Objects or locations in vision for action? Evidence from the MILO task

In the Multi-Item Localization task (MILO; Thornton & Horowitz, 2004), observers are asked to find an ordered sequence of targets. We can measure the influence of both past actions and future plans on search for the current target. Our previous work with static search arrays found evidence for both retrospective and prospective memory. Responding to a target eliminated its influence on subsequent responses, while observers consistently planned ahead at least one item into the future. Here we asked whether these effects were based in location- or object-based reference frames. We used dynamic arrays in which observers had to search for multiple moving targets. Our results suggest that observers can still plan ahead effectively in this dynamic environment, indicating that future target objects can be tracked as they change position. However, memory for previous targets is essentially eliminated, suggesting that locations, not objects, were being tagged in our previous work.     

Visual detection of multi-letter patterns

This study addressed two basic questions about the detection of multi-letter patterns: (a) How is the detection of a multi-letter pattern related to the detection of its individual components? (b) How is the detection of a sequence of letters influenced by the observer's familiarity with that sequence? In three experiments observers searched for one-, two-, or three letter patterns embedded in a rapid series of multiple six-letter frames. In Experiment 1, unfamiliar two-letter patterns were detected more accurately than their one-letter components. This two-letter advantage reflects the fact that in an array of fixed size, larger target stimuli contain more information and are easier to discriminate from nontarget alternatives. Quantitative analyses indicated that observers combine information not decisions, about the component letters in a pattern. In Experiment 2, with statistical and physical properties equated, a familiar three-letter pattern (i.e., CAT) was detected more accurately than its unfamiliar anagram (i.e., TCA). This word advantage in word (not letter) detection persisted even after extensive practice and was uninfluenced by the lexical character of distractor items. In Experiment 3, words (e.g., FIB), pronounceable non words (e.g., FIF(, and familiar acronyms (e.g., FBI) were detected more readily than unfamiliar items (e.g., IBF). Thus both orthographic knowledge and familiarity with specific sequences can facilitate perceptual processing in "word" detection.     

Attentional weights in vision as products of spatial and nonspatial components

The relationship between visual attentional selection of items in particular spatial locations and selection by nonspatial criteria was investigated in a partial report experiment with report of letters (as many as possible) from brief postmasked exposures of circular arrays of letters and digits. The data were fitted by mathematical models based on Bundesen’s (Psychological Review, 97, 523-547, 1990) theory of visual attention (TVA). Both attentional weights of targets (letters) and attentional weights of distractors (digits) showed strong variations across the eight possible target locations, but for each of the ten participants, the ratio of the weight of a distractor at a given location to the weight of a target at the same location was approximately constant. The results were accommodated by revising the weight equation of TVA such that the attentional weight of an object equals a product of a spatial weight component (weight due to being at a particular location) and a nonspatial weight component (weight due to having particular features other than locations), the two components scaling the effects of each other multiplicatively.     

Rejecting salient distractors: Generalization from experience

Distraction impairs performance of many important, everyday tasks. Attentional control limits distraction by preferentially selecting important items for limited-capacity cognitive operations. Research in attentional control has typically investigated the degree to which selection of items is stimulus-driven versus goal-driven. Recent work finds that when observers initially learn a task, the selection is based on stimulus-driven factors, but through experience, goal-driven factors have an increasing influence. The modulation of selection by goals has been studied within the paradigm of learned distractor rejection, in which experience over a sequence of trials enables individuals eventually to ignore a perceptually salient distractor. The experiments presented examine whether observers can generalize learned distractor rejection to novel distractors. Observers searched for a target and ignored a salient color-singleton distractor that appeared in half of the trials. In Experiment 1, observers who learned distractor rejection in a variable environment rejected a novel distractor more effectively than observers who learned distractor rejection in a less variable, homogeneous environment, demonstrating that variable, heterogeneous stimulus environments encourage generalizable learned distractor rejection. Experiments 2 and 3 investigated the time course of learned distractor rejection across the experiment and found that after experiencing four color-singleton distractors in different blocks, observers could effectively reject subsequent novel color-singleton distractors. These results suggest that the optimization of attentional control to the task environment can be interpreted as a form of learning, demonstrating experience’s critical role in attentional control.     

Span of apprehension in schizophrenic patients as a function of distractor masking and laterality.

Twenty schizophrenic patients, 10 depressed control patients, and 20 normal control subjects were compared in a forced-choice, target-detection method for assessing the span of apprehension. The detection task required the subject to report which of 2 target letters was presented among 7 other (distractor) letters. Performance accuracy was examined as a function of target location and whether the distractor letters were masked after their presentation. The backward masking of the distractors improved target-detection accuracy of both control groups but reduced accuracy of the schizophrenic group. In addition, schizophrenics performed particularly poorly on targets located in the left half or lower half of the display. These results suggest that response to the masking of distractors may be a new index of attentional shortcoming in schizophrenia. Various theoretical explanations for the target location findings are also discussed.     

Data-driven recognition memory: a new technique and some data on age differences

In this study, we investigate the effect on recognition memory of having target and distractor stimuli consisting of different combinations of low-level elements (letters), relative to when targets and distractors consist of combinations of the same elements (nonoverlap and overlap conditions, respectively). It was found that recognition memory was enhanced in the nonoverlap condition, even though subjects reported being unaware of this experimental manipulation. This confirms the importance of perceptually driven processing in the implicit memory component of recognition memory. The extent to which this effect occurs is found to be age dependent, with elderly subjects benefiting more from having targets and distractors consisting of nonoverlapping elements. This is consistent with the notion that elderly subjects show less reliance on item-specific/contextual detail to support recognition memory.     

Laboratory vs. naturalistic prospective memory task predictions: young adults are overconfident outside of the laboratory

ABSTRACT

This study investigated whether individuals can predict their future prospective memory (PM) performance in a lab-based task and in a naturalistic task. Metacognitive awareness was assessed by asking participants to give judgments-of-learning (JOLs) on an item-level for the prospective (that something has to be done) and retrospective (what to do) PM component. In addition, to explore whether giving predictions influences PM performance, we compared a control group (without predictions) to a prediction group. Results revealed that giving predictions did not change PM performance. Moreover, participants were underconfident in their PM performance in the lab-based task, while they were overconfident in the naturalistic task. In addition, item-level JOLs indicated that they were inaccurate in predicting what items they will recall or not, but only for the prospective component of the PM task. As for the retrospective component, they were equally accurate in both task settings. This study suggests a dissociation of metacognitive awareness for PM according to both task setting and processing component.     

Evidence for attentional processