Visual salience in the change detection paradigm: the special role of object onset

Object-based attention is mediated by collinearity of targets

Same-object bias occurs when tasks associated with processing a single object are faster than tasks associated with two objects. Over five experiments we assessed whether same-object bias is mediated by the collinearity of the targets. Participants decided whether two targets, presented either within a single object or across two objects, were the same or different. Results showed that same-object bias only occurred when targets appeared on the same straight line within the same object. When targets appeared in the same object but were separated by an angle or corner, within-object facilitation was eliminated or greatly reduced. In a final experiment, response times to two targets that were collinear but on separate objects were responded to faster than were noncollinear targets on the same object. This suggests that collinearity between targets mediates the effect found in this paradigm, at least to a greater extent than colour grouping.

The trickle-down effect of predictability: Secondary task performance benefits from predictability in the primary task

Predictions optimize processing by reducing attentional resources allocation to expected or predictable sensory data. Our study demonstrates that these saved processing resources can be then used on concurrent stimuli, and in consequence improve their processing and encoding. We illustrate this "trickle-down" effect with a dual task, where the primary task varied in terms of predictability. The primary task involved detection of a pre-specified symbol that appeared at some point of a short video of a dot moving along a random, semi-predictable or predictable trajectory. The concurrent secondary task involved memorization of photographs representing either emotionally neutral or non-neutral (social or threatening) content. Performance in the secondary task was measured by a memory test. We found that participants allocated more attention to unpredictable (random and semi-predictable) stimuli than to predictable stimuli. Additionally, when the stimuli in the primary task were more predictable, participants performed better in the secondary task, as evidenced by higher sensitivity in the memory test. Finally, social or threatening stimuli were allocated more "looking time" and a larger number of saccades than neutral stimuli. This effect was stronger for the threatening stimuli than social stimuli. Thus, predictability of environmental input is used in optimizing the allocation of attentional resources, which trickles-down and benefits the processing of concurrent stimuli.

Detection of object onsets and offsets: Does the primacy of onset persist even with bias for detecting offset?

Onset primacy is a robust visual phenomenon in which appearance of new objects (onsets) in a scene more effectively captures observers' attention compared with disappearance of previously viewed objects (offsets). We hypothesized that the human attentional system is programmed by default to prioritize the processing of onsets, because quick detection of them is advantageous in most situations. However, the attentional priority may be able to flexibly adapt to the detection of object offsets depending on observers' behavioral goals. To test these hypotheses, two experiments were conducted in which participants were biased toward finding offset of an existing object through top-down and bottom-up manipulations. Results showed that although onset primacy was reduced to some degree under strong offset bias, in general participants continued to detect onsets efficiently. These findings did not eliminate the possibility of attentional flexibility, but they do demonstrate the robustness of onset primacy, suggesting that environmental demands or motivational factors would need to be sufficiently strong for people to switch to an adaptive attentional mode.

Representational pseudoneglect for detecting changes to Rey-Osterrieth figures

When dividing attention between the left and right sides of physical space, most individuals pay slightly more attention to the left side. This phenomenon, known as pseudoneglect, may also occur for the left and right sides of mental representations of stimuli. Representational pseudoneglect has been shown for the recall of real-world scenes and for simple, briefly presented stimuli. The current study sought to investigate the effect of exposure duration and complexity using adaptations of the Rey-Osterrieth figures. Undergraduates (n = 97) were shown a stimulus for 20 s and asked to remember it. Participants were then shown a probe and indicated whether it was the same or different. Results showed that, irrespective of whether an element was added or subtracted, changes on the left side of the remembered image were better detected. These results are consistent with representational pseudoneglect and demonstrate that this effect occurs for complex stimuli when presented for an extended period of time. Representation neglect is therefore unlikely to be the result of an initial saccade to the left-but could be related to the formation or recall of the representation.

