Do Simultaneously Viewed Objects Influence Scene Recognition Individually or as Groups? Two Perceptual Studies

The ability to quickly categorize visual scenes is critical to daily life, allowing us to identify our whereabouts and to navigate from one place to another. Rapid scene categorization relies heavily on the kinds of objects scenes contain; for instance, studies have shown that recognition is less accurate for scenes to which incongruent objects have been added, an effect usually interpreted as evidence of objects'' general capacity to activate semantic networks for scene categories they are statistically associated with. Essentially all real-world scenes contain multiple objects, however, and it is unclear whether scene recognition draws on the scene associations of individual objects or of object groups. To test the hypothesis that scene recognition is steered, at least in part, by associations between object groups and scene categories, we asked observers to categorize briefly-viewed scenes appearing with object pairs that were semantically consistent or inconsistent with the scenes. In line with previous results, scenes were less accurately recognized when viewed with inconsistent versus consistent pairs. To understand whether this reflected individual or group-level object associations, we compared the impact of pairs composed of mutually related versus unrelated objects; i.e., pairs, which, as groups, had clear associations to particular scene categories versus those that did not. Although related and unrelated object pairs equally reduced scene recognition accuracy, unrelated pairs were consistently less capable of drawing erroneous scene judgments towards scene categories associated with their individual objects. This suggests that scene judgments were influenced by the scene associations of object groups, beyond the influence of individual objects. More generally, the fact that unrelated objects were as capable of degrading categorization accuracy as related objects, while less capable of generating specific alternative judgments, indicates that the process by which objects interfere with scene recognition is separate from the one through which they inform it.     

Animal Detection Precedes Access to Scene Category

The processes underlying object recognition are fundamental for the understanding of visual perception. Humans can recognize many objects rapidly even in complex scenes, a task that still presents major challenges for computer vision systems. A common experimental demonstration of this ability is the rapid animal detection protocol, where human participants earliest responses to report the presence/absence of animals in natural scenes are observed at 250–270 ms latencies. One of the hypotheses to account for such speed is that people would not actually recognize an animal per se, but rather base their decision on global scene statistics. These global statistics (also referred to as spatial envelope or gist) have been shown to be computationally easy to process and could thus be used as a proxy for coarse object recognition. Here, using a saccadic choice task, which allows us to investigate a previously inaccessible temporal window of visual processing, we showed that animal – but not vehicle – detection clearly precedes scene categorization. This asynchrony is in addition validated by a late contextual modulation of animal detection, starting simultaneously with the availability of scene category. Interestingly, the advantage for animal over scene categorization is in opposition to the results of simulations using standard computational models. Taken together, these results challenge the idea that rapid animal detection might be based on early access of global scene statistics, and rather suggests a process based on the extraction of specific local complex features that might be hardwired in the visual system.     

The Processing of Object Identity Information by Women and Men

The study examined whether women excel at tasks which require processing the identity of objects information as has been suggested in the context of the well-known object location memory task. In a computer-simulated task, university students were shown simulated indoor and outdoor house scenes. After studying a scene the students were presented with two images. One was the original image and the other a modified version in which one object was either rotated by ninety degrees or substituted with a similar looking object. The participants were asked to indicate the original image. The main finding was that no sex effect was obtained in this task. The female and male students did not differ on a verbal ability test, and their 2D:4D ratios were found to be comparable.     

Directed attention eliminates 'change deafness' in complex auditory scenes

In natural environments that contain multiple sound sources, acoustic energy arising from the different sources sums to produce a single complex waveform at each of the listener's ears. The auditory system must segregate this waveform into distinct streams to permit identification of the objects from which the signals emanate [1]. Although the processes involved in stream segregation are now reasonably well understood [1, 2 and 3], little is known about the nature of our perception of complex auditory scenes. Here, we examined complex scene perception by having listeners detect a discrete change to an auditory scene comprising multiple concurrent naturalistic sounds. We found that listeners were remarkably poor at detecting the disappearance of an individual auditory object when listening to scenes containing more than four objects, but they performed near perfectly when their attention was directed to the identity of a potential change. In the absence of directed attention, this "change deafness" [4] was greater for objects arising from a common location in space than for objects separated in azimuth. Change deafness was also observed for changes in object location, suggesting that it may reflect a general effect of the dependence of human auditory perception on attention.     

