish to perceive objects even in complete darkness. The ability to perceive objects is provided by the electrosensory system of the fish. Electroreceptors distributed on the fish's skin surface can sense the modulated field, on the basis of transdermal voltage across the skin surface, called electric images. The fish can extract object's features such as lateral distance, size, shape, and electric property from an electric image. Although previous studies have demonstrated the relationship between electric-image features and object's distance and size, it remains unclear what features of an electric image represent the object's shape. We make here a hypothesis that shape information is not represented by a single image but by multiple images caused by the object's rotation or fish movement around the object. To test the hypothesis, we develop a computational model that can predict electric images produced by the rotation of differently shaped objects. We used five different shapes of resistive objects: a circle, a square, an equilateral triangle, a rectangle, and an ellipsoid. We show that differently shaped objects of a fixed arrangement generate similar Gaussian electric images, irrespective of their shapes. We also show that the features of an electric image such as the peak amplitude, half-maximum width, and peak position exhibit the angle-dependent variations characteristic to object rotation, depending on object shapes and lateral distances. Furthermore, we demonstrate that an integration effect of the peak amplitude and half-maximum width could be an invariant measure of object shape. These results suggest that the fish could perceive an object shape by combining those image features produced during exploratory behaviors around the object.

Dissociations and Associations between Shape and Category Representations in the Two Visual Pathways.

The dorsal and ventral visual pathways represent both visual and conceptual object properties. Yet the relative contribution of these two factors in the representational content of visual areas is unclear. Indeed, research investigating brain category representations rarely dissociate visual and semantic properties of objects. We present a human event-related fMRI study with a two-factorial stimulus set with 54 images that explicitly dissociates shape from category to investigate their independent contribution as well as their interactions through representational similarity analyses. Results reveal a contribution from each dimension in both streams, with a transition from shape to category along the posterior-to-anterior anatomical axis. The nature of category representations differs in the two pathways: ventral areas represent object animacy and dorsal areas represent object action properties. Furthermore, information about shape evolved from low-level pixel-based to high-level perceived shape following a posterior-to-anterior gradient similar to the shape-to-category emergence. To conclude, results show that representations of shape and category independently coexist, but at the same time they are closely related throughout the visual hierarchy. SIGNIFICANCE STATEMENT: Research investigating visual cortex conceptual category representations rarely takes into account visual properties of objects. In this report, we explicitly dissociate shape from category and investigate independent contributions and interactions of these two highly correlated dimensions.

Three-dimensional finger joint angles by hand posture and object properties.

The objective of this study was to identify three-dimensional finger joint angles for various hand postures and object properties. Finger joint angles were measured using a VICON system for 10 participants while they pinched objects with two, three, four and five fingers and grasped them with five fingers. The objects were cylinders and square pillars with diameters of 2, 4, 6 and 8 cm and weights of 400, 800, 1400 and 1800 g. Hand posture and object size more significantly affected the joint flexion angles than did object shape and weight. Object shape affected only the metacarpophalangeal (MCP) joint angle of the index finger and the flexion angle of the MCP joint of the little finger. Larger flexion angles resulted when the hand posture was grasping with five fingers. The joint angle increased linearly as the object size decreased. This report provides fundamental information about the specific joint angles of the thumb and fingers. Practitioner Summary: Three-dimensional finger joint angles are of special interest in ergonomics because of their importance in handheld devices and musculoskeletal hand disorders. In this study, the finger joint angles corresponding to various hand postures and objects with different properties were determined.

Neuroanatomical correlates of haptic object processing: combined evidence from tractography and functional neuroimaging.

