Object-based attention: sensory modulation or priority setting?

The detection of an invalidly cued target is faster when it appears within a cued object than when it appears in an uncued object equally distant from the cued location; this is a manifestation of object based attention. Five experiments are reported in which it was investigated whether early sensory enhancement (in which attention "spreads" within an attended object but stops at its borders) or a later attentional prioritization mechanism best accounts for these effects. In Experiments 1-4, subjects identified a centrally located target with a buttonpress while attempting to ignore flanking distractors that were mapped to either a compatible or an incompatible response. The flankers appeared either within the object occupied by the target or in a different object but at the same distance from the target. The well-known effect of distance between the target and the flankers on the magnitude of the compatibility effect was replicated. However, whether the target and the flankers were in the same or different objects had no effect on the magnitude of the compatibility effect. In Experiment 5, when attention could not be narrowly focused in advance, object-based modulation of the flanker effect was observed. These results suggest that object-based selection may reflect an object-specific attentional prioritization strategy, rather than object-based attentional modulation of an early sensory representation.     

Processing of distractors inside and outside the attentional focus in a priming procedure

A priming procedure was used to study the processing of distractors located either inside (between the location of two targets) or outside (peripherally to the locations of the targets) the focus of attention. The stimuli were five-letter arrays, and participants had to decide whether two marked target letters were the same or different. In Experiments 1 and 2, positive priming was obtained both when targets and in-distractors in primes repeated as targets in probes; negative priming was found when out-distractor primes repeated as targets in probes. In Experiment 3, we also manipulated the match in letter case from primes to probes. In-distractors produced reliable positive priming, irrespective of whether the letters matched in case. In contrast out-distractors produced negative priming but only when the letters had the same case in primes and probes. These results are attributed to a spatial attention process operating (in this case) on low-level visual features, and an object-based selection process that enables more abstract information to be processed for selected stimuli.     

Capacity limits for face processing

We present three experiments in which subjects were asked to make speeded sex judgements (Experiment 1) or semantic judgements (Experiments 2 and 3) to face targets and nonface items, while ignoring a solitary flanking distractor face or a nonface stimulus. Distractors could be either congruent (same response category) or incongruent (different response category) with the target. Distractor congruency effects were consistently observed in all combinations of target-distractor stimulus pairs, except when a distractor face flanked a target face. The failure to find congruency effects in this condition was explored further in a fourth experiment, in which four task-irrelevant flankers were simultaneously presented. Once again, no face-face congruency effects were found, even though comparison distractors interfered with face and nonface targets alike. However, four simultaneously presented distractor faces did not interfere with nonface targets either. We suggest that these experiments demonstrate a capacity limit for visual processing in these conditions, such that no more than one face is processed at a time.     

Reinstating object-based attention under positional certainty: the importance of subjective parsing

Previous studies have shown that interference from flanking distractors can be modulated by the object organization of the scene. The experiments reported here test for object-based attention under conditions of positional certainty, which allow a narrow focus of attention to the target. Prior research has suggested that object-based attention does not arise in these circumstances, but the experiments presented here show that object-based attention can still appear if previous experience with the stimuli leads participants to interpret the stimulus pattern as two separate objects. Two control experiments demonstrate that the appearance of object-based attention is not due simply to a widening of the focus of spatial attention. The presence of object-based attention in such a focused-attention task argues against Shomstein and Yantis's (2002) proposed explanation of object-based attention based on priority in the order of visual search.     

Intra- and cross-dimensional visual search for single-feature targets

Cross-dimensional visual search for single-feature targets that differed from the distractors along two dimensions (color and orientation) was compared with intradimensional search for targets that differed from the distractors along a single dimension (either orientation or color). The design of the first three experiments differed from those of previous studies in that participants were required to respond differently to each of the targets. Experiments 1-3 were similar except that in Experiment 1, the distractors were homogeneous; in Experiment 2, two types of distractors were used in equal proportions; and in Experiment 3, two types of distractors were used but one of the distractors was a singleton. The findings, contrary to those of previous studies, revealed that cross-dimensional search is at least as efficient and for some targets even more efficient than intradimensional search. These results suggest that the details of stimulus-to-response mapping are essential in comparing intra- and cross-dimensional tasks. Experiment 4 used a priming design and did not support an explanation based on grouping processes. We outline an explanation for all the findings based on a recent cross-dimensional response selection model by Cohen and Shoup (1997).     

