Differences in the coding of spatial relations in face identification and basic-level object recognition

Regional Variation in the Inversion Effect for Faces: Differential Effects for Feature Shape, Feature Configuration, and External Contour

Faces are perceived via an orientation-dependent expert mechanism. We previously showed that inversion impaired perception of the spatial relations of features more in the lower face than in the (more salient) upper face, suggests a failure to rapidly process this type of structural data from the entire face. In this study we wished to determine if this interaction between inversion and regional salience, which we consider a marker for efficient whole-face processing, was specific to second-order (coordinate) spatial relations or also affected other types of structural information in faces. We used an oddity paradigm to test the ability of seventeen subjects to discriminate changes in feature size, feature spatial relations, and external contour in both the upper and lower face. We also tested fourteen subjects on perception of two different types of spatial relations: second-order changes that create plausible alternative faces, and illegal spatial changes that transgress normal rules of facial geometry. In both experiments we examined for asymmetries between upper-face and lower-face perceptual accuracy with brief stimulus presentations. While all structural changes were less easily discerned in inverted faces, only changes to spatial relations showed a marked asymmetry between the upper and lower face, with far worse performance in the mouth region. Furthermore, this asymmetry was found only for second-order spatial relations and not illegal spatial changes. These results suggest that the orientation-dependent face mechanism has a rapid whole-face processing capacity specific to the internal second-order (coordinate) spatial relations of facial features.

Face Detection: Mapping Human Performance

The recognition of faces has been the focus of an extensive body of research, whereas the preliminary and prerequisite task of detecting a face has received limited attention from psychologists. Four experiments are reported that address the question how we detect a face. Experiment 1 reveals that we use information from the scene to aid detection. In experiment 2 we investigated which features of a face speed the detection of faces. Experiment 3 revealed inversion effects and an interaction between the effects of blurring and reduction of contrast. In experiment 4 the sizes of effects of reversal of orientation, luminance, and hue were compared. Luminance was found to have the greatest effect on reaction time to detect faces. The results are interpreted as suggesting that face detection proceeds by a pre-attentive stage that identifies possible face regions, which is followed by a focused-attention stage that employs a deformable template. Comparisons are drawn with automatic face-detection systems.

Attention to Configural Information in Change Detection for Faces

In recent research the change-detection paradigm has been used along with cueing manipulations to show that more attention is allocated to the upper than lower facial region, and that this attentional allocation is disrupted by inversion. We report two experiments the object of which was to investigate how the type of information changed might be a factor in these findings by explicitly comparing the role of attention in detecting change to information thought to be ‘special’ to faces (second-order relations) with information that is more useful for basic-level object discrimination (first-order relations). Results suggest that attention is automatically directed to second-order relations in upright faces, but not first-order relations, and that this pattern of attentional allocation is similar across features.

Facial Composite Production by Eyewitnesses

The creation of facial images by eyewitnesses using composite-production systems can be important for the investigation of crimes when the identity of the perpetrator is at issue. Despite technological advances, research indicates that composite-production systems produce poor likenesses of intended faces, even familiar faces. Furthermore, producing a composite appears to harm later recognition performance. Although morphing composites from multiple witnesses helps, likeness is still limited. The problem might stem from a mismatch between how faces are represented in memory (holistically) and how composite systems attempt to retrieve the memories (at the feature level). New methods of face recall involving judgments of whole faces hold greater promise.

Hemispheric differences in relational reasoning: novel insights based on an old technique

Relational reasoning, or the ability to integrate multiple mental relations to arrive at a logical conclusion, is a critical component of higher cognition. A bilateral brain network involving lateral prefrontal and parietal cortices has been consistently implicated in relational reasoning. Some data suggest a preferential role for the left hemisphere in this form of reasoning, whereas others suggest that the two hemispheres make important contributions. To test for a hemispheric asymmetry in relational reasoning, we made use of an old technique known as visual half-field stimulus presentation to manipulate whether stimuli were presented briefly to one hemisphere or the other. Across two experiments, 54 neurologically healthy young adults performed a visuospatial transitive inference task. Pairs of colored shapes were presented rapidly in either the left or right visual hemifield as participants maintained central fixation, thereby isolating initial encoding to the contralateral hemisphere. We observed a left-hemisphere advantage for encoding a series of ordered visuospatial relations, but both hemispheres contributed equally to task performance when the relations were presented out of order. To our knowledge, this is the first study to reveal hemispheric differences in relational encoding in the intact brain. We discuss these findings in the context of a rich literature on hemispheric asymmetries in cognition.

