Concurrent processing of spatial relations and objects in two cerebral hemispheres

This study examined hemispheric asymmetry for concurrent processing of object and spatial information. Participants viewed two successive stimuli, each of which consisted of two digits and two pictures that were randomly located and judged them as identical or different. A sample stimulus was presented in a central visual field, followed by a matching stimulus presented briefly in a left or right visual field. The matching stimuli were different from the sample stimuli with respect to the object (digit or picture) or spatial (locations or distances of items) aspect. No visual field asymmetry was found in the detection of object change. However, a left visual field advantage was found in the detection of spatial change. This result can be explained by the double filtering by frequency theory of Ivry and Robertson, who asserted that the left hemisphere has a bias for processing information contained in relatively high spatial frequencies whereas the right hemisphere has a bias for processing information contained in relatively low spatial frequencies. Based upon this evidence, the importance of interhemispheric integration for visual scene perception is discussed.     

Effect of spatial position on visual search for 3-D objects

We examined whether the position of objects in external space affects the visual-search task associated with the tilt of 3-D objects. An array of cube-like objects was stereoscopically displayed at a distance of 4.5 m on a large screen 1.5 m above or below eye height. Subjects were required to detect a downward-tilted target among upward-tilted distractors or an upward-tilted target among downward-tilted distractors. When the stimuli consisted of shaded parallelepipeds whose upper/bottom faces were lighter than their side faces, the upward-tilted target was detected faster. This result was in accordance with the 'top-view assumption' reported in previous research. Displaying stimuli in the upper position degraded overall performance. However, when the shaded objects whose upper/bottom faces were darker than their side faces were displayed, the detection of a downward-tilted target became as efficient as that of an upward-tilted target only at the upper position. These results indicate that it is possible for the spatial position of the stimulus to promote the detection of a downward-tilted target when shading and perspective information are consistent with the viewing direction.     

Independent processing of parts and of their spatial organization in complex visual objects

A visual search experiment using synthetic three-dimensional objects is reported. The target shared its constituent parts, the spatial organization of its parts, or both with the distractors displayed with it. Sharing of parts and sharing of spatial organization both negatively affected visual search performance, and these effects were strictly additive. These findings support theories of complex visual object perception that assume a parsing of the stimulus into its higher-order constituents (volumetric parts or visible surfaces). The additivity of the effects demonstrates that information on parts and information on spatial organization are processed independently in visual search.     

Facilitation of learning spatial relations among locations by visual cues: generality across spatial configurations

Spatial pattern learning permits the learning of the location of objects in space relative to each other without reference to discrete visual landmarks or environmental geometry. In the present experiment, we investigated conditions that facilitate spatial pattern learning. Specifically, human participants searched in a real environment or interactive 3-D computer-generated virtual environment open-field search task for four hidden goal locations arranged in a diamond configuration located in a 5 × 5 matrix of raised bins. Participants were randomly assigned to one of three groups: Pattern Only, Landmark + Pattern, or Cues + Pattern. All participants experienced a Training phase followed by a Testing phase. Visual cues were coincident with the goal locations during Training only in the Cues + Pattern group whereas a single visual cue at a non-goal location maintained a consistent spatial relationship with the goal locations during Training only in the Landmark + Pattern group. All groups were then tested in the absence of visual cues. Results in both environments indicated that participants in all three groups learned the spatial configuration of goal locations. The presence of the visual cues during Training facilitated acquisition of the task for the Landmark + Pattern and Cues + Pattern groups compared to the Pattern Only group. During Testing the Landmark + Pattern and Cues + Pattern groups did not differ when their respective visual cues were removed. Furthermore, during Testing the performance of these two groups was superior to the Pattern Only group. Results generalize prior research to a different configuration of spatial locations, isolate spatial pattern learning as the process facilitated by visual cues, and indicate that the facilitation of learning spatial relations among locations by visual cues does not require coincident visual cues.     

