What makes a route appear longer? An experimental perspective on features, route segmentation, and distance knowledge

Five experiments performed in a desktop virtual-reality setting investigated the influence of environmental features—that is, noticeable landmarks along the route—on distance estimation. Landmarks were of two types: Either they simply “filled” the route or they “filled” and also segmented it, thereby inducing a hierarchical structuring of the route. Previous research had left the question open of whether a filling or a segmenting feature leads to an overestimation of a distance along the route. Our experiments showed different results dependent on the kind of space: If an environment was learned from a route perspective, filling and segmenting environmental features led to overestimations of distances, while the segmenting of a route induced by a grouping of similar features did not. If the environment was learned from a map that afforded a survey perspective, route structuring induced through a segmenting feature or by phenomenal grouping led to an overestimation of distances, whereas features that merely filled the route did not.     

Unified framework for recognition, localization and mapping using wearable cameras

Monocular approaches to simultaneous localization and mapping (SLAM) have recently addressed with success the challenging problem of the fast computation of dense reconstructions from a single, moving camera. Thus, if these approaches initially relied on the detection of a reduced set of interest points to estimate the camera position and the map, they are currently able to reconstruct dense maps from a handheld camera while the camera coordinates are simultaneously computed. However, these maps of 3-dimensional points usually remain meaningless, that is, with no memorable items and without providing a way of encoding spatial relationships between objects and paths. In humans and mobile robotics, landmarks play a key role in the internalization of a spatial representation of an environment. They are memorable cues that can serve to define a region of the space or the location of other objects. In a topological representation of the space, landmarks can be identified and located according to its structural, perceptive or semantic significance and distinctiveness. But on the other hand, landmarks may be difficult to be located in a metric representation of the space. Restricted to the domain of visual landmarks, this work describes an approach where the map resulting from a point-based, monocular SLAM is annotated with the semantic information provided by a set of distinguished landmarks. Both features are obtained from the image. Hence, they can be linked by associating to each landmark all those point-based features that are superimposed to the landmark in a given image (key-frame). Visual landmarks will be obtained by means of an object-based, bottom-up attention mechanism, which will extract from the image a set of proto-objects. These proto-objects could not be always associated with natural objects, but they will typically constitute significant parts of these scene objects and can be appropriately annotated with semantic information. Moreover, they will be affine covariant regions, that is, they will be invariant to affine transformation, being detected under different viewing conditions (view-point angle, rotation, scale, etc.). Monocular SLAM will be solved using the accurate parallel tracking and mapping (PTAM) framework by Klein and Murray in Proceedings of IEEE/ACM international symposium on mixed and augmented reality, 2007.     

Incremental grouping of image elements in vision

One important task for the visual system is to group image elements that belong to an object and to segregate them from other objects and the background. We here present an incremental grouping theory (IGT) that addresses the role of object-based attention in perceptual grouping at a psychological level and, at the same time, outlines the mechanisms for grouping at the neurophysiological level. The IGT proposes that there are two processes for perceptual grouping. The first process is base grouping and relies on neurons that are tuned to feature conjunctions. Base grouping is fast and occurs in parallel across the visual scene, but not all possible feature conjunctions can be coded as base groupings. If there are no neurons tuned to the relevant feature conjunctions, a second process called incremental grouping comes into play. Incremental grouping is a time-consuming and capacity-limited process that requires the gradual spread of enhanced neuronal activity across the representation of an object in the visual cortex. The spread of enhanced neuronal activity corresponds to the labeling of image elements with object-based attention.     

An artificial eye for evaluating videobased eye recording systems

Videobased corneal-reflection-to-pupil-center systems are widely used in eye movement research. In this paper, an artificial eye drawn on a computer screen is presented. The artificial eye provides a way to simulate measurements of eye position in human subjects. The method allows testing videobased systems on the level of the signal and on the level of the calibration algorithm used to map the eye position parameters to stimulus space. In addition, the artificial eye can be used to evaluate specific hypotheses concerning the functioning or malfunctioning of the eye recorder and as a help in developing data analysis programs.     

Homing in rocky intertidal fish. Are Lipophrys pholis L. able to perform true navigation?

Although navigation is common in many animals, only a few perform true navigation, meaning that they have the ability to return to a given place by relying on indirect cues obtained at the release site (i.e., by relying on information from a “map and compass” mechanism). The common intertidal fish, Lipophrys pholis, is thought to have homing abilities through a mechanism that primarily makes use of familiar landmarks (i.e., piloting). Anecdotal reports that individuals return to their home pools after release at unfamiliar sites suggest that L. pholis might use cues collected at the release site to find their way back (i.e., they might use map and compass information). Using a completely artificial setup, we tested the homing abilities of L. pholis as a function of age, sex, and familiarity with the release site. The findings showed that motivation for homing is present only in the adult phase and is independent of sex and/or familiarity with the release site. Moreover, adults released at a completely unfamiliar place oriented themselves in a direction roughly similar to that of their home pools. The fact that L. pholis were tested in a complete artificial environment means that hydrodynamic cues can be excluded as playing a role in this process and restricts the candidate options (e.g., magnetic cues). The ability to perform navigation based on a “map and compass” mechanism raises many interesting questions about the learning process, once these individuals have restricted home ranges during their lives. In vertebrate navigation, the cues used during the navigation process are a question of debate, and L. pholis offers an outstanding model to test hypotheses and ultimately provide answers.     