Perceptual organization and focused attention: The role of objects and proximity in visual processing

The influence of the Gestalt grouping principles of similarity, closure, and proximity on the size of the response-compatibility effect was examined in a focused attention task. In three studies, subjects responded to a centrally located target and attempted to ignore adjacent distractors. The distractors, which served as targets on other trials, could be compatible, incompatible, or neutral with respect to the response of the target. In addition, the distractors and the target could be embedded in the same object, presented in the same color, presented on different objects, or presented in different colors. The typical response-compatibility effect (B. A. Eriksen & C. W. Eriksen, 1974) was found when the target and distractors were embedded in the same object or presented in the same color. Performance was poorer when the target was surrounded by response-incompatible distractors than when it was surrounded by response-compatible distractors. However, the response-compatibility effect was eliminated-w-hen. the target and distractors were embedded in different objects, even when the distance between the items was less than.25° of visual angle. Furthermore, the response-compatibility effect was of intermediate size when the distractors were not grouped strongly with the target or with neutral flankers. The results are discussed in terms of space- and object-based models of visual attention.     

Perceptual organization and focused attention: the role of objects and proximity in visual processing.

The influence of the Gestalt grouping principles of similarity, closure, and proximity on the size of the response-compatibility effect was examined in a focused attention task. In three studies, subjects responded to a centrally located target and attempted to ignore adjacent distractors. The distractors, which served as targets on other trials, could be compatible, incompatible, or neutral with respect to the response of the target. In addition, the distractors and the target could be embedded in the same object, presented in the same color, presented on different objects, or presented in different colors. The typical response-compatibility effect (B. A. Eriksen & C. W. Eriksen, 1974) was found when the target and distractors were embedded in the same object or presented in the same color. Performance was poorer when the target was surrounded by response-incompatible distractors than when it was surrounded by response-compatible distractors. However, the response-compatibility effect was eliminated when the target and distractors were embedded in different objects, even when the distance between the items was less than .25 degrees of visual angle. Furthermore, the response-compatibility effect was of intermediate size when the distractors were not grouped strongly with the target or with neutral flankers. The results are discussed in terms of space- and object-based models of visual attention.     

The role of target salience in crowding

We studied 'crowding' in the parafovea using orientation identification of a Gabor target as the task, and flanking Gabors on an isoeccentric circle as distractors. Orientation-discrimination thresholds were raised by nearby flanking distractors. This crowding effect was increased by the number of distractors and decreased by the spatial separation between target and distractors. Crowding was greatest when the target was in the centre of the distractor array and smallest when the target was on the edge of the array. A cue indicating the position of the target improved performance when the position was otherwise unknown and the spatial separation between target and distractors was large, but the cue had no significant effect when separation was small. Increasing the contrast of the target relative to the distractors reduced crowding, but targets of smaller contrast than that of the distractors are even harder to identify than those of the same contrast. Putting the target and distractors in different depth planes decreased crowding for some observers, but there were qualitative individual differences. A large (say, 45 degrees) difference in orientation between target and distractors caused the target to 'pop out' in a presence/absence task, despite the evidence from other studies that crowding is still found in these conditions. We conclude that salience has, at best, modest effects on crowding.     

The effects of distractors in multiple object tracking are modulated by the similarity of distractor and target features

Is the effect of distractors in multiple object tracking dependent on the distractors sharing the features of the targets? In experiment 1, observers tracked five targets among five distractors that were identical to the targets and a number of additional distractors that were either identical to or featurally distinct from the targets. Results showed that distractors that are distinct from the targets in shape or color, or are stationary, impair tracking less than distractors that are identical to the targets. However, tracking performance declined as the number of distractors increased, even for featurally distinct distractors. Experiment 2 showed that distractors that differ from the targets on two features impair tracking less than distractors that differ from the targets on only one feature, but only when target tracking load is low. These results indicate that shape, color, and motion information about distractors can be used to distinguish them from targets during tracking, although even distractors with a different feature from the targets produce some interference with tracking. These findings suggest that the effect of distractors on tracking is dependent on top-down settings for target features.     

