Spatial selection via feature-driven inhibition of distractor locations

Inattentional blindness to unexpected hazard in augmented reality head-up display assisted driving: The impact of the relative position between stimulus and augmented graph

OBJECTIVE

An augmented reality head-up display (AR-HUD) is a promising technology in assisted driving. It provides additional information in the driving environment. However, considering the registration problem related to the limitations of interactive technology, we suspect that an AR-HUD may not be able to recognize unpredictable stimuli in a timely manner, inducing inattentional blindness to these non-augmented stimuli. Actually, non-augmented stimuli may accidentally have a brief superimposition to AR graphics. This condition may also influence the rate of inattentional blindness accordingly. Thus, this study examined the problem of inattentional blindness in AR-HUD systems that may result from the immaturity of AR technology.

METHOD

We investigated the impact of AR graphic position (peripheral AOI v.s. central AOI) and the relative position of the AR graphic on unpredictable stimuli (on-HUD hazard v.s. off-HUD hazard) on the occurrence of inattentional blindness. Thirty Participants watched an AR-augmented driving video that included four augmented conditions. Participants were instructed to respond to four critical events (speeding, running of red lights, unexpected pedestrians or motorcycles). The rate of inattentional blindness and response time were recorded. We only analyzed data on unexpected pedestrian and motorcycle incidents.

RESULTS

The relative position of the AR graphic on unpredictable stimuli and AR graphic positions significantly affected the rate of inattentional blindness and response time. Drivers had a higher rate of inattentional blindness to the unpredictable stimulus briefly superimposed on the AR graphic (i.e., on-HUD hazard) in the peripheral visual field (i.e., peripheral AOI). Also, drivers exhibited a higher rate of inattentional blindness to the unpredictable stimuli outside the AR graphic (i.e., off-HUD hazard) in the central visual field (i.e., central AOI).

CONCLUSION

The study is expected to be beneficial for furthering the design of an AR-HUD-assisted system to reduce inattentional blindness in driving. Our results found that in the peripheral visual field, unpredictable stimuli accidentally superimposed on the AR graphic (i.e., on-HUD hazard) lead to a higher probability of ignoring the accidental events and seemed to require a longer response time for drivers. This study illustrated that inattentional blindness to non-augmented stimuli is also influenced by the AR graphic position when AR technology fails to augment them in a timely manner. An important recommendation emerging from this work is to consider the design of AR graphics according to the AR graphic positions and stimulus types to reduce the occurrence of inattentional blindness.

Both feature comparisons and location comparisons are subject to bias

Four experiments explore the generalizability of two different types of bias in visual comparison. The first type is a spatial congruency bias, in which two target stimuli are more likely to be classified as matching ('same') if they appear successively at the same location. The second type is an analytic bias, which varies depending on the overall similarity of the displays and the need to select specific parts from each object. Both types of bias had previously been demonstrated in comparisons based on shape and other visual features. The current tasks move beyond feature comparisons, requiring the comparison of the local positions of visual elements (dots or letters) that appear within each pattern. Given the privileged role of location in visual representations and attentional selection, it is important to test how visual comparisons of location differ from comparisons of shape and other features. The spatial congruency bias is replicated in the comparison of local positions and, as in previous experiments, its strength diminishes when the displays being compared are less similar to one another. Also, as demonstrated previously with letter comparisons, there is an analytic bias shifting responses toward 'different' when the displays being compared are less similar to one another. Responses are also shifted more toward 'same' in location comparisons relative to feature comparisons. The general pattern of results suggests that as more attentional selection is required in a comparison task, there is a stronger overall bias to respond 'different'.