Tracking multiple targets with multifocal attention

Attention allows us to monitor objects or regions of visual space and select information from them for report or storage. Classical theories of attention assumed a single focus of selection but many everyday activities, such as video games, navigating busy intersections, or watching over children at a swimming pool, require attention to multiple regions of interest. Laboratory tracking tasks have indeed demonstrated the ability to track four or more targets simultaneously. Although the mechanisms by which attention maintains contact with several targets are not yet established, recent studies have identified several characteristics of the tracking process, including properties defining a 'trackable' target, the maximum number of targets that can be tracked, and the hemifield independence of the tracking process. This research also has implications for computer vision, where there is a growing demand for multiple-object tracking.     

Global precedence effect in audition and vision: evidence for similar cognitive styles across modalities

This study aimed to provide evidence for a Global Precedence Effect (GPE) in both vision and audition modalities. In order to parallel Navon's paradigm, a novel auditory task was designed in which hierarchical auditory stimuli were used to involve local and global processing. Participants were asked to process auditory and visual hierarchical patterns at the local or global level. In both modalities, a global-over-local advantage and a global interference on local processing were found. The other compelling result is a significant correlation between these effects across modalities. Evidence that the same participants exhibit similar processing style across modalities strongly supports the idea of a cognitive style to process information and common processing principle in perception.     

Looking beyond the boundaries: time to put landmarks back on the cognitive map?

Since the proposal of Tolman (1948) that mammals form maplike representations of familiar environments, cognitive map theory has been at the core of debates on the fundamental mechanisms of animal learning and memory. Traditional formulations of cognitive map theory emphasize relations between landmarks and between landmarks and goal locations as the basis of the map. More recently, several models of spatial coding have taken the boundaries of an environment as the basis of the cognitive map, with landmark relations being processed through alternative, operant learning mechanisms. In this review, the evidence for this proposed dichotomy is analyzed. It is suggested that 2 factors repeatedly confound efforts to compare spatial coding based on landmark arrays, formed by 2 or more landmarks, and that based on the boundaries of an environment. The factors are the perceived stability of the landmark arrays and their placement relative to the larger environment. Although the effects of landmark stability and of placement on spatial navigation have been studied extensively, the implications of this work for debates concerning the role of boundaries in cognitive map formation have not been fully realized. It is argued that when these 2 factors are equated between landmark arrays and bounded environments, current evidence supports a commonality of spatial coding mechanism rather than a dichotomy. The analysis places further doubt on the existence of a dedicated geometric module for reorientation and is consistent with models of navigation containing mapping and operant learning components, both taking as input local views (Sheynikhovich et al., 2009).     

Sit Still and Pay Attention?

Sitting still while trying to pay attention implicitly reinforces the idea that to pay attention one should focus on a single aspect of the stimulus. Movement encourages attending to different aspects of the stimulus and as such is hypothesized to increase attention. We tested this with students from a traditional and a nontraditional school. Students were asked to observe and recall landmarks on a map. Students from the traditional school who viewed the map from multiple perspectives remembered more landmarks and locations than students who viewed the map from a single perspective. Students from a nontraditional school who are accustomed to movement while learning, did not show this effect. The experiment is discussed in terms of mindfulness theory.     

Exogenous spatial attention influences figure-ground assignment

Abstract— In a hierarchical stage account of vision, figure-ground assignment is thought to be completed before the operation of focal spatial attention. Results of previous studies have supported this account by showing that unpredictive, exogenous spatial precues do not influence figure-ground assignment, although voluntary attention can influence figure-ground assignment. However, in these studies, attention was not summoned directly to a region in a figure-ground display. In three experiments, we addressed the relationship between figure-ground assignment and visuospatial attention. In Experiment 1, we replicated the finding that exogenous precues do not influence figure-ground assignment when they direct attention outside of a figure-ground stimulus. In Experiment 2, we demonstrated that exogenous attention can influence figure-ground assignment if it is directed to one of the regions in a figure-ground stimulus. In Experiment 3, we demonstrated that exogenous attention can influence figure-ground assignment in displays that contain a Gestalt figure-ground cue; this result suggests that figure-ground processes are not entirely completed prior to the operation of focal spatial attention. Exogenous spatial attention acts as a cue for figure-ground assignment and can affect the outcome of figure-ground processes.     