Searching for one versus two identical targets: when visual search has a memory

A recent study has suggested that observers' visual explorations of the external world can proceed unimpaired when the visual environment precludes the operation of memory processes (as, for instance, when the display elements change locations every 100 ms). One theoretical limitation of this study was that distractors were the only elements that had the potential to be tagged during visual search. The present study sought to clarify the amnesic-search hypothesis by investigating whether memory processes can guide search in other contexts in which targets also have the potential to be tagged. Accordingly, the experimental conditions of the previous study were repeated using a different search task in which observers had to decide whether one target or two were present among a variable number of similar distractors. Under these search conditions, the present findings provided strong evidence that memory processes can guide visual search.     

Response conflict reverses priming: a replication

Subjects named target words that followed a masked prime word of 33-msec (Experiments 1A and 1B) or 200-msec (Experiment 2) duration. The target word was either presented alone or accompanied by an interleaved distractor word. Targets presented alone were named more quickly following an identical prime than following an unrelated prime (repetition priming). In Experiment 1A, targets with distractors were named more slowly following an identical prime than following an unrelated prime (negative priming), replicating Milliken, Joordens, Merikle, and Seiffert (Psychological Review, 1998). In Experiments 1B and 2, repetition priming was reduced, although not reversed, for targets with distractors. The results of all three experiments are opposite to the usual finding of enhanced priming for perceptually degraded targets and suggest that response conflict engages retrospective mechanisms that counteract the facilitatory effects of priming.     

Moray revisited: High-priority affective stimuli and visual search

Previous research offers conflicting suggestions about whether “high-priority” verbal stimuli such as an individual's own name or emotionally charged words automatically grab attention and/or can be detected without the usual capacity limitations. Nine experiments investigated this issue, using visual search through displays of words. In speeded search tasks, the subject's own name was detected more quickly than other targets, but in no case were search slopes flat enough to suggest parallel search or “pop-out”. Further, names were not found to be unusually potent distractors. Emotionally charged words were neither more readily detected as targets nor more potent as distractors than neutral words. Acomparison of observers' accuracy in searching briefly exposed simultaneous vs. successive displays provided further evidence that search for “high-priority” word targets is subject to the same severe capacity limitations as those that are found with search for neutral words.     

The attentional blink: Increasing target salience provides no evidence for resource depletion. A commentary on Dux, Asplund, and Marois (2008)

The authors have argued elsewhere that the attentional blink (AB; i.e., reduced target detection shortly after presentation of an earlier target) arises from blocked or disrupted perceptual input in response to distractors presented between the targets. When targets replace the intervening distractors, so that three targets (T1, T2, and T3) are presented sequentially, performance on T2 and T3 improves. Dux, Asplund, and Marois (2008) argued that T3 performance improves at the expense of T1, and thus provides evidence for resource depletion. They showed that when T1 is made more salient (and presumably draws more resources), an AB for T3 appears to reemerge. These findings can be better explained, however, by (1) the relationship between T1 and T2 (not T1 and T3) and (2) differential salience for T3 in the long-lag condition of Dux et al.’s study. In conclusion, the Dux et al. study does not present a severe challenge to input control theories of the AB.     

Response to an intervening event reverses nonspatial repetition effects in 2AFC tasks: Nonspatial IOR?

The repetition effect in two-alternatiave forced choice (2AFC) tasks is a cornerstone effect in human cognition. Yet the experiments described here show that the customary benefit of repetition reverses to a cost of repetition when participants respond to an irrelevant event between targets. In Experiments 1A-1C, participants made manual 2AFC decisions to both of two consecutive targets on a trial and, on some trials, also made a manual response to an intervening event that appeared between the two targets. A repetition benefit was observed when no intervening event appeared, whereas a repetition cost was observed when a response was required to an intervening event. Experiment 2 ruled out a solely strategic interpretation of the repetition cost effect observed on intervening event trials. In Experiments 3A and 3B, an intervening event that required a simple vocal "go" response also produced a repetition cost. In Experiment 4, a repetition cost was observed when the intervening event was changed to a tone presented aurally. In Experiment 5, the repetition benefit was observed when a response was withheld to an intervening event. A dual-process interpretation of these results is discussed, with one process related to episodic integration, and the other related to processes that produce inhibition of return.     