Object Onset and Parvocellular Guidance of Attentional Allocation

The parvocellular visual pathway in the primate brain is known to be involved with the processing of color. However, a subject of debate is whether an abrupt change in color, conveyed via this pathway, is capable of automatically attracting attention. It has been shown that the appearance of new objects defined solely by color is indeed capable of modulating attention. However, given evidence suggesting that the visual system is particularly sensitive to new onsets, it is unclear to what extent such results reflect effects of color change per se, rather than effects of object onset. We assessed attentional capture by color change that occurred as a result of either new objects appearing or already-present “old” objects changing color. Results showed that although new object onsets accrued attention, changing the color of old objects did not. We conclude that abrupt color change per se is not sufficient to capture attention.

Altering attentional control settings causes persistent biases of visual attention

Attentional control settings have an important role in guiding visual behaviour. Previous work within cognitive psychology has found that the deployment of general attentional control settings can be modulated by training. However, research has not yet established whether long-term modifications of one particular type of attentional control setting can be induced. To address this, we investigated persistent alterations to feature search mode, also known as an attentional bias, towards an arbitrary stimulus in healthy participants. Subjects were biased towards the colour green by an information sheet. Attentional bias was assessed using a change detection task. After an interval of either 1 or 2 weeks, participants were then retested on the same change detection task, tested on a different change detection task where colour was irrelevant, or were biased towards an alternative colour. One experiment included trials in which the distractor stimuli (but never the target stimuli) were green. The key finding was that green stimuli in the second task attracted attention, despite this impairing task performance. Furthermore, inducing a second attentional bias did not override the initial bias toward green objects. The attentional bias also persisted for at least two weeks. It is argued that this persistent attentional bias is mediated by a chronic change to participants' attentional control settings, which is aided by long-term representations involving contextual cueing. We speculate that similar changes to attentional control settings and continuous cueing may relate to attentional biases observed in psychopathologies. Targeting these biases may be a productive approach to treatment.

The role of prediction in perception: Evidence from interrupted visual search

Recent studies of rapid resumption-an observer's ability to quickly resume a visual search after an interruption-suggest that predictions underlie visual perception. Previous studies showed that when the search display changes unpredictably after the interruption, rapid resumption disappears. This conclusion is at odds with our everyday experience, where the visual system seems to be quite efficient despite continuous changes of the visual scene; however, in the real world, changes can typically be anticipated based on previous knowledge. The present study aimed to evaluate whether changes to the visual display can be incorporated into the perceptual hypotheses, if observers are allowed to anticipate such changes. Results strongly suggest that an interrupted visual search can be rapidly resumed even when information in the display has changed after the interruption, so long as participants not only can anticipate them, but also are aware that such changes might occur.

Global scene layout modulates contextual learning in change detection

Change in the visual scene often goes unnoticed – a phenomenon referred to as “change blindness.” This study examined whether the hierarchical structure, i.e., the global–local layout of a scene can influence performance in a one-shot change detection paradigm. To this end, natural scenes of a laid breakfast table were presented, and observers were asked to locate the onset of a new local object. Importantly, the global structure of the scene was manipulated by varying the relations among objects in the scene layouts. The very same items were either presented as global-congruent (typical) layouts or as global-incongruent (random) arrangements. Change blindness was less severe for congruent than for incongruent displays, and this congruency benefit increased with the duration of the experiment. These findings show that global layouts are learned, supporting detection of local changes with enhanced efficiency. However, performance was not affected by scene congruency in a subsequent control experiment that required observers to localize a static discontinuity (i.e., an object that was missing from the repeated layouts). Our results thus show that learning of the global layout is particularly linked to the local objects. Taken together, our results reveal an effect of “global precedence” in natural scenes. We suggest that relational properties within the hierarchy of a natural scene are governed, in particular, by global image analysis, reducing change blindness for local objects through scene learning.