Repetition priming with no antipriming in picture identification

Previous studies have shown that the processing of a stimulus is facilitated when that stimulus is repeated compared to when it appears the first time, and this phenomenon is called repetition priming (RP). One explanation for RP is that initial processing of a stimulus strengthens connections within the visual representation, enabling subsequent processing of the same stimulus to be more efficient. More recently, it has been reported that presenting an object with features that overlap with those in a subsequent stimulus impairs the latter's processing, and this cost is termed antipriming (AP). AP is said to be the natural antithesis of RP, and it manifests when two objects share component features, thereby having overlapping representations. In two experiments, we investigated RP and AP in a picture naming task. Following previous research, we used a 4-phase paradigm, in which RP and AP were measured, respectively, by an increase or a decrease in performance for repeated or novel stimuli in Phase 4 compared with the baseline performance in Phase 2. We used a fully randomized design in Experiment 1, and a pseudo-randomized design in stimulus selection but a randomized design in presentation location in Experiment 2. We found robust RP in both experiments, but neither experiment showed any evidence of AP. Our results indicate that RP and AP do not always manifest within the same experiment, and that the relationship between these two effects may be more complex than previously understood.

Inhibition as a potential resolution to the attentional capture debate

Physically salient stimuli, such as uniquely colored objects, seem to have an inherent power to capture our attention, but formal research on this topic has produced conflicting results and theories. Here, we review evidence that the attentional capture debate can be resolved by positing a new suppressive process. This suppressive process can occur before attentional shifting to prevent salient items from attracting attention. In the current article, we review converging evidence that salient items are suppressed to avoid attentional capture comes from studies of psychophysics, eye movements, single-unit recordings, and event-related potentials (ERPs). Crucially, the ability to inhibit salient distractors seems to be learned as participants gain experience with the simple features of the to-be-ignored stimuli.

The transfer of location-based control requires location-based conflict

It is well supported that stimulus-driven control of attention varies depending on the degree of conflict previously encountered in a given location. Previous research has further shown that control settings established in conflict-biased locations can transfer to nearby unbiased items. However, these spatial transfer effects have only been shown using incompatible flanking arrows (i.e., stimuli that trigger spatial information) to elicit conflict in a flanker task. Here we examine the generalizability of transfer of control by examining if it can occur across a range of tasks. We employ a classic Stroop task (Experiment 1), a spatially segregated Stroop task (Experiment 2), and a spatial Stroop task (Experiment 3). Location-specific proportion compatibility effects were observed in all variations of the Stroop task tested; however, transfer to unbiased items occurred only in the spatial Stroop task in Experiment 3. This suggests that the transfer of cognitive control settings within spatial categories may occur only in tasks where the source of conflict is spatial, as arises in tasks with arrow and direction word stimuli.

Age-related differences in the attentional white bear

The cognitive aging literature suggests that aging populations exhibit impairments in the proactive inhibition of attention. Although proactive inhibition is often preceded by the allocation of attention toward the predicted or known spatial location of to-be-ignored stimuli, proactive allocation of attention has not been assessed in aging populations. In this study, an older and younger cohort engaged in the attentional-white-bear paradigm which measures proactive allocation of attention. In this task, on 80% of trials, participants must identify a centrally located letter surrounded by congruent or incongruent flanker letters. The flanker locations are fixed and predictable within each block of the study. On 20% of trials, they must identify which of two dots appear first on the screen. One dot appears in the same location as the flanker, and one appears in an empty location during the flanker task. The typical white-bear effect is that, despite the dots appearing at the same time, participants more often report the dot in the location of the flanker (i.e., the potentially to-be-ignored location) to appear first. The magnitude of this effect is interpreted as the magnitude of attentional allocation prior to inhibition. In Experiment 1, there was no difference in the magnitude of the attentional white bear between younger and aging cohorts. However, when the attentional system was sufficiently taxed by reducing the flanker presentation (Experiments 2a and 2b), age-related differences emerged. In particular, older participants showed a reduced white-bear effect, reflecting a potential impairment in the proactive allocation of attention toward the location of expected distractors.