Electrophysiological correlates of object location and object identity processing in spatial scenes

The ability to quickly detect changes in our surroundings has been crucial to human adaption and survival. In everyday life we often need to identify whether an object is new and if an object has changed its location. In the current event-related potential (ERP) study we investigated the electrophysiological correlates and the time course in detecting different types of changes of an objecṫs location and identity. In a delayed match-to-sample task participants had to indicate whether two consecutive scenes containing a road, a house, and two objects, were either the same or different. In six randomly intermixed conditions the second scene was identical, one of the objects had changed its identity, one of the objects had changed its location, or the objects had switched locations. The results reveal different time courses for the processing of identity and location changes in spatial scenes. Whereas location changes elicited a posterior N2 effect, indicating early mismatch detection, followed by a P3 effect reflecting post-perceptual processing, identity changes elicited an anterior N3 effect, which was delayed and functionally distinct from the N2 effect found for the location changes. The condition in which two objects switched position elicited a late ERP effect, reflected by a P3 effect similar to that obtained for the location changes. In sum, this study is the first to cohesively show different time courses for the processing of location changes, identity changes, and object switches in spatial scenes, which manifest themselves in different electrophysiological correlates.     

The graded and dichotomous nature of visual awareness

Is our visual experience of the world graded or dichotomous? Opposite pre-theoretical intuitions apply in different cases. For instance, when looking at a scene, one has a distinct sense that our experience has a graded character: one cannot say that there is no experience of contents that fall outside the focus of attention, but one cannot say that there is full awareness of such contents either. By contrast, when performing a visual detection task, our sense of having perceived the stimulus or not exhibits a more dichotomous character. Such issues have recently been the object of intense debate because different theoretical frameworks make different predictions about the graded versus dichotomous character of consciousness. Here, we review both relevant empirical findings as well as the associated theories (i.e. local recurrent processing versus global neural workspace theory). Next, we attempt to reconcile such contradictory theories by suggesting that level of processing is an often-ignored but highly relevant dimension through which we can cast a novel look at existing empirical findings. Thus, using a range of different stimuli, tasks and subjective scales, we show that processing low-level, non-semantic content results in graded visual experience, whereas processing high-level semantic content is experienced in a more dichotomous manner. We close by comparing our perspective with existing proposals, focusing in particular on the partial awareness hypothesis.     

Contextual Effects of Scene on the Visual Perception of Object Orientation in Depth

We investigated the effect of background scene on the human visual perception of depth orientation (i.e., azimuth angle) of three-dimensional common objects. Participants evaluated the depth orientation of objects. The objects were surrounded by scenes with an apparent axis of the global reference frame, such as a sidewalk scene. When a scene axis was slightly misaligned with the gaze line, object orientation perception was biased, as if the gaze line had been assimilated into the scene axis (Experiment 1). When the scene axis was slightly misaligned with the object, evaluated object orientation was biased, as if it had been assimilated into the scene axis (Experiment 2). This assimilation may be due to confusion between the orientation of the scene and object axes (Experiment 3). Thus, the global reference frame may influence object orientation perception when its orientation is similar to that of the gaze-line or object.     

Computational modelling of visual attention

Five important trends have emerged from recent work on computational models of focal visual attention that emphasize the bottom-up, image-based control of attentional deployment. First, the perceptual saliency of stimuli critically depends on the surrounding context. Second, a unique 'saliency map' that topographically encodes for stimulus conspicuity over the visual scene has proved to be an efficient and plausible bottom-up control strategy. Third, inhibition of return, the process by which the currently attended location is prevented from being attended again, is a crucial element of attentional deployment. Fourth, attention and eye movements tightly interplay, posing computational challenges with respect to the coordinate system used to control attention. And last, scene understanding and object recognition strongly constrain the selection of attended locations. Insights from these five key areas provide a framework for a computational and neurobiological understanding of visual attention.     