Semantic consistency versus perceptual salience in visual scenes: findings from change detection

In a one-shot change detection task, we investigated the relationship between semantic properties (high consistency, i.e., diagnosticity, versus inconsistency with regard to gist) and perceptual properties (high versus low salience) of objects in guiding attention in visual scenes and in constructing scene representations. To produce the change an object was added or deleted in either the right or left half of coloured drawings of daily-life events. Diagnostic object deletions were more accurately detected than inconsistent ones, indicating rapid inclusion into early scene representation for the most predictable objects. Detection was faster and more accurate for high salience than for low salience changes. An advantage was found for diagnostic object changes in the high salience condition, although it was limited to additions when considering response speed. For inconsistent objects of high salience, deletions were detected faster than additions. These findings may indicate that objects are primarily selected on a perceptual basis with subsequent and supplementary effect of semantic consistency, in the sense of facilitation due to object diagnosticity or lengthening of processing time due to inconsistency.

Visual cognition during real social interaction

Laboratory studies of social visual cognition often simulate the critical aspects of joint attention by having participants interact with a computer-generated avatar. Recently, there has been a movement toward examining these processes during authentic social interaction. In this review, we will focus on attention to faces, attentional misdirection, and a phenomenon we have termed social inhibition of return (Social IOR), that have revealed aspects of social cognition that were hitherto unknown. We attribute these discoveries to the use of paradigms that allow for more realistic social interactions to take place. We also point to an area that has begun to attract a considerable amount of interest-that of Theory of Mind (ToM) and automatic perspective taking-and suggest that this too might benefit from adopting a similar approach.

Visual awareness of objects and their colour

At any given moment, our awareness of what we 'see' before us seems to be rather limited. If, for instance, a display containing multiple objects is shown (red or green disks), when one object is suddenly covered at random, observers are often little better than chance in reporting about its colour (Wolfe, Reinecke, & Brawn, Visual Cognition, 14, 749-780, 2006). We tested whether, when object attributes (such as colour) are unknown, observers still retain any knowledge of the presence of that object at a display location. Experiments 1-3 involved a task requiring two-alternative (yes/no) responses about the presence or absence of a colour-defined object at a probed location. On this task, if participants knew about the presence of an object at a location, responses indicated that they also knew about its colour. A fourth experiment presented the same displays but required a three-alternative response. This task did result in a data pattern consistent with participants' knowing more about the locations of objects within a display than about their individual colours. However, this location advantage, while highly significant, was rather small in magnitude. Results are compared with those of Huang (Journal of Vision, 10(10, Art. 24), 1-17, 2010), who also reported an advantage for object locations, but under quite different task conditions.

Change detection in complex scenes: hemispheric contribution and the role of perceptual and semantic factors

The perceptual salience and semantic relevance of objects for the meaning of a scene were evaluated with multiple criteria and then manipulated in a change-detection experiment that used an original combination of one-shot and tachistoscopic divided-visual-field paradigms to study behavioural hemispheric asymmetry. Coloured drawings that depicted meaningful situations were presented centrally and very briefly (120 ms) and only the changes were lateralised by adding an object in the right or in the left visual hemifield. High salience and high relevance improved both response times (RTs) and accuracy, although the overall contribution of salience was greater than that of relevance. Moreover, only for low-salience changes did relevance affect speed. RTs were shorter when a change occurred in the left visual hemifield, suggesting a right-hemisphere advantage for detection of visual change. Also, men responded faster than women. The theoretical and methodological implications are discussed.

Non-transient luminance changes do not capture attention

The processing of luminance change is a ubiquitous feature of the human visual system and provides the basis for the rapid orienting of attention to potentially important events (e.g., motion onset, object onset). However, despite its importance for attentional capture, it is not known whether a luminance change attracts attention solely because of its status as a sensory transient or can attract attention at a relatively high cognitive level. In a series of six experiments, we presented visual displays in which a single object underwent a luminance change that was either visible or obscured by a mask. A target then appeared either at the change location or elsewhere. The results showed that the luminance change attracted attention only in the visible condition. This was even observed with the largest change we could generate (> 75 cd/m(2)). These data suggest that the importance of a luminance change is only in its status as a low-level sensory transient.