Spatial sampling in human visual cortex is modulated by both spatial and feature-based attention

Spatial attention changes the sampling of visual space. Behavioral studies suggest that feature-based attention modulates this resampling to optimize the attended feature's sampling. We investigate this hypothesis by estimating spatial sampling in visual cortex while independently varying both feature-based and spatial attention. Our results show that spatial and feature-based attention interacted: resampling of visual space depended on both the attended location and feature (color vs. temporal frequency). This interaction occurred similarly throughout visual cortex, regardless of an area's overall feature preference. However, the interaction did depend on spatial sampling properties of voxels that prefer the attended feature. These findings are parsimoniously explained by variations in the precision of an attentional gain field. Our results demonstrate that the deployment of spatial attention is tailored to the spatial sampling properties of units that are sensitive to the attended feature.

Retinotopic effects of visual attention revealed by dichoptic multifocal pupillography

Multifocal pupillographic objective perimetry (mfPOP) has recently been shown to be able to measure cortical function. Here we assessed 44 regions of the central 60 degrees of the visual fields of each eye concurrently in 7 minutes/test. We examined how foveally- and peripherally-directed attention changed response sensitivity and delay across the 44 visual field locations/eye. Four experiments were completed comparing white, yellow and blue stimulus arrays. Experiments 1 to 4 tested 16, 23, 9 and 6 subjects, 49/54 being unique. Experiment 1, Experiments 2 and 3, and Experiment 4 used three variants of the mfPOP method that provided increasingly improved signal quality. Experiments 1 to 3 examined centrally directed attention, and Experiment 4 compared effects of attention directed to different peripheral targets. Attention reduced the sensitivity of the peripheral locations in Experiment 1, but only for the white stimuli not yellow. Experiment 2 confirmed that result. Experiment 3 showed that blue stimuli behaved like white. Peripheral attention showed increased sensitivity around the attentional targets. The results are discussed in terms of the cortical inputs to the pupillary system. The results agree with those from multifocal and other fMRI and VEP studies. mfPOP may be a useful adjunct to those methods.

The spatial distribution of attention in perceptual latency priming

The spatial distribution of visual attention is a yet unresolved question. One of the main topics is whether attention is distributed in a graded fashion around an attended location (e.g., Downing, 1988; Zimba & Hughes, 1987). The present experiments explore whether, and on which conditions, gradients of attention arise and contribute to perceptual facilitation. A masked or unmasked prime precedes one of two targets whose temporal order has to be judged. The prime captures attention, which shortens the perceptual latency of the primed target (perceptual latency priming; Scharlau & Neumann, 2003a; Shore, Spence, & Klein, 2001). No strong evidence for an attentional gradient was found. (1) Accuracy of temporal order judgements was independent of the distance between the two targets that were judged. That is, facilitation of the second target by the first target was spatially invariant. (2) With targets of short duration, facilitation was independent of prime-target distance. (3) With targets of long duration, gradients were found: Facilitation declined continuously with distance. Thus, long duration of stimuli may be a sufficient precondition for an attentional gradient. A control experiment showed that object-based attention contributes only marginally to perceptual latency priming.

Feature Confirmation in Object Perception: Feature Integration Theory 26 Years on from the Treisman Bartlett Lecture

The Treisman Bartlett lecture, reported in the Quarterly Journal of Experimental Psychology in 1988, provided a major overview of the feature integration theory of attention. This has continued to be a dominant account of human visual attention to this day. The current paper provides a summary of the work reported in the lecture and an update on critical aspects of the theory as applied to visual object perception. The paper highlights the emergence of findings that pose significant challenges to the theory and which suggest that revisions are required that allow for (a) several rather than a single form of feature integration, (b) some forms of feature integration to operate preattentively, (c) stored knowledge about single objects and interactions between objects to modulate perceptual integration, (d) the application of feature-based inhibition to object files where visual features are specified, which generates feature-based spreading suppression and scene segmentation, and (e) a role for attention in feature confirmation rather than feature integration in visual selection. A feature confirmation account of attention in object perception is outlined.