Categorical and coordinate processing in object recognition depends on different spatial frequencies

Previous studies have suggested that processing categorical spatial relations requires high spatial frequency (HSF) information, while coordinate spatial relations require low spatial frequency (LSF) information. The aim of the present study was to determine whether spatial frequency influences categorical and coordinate processing in object recognition. Participants performed two object-matching tasks for novel, non-nameable objects consisting of "geons" (c.f. Brain Cogn 71:181-186, 2009). For each original stimulus, categorical and coordinate transformations were applied to create comparison stimuli. These stimuli were high-pass/low-cut-filtered or low-pass/high-cut-filtered by a filter with a 2D Gaussian envelope. The categorical task consisted of the original and categorical-transformed objects. The coordinate task consisted of the original and coordinate-transformed objects. The non-filtered object image was presented on a CRT monitor, followed by a comparison object (non-filtered, high-pass-filtered, and low-pass-filtered stimuli). The results showed that the removal of HSF information from the object image produced longer reaction times (RTs) in the categorical task, while removal of LSF information produced longer RTs in the coordinate task. These results support spatial frequency processing theory, specifically Kosslyn's hypothesis and the double filtering frequency model.

Face perception is whole or none: disentangling the role of spatial contiguity and interfeature distances in the composite face illusion

Compelling evidence that faces are perceived holistically or configurally comes from the composite face illusion: identical top halves of a face are perceived as being different if they are aligned with different bottom halves. The visual illusion disappears when the top and bottom face halves are spatially misaligned. Whether this is because the two halves no longer form a whole face (ie they form two segmented parts), or because of an increase in interfeatures distance in the misaligned condition (eg eyes-mouth distance) remains unclear. Here, thirty-four participants performed a delayed matching composite task in which the amount of spatial misalignment between face halves varied parametrically (from 8.33% of face width to 100%). The difference in performance between aligned and misaligned faces (ie the composite face effect) was already of full magnitude at the smallest level of misalignment. These results imply that a small spatial misalignment is sufficient to measure the composite face effect. From a theoretical standpoint, they indicate that it is the breaking of a whole configuration rather than the increase in relative distance between the face parts that explains the presence or absence of the composite face effect, clarifying an outstanding issue concerning the nature of holistic face perception.

The Composite-Face Effect Survives Asymmetric Face Distortions

In two experiments, we investigated whether adults use holistic processing even for faces that are grossly distorted because their eyes have been moved asymmetrically to violate the common layout of a face (distorting its first-order relations). To this end we used a compelling demonstration that faces are processed as wholes, the composite-face effect. Specifically, adults judged the similarity of sequentially presented top halves of normal (original condition) and distorted faces with one eye (one-eye condition) or two eyes (two-eyes condition) shifted up by an abnormal amount. Trials were either blocked by type of distortion (experiment 1) or intermixed within the experiment (experiment 2). In both experiments, participants demonstrated a composite-face effect of the same magnitude in the three conditions, a pattern suggesting that they processed holistically even faces whose first-order relations were violated.

Exogenous attention differentially modulates the processing of categorical and coordinate spatial relations

Carrasco and her colleagues have suggested that exogenous attention reduces the size of receptive fields at an attended location (Gobell & Carrasco, 2005; Yeshurun & Carrasco, 1998, 2000). Based on the hypothesis that categorical and coordinate spatial relations are more efficiently processed by smaller and larger receptive fields, respectively, we predicted that exogenous attention would be more beneficial to the processing of categorical spatial relations than coordinate spatial relations while it would disrupt the processing of coordinate spatial relations. To test these hypotheses, participants were tested using a variant of Posner's (1980) attentional cueing paradigm. Exogenous attention produced larger facilitative effects on categorical spatial processing than on coordinate spatial processing at a short cue-target stimulus onset asynchrony (100 ms, Experiment 1, N=28), and this result was replicated regardless of cue size in Experiment 2 (N=24). When the coordinate judgment was sufficiently difficult, exogenous attention disrupted the processing of coordinate spatial relations (Experiment 3, N=28). These findings indicate that exogenous attention can differentially modulate the processing of categorical and coordinate spatial relations.