New objects do not capture attention without a sensory transient

Attention capture occurs when a stimulus event involuntarily recruits attention. The abrupt appearance of a new object is perhaps the most well-studied attention-capturing event, yet there is debate over the root cause of this capture. Does a new object capture attention because it involves the creation of a new object representation or because its appearance creates a characteristic luminance transient? The present study sought to resolve this question by introducing a new object into a search display, either with or without a unique luminance transient. Contrary to the results of a recent study (Davoli, Suszko, & Abrams, 2007), when the new object's transient was masked by a brief interstimulus interval introduced between the placeholder and search arrays, a new object did not capture attention. Moreover, when a new object's transient was masked, participants could not locate a new object efficiently even when that was their explicit goal. Together, these data suggest that luminance transient signals are necessary for attention capture by new objects.

Attentional capture by object appearance and disappearance

In two experiments we examined whether the appearance of a new object has attentional priority over disappearance. Previous failures to show differences are possibly due to onsets and offsets always being presented as a sole visual transient. Rather than presenting each alone, we presented onset and offset singletons simultaneously with a display-wide luminance transient in order to force each to compete with other visual events. Results from Experiment 1 showed that targets associated with onsets accrued a reaction time benefit whilst targets associated with offsets did not. Experiment 2 showed that onsets attracted attention even when observers were attentionally set to look for offset. By contrast, offsets needed a relevant attentional set in order to attract attention. We argue that the appearance of an object has attentional priority over disappearance.

The Prioritization of Feature Singletons in the Change Detection Paradigm

Six experiments are reported investigating whether a discontinuity in colour can accrue attentional priority. In addition to a standard visual search paradigm, we examined the degree to which colour singletons and nonsingletons are susceptible to change blindness. Results showed that changes occurring at colour singletons were relatively more resistant to change blindness. Although suggestive of bottom-up marshalling of attention, no prioritization of the singleton occurred when the most stringent test of stimulus-driven attentional attraction was employed, that is, when attending to the singleton was detrimental to the task. We conclude that a discontinuity in colour will attract attention unless an attentional set is contrary to singletons.

Change detection is easier at texture border bars when they are parallel to the border: evidence for V1 mechanisms of bottom-up salience

A vertical bar is salient among horizontal ones by orientation contrast, and, traditionally, bottom up salience is viewed as caused only by feature contrast. Recently, it has been proposed that the primary visual cortex (V1) creates a bottom-up salience map in its outputs, which depends on direct inputs and on contextual inputs by intra-cortical interactions (Li Zhaoping, 2002 Trends in Cognitive Sciences 6 9-16). Since the interactions include iso-feature (eg iso-orientation) suppression, responsible for salience by feature contrast, and collinear facilitation, the V1 proposal predicts that collinear grouping contributes to salience additionally. Accordingly, in orientation textures, texture bars are more salient near texture borders owing to orientation contrast, and are even more salient when they are additionally parallel to the border by collinear grouping. We show that colour changes in texture bars are more detectable when the bars are parallel to the texture border. Since changes are more detectable at salient locations, our finding supports V1 mechanisms for bottom-up salience.

Change blindness and the primacy of object appearance

A large body of work suggests that the visual system is particularly sensitive to the appearance of new objects. This is based partly on evidence from visual search studies showing that onsets capture attention whereas many other types of visual event do not. Recently, however, the notion that object onset has a special status in visual attention has been challenged. For instance, an object that looms toward an observer has also been shown to capture attention. In two experiments, we investigated whether onset receives processing priority over looming. Observers performed a change detection task in which one of the display objects either loomed or receded, or a new object appeared. Results showed that looming objects were more resistant to change blindness than receding objects. Crucially, however, the appearance of a new object was less susceptible to change blindness than both looming and receding. We argue that the visual system is particularly sensitive to object onsets.