Embodied spatial transformations: "body analogy" for the mental rotation of objects

The cognitive advantage of imagined spatial transformations of the human body over that of more unfamiliar objects (e.g., Shepard-Metzler [S-M] cubes) is an issue for validating motor theories of visual perception. In 6 experiments, the authors show that providing S-M cubes with body characteristics (e.g., by adding a head to S-M cubes to evoke a posture) facilitates the mapping of the cognitive coordinate system of one's body onto the abstract shape. In turn, this spatial embodiment improves object shape matching. Thanks to the increased cohesiveness of human posture in people's body schema, imagined transformations of the body operate in a less piecemeal fashion as compared with objects (S-M cubes or swing-arm desk lamps) under a similar spatial configuration, provided that the pose can be embodied. If the pose cannot be emulated (covert imitation) by the sensorimotor system, the facilitation due to motoric embodiment will also be disrupted.     

A consistent but non-coincident visual pattern facilitates the learning of spatial relations among locations

Human participants searched in a dynamic three-dimensional computer-generated virtual-environment open-field search task for four hidden goal locations arranged in a diamond configuration located in a 5 × 5 matrix of raised bins. Participants were randomly assigned to one of two groups: visual pattern or visual random. All participants experienced 30 trials in which four goal locations maintained the same spatial relations to each other (i.e., a diamond pattern), but this diamond pattern moved to random locations within the 5 × 5 matrix from trial to trial. For participants in the visual pattern group, four locations were marked in a distinct color and arranged in a diamond pattern that moved to a random location independent of the hidden spatial pattern from trial to trial throughout the experimental session. For participants in the visual random group, four random locations were marked with a distinct color and moved to random locations independent from the hidden spatial pattern from trial to trial throughout the experimental session. As a result, the visual cues for the visual pattern group were consistent but not coincident with the hidden spatial pattern, whereas the visual cues for the visual random group were neither consistent nor coincident with the hidden spatial pattern. Results indicated that participants in both groups learned the spatial configuration of goal locations and that the presence of consistent but noncoincident visual cues facilitated the learning of spatial relations among locations.     

Facilitation of learning spatial relations among locations by visual cues: Implications for theoretical accounts of spatial learning

Human participants searched in a real environment or interactive 3-D virtual environment open field for four hidden goal locations arranged in a 2 × 2 square configuration in a 5 × 5 matrix of raised bins. The participants were randomly assigned to one of two groups: cues 1 pattern or pattern only. The participants experienced a training phase, followed by a testing phase. Visual cues specified the goal locations during training only for the cues 1 pattern group. Both groups were then tested in the absence of visual cues. The results in both environments indicated that the participants learned the spatial relations among goal locations. However, visual cues during training facilitated learning of the spatial relations among goal locations: In both environments, the participants trained with the visual cues made fewer errors during testing than did those trained only with the pattern. The results suggest that learning based on the spatial relations among locations may not be susceptible to cue competition effects and have implications for standard associative and dual-system accounts of spatial learning.     

Action relations facilitate the identification of briefly-presented objects

The link between perception and action allows us to interact fluently with the world. Objects which 'afford' an action elicit a visuomotor response, facilitating compatible responses. In addition, positioning objects to interact with one another appears to facilitate grouping, indicated by patients with extinction being better able to identify interacting objects (e.g. a corkscrew going towards the top of a wine bottle) than the same objects when positioned incorrectly for action (Riddoch, Humphreys, Edwards, Baker, & Willson, Nature Neuroscience, 6, 82-89, 2003). Here, we investigate the effect of action relations on the perception of normal participants. We found improved identification of briefly-presented objects when in correct versus incorrect co-locations for action. For the object that would be 'active' in the interaction (the corkscrew), this improvement was enhanced when it was oriented for use by the viewer's dominant hand. In contrast, the position-related benefit for the 'passive' object was stronger when the objects formed an action-related pair (corkscrew and bottle) compared with an unrelated pair (corkscrew and candle), and it was reduced when spatial cues disrupted grouping between the objects. We propose that these results indicate two separate effects of action relations on normal perception: a visuomotor response to objects which strongly afford an action; and a grouping effect between objects which form action-related pairs.     

Bodies and other visual objects: the dialectics of reaching toward objects

Participants viewed video clips of a left or right-handed reach toward an object that was orientated with a handle to the left or right. They were required to classify the object by making a left or right-handed key-press and ignore the reach. These responses were, never-the-less, affected by the observed reach in ways which largely reflected the opportunities for complementary actions in the viewed scenes, given the simultaneous constraints of the object orientation combined with the direction and hand of reach. These influences are claimed to reflect the interdependency of the action possibilities that arise from a set of objects and agents in three-dimensional space that together determine behaviour.     