Unmasking saccadic uncrowding

Stimuli that are briefly presented around the time of saccades are often perceived with spatiotemporal distortions. These distortions do not always have deleterious effects on the visibility and identification of a stimulus. Recent studies reported that when a stimulus is the target of an intended saccade, it is released from both masking and crowding. Here, we investigated pre-saccadic changes in single and crowded letter recognition performance in the absence (Experiment 1) and the presence (Experiment 2) of backward masks to determine the extent to which saccadic "uncrowding" and "unmasking" mechanisms are similar. Our results show that pre-saccadic improvements in letter recognition performance are mostly due to the presence of masks and/or stimulus transients which occur after the target is presented. More importantly, we did not find any decrease in crowding strength before impending saccades. A simplified version of a dual-channel neural model, originally proposed to explain masking phenomena, with several saccadic add-on mechanisms, could account for our results in Experiment 1. However, this model falls short in explaining how saccades drastically reduced the effect of backward masking (Experiment 2). The addition of a remapping mechanism that alters the relative spatial positions of stimuli was needed to fully account for the improvements observed when backward masks followed the letter stimuli. Taken together, our results (i) are inconsistent with saccadic uncrowding, (ii) strongly support saccadic unmasking, and (iii) suggest that pre-saccadic letter recognition is modulated by multiple perisaccadic mechanisms with different time courses.

Expect the unexpected: a paradoxical effect of cue validity on the orienting of attention

Predictive central cues generate location-based expectancies, voluntary shifts of attention, and facilitate target processing. Often, location-based expectancies and voluntary attention are confounded in cueing tasks. Here we vary the predictability of central cues to determine whether they can evoke the inhibition of target processing in three go/no-go experiments. In the first experiment, the central cue was uninformative and did not predict the target's location. Importantly, these cues did not seem to affect target processing. In the second experiment, the central cue indicated the most or the least likely location of the target. Surprisingly, both types of cues facilitated target processing at the cued location. In the third experiment, the central cue predicted the most likely location of a no-go target, but it did not provide relevant information pertaining to the location of the go target. Again, the central cue facilitated processing of the go target. These results suggest that efforts to strategically allocate inhibition may be thwarted by the paradoxical monitoring of the cued location. The current findings highlight the need to further explore the relationship between location-based expectancies and spatial attention in cueing tasks.

Spatial attention and reading ability: ERP correlates of flanker and cue-size effects in good and poor adult phonological decoders

To investigate facilitatory and inhibitory processes during selective attention among adults with good (n=17) and poor (n=14) phonological decoding skills, a go/nogo flanker task was completed while EEG was recorded. Participants responded to a middle target letter flanked by compatible or incompatible flankers. The target was surrounded by a small or large circular cue which was presented simultaneously or 500ms prior. Poor decoders showed a greater RT cost for incompatible stimuli preceded by large cues and less RT benefit for compatible stimuli. Poor decoders also showed reduced modulation of ERPs by cue-size at left hemisphere posterior sites (N1) and by flanker compatibility at right hemisphere posterior sites (N1) and frontal sites (N2), consistent with processing differences in fronto-parietal attention networks. These findings have potential implications for understanding the relationship between spatial attention and phonological decoding in dyslexia.

The geometry of expertise

Theories of expertise based on the acquisition of chunk and templates suggest a differential geometric organization of perception between experts and novices. It is implied that expert representation is less anchored by spatial (Euclidean) proximity and may instead be dictated by the intrinsic relation in the structure and grammar of the specific domain of expertise. Here we set out to examine this hypothesis. We used the domain of chess which has been widely used as a tool to study human expertise. We reasoned that the movement of an opponent piece to a specific square constitutes an external cue and the reaction of the player to this “perturbation” should reveal his internal representation of proximity. We hypothesized that novice players will tend to respond by moving a piece in closer squares than experts. Similarly, but now in terms of object representations, we hypothesized weak players will more likely focus on a specific piece and hence produce sequence of actions repeating movements of the same piece. We capitalized on a large corpus of data obtained from internet chess servers. Results showed that, relative to experts, weaker players tend to (1) produce consecutive moves in proximal board locations, (2) move more often the same piece and (3) reduce the number of remaining pieces more rapidly, most likely to decrease cognitive load and mental effort. These three principles might reflect the effect of expertise on human actions in complex setups.