Acoustic facilitation of object movement detection during self-motion

In humans, as well as most animal species, perception of object motion is critical to successful interaction with the surrounding environment. Yet, as the observer also moves, the retinal projections of the various motion components add to each other and extracting accurate object motion becomes computationally challenging. Recent psychophysical studies have demonstrated that observers use a flow-parsing mechanism to estimate and subtract self-motion from the optic flow field. We investigated whether concurrent acoustic cues for motion can facilitate visual flow parsing, thereby enhancing the detection of moving objects during simulated self-motion. Participants identified an object (the target) that moved either forward or backward within a visual scene containing nine identical textured objects simulating forward observer translation. We found that spatially co-localized, directionally congruent, moving auditory stimuli enhanced object motion detection. Interestingly, subjects who performed poorly on the visual-only task benefited more from the addition of moving auditory stimuli. When auditory stimuli were not co-localized to the visual target, improvements in detection rates were weak. Taken together, these results suggest that parsing object motion from self-motion-induced optic flow can operate on multisensory object representations.     

Attention-memory interactions in scene perception

The perception of natural scenes relies on the integration of pre-existing knowledge with the immediate results of attentional processing, and what can be remembered from a scene depends in turn on how that scene is perceived and understood. However, there are conflicting results in the literature as to whether people are more likely to remember those objects that are consistent with the scene or those that are not. Moreover, whether any discrepancy between the likelihood of remembering schema-consistent or schema-inconsistent objects should be attributed to the schematic effects on attention or on memory remains unclear. To address this issue, the current study attempted to directly manipulate attention allocation by requiring participants to look at (i) schema-consistent objects, (ii) schema-inconsistent objects, or (iii) to share attention equally across both. Regardless of the differential allocation of attention or object fixation, schema-consistent objects were better recalled whereas recognition was independent of schema-consistency, but depended on task instruction. These results suggest that attention is important both for remembering low-level object properties, and information whose retrieval is not supported by the currently active schema. Specific knowledge of the scenes being viewed can result in the recall of non-fixated objects, but without such knowledge attention is required to encode sufficient detail for subsequent recognition. Our results demonstrate therefore that attention is not critical for the retrieval of objects that are consistent with a scene's schematic content.     

Detecting Unidentified Changes

Does becoming aware of a change to a purely visual stimulus necessarily cause the observer to be able to identify or localise the change or can change detection occur in the absence of identification or localisation? Several theories of visual awareness stress that we are aware of more than just the few objects to which we attend. In particular, it is clear that to some extent we are also aware of the global properties of the scene, such as the mean luminance or the distribution of spatial frequencies. It follows that we may be able to detect a change to a visual scene by detecting a change to one or more of these global properties. However, detecting a change to global property may not supply us with enough information to accurately identify or localise which object in the scene has been changed. Thus, it may be possible to reliably detect the occurrence of changes without being able to identify or localise what has changed. Previous attempts to show that this can occur with natural images have produced mixed results. Here we use a novel analysis technique to provide additional evidence that changes can be detected in natural images without also being identified or localised. It is likely that this occurs by the observers monitoring the global properties of the scene.     