Sensitivity to viewpoint in children's drawings of objects and relations between objects.

Previous literature suggests that young children are relatively insensitive to viewpoint, only showing their view when the task is manipulated to provoke it. In contrast, older children appear to become more sensitive to viewpoint and it has been claimed that there is a developmental progression toward use of linear perspective as a means of drawing a view-specific scene. This study investigates sensitivity to viewpoint by manipulating it directly. Children between the ages of 6 and 14 years were asked to draw an L-shaped array of three cubes from one of three views: frontal eye level, frontal looking down, and corner looking down. At every age children showed sensitivity to their view in the sense that there were consistent differences between the drawings produced in the three viewing conditions. In the case of younger children this did not lead to an accurate portrayal of either their view or the array relations. Older children portrayed their view and the array relations more accurately, and viewpoint had a strong effect on the choice of projection system both within and between objects. There was no evidence of a general progression toward use of linear perspective.     

Distortions in judged spatial relations

In three experiments, we explore distortions in subjects' judgments of relative geographical relations. People make large systematic errors in judging the geographical relations between two locations that are in different geographical or political units. There is a strong tendency to distort the judged relation to conform with the relation of the superordinate political unit. To account for this result, we present a model in which spatial information is stored hierarchically. Spatial relations between any two locations are stored explicitly only if those locations are within the same superordinate unit. Spatial relations not stored are inferred by combining the relations from between and within superordinate units.     

Individuation of visual objects over time

How does an observer decide that a particular object viewed at one time is actually the same object as one viewed at a different time? We explored this question using an experimental task in which an observer views two objects as they simultaneously approach an occluder, disappear behind the occluder, and re-emerge from behind the occluder, having switched paths. In this situation the observer either sees both objects continue straight behind the occluder (called "streaming") or sees them collide with each other and switch directions ("bouncing"). This task has been studied in the literature on motion perception, where interest has centered on manipulating spatiotemporal aspects of the motion paths (e.g. velocity, acceleration). Here we instead focus on featural properties (size, luminance, and shape) of the objects. We studied the way degrees and types of featural dissimilarity between the two objects influence the percept of bouncing vs. streaming. When there is no featural difference, the preference for straight motion paths dominates, and streaming is usually seen. But when featural differences increase, the preponderance of bounce responses increases. That is, subjects prefer the motion trajectory in which each continuously existing individual object trajectory contains minimal featural change. Under this model, the data reveal in detail exactly what magnitudes of each type of featural change subjects implicitly regard as reasonably consistent with a continuously existing object. This suggests a simple mathematical definition of "individual object:" an object is a path through feature-trajectory space that minimizes feature change, or, more succinctly, an object is a geodesic in Mahalanobis feature space.     

Representational content and computation in the human visual system

Summary Information-processing systems can be characterized by their ability to transform systematically certain internal representational states (symbols) into one another. The presence of such an information-processing capacity calls for an explanation. How could such an explanation in principle be formulated? How is it possible to specify internal representational states and to ascribe to them certain representational contents? What has to be demonstrated by such explanations is how an information-processing capacity is actually instantiated in a system. In this paper, the outlines of an explanation by instantiation are sketched for a specific human visual capacity. In addition, some fundamental problems facing the development of this explanation will be discussed.     

Incidental visual memory for objects in scenes

Three experiments were conducted to investigate the existence of incidentally acquired, long-term, detailed visual memory for objects embedded in previously viewed scenes. Participants performed intentional memorization and incidental visual search learning tasks while viewing photographs of real-world scenes. A visual memory test for previously viewed objects from these scenes then followed. Participants were not aware that they would be tested on the scenes following incidental learning in the visual search task. In two types of memory tests for visually specific object information (token discrimination and mirror-image discrimination), performance following both the memorization and visual search conditions was reliably above chance. These results indicate that recent demonstrations of good visual memory during scene viewing are not due to intentional scene memorization. Instead, long-term visual representations are incidentally generated as a natural product of scene perception.     