Lateralized effects of categorical and coordinate spatial processing of component parts on the recognition of 3D non-nameable objects

Participants performed two object-matching tasks for novel, non-nameable objects consisting of geons. For each original stimulus, two transformations were applied to create comparison stimuli. In the categorical transformation, a geon connected to geon A was moved to geon B. In the coordinate transformation, a geon connected to geon A was moved to a different position on geon A. The Categorical task consisted of the original and the categorically transformed objects. The Coordinate task consisted of the original and the coordinately transformed objects. The original object was presented to the central visual field, followed by a comparison object presented to the right or left visual half-fields (RVF and LVF). The results showed an RVF advantage for the Categorical task and an LVF advantage for the Coordinate task. The possibility that categorical and coordinate spatial processing subsystems would be basic computational elements for between- and within-category object recognition was discussed.

The caricature effect in drawing: evidence for the use of categorical relations when drawing abstract pictures

Five experiments were conducted to determine how novice and expert drawers represent relative size for the purposes of drawing. Participants were shown images of two-part or three-part geometric figures composed of two spatially separated shapes. In each picture there was a small but noticeable relative-size difference between the constituent shapes (one part of the picture was always 25% larger than another part). Participants later drew the pictures from memory. The results showed that novice and expert drawers consistently exaggerated the relative size relationship between the shapes in the picture when attempting to draw it from memory and when copying (the 'caricature effect'), although the effect was reduced for the experts. The results are consistent with the idea that people represent size in memory using categorical descriptors (e.g., 'smaller than', 'larger than') rather than as precise metrics. Further, the results suggest that the process of becoming a skilled drawer may involve overcoming this categorical bias.

A tale of two recognition systems: implications of the fusiform face area and the visual word form area for lateralized object recognition models

Two areas of current intense interest in the neuroimaging literature are that of the visual word form area (VWFA) and of the fusiform face area (FFA) and their roles in word and face perception, respectively. These two areas are of particular relevance to laterality research because visual word identification and face identification have long been shown to be especially lateralized to the left hemisphere and the right hemisphere, respectively. This review therefore seeks to evaluate their significance for the broader understanding of lateralization of object recognition. A multi-level model of lateralized object recognition is proposed based on a combination of behavioral and neuroimaging findings. Rather than seek to characterize hemispheric asymmetries according to a single principle (e.g., serial-parallel), it is suggested that current observations can be understood in terms of three asymmetric levels of processing, using the framework of the Janus model of hemispheric function. It is suggested that the left hemisphere represents features using an abstract-category code whereas the RH utilizes a specific-exemplar code. The relationships between these features are also coded asymmetrically, with the LH relying on associative co-occurrence values and the RH relying on spatial metrics. Finally, the LH controlled selection system focuses on isolating features and the RH focuses on conjoining features. It is suggested that each hemisphere utilizes efficient (apparently parallel) processing when stimuli are congruent with its preferred processing style and inefficient (apparently serial) processing when they are not, resulting in the typical left-lateralization for orthographic analysis and right-lateralization for face analysis.

The effects of inversion and eye displacements of familiar and unknown faces on early and late-stage ERPs

OBJECTIVES

The objective of this study is to examine whether configural alterations of faces affect early or late processing stages as a function of their familiarity and their level of representation in memory. We then sought to verify whether the structural encoding stage is susceptible to top-down influences.

METHODS

Electrophysiologic and behavioral studies were undertaken, during which unknown and familiar faces were presented upright or upside-down with or without feature alterations. The subjects were asked to determine whether the faces were familiar or not.

RESULTS

N170 and N360 amplitudes were larger for familiar faces as well as altered ones. A higher degree of familiarity decreased reaction times (RTs) and N360 latencies, but increased N170 latencies, whereas face alterations increased RTs and latencies of both components examined. However, familiarity interacted with altered face configurations only for RTs and the N170.

SIGNIFICANCE

In the perceptual stage, familiar faces seem to develop a more elaborate type of processing because of top-down influences linked to the robust nature of their representations in memory. The more elaborate type of processing for familiar faces has advantageous consequences for the following steps of information processing, by facilitating access to structural representations in memory (N360) as well as the final step reflected by RTs. The fact that configural alterations cause different effects for familiar as opposed to unfamiliar faces indicate that these stimuli are processed in a qualitatively different manner and solicit different representations in memory.