Facial Mimicry and Emotion Consistency: Influences of Memory and Context

This study investigates whether mimicry of facial emotions is a stable response or can instead be modulated and influenced by memory of the context in which the emotion was initially observed, and therefore the meaning of the expression. The study manipulated emotion consistency implicitly, where a face expressing smiles or frowns was irrelevant and to be ignored while participants categorised target scenes. Some face identities always expressed emotions consistent with the scene (e.g., smiling with a positive scene), whilst others were always inconsistent (e.g., frowning with a positive scene). During this implicit learning of face identity and emotion consistency there was evidence for encoding of face-scene emotion consistency, with slower RTs, a reduction in trust, and inhibited facial EMG for faces expressing incompatible emotions. However, in a later task where the faces were subsequently viewed expressing emotions with no additional context, there was no evidence for retrieval of prior emotion consistency, as mimicry of emotion was similar for consistent and inconsistent individuals. We conclude that facial mimicry can be influenced by current emotion context, but there is little evidence of learning, as subsequent mimicry of emotionally consistent and inconsistent faces is similar.     

Unconscious Local Motion Alters Global Image Speed

Accurate motion perception of self and object speed is crucial for successful interaction in the world. The context in which we make such speed judgments has a profound effect on their accuracy. Misperceptions of motion speed caused by the context can have drastic consequences in real world situations, but they also reveal much about the underlying mechanisms of motion perception. Here we show that motion signals suppressed from awareness can warp simultaneous conscious speed perception. In Experiment 1, we measured global speed discrimination thresholds using an annulus of 8 local Gabor elements. We show that physically removing local elements from the array attenuated global speed discrimination. However, removing awareness of the local elements only had a small effect on speed discrimination. That is, unconscious local motion elements contributed to global conscious speed perception. In Experiment 2 we measured the global speed of the moving Gabor patterns, when half the elements moved at different speeds. We show that global speed averaging occurred regardless of whether local elements were removed from awareness, such that the speed of invisible elements continued to be averaged together with the visible elements to determine the global speed. These data suggest that contextual motion signals outside of awareness can both boost and affect our experience of motion speed, and suggest that such pooling of motion signals occurs before the conscious extraction of the surround motion speed.     

Unifying shading and texture through an active observer

Shading (variations of image intensity) provides an important cue for understanding the shape of three-dimensional surfaces from monocular views. On the other hand, texture (distribution of discontinuities on the surface) is a strong cue for recovering surface orientation by using monocular images. But given the image of an object or scene, what technique should we use to recover the shape of what is image? Resolution of shape from shading requires knowledge of the reflectance of the imaged surface and, usually, the fact that it is smooth (i.e. it shows no discontinuities). Determination of shape from texture requires knowledge of the distribution of surface markings (i.e. discontinuities). One might expect that one method would work when the other does not. I present a theory on how an active observer can determine shape from the image of an object or scene regardless of whether the image is shaded, textured, or both, and without any knowledge of reflectance maps or the distribution of surface markings. The approach is successful because the active observer is able to manipulate the constraints behind the perceptual phenomenon at hand and thus derive a simple solution. Several experimental results are presented with real and synthetic images.     

Is object search mediated by object-based or image-based representations?

Recent research suggests that visually specific memory representations for previously fixated objects are maintained during scene perception. Here we investigate the degree of visual specificity by asking whether the memory representations are image-based or object-based. To that end we measured the effects of object orientation on the time to search for a familiar object from amongst a set of 7 familiar distractors arranged in a circular array. Search times were found to depend on the relative orientations of the target object and the probe object for both familiar and novel objects. This effect was found to be partly an image matching effect but there was also an advantage shown for the object's canonical view for familiar objects. Orientation effects were maintained even when the target object was specified as having unique or similar shape properties relative to the distractors. Participants' eye movements were monitored during two of the experiments. Eye movement patterns revealed selection for object shape and object orientation during the search process. Our findings provide evidence for object representations during search that are detailed and share image-based characteristics with more high-level characteristics from object memory.     