White bear everywhere: exploring the boundaries of the attentional white bear phenomenon

Some failures of selective attention may be explained by the attentional white bear (AWB) phenomenon Tsal & Makovski (Journal of Experimental Psychology: Human Perception and Performance 32:351-363, 2006), which indicates that prior knowledge of a distractor location causes attention to be actively allocated to it. The AWB effect is demonstrated in a task that includes infrequent trials that involve two simultaneous dots embedded among flanker trials. The dot positioned at an expected distractor location is perceived as appearing before the dot at an expected empty location, indicating that attentional resources have initially been allocated to the expected distractor locations. The main goal of this study was to explore the boundaries of the AWB phenomenon by imposing perceptual, memory, and sensory constraints on the flanker task. The results showed that the AWB effect was obtained even when additional constraints severely taxed the information-processing system. We propose that a mandatory mechanism guides a fixed minimal amount of attention to expected distractor locations in a top-down manner.

Neuronal correlates of multiple top-down signals during covert tracking of moving objects in macaque prefrontal cortex

Resistance to distraction is a key component of executive functions and is strongly linked to the prefrontal cortex. Recent evidence suggests that neural mechanisms exist for selective suppression of task-irrelevant information. However, neuronal signals related to selective suppression have not yet been identified, whereas nonselective surround suppression, which results from attentional enhancement for relevant stimuli, has been well documented. This study examined single neuron activities in the lateral PFC when monkeys covertly tracked one of randomly moving objects. Although many neurons responded to the target, we also found a group of neurons that exhibited a selective response to the distractor that was visually identical to the target. Because most neurons were insensitive to an additional distractor that explicitly differed in color from the target, the brain seemed to monitor the distractor only when necessary to maintain internal object segregation. Our results suggest that the lateral PFC might provide at least two top-down signals during covert object tracking: one for enhancement of visual processing for the target and the other for selective suppression of visual processing for the distractor. These signals might work together to discriminate objects, thereby regulating both the sensitivity and specificity of target choice during covert object tracking.

Parallel distractor rejection as a binding mechanism in search

The relatively common experimental visual search task of finding a red X amongst red O's and green X's (conjunction search) presents the visual system with a binding problem. Illusory conjunctions (ICs) of features across objects must be avoided and only features present in the same object bound together. Correct binding into unique objects by the visual system may be promoted, and ICs minimized, by inhibiting the locations of distractors possessing non-target features (e.g., Treisman and Sato, 1990). Such parallel rejection of interfering distractors leaves the target as the only item competing for selection; thus solving the binding problem. In the present article we explore the theoretical and empirical basis of this process of active distractor inhibition in search. Specific experiments that provide strong evidence for a process of active distractor inhibition in search are highlighted. In the final part of the article we consider how distractor inhibition, as defined here, may be realized at a neurophysiological level (Treisman and Sato, 1990).

Attentional inhibition mediates inattentional blindness

Salient stimuli presented at unattended locations are not always perceived, a phenomenon termed inattentional blindness. We hypothesized that inattentional blindness may be mediated by attentional inhibition. It has been shown that attentional inhibition effects are maximal near an attended location. If our hypothesis is correct, inattentional blindness effects should similarly be maximal near an attended location. During central fixation, participants viewed rapidly presented colored digits at a peripheral location. An unexpected black circle (the critical stimulus) was concurrently presented. Participants were instructed to maintain central fixation and name each color/digit, requiring focused attention to that location. For each participant, the critical stimulus was presented either near to or far from the attended location (at the same eccentricity). In support of our hypothesis, inattentional blindness effects were maximal near the attended location, but only at intermediate task accuracy.