Redundancy effects in the perception and memory of visual objects

Is visual representation of an object affected by whether surrounding objects are identical to it, different from it, or absent? To address this question, we tested perceptual priming, visual short-term, and long-term memory for objects presented in isolation or with other objects. Experiment 1 used a priming procedure, where the prime display contained a single face, four identical faces, or four different faces. Subjects identified the gender of a subsequent probe face that either matched or mismatched with one of the prime faces. Priming was stronger when the prime was four identical faces than when it was a single face or four different faces. Experiments 2 and 3 asked subjects to encode four different objects presented on four displays. Holding memory load constant, visual memory was better when each of the four displays contained four duplicates of a single object, than when each display contained a single object. These results suggest that an object's perceptual and memory representations are enhanced when presented with identical objects, revealing redundancy effects in visual processing.     

Haptic perception of spatial relations

There are some indications that haptic space like visual space is not Euclidean (e.g. Blumenfeld, 1937 Acta Psychologica 2 125-174). In a series of experiments, we investigated the haptic perception of spatial relations in a systematic way. We restricted ourselves to a horizontal plane at waist height. Blindfolded subjects were asked to perform three tasks with their right hand: (i) a reference bar was presented under four different orientations and subjects were asked to rotate a test bar such that it felt to be parallel to the reference bar; (ii) subjects had to rotate two test bars in such a way that they felt collinear; (iii) subjects had to point a test bar in the direction of a marker. Bars and marker could appear at nine different locations. In all experiments large systematic deviations (up to 40 degrees) were made. The deviations strongly correlated with horizontal (right-left) but not with vertical (forward-backward) distance. Subjects showed qualitatively identical trends but the size of the deviations was strongly subject-dependent. In addition, a significant haptic oblique effect was found. These results provide strong evidence that haptic space in non-Euclidean.     

Effects of action relations on the configural coding between objects

Configural coding is known to take place between the parts of individual objects but has never been shown between separate objects. We provide novel evidence here for configural coding between separate objects through a study of the effects of action relations between objects on extinction. Patients showing visual extinction were presented with pairs of objects that were or were not co-located for action. We first confirmed the reduced extinction effect for objects co-located for action. Consistent with prior results showing that inversion disrupts configural coding, we found that inversion disrupted the benefit for action-related object pairs. This occurred both for objects with a standard canonical orientation (e.g., teapot and teacup) and those without, but where grasping and using the objects was made more difficult by inversion (e.g., spanner and nut). The data suggest that part of the affordance effect may reflect a visuo-motor response to the configural relations between stimuli. Experiment 2 showed that distorting the relative sizes of the objects also reduced the advantage for action-related pairs. We conclude that action-related pairs are processed as configurations.     

On the theory of relations based on the theory of objects

Summary The theory of relations presented in this article consists of the general and the special theory of relations. The formulae of the former are meaningful and its laws valid for relations of any type. The meaningfulness of expressions and the validity of laws of the latter are restricted to relations of a certain special type. The special theory of relations is distinguished from the applied theory of relations. The applied theory of relations is the general theory applied to relations of a special type, the difference between the general and the applied being in the form of the variables. The special theory of relations and the applied theory, when concerned with relations of the same special type, may differ with respect to the form of constants without differing with respect to variables.     

Age-related effects in the marking of old objects in visual search

Two studies were performed to examine potential age-related differences in visual marking. Visual marking is a limited capacity process that enhances visual search through the inhibition of old objects. In Experiment 1, young and old adults performed three different search conditions: a full-element baseline, a half-element baseline, and a gap condition in which they searched through displays similar to the full-element baseline condition but with half of the letters presented before and the other half of the letters and the target presented after a 1000-ms gap. Both old and young adults displayed search slopes in the gap condition that were equivalent to slopes obtained in the half-element condition, suggesting that they were able to successfully inhibit the old letters. In Experiment 2, old and young adults also performed in three different visual search conditions but in this case with targets defined either by a form difference or by a conjunction of form and color. Both old and young adults showed a reduced slope in the gap as compared to the conjunction condition, suggesting inhibition of the old objects. The data are discussed in terms of age-related differences in the top-down control of attention in visual search.