Perceptual Grouping over Time within and across Auditory and Tactile Modalities

In auditory scene analysis, population separation and temporal coherence have been proposed to explain how auditory features are grouped together and streamed over time. The present study investigated whether these two theories can be applied to tactile streaming and whether temporal coherence theory can be applied to crossmodal streaming. The results show that synchrony detection between two tones/taps at different frequencies/locations became difficult when one of the tones/taps was embedded in a perceptual stream. While the taps applied to the same location were streamed over time, the taps applied to different locations were not. This observation suggests that tactile stream formation can be explained by population-separation theory. On the other hand, temporally coherent auditory stimuli at different frequencies were streamed over time, but temporally coherent tactile stimuli applied to different locations were not. When there was within-modality streaming, temporally coherent auditory stimuli and tactile stimuli were not streamed over time, either. This observation suggests the limitation of temporal coherence theory when it is applied to perceptual grouping over time.     

Urbanization and its effects on personality traits: a result of microevolution or phenotypic plasticity?

Human‐altered environmental conditions affect many species at the global scale. An extreme form of anthropogenic alteration is the existence and rapid increase of urban areas. A key question, then, is how species cope with urbanization. It has been suggested that rural and urban conspecifics show differences in behaviour and personality. However, (i) a generalization of this phenomenon has never been made; and (ii) it is still unclear whether differences in personality traits between rural and urban conspecifics are the result of phenotypic plasticity or of intrinsic differences. In a literature review, we show that behavioural differences between rural and urban conspecifics are common and taxonomically widespread among animals, suggesting a significant ecological impact of urbanization on animal behaviour. In order to gain insight into the mechanisms leading to behavioural differences in urban individuals, we hand‐raised and kept European blackbirds (Turdus merula) from a rural and a nearby urban area under common‐garden conditions. Using these birds, we investigated individual variation in two behavioural responses to the presence of novel objects: approach to an object in a familiar area (here defined as neophilia), and avoidance of an object in a familiar foraging context (defined as neophobia). Neophilic and neophobic behaviours were mildly correlated and repeatable even across a time period of one year, indicating stable individual behavioural strategies. Blackbirds from the urban population were more neophobic and seasonally less neophilic than blackbirds from the nearby rural area. These intrinsic differences in personality traits are likely the result of microevolutionary changes, although we cannot fully exclude early developmental influences.     

The electric image in Gnathonemus petersii.

We review modelling and experimental work dealing with the mechanisms of generation of electric image. We discuss: (1) the concept of electric image in the context of the reafference principle; (2) how waveform codes an impedance related qualia of the object image, referred to as "electric colour"; (3) that some characteristics of the spatial profiles generated by pre-receptor mechanisms are suitable for edge detection; (4) which parameters of the spatial profiles provide information for distance discrimination; (5) that electric images are distributed representations of the scene.     

Oculomotor Examination of the Weapon Focus Effect: Does a Gun Automatically Engage Visual Attention?

Background

A person is less likely to be accurately remembered if they appear in a visual scene with a gun, a result that has been termed the weapon focus effect (WFE). Explanations of the WFE argue that weapons engage attention because they are unusual and/or threatening, which causes encoding deficits for the other items in the visual scene. Previous WFE research has always embedded the weapon and nonweapon objects within a larger context that provides information about an actor''s intention to use the object. As such, it is currently unknown whether a gun automatically engages attention to a greater extent than other objects independent of the context in which it is presented.

Method

Reflexive responding to a gun compared to other objects was examined in two experiments. Experiment 1 employed a prosaccade gap-overlap paradigm, whereby participants looked toward a peripheral target, and Experiment 2 employed an antisaccade gap-overlap paradigm, whereby participants looked away from a peripheral target. In both experiments, the peripheral target was a gun or a nonthreatening object (i.e., a tomato or pocket watch). We also controlled how unexpected the targets were and compared saccadic reaction times across types of objects.

Results

A gun was not found to differentially engage attention compared to the unexpected object (i.e., a pocket watch). Some evidence was found (Experiment 2) that both the gun and the unexpected object engaged attention to a greater extent compared the expected object (i.e., a tomato).

Conclusion

An image of a gun did not engage attention to a larger extent than images of other types of objects (i.e., a pocket watch or tomato). The results suggest that context may be an important determinant of WFE. The extent to which an object is threatening may depend on the larger context in which it is presented.