The blind, the lame, and the poor signals of brain function--a comment on Sirotin and Das (2009)

Last year, a study appeared that questioned the generally held assumption of a generic coupling between electrical and hemodynamic signs of neural activity (Sirotin and Das, 2009). Although the findings of that study can barely surprise the specialists in the field, it has caused a considerable confusion in the nonspecialist community due to the unwarranted claim of having discovered a "hitherto unknown signal." According to this claim, functional magnetic resonance imaging (fMRI) would pick up not only signals that reflect electrical brain activity but also purely hemodynamic signals that are not linked to neural activity. Here, we show that that study's failure to obtain significant electrophysiological responses to task structure is easily understood on the basis of findings reported for related functional paradigms. Ironically and counter its intention, the study by Sirotin and Das reminds us of the exquisite sensitivity of spatially pooled hemodynamic signals and the limitations of recording only very local samples of electrical activity by microelectrodes. We suggest that this sensitivity of hemodynamic signals should be converted into spatial resolution. In other words, hemodynamic signals should be used to create maps. Further, we suggest that electrical recordings should be obtained at systematically varying functional positions across these maps. And we speculate that under such appropriate experimental and analytical circumstances correspondence between the two modalities would be retrieved-at the expense of a novel signal lost in oblivion.

Attentional enhancement during multiple-object tracking

What is the role of attention in multiple-object tracking? Does attention enhance target representations, suppress distractor representations, or both? It is difficult to ask this question in a purely behavioral paradigm without altering the very attentional allocation one is trying to measure. In the present study, we used event-related potentials to examine the early visual evoked responses to task-irrelevant probes without requiring an additional detection task. Subjects tracked two targets among four moving distractors and four stationary distractors. Brief probes were flashed on targets, moving distractors, stationary distractors, or empty space. We obtained a significant enhancement of the visually evoked P1 and N1 components (approximately 100-150 msec) for probes on targets, relative to distractors. Furthermore, good trackers showed larger differences between target and distractor probes than did poor trackers. These results provide evidence of early attentional enhancement of tracked target items and also provide a novel approach to measuring attentional allocation during tracking.

Electrophysiological Indices of Target and Distractor Processing in Visual Search

Attentional selection of a target presented among distractors can be indexed with an event-related potential (ERP) component known as the N2pc. Theoretical interpretation of the N2pc has suggested that it reflects a fundamental mechanism of attention that shelters the cortical representation of targets by suppressing neural activity stemming from distractors. Results from fields other than human electrophysiology, however, suggest that attention does not act solely through distractor suppression; rather, it modulates the processing of both target and distractors. We conducted four ERP experiments designed to investigate whether the N2pc reflects multiple attentional mechanisms. Our goal was to reconcile ostensibly conflicting outcomes obtained in electrophysiological studies of attention with those obtained using other methodologies. Participants viewed visual search arrays containing one target and one distractor. In Experiments 1 through 3, the distractor was isoluminant with the background, and therefore, did not elicit early lateralized ERP activity. This work revealed a novel contralateral ERP component that appears to reflect direct suppression of the cortical representation of the distractor. We accordingly name this component the distractor positivity (PD). In Experiment 4, an ERP component associated with target processing was additionally isolated. We refer to this component as the target negativity (NT). We believe that the N2pc reflects the summation of the PD and NT, and that these discrete components may have been confounded in earlier electrophysiological studies. Overall, this study demonstrates that attention acts on both target and distractor representations, and that this can be indexed in the visual ERP.

Not all features are created equal: Processing asymmetries between location and object features

Previous research has shown spontaneous location processing when location is not a task relevant feature and when a target is presented together with distractors. The present study investigates whether such processing can occur in the absence of distractor inhibition, and whether there is a processing asymmetry between location and an object feature. The results show that not all features are created equal. Whereas attending to an object's color or texture led to the involuntary processing of that object's location, attending to an object's location did not necessarily result in the encoding of its color or texture when these nonspatial properties were not task relevant. These results add to the body of evidence demonstrating the special role of location in attentional selection. They also provide a clearer picture of the interactions among location, object features, and participants' behavioral goals.