Categorical and coordinate relations in faces, or Fechner's law and face space instead?

E. E. Cooper and T. J. Wojan (2000) applied the categorical-coordinate relations distinction to faces on the basis of a finding that two-eyes-up versus one-eye-up distortions had opposite effects in between-class (face normality) and within-class (face identity) tasks. However, Cooper and Wojan failed to match amount of metric change between their 2 deviation types and tested only 1 deviation level. In the present study, eyeheight was shifted (e.g., both eyes up or both eyes down vs. one eye up and one eye down) parametrically (11 levels) and normality and identity ratings obtained. There was no evidence of categorical changes in perception where these would have been predicted by Cooper and Wojan's theory. In all cases, the relationship between physical and perceived distortion followed Fechner's law. Differences across distortion types in Fechner threshold (the minimum deviation altering perceived normality or identity) are explained in terms of the variability associated with different dimensions in face space.

What types of visual recognition tasks are mediated by the neural subsystem that subserves face recognition?

Three divided visual field experiments tested current hypotheses about the types of visual shape representation tasks that recruit the cognitive and neural mechanisms underlying face recognition. Experiment 1 found a right hemisphere advantage for subordinate but not basic-level face recognition. Experiment 2 found a right hemisphere advantage for basic but not superordinate-level animal recognition. Experiment 3 found that inverting animals eliminates the right hemisphere advantage for basic-level animal recognition. This pattern of results suggests that the cognitive and neural mechanisms underlying face recognition are recruited when computational demands of a shape representation task are best served through the use of coordinate (rather than categorical) spatial relations.

Perceptual functions in prosopagnosia

Some patients with prosopagnosia may have an apperceptive basis to their recognition defect. Perceptual abnormalities have been reported in single cases or small series, but the causal link of such deficits to prosopagnosia is unclear. Our goal was to identify candidate perceptual processes that might contribute to prosopagnosia, by subjecting several prosopagnosic patients to a battery of functions that may be necessary for accurate facial perception. We tested seven prosopagnosic patients. Three had unilateral right occipitotemporal lesions, two had bilateral posterior occipitotemporal lesions, and one had right anterior-to-occipital temporal damage along with a small left temporal lesion. These lesions all included the fusiform face area, in contrast to one patient with bilateral anterior temporal lesions. Most patients had impaired performance on face-matching tests and difficulty with subcategory judgments for non-face objects. The most consistent deficits in patients with lesions involving the fusiform face area were impaired perception of spatial relations in dot patterns and reduced contrast sensitivity in the 4 to 8 cycles deg(-1) range. Patients with bilateral lesions were impaired in saturation discrimination. Luminance discrimination was normal in all but two patients, and spatial resolution was uniformly spared. Curvature and line-orientation discrimination were impaired in only one patient, who also had the most difficulty with more basic-level object recognition. We conclude that deficits in luminance, spatial resolution, curvature, line orientation, and contrast at low spatial frequencies are unlikely to contribute to apperceptive prosopagnosia. More relevant may be contrast sensitivity at higher spatial frequencies and the analysis of object spatial structure. Deficits in these functions may impair perception of subtle variations in object shape, and may be one mechanism by which the recognition defect in prosopagnosia can extend to other classes of object subcategorization.

The Role of High Spatial Frequencies in Hemispheric Processing of Categorical and Coordinate Spatial Relations

Right-handed participants performed categorical and coordinate spatial relation tasks on stimuli presented either to the left visual field-right hemisphere (LVF-RH) or to the right visual field-left hemisphere (RVF-LH). The stimuli were either unfiltered or low-pass filtered (i.e., devoid of high spatial frequency content). Consistent with previous studies, the unfiltered condition produced a significant RVF-LH advantage for the categorical task and an LVF-RH advantage for the coordinate task. Low-pass filtering eliminated this Task × Visual Field interaction; thus, the RVF-LH advantage disappeared for the categorical task. The present results suggest that processing of high spatial frequency contributes to the left hemispheric advantage for categorical spatial processing.

Recognition without picture identification: Geons as components of the pictorial memory trace

Participants viewed a list of black-and-white line drawings and were then presented with a picture fragment identification task in which half of the fragments corresponded to studied pictures and half corresponded to unstudied pictures. In addition to trying to identify each picture fragment, participants gave a rating to indicate the likelihood that the fragment came from a studied picture. When participants could not identify the picture fragments, they were still able to discriminate between fragments that came from studied pictures and fragments that came from unstudied pictures (as shown by their recognition ratings), but only when the fragments contained information about the geometric components (geons) that underlay the original pictures. No recognition without identification was found when the fragments contained only line segment information.