Preceding stimulus awareness augments offset-evoked potentials: evidence from motion-induced blindness

Event-related potentials (ERPs) were measured in response to the objective offset of a visual disk under two physically similar conditions: (1) visible conditions in which the target disk was well perceived and (2) invisible conditions in which participants reported to have not seen the target because of motion-induced blindness (Bonneh, Cooperman, & Sagi in Nature 411:798-801, 2001). Electrophysiological responses to the physical offset of the target disk were almost completely absent in the invisible conditions (Experiment 2). In the same conditions, the physical offset was almost completely invisible (Experiment 1). Results suggest an augmenting function of prior awareness of a stimulus for the offset-triggered ERP of that stimulus.

When is search for a static target among dynamic distractors efficient?

Intuitively, dynamic visual stimuli, such as moving objects or flashing lights, attract attention. Visual search tasks have revealed that dynamic targets among static distractors can indeed efficiently guide attention. The present study shows that the reverse case, a static target among dynamic distractors, allows for relatively efficient selection in certain but not all cases. A static target was relatively efficiently found among distractors that featured apparent motion, corroborating earlier findings. The important new finding was that static targets were equally easily found among distractors that blinked on and off continuously, even when each individual item blinked at a random rate. However, search for a static target was less efficient when distractors abruptly varied in luminance but did not completely disappear. The authors suggest that the division into the parvocellular pathway dealing with static visual information, on the one hand, and the magnocellular pathway common to motion and new object onset detection, on the other hand, allows for efficient filtering of dynamic and static information.

Perceptual bias following visual target selection

Attending to a relevant item in a visual display is thought to require not only selective attention to this item, but also active inhibition of surrounding distractor items. As a consequence of this spatial inhibition, selection of a relevant item in a previous distractor location is slowed (i.e., the spatial inhibition effect). The goal of this study is to identify brain regions that are involved in this spatial inhibition effect using functional magnetic resonance imaging (fMRI). Subjects had to select a target from a display which also included a distractor, while that target was presented in either a new location (control) or in a location previously occupied by a distractor (spatial inhibition). A region of interest analysis revealed decreased activation in the superior parietal lobe (SPL), but increased activation in the motor areas (supplementary motor area, putamen) when the target was presented in a previously inhibited compared to a new location. We take these results to suggest that presenting a target in a previously inhibited location negatively biases the selection of that target in favor of an accompanying distractor. This may result in an initially more efficient selection process, resulting in lower activation in the SPL. Counteracting this perceptual bias possibly requires additional motor activation. This study provides evidence for the notion that to make selection more efficient, prior information concerning an item is used. When this prior information conflicts with the current stimulus demands, compensatory motor actions are taken to correct this perceptual bias.

Task Demands Control Acquisition and Storage of Visual Information

Attention and working memory limitations set strict limits on visual representations, yet researchers have little appreciation of how these limits constrain the acquisition of information in ongoing visually guided behavior. Subjects performed a brick sorting task in a virtual environment. A change was made to 1 of the features of the brick being held on about 10% of trials. Rates of change detection for feature changes were generally low and depended on the pick-up and put-down relevance of the feature to the sorting task. Subjects' sorting decision suggests that changes may be missed because of a failure to update the changed feature. The authors also explore how hand and eye behavior are coordinated for strategic acquisition and storage of visual information throughout the task.

Attentional capture by colour and motion in cerebral achromatopsia

Cerebral achromatopsia is a rare condition in which damage to the ventromedial occipital area of the cortex results in the loss of colour experience. Nevertheless, cortically colour-blind patients can still use wavelength variation to perceive form and motion. In a series of six experiments we examined whether colour could also direct exogenous attention in an achromatopsic observer. We employed the colour singleton paradigm, the phi motion effect, and the correspondence process to assess attentional modulation. Although colour singletons failed to capture attention, a motion signal, based solely on chromatic information, was able to direct attention in the patient. We then show that the effect is abolished when the chromatic contours of stimuli are masked with simultaneous luminance contrast. We argue that the motion effect is dependent on chromatic contrast mediated via intact colour-opponent mechanisms. The results are taken as further evidence for the processing of wavelength variation in achromatopsia despite the absence of colour experience.