Cueing the location of a distractor: an inhibitory mechanism of spatial attention?

Presenting an irrelevant distractor increases reaction times to a target. The current study shows that cueing the location of an upcoming 'distractor' can help to reduce the effects the distractor has on target processing. It is hypothesized that this reduction is due to the active inhibition of the cued location. In two experiments in which the location of the distractor was cued in advance, a reduced effect of the distractor on target-processing was observed. Analyses indicated that this effect was most likely caused by inhibition of the distractor location. The present findings suggest that inhibition plays an important role in visual-spatial selection processes and that this inhibitory mechanism can be controlled in a top-down fashion.

A model of contour extraction including multiple scales, flexible inhibition and attention

A mathematical model of contextual integration and contour extraction in the primary visual cortex developed in a recent work [Ursino, M., & La Cara, G. E. (2004). A model of contextual interactions and contour detection in primary visual cortex. Neural Networks, 17, 719-735] has been significantly improved to include two fundamental additional aspects, i.e., multi-scale decomposition and attention. The model incorporates two independent paths for visual processing corresponding to two different scales. Attention from higher hierarchical levels works by modifying different properties of the network: by selecting the portion of the image to be scrutinized and the appropriate scale, by modulating the threshold of a gating mechanism, and by modifying the width and/or strength of lateral inhibition. Through computer simulations of real complex and noisy black-and-white images, we demonstrate that appropriate selection of the above factors allows accurate analysis of image contours at different levels, from global perception of the overall objects without details, down to a fine examination of minute particulars (such as the lips in a face or the fingers of a hand). Attentive reconfiguration of lateral inhibition plays a key role in the analysis of images at different detail levels.

Distractor Eccentricity and its Effect on Selective Attention

Abstract. Previous research has shown conflicting results regarding the effect of distractor eccentricity on selective attention. The present study examines the relationship between a distractor's retinal location and participants' response latencies to a target while holding constant the distribution of attention. In three experiments, the participants searched for a target among several distractors. The retinal location of the critical distractor was manipulated so that it was at either a central or a peripheral location. The results show that all else being equal, an incompatible distractor causes more interference at a peripheral location than at a central location. This distractor eccentricity effect suggests that the visual system can overcome the default bias in the distribution of attention that favors a central stimulus.

The time course of preview search with color-defined, not luminance-defined, stimuli

We examined the time course of preview search, using stimuli that were defined by color, but not by luminance changes. We demonstrate that, under these conditions, search performance in a preview condition improved selectively over time, relative to a baseline condition in which all the items appeared together. The data confirm earlier reports from Humphreys, Kyllinsbaek, et al. (2004) and Watson and Humphreys (1997), who used luminance-defined stimuli and showed a long time course to preview search. The data contradict Donk and Verburg (2004), who argued that the preview benefit was instantaneous but did not include baseline conditions with which to test for any influence of distractors equivalent to the old items in preview search, even under nonpreview conditions. The data support the proposal that the prioritization of new items in preview search is a time-consuming business.

The attentional white bear phenomenon: The mandatory allocation of attention to expected distractor locations

The authors devised a prestimulus-probe method to assess the allocation of attention as a function of participants' top-down expectancies concerning distractor and target locations. Participants performed the flanker task, and distractor locations remained fixed. On some trials, instead of the flanker display, either 2 simultaneous dots or a horizontal line appeared. The dot in the expected distractor location was perceived to occur before the dot in the expected empty location, and the line appeared to extend from the expected distractor location to the expected empty location, suggesting that attention is allocated to expected distractor locations prior to stimulus onset. The authors propose that a process-all mechanism guides attention to expected locations of all stimuli regardless of task demands and that this constitutes a major cause for failures of selective attention.