Touch delivers a wealth of information already from birth, helping infants to acquire knowledge about a variety of important object properties using their hands. Despite the fact that we are touch experts as much as we are visual experts, surprisingly, little is known how our perceptual ability in touch is linked to either functional or structural aspects of the brain. The present study, therefore, investigates and identifies neuroanatomical correlates of haptic perceptual performance using a novel, multi-modal approach. For this, participants' performance in a difficult shape categorization task was first measured in the haptic domain. Using a multi-modal functional magnetic resonance imaging and diffusion-weighted magnetic resonance imaging analysis pipeline, functionally defined and anatomically constrained white-matter pathways were extracted and their microstructural characteristics correlated with individual variability in haptic categorization performance. Controlling for the effects of age, total intracranial volume and head movements in the regression model, haptic performance was found to correlate significantly with higher axial diffusivity in functionally defined superior longitudinal fasciculus (fSLF) linking frontal and parietal areas. These results were further localized in specific sub-parts of fSLF. Using additional data from a second group of participants, who first learned the categories in the visual domain and then transferred to the haptic domain, haptic performance correlates were obtained in the functionally defined inferior longitudinal fasciculus. Our results implicate SLF linking frontal and parietal areas as an important white-matter track in processing touch-specific information during object processing, whereas ILF relays visually learned information during haptic processing. Taken together, the present results chart for the first time potential neuroanatomical correlates and interactions of touch-related object processing.

Infants' perceptions of constraints on object motion as a function of object shape.

Three studies examined young infants' ability to distinguish between expected and unexpected motion of objects based on their shape. Using a preferential-looking paradigm, 8- and 12-month-old infants' looking time towards expected and unexpected motion displays of familiar, everyday objects (e.g., balls and cubes) was examined. Experiment 1 demonstrated that two factors drive infants' preferential fixations of object motion displays. Both 8- and 12-month-olds displayed a tendency to look at rotating information over non-rotating, stationary visual information. In contrast, only 12-month-olds showed a tendency to look at object motions that were inconsistent or "unexpected" based on shape. After controlling for the preference for more complex (rolling) by adding rolling motion to both displays (Experiment 2), 12-month-olds' ability to distinguish between expected and unexpected motion displays was facilitated. Experiment 3 provided a control by demonstrating that the preference for the unexpected object motion was not due to any other motion properties of the objects. Overall, these results indicate that 12-month-old infants have the ability to recognize the role that object shape plays in constraining object motion, which has important theoretical implications for the development of object perception.

Vibrotactile feedback for conveying object shape information as perceived by artificial sensing of robotic arm.

This work is a preliminary study towards developing an alternative communication channel for conveying shape information to aid in recognition of items when tactile perception is hindered. Tactile data, acquired during object exploration by sensor fitted robot arm, are processed to recognize four basic geometric shapes. Patterns representing each shape, classified from tactile data, are generated using micro-controller-driven vibration motors which vibrotactually stimulate users to convey the particular shape information. These motors are attached on the subject's arm and their psychological (verbal) responses are recorded to assess the competence of the system to convey shape information to the user in form of vibrotactile stimulations. Object shapes are classified from tactile data with an average accuracy of 95.21 %. Three successive sessions of shape recognition from vibrotactile pattern depicted learning of the stimulus from subjects' psychological response which increased from 75 to 95 %. This observation substantiates the learning of vibrotactile stimulation in user over the sessions which in turn increase the system efficacy. The tactile sensing module and vibrotactile pattern generating module are integrated to complete the system whose operation is analysed in real-time. Thus, the work demonstrates a successful implementation of the complete schema of artificial tactile sensing system for object-shape recognition through vibrotactile stimulations.

The Role of Shape in Semantic Memory Organization of Objects: An Experimental Study Using PI-Release.

Visual information contributes fundamentally to the process of object categorization. The present study investigated whether the degree of activation of visual information in this process is dependent on the contextual relevance of this information. We used the Proactive Interference (PI-release) paradigm. In four experiments, we manipulated the information by which objects could be categorized and subsequently be retrieved from memory. The pattern of PI-release showed that if objects could be stored and retrieved both by (non-perceptual) semantic and (perceptual) shape information, then shape information was overruled by semantic information. If, however, semantic information could not be (satisfactorily) used to store and retrieve objects, then objects were stored in memory in terms of their shape. The latter effect was found to be strongest for objects from identical semantic categories.

The role of surface-based representations of shape in visual object recognition.