The effects of divided attention at encoding on item and associative memory

Divided attention at encoding is well known to have adverse effects on episodic memory performance (e.g., Naveh-Benjamin & Greg, 2000). This article attempts to determine whether these effects are a result of the interruption of encoding of associative information among the components of an episode. Five experiments, using different types of episodes and episodes components, were conducted. Participants studied information under either full or divided attention and were then tested on their memory for both the episodes' components and the associations between them. Divided attention did not produce a differential deficit in memory for associative information; memory for the components suffered to the same degree as memory for the associations among the components. The cause of the divided-attention effect at encoding lies somewhere other than in the associative processes that are engaged.

Perception of global facial geometry in the inversion effect and prosopagnosia

We investigated how efficiently combinations of positional shifts in facial features were perceived and whether the effects of combinations on the overall geometry of the face were reflected in discriminative performance. We moved the eyes closer together or further apart, and moved the mouth up or down. Trials with combinations of changes to both the mouth and the eyes were contrasted with trials with single changes to either the mouth or the eyes. As a contrast, we also examined combinations of changes in eye colour (brightness) and the same spatial manipulations. In addition, we specifically contrasted spatial combinations that more severely distorted the original triangular relation of the mouth and eyes (e.g. eyes closer and mouth down) to those that better preserved the original aspect ratio (e.g. eyes farther and mouth down). This we termed the "geometric context effect". We found that combinations of two spatial changes were detected more quickly and accurately by normal subjects viewing upright faces but not when faces were inverted. In contrast, combinations of spatial shifts and eye colour changes showed no advantage over faces with only one type of change. Combinations of spatial changes that distorted overall facial geometry more were detected more efficiently than less distorting combinations, showing that the spatial shifts were perceived in the context of the global facial structure. Again, this was found for upright but not inverted faces. We also tested a prosopagnosic patient, who showed the advantage for two spatial changes over one but lacked this geometric context effect, implying that she did not integrate local spatial information into overall facial structure.

Developmental prosopagnosia: a study of three patients

We studied perception in three patients with prosopagnosia of childhood onset. All had trouble with other 'within-category' judgments. All were deficient on face matching tests and severely impaired on tests of perception of the spatial relations of facial features and abstract designs, indicating a deficit in the encoding of coordinate relationships, similar to adult-onset prosopagnosia with lesions of the fusiform face area. Two had difficulty perceiving feature colour, which correlated with reduced luminance sensitivity. In contrast to adult-onset patients, saturation discrimination was spared in two and spatial resolution impaired in two. Curvature discrimination was relatively spared. Contrast sensitivity showed variable reductions at different spatial frequencies. We conclude that developmental prosopagnosia is similar to the adult-onset form in encoding deficits for the spatial arrangement of facial elements. Deficits in luminance perception and spatial resolution are more associated with defective encoding for basic object-level recognition, as shown on tests of object and spatial perception.

Effects of geometric distortions on face-recognition performance

The importance of 'configural' processing for face recognition is now well established, but it remains unclear precisely what it entails. Through four experiments we attempted to clarify the nature of configural processing by investigating the effects of various affine transformations on the recognition of familiar faces. Experiment 1 showed that recognition was markedly impaired by inversion of faces, somewhat impaired by shearing or horizontally stretching them, but unaffected by vertical stretching of faces to twice their normal height. In experiment 2 we investigated vertical and horizontal stretching in more detail, and found no effects of either transformation. Two further experiments were performed to determine whether participants were recognising stretched faces by using configural information. Experiment 3 showed that nonglobal vertical stretching of faces (stretching either the top or the bottom half while leaving the remainder undistorted) impaired recognition, implying that configural information from the stretched part of the face was influencing the process of recognition--ie that configural processing involves global facial properties. In experiment 4 we examined the effects of Gaussian blurring on recognition of undistorted and vertically stretched faces. Faces remained recognisable even when they were both stretched and blurred, implying that participants were basing their judgments on configural information from these stimuli, rather than resorting to some strategy based on local featural details. The tolerance of spatial distortions in human face recognition suggests that the configural information used as a basis for face recognition is unlikely to involve information about the absolute position of facial features relative to each other, at least not in any simple way.