The inhibitory effect of a recent distracter

A series of experiments were conducted to examine the inhibitory effect of a visual distracter on saccadic eye movements. Participants were presented with a sequence of two critical displays. In one display a red target was presented together with a green distracter. This was followed by a display with a new red target presented in isolation at one of three locations with respect to the previous display. The lone target was presented either at the location of the recent target, the location of the recent distracter, or a new location. Participants were instructed to fixate the target in both displays and to ignore the green distracter. Experiment 1 revealed a significant increase in saccadic reaction times (SRTs) when the target was presented at the location of the recent distracter. Experiment 2 revealed that SRTs increased only in the conditions where the new target was presented at the location of the recent distracter, irrespective of its colour. Experiment 3 found that the inhibitory effect lasted for at least 2 s. In Experiment 4 the inhibitory effect was abolished when a lone distracter (i.e., anti-target) was presented without a target. Experiments 5 and 6 revealed that inhibition at the location of the recent target ('inhibition-of-return') also emerged with a shorter inter-display interval and when the distracter was removed from the recent display. These results distinguished between inhibition of a recent distracter and 'inhibition-of-return' and are consistent with models of competitive interactions which generate inhibitory effects on the spatial representation of a distracter.

Dissociating object- and response-based components of negative priming through effects of practice

The negative priming (NP) effect is the slowing of responses to an imperative stimulus (probe) that has recently been ignored (prime). Prevailing accounts of the phenomenon attribute it to a variety of causes, all centered on a representation of the stimulus event itself. However, we argue that the most commonly used NP paradigms confound stimulus- and response-based factors. In two experiments, we demonstrate the importance of response factors in producing NP and show clear empirical dissociations between object- and response-centered NP when studying their time courses over extended practice. When distractors compete for a response (response-based), the NP effect is both more robust and more resistant to the effects of practice. On the other hand, when prime distractors do not compete for response (object-based), they yield weaker NP effects that disappear with practice. We conclude that the NP effects shown in the most common procedures are produced by a combination of distinct factors that tend to act in the same direction.

The control of visual attention and its influence on prioritized processing in a location negative priming paradigm

In a location-based negative priming paradigm, the possibility of a disengagement option of the underlying inhibitory mechanism was tested. Whereas in previous studies disengagement was observed when providing utility information about the probe trial structure, in the present study the allocation of visual attention to the stimuli was manipulated. In the first step an automatic deployment of visual attention was implemented by presenting all stimuli as abrupt onsets (Experiment 1), which demonstrated commonly observed negative priming effects. In further conditions of non-automatic allocation of visual attention in which target and distractor were presented as no-onset stimuli, negative priming effects were eliminated (Experiments 2 and 3). The preferred interpretation is that in conditions of automatic control of attention, target and distractor compete for control of action. A non-automatic control of visual attention, on the other hand, leads to a top-down modulated selection, which results in prioritized target encoding and a loss of distractor impact on the selection process. Alternative accounts and the role of no-onset distractor processing were investigated in Experiment 4.

Interruption from irrelevant auditory and visual onsets even when attention is in a focused state

The common view on the interplay between exogenous and endogenous orienting holds that abrupt onsets are not capable of attracting attention when they occur outside the current focus of attention. Does this also apply to sudden irrelevant auditory onsets and when irrelevant visual onsets occur far in the periphery? In addition, does focused attention also reduce the alerting effect of auditory onsets, or vice versa, do highly alerting stimuli distort the attentional state? Crossmodal and unimodal variants of the Posner paradigm were examined in two experiments with targets and irrelevant onsets occurring at 28.3 and 19.3 degrees from fixation. Either centrally presented arrows indicated the forthcoming position of visual targets to be discriminated, or warning cues signaled the likely moment of target occurrence. The targets could be preceded by peripheral auditory or visual onsets that were to be ignored. Crossmodal and unimodal exogenous orienting effects of these irrelevant onsets were observed while participants focused at the relevant side. In addition, no evidence was found that the alerting effect of auditory onsets was dependent on focused attention. Our findings indicate that, at least under the current conditions, neither crossmodal nor unimodal orienting effects of peripheral events dissipate when attention is in a focused state.