CLUSTERS PRECEDE SHAPES IN PERCEPTUAL ORGANIZATION

Abstract —Does perceptual grouping require attention? Recent controversy on this question may be caused by a conflation of two aspects of grouping: element clustering (determining which elements belong together) and shape formation (determining cluster boundaries). In Experiment 1, observers enumerated diamonds that were drawn with either lines or dots. These two types of stimuli were subitized (enumerated rapidly and accurately in the range from one to three items) equally well, suggesting that clustering dots into countable entities did not detnand attention. In contrast, when target diamonds were enumerated among distractor squares in Experiment 2. only line-drawn items could be subitized. We propose that clustering and shape formation not only involve different perceptual processes, but play different functional roles in vision.     

Comment on Shomstein, Kimchi, Hammer, and Behrmann (2010): A case study in methodological anosagnosia?

Shomstein, Kimchi, Hammer, and Behrmann (2010) try to capitalize on the apparent dissociation between vision and the processes that seem to mediate neglect patients’ attentional selection and awareness to investigate the processing of perceptual grouping in the absence of visual attention. We argue that to assess this type of dissociation requires specific methodological adaptations to determine whether visual attention is in operation. We caution that Shomstein et al.’s article does not present convincing evidence of grouping without attentional selection because they do not directly assess attentional selection in their experimental task.     

SPREADING OF VISUAL ATTENTION TO MODALLY VERSUS AMODALLY COMPLETED REGIONS

Abstract— Regions of objects that are partially obscured at the current retinal image are often perceptually filled in by the visual system (Kanizsa, 1979). In some cases (modal completion), this causes the filled-in region to appear tinged with the color and brightness of unobscured parts of that object, but m other cases (amodal completion), it does not (Michotte & Burke, 1951). It has recently been argued that modal and amodal completion both arise in preattentive vision, and may operate equivalently at that level (Davis & Driver, 1994, He & Nakayama, 1992, Shipley & Kellman, 1992). In this article, we show that they have different effects on attentive vision, with attention tending to spread to (and from) modally completed regions and their visible inducers, but not to (or from) comparable amodally completed regions and their inducers. This finding is consistent with visual attention operating on surfaces (e g, He & Nakayama, 1995) in a viewer-centered representation of the scene, after the operation of filling-in processes.     

The return of object-based attention: selection of multiple-region objects

Objects can control the focus of attention, allowing features on the same object to be selected more easily than features on different objects. In the present experiments, we investigated the perceptual processes that contribute to such object-based attentional effects. Previous research has demonstrated that object-based effects occur for single-region objects but not for multiple-region objects under some conditions (Experiment 1, Watson & Kramer, 1999). Such results are surprising, because most objects in natural scenes are composed of multiple regions. Previous findings could therefore limit the usefulness of an object-based selection mechanism. We explored the generality of these single-region selection results by manipulating the extent to which different (i.e., multiple) regions of a single object perceptually grouped together. Object-based attentional effects were attenuated when multiple regions did not group into a single perceptual object (Experiment 1). However, when multiple regions grouped together based on (1) edge continuation (Experiments 2 and 3) or (2) part and occlusion cues (Experiment 4), we observed object-based effects. Our results suggest that object-based attention is a robust process that can select multiple-region objects, provided the regions of such objects cohere on the basis of perceptual grouping cues.     

Active navigation and orientation-free spatial representations

In this study, we examined the orientation dependency of spatial representations following various learning conditions. We assessed the spatial representations of human participants after they had learned a complex spatial layout via map learning, via navigating within a real environment, or via navigating through a virtual simulation of that environment. Performances were compared between conditions involving (1) multiple- versus single-body orientation, (2) active versus passive learning, and (3) high versus low levels of proprioceptive information. Following learning, the participants were required to produce directional judgments to target landmarks. Results showed that the participants developed orientation-specific spatial representations following map learning and passive learning, as indicated by better performance when tested from the initial learning orientation. These results suggest that neither the number of vantage points nor the level of proprioceptive information experienced are determining factors; rather, it is the active aspect of direct navigation that leads to the development of orientation-free representations.     

Saliency on a natural scene background: Effects of color and luminance contrast add linearly

In natural vision, shifts in spatial attention are associated with shifts of gaze. Computational models of such overt attention typically use the concept of a saliency map: Normalized maps of center-surround differences are computed for individual stimulus features and added linearly to obtain the saliency map. Although the predictions of such models correlate with fixated locations better than chance, their mechanistic assumptions are less well investigated. Here, we tested one key assumption: Do the effects of different features add linearly or according to a max-type of interaction? We measured the eye position of observers viewing natural stimuli whose luminance contrast and/or color contrast (saturation) increased gradually toward one side. We found that these feature gradients biased fixations toward regions of high contrasts. When two contrast gradients (color and luminance) were superimposed, linear summation of their individual effects predicted their combined effect. This demonstrated that the interaction of color and luminance contrast with respect to human overt attention is—irrespective of the precise model—consistent with the assumption of linearity, but not with a max-type interaction of these features.