This study contrasted the role of surfaces and volumetric shape primitives in three-dimensional object recognition. Observers (N = 50) matched subsets of closed contour fragments, surfaces, or volumetric parts to whole novel objects during a whole-part matching task. Three factors were further manipulated: part viewpoint (either same or different between component parts and whole objects), surface occlusion (comparison parts contained either visible surfaces only, or a surface that was fully or partially occluded in the whole object), and target-distractor similarity. Similarity was varied in terms of systematic variation in nonaccidental (NAP) or metric (MP) properties of individual parts. Analysis of sensitivity (d') showed a whole-part matching advantage for surface-based parts and volumes over closed contour fragments--but no benefit for volumetric parts over surfaces. We also found a performance cost in matching volumetric parts to wholes when the volumes showed surfaces that were occluded in the whole object. The same pattern was found for both same and different viewpoints, and regardless of target-distractor similarity. These findings challenge models in which recognition is mediated by volumetric part-based shape representations. Instead, we argue that the results are consistent with a surface-based model of high-level shape representation for recognition.

Evidence for the role of shape in mental representations of similes.

People mentally represent the shapes of objects. For instance, the mental representation of an eagle is different when one thinks about a flying or resting eagle. This study examined the role of shape in mental representations of similes (i.e., metaphoric comparisons). We tested the prediction that when people process a simile they will mentally represent the entities of the comparison as having a similar shape. We conducted two experiments in which participants read sentences that either did (experimental sentences) or did not (control sentences) invite comparing two entities. For the experimental sentences, the ground of the comparison was explicit in Experiment 1 ("X has the ability to Z, just like Y") and implicit in Experiment 2 ("X is like Y"). After having read the sentence, participants were presented with line drawings of the two objects, which were either similarly or dissimilarly shaped. They judged whether both objects were mentioned in the preceding sentence. For the experimental sentences, recognition latencies were shorter for similarly shaped objects than for dissimilarly shaped objects. For the control sentences, we did not find such an effect of similarity in shape. These findings suggest that a perceptual symbol of shape is activated when processing similes.

Gesturing Meaning: Non-action Words Activate the Motor System.

Across cultures, speakers produce iconic gestures, which add - through the movement of the speakers' hands - a pictorial dimension to the speakers' message. These gestures capture not only the motor content but also the visuospatial content of the message. Here, we provide first evidence for a direct link between the representation of perceptual information and the motor system that can account for these observations. Across four experiments, participants' hand movements captured both shapes that were directly perceived, and shapes that were only implicitly activated by unrelated semantic judgments of object words. These results were obtained even though the objects were not associated with any motor behaviors that would match the gestures the participants had to produce. Moreover, implied shape affected not only gesture selection processes but also their actual execution - as measured by the shape of hand motion through space - revealing intimate links between implied shape representation and motor output. The results are discussed in terms of ideomotor theories of action and perception, and provide one avenue for explaining the ubiquitous phenomenon of iconic gestures.

Affine Registration of label maps in Label Space.

Two key aspects of coupled multi-object shape analysis and atlas generation are the choice of representation and subsequent registration methods used to align the sample set. For example, a typical brain image can be labeled into three structures: grey matter, white matter and cerebrospinal fluid. Many manipulations such as interpolation, transformation, smoothing, or registration need to be performed on these images before they can be used in further analysis. Current techniques for such analysis tend to trade off performance between the two tasks, performing well for one task but developing problems when used for the other. This article proposes to use a representation that is both flexible and well suited for both tasks. We propose to map object labels to vertices of a regular simplex, e.g . the unit interval for two labels, a triangle for three labels, a tetrahedron for four labels, etc. This representation, which is routinely used in fuzzy classification, is ideally suited for representing and registering multiple shapes. On closer examination, this representation reveals several desirable properties: algebraic operations may be done directly, label uncertainty is expressed as a weighted mixture of labels (probabilistic interpretation), interpolation is unbiased toward any label or the background, and registration may be performed directly. We demonstrate these properties by using label space in a gradient descent based registration scheme to obtain a probabilistic atlas. While straightforward, this iterative method is very slow, could get stuck in local minima, and depends heavily on the initial conditions. To address these issues, two fast methods are proposed which serve as coarse registration schemes following which the iterative descent method can be used to refine the results. Further, we derive an analytical formulation for direct computation of the "group mean" from the parameters of pairwise registration of all the images in the sample set. We show results on richly labeled 2D and 3D data sets.