The time course of negative repetition effects in post-cue naming

It has previously been shown that when picture pairs are repeated across blocks in a post-cue naming task, former distractors are named faster than former targets: the “negative repetition effect” (Mayall, Humphreys, & Kotsanis, 2002). In the present study the time course of this effect was examined. Experiment 1 demonstrated that the effect became apparent after a lag of only two intervening trials, with former targets being named faster than former distractors after a lag of zero trials. Experiment 2 used a new baseline condition with repeated picture pairs for which no response was required on the first presentation. Comparisons with this baseline indicated that the negative repetition effect is the result of suppression of former targets as opposed to facilitation of former distractors. The results support the proposal of Mayall et al. that the negative repetition effect reflects a form of speech monitoring that is applied when there is competition in the process of mapping from semantics to name representations.     

From interpretation to segmentation

In visual perception, part segmentation of an object is considered to be guided by image-based properties, such as occurrences of deep concavities in the outer contour. However, object-based properties can also provide information regarding segmentation. In this study, outer contours and interpretations of object configurations were manipulated to examine differences between image-based and object-based segmentation in a visual search task. We found that locating a two-dimensional object configuration with deep concavities in the outer contour depends on the type of outer contour of the surrounding distractors. In addition, locating a three-dimensional object configuration was harder when it was surrounded by object-based-disconnected distractors, as compared with object-based-connected distractors, regardless of image-based connections in these distractors. We conclude that segmentation based on the outer contours of a target facilitates its localization. However, when three-dimensional information is available, segmentation strongly depends on object-based properties, rather than on image-based properties.     

Object-based attention overrides perceptual load to modulate visual distraction

The ability to ignore task-irrelevant information and overcome distraction is central to our ability to efficiently carry out a number of tasks. One factor shown to strongly influence distraction is the perceptual load of the task being performed; as the perceptual load of task-relevant information processing increases, the likelihood that task-irrelevant information will be processed and interfere with task performance decreases. However, it has also been demonstrated that other attentional factors play an important role in whether or not distracting information affects performance. Specifically, object-based attention can modulate the extent of distractor processing, leaving open the possibility that object-based attention mechanisms may directly modulate the way in which perceptual load affects distractor processing. Here, we show that object-based attention dominates perceptual load to determine the extent of task-irrelevant information processing, with distractors affecting performance only when they are contained within the same object as the task-relevant search display. These results suggest that object-based attention effects play a central role in selective attention regardless of the perceptual load of the task being performed.     

On the fate of distractor stimuli in rapid serial visual presentation

Observers demonstrate an impaired ability to report the second of two targets in a rapid serial visual presentation (RSVP) stream if it appears within 500 ms of the first target--a phenomenon known as the attentional blink. This study investigated the fate of stimuli in dual-target RSVP streams that do not require report--the distractors. In five experiments, observers viewed dual-target RSVP streams where the items flanking Target 1 either had the same identity (repeats) or a different identity (non-repeats). Repeated distractors reduced the attentional blink, but only if two conditions were met (1) the items flanking Target 1 were featurally identical and (2) the distractors were drawn from a different alphanumeric category to the targets (e.g. digits vs. letters). We interpret this reduced blink magnitude in the repeat trials as evidence that in RSVP streams distractor items that appear in close temporal proximity to Target 1 are inhibited and we propose that this inhibition occurs both at the level of alphanumeric features and abstract identities.     

Correspondence effects for objects with opposing left and right protrusions

Choice reactions to a property of an object stimulus are often faster when the location of a graspable part of the object corresponds with the location of a keypress response than when it does not, a phenomenon called the object-based Simon effect. Experiments 1-3 examined this effect for variants of teapot stimuli that were oriented to the left or right. Whether keypress responses were made with fingers within the same hand or between different hands was also manipulated. Experiment 1 showed that, for judgments of stimulus color and upright-inverted orientation, the Simon effect for intact teapots occurred in the direction of the spout location and was larger for within- than between-hand response modes. In Experiments 2 and 3, teapots with the handle or spout removed showed separate contributions of each component to the Simon effect. In Experiment 4, we clarified a discrepancy between our findings of object-based Simon effects and a previously reported absence of effect with color judgments for door-handle stimuli. We obtained an object-based Simon effect with respect to handle position when the bases of the door handles were centered but not when the handles were centered. The findings that object-based Simon effects occur with color judgments and when responses are fingers on the same hand are in closer agreement with a location coding account than with a grasping affordance account.