Different spatial-relational information is used to recognise faces and emotional expressions

In a face photo in which the two eyes have been moved up into the forehead region, configural spatial relations are altered more than categorical relations; in a photo in which only one eye is moved up, categorical relations are altered more. Matching the identities of two faces was slower when an unaltered photo was paired with a two-eyes-moved photo than when paired with a one-eye-moved photo, implicating configural relations in face identification. But matching the emotional expressions of the same faces was slower when an unaltered photo was paired with a one-eye-moved photo than when paired with a two-eyes-moved photo, showing that expression recognition uses categorically coded relations. The findings also indicate that changing spatial-relational information affects the perceptual encoding of identities and expressions rather than their memory representations.

Attentional coding of categorical relations in scene perception: evidence from the flicker paradigm

The purpose of the present investigation was to determine whether the positions of objects in a scene are coded relative to one another categorically (i.e., above, below, or side of; Experiment 1) and to determine whether spatial position in scene perception is coded preattentively or only under focused attention (Experiment 2). In Experiment 1, participants viewed alternating versions of a scene in which one of the objects in the scene changed its categorical relationship to the closest object in the scene, changed only its metric relationship to the closest object in a scene, or appeared and disappeared. Participants were faster at detecting changes that disrupted categorical relations than at detecting changes that disrupted only metric relations. In Experiment 2, this categorical advantage still occurred even when participants were cued to the location of the change. These results suggest that categorical spatial relations are being coded in scene perception and that attention is required in order to encode spatial relations.

The priming of face recognition after metric transformations

Four experiments were performed to test whether the perceptual priming of face recognition would show invariance to changes in size, position, reflectional orientation (mirror reversal), and picture-plane rotation. In all experiments, subjects recognized faces in two blocks of trials; in the second block, some of the faces were identical to those in the first, and others had undergone metric transformations. The results show that subjects were equally fast to recognize faces whether or not the faces had changed in size, position, or reflectional orientation between the first and second presentations of the faces. In contrast, subjects were slower to recognize both faces and objects when they were planar-rotated between the first and second presentations. The results suggest that the same metric invariances are shown by both face recognition and basic-level object recognition.

Is there a linear or a nonlinear relationship between rotation and configural processing of faces?

Research suggests that inverted faces are harder to recognise than upright faces because of a disruption in processing their configural properties. Reasons for this difficulty were explored by investigating people's ability to identify faces at intermediate angles of rotation. Participants were asked to discriminate blurred famous and unfamiliar faces presented at nine angles. Blurred faces were used to minimise featural processing strategies, and to assess the effects of rotation that are specific to configural processing. The results indicate a linear relationship between angle of rotation and recognition accuracy. It appears that configural processing becomes gradually more disrupted the further a face is oriented away from the upright. The implications of these findings for competing explanations of the face-inversion effect are discussed.

Effect of photographic negation on matching the expressions and identities of faces

In four experiments, participants made speeded same-different responses to pairs of face photographs showing the same woman or different women with the same expression or different expressions. Compared with responses to positive pairs, negative pairs were matched more slowly on identity than on expression. A secondary finding showed that face expressions (same, different) influenced identity responses, and identities influenced expression responses, equally for positive and negative pairs. The independence of this irrelevant-dimension effect from the contrast effect supports the conclusion required by the main finding that negation slows perceptual encoding of surface-based information used for identification more than it does encoding of edge-based information used for expression recognition.

Categorical perception of relative orientation in visual object recognition

The purpose of the present investigation was to determine whether the orientation between an object's parts is coded categorically for object recognition and physical discrimination. In three experiments, line drawings of novel objects in which the relative orientation of object parts varied by steps of 30 degrees were used. Participants performed either an object recognition task, in which they had to determine whether two objects were composed of the same set of parts, or a physical discrimination task, in which they had to determine whether two objects were physically identical. For object recognition, participants found it more difficult to compare the 0 degrees and 30 degrees versions and the 90 degrees and 60 degrees versions of an object than to compare the 30 degrees and 60 degrees versions, but only at an extended interstimulus interval (ISI). Categorical coding was also found in the physical discrimination task. These results suggest that relative orientation is coded categorically for both object recognition and physical discrimination, although metric information appears to be coded as well, especially at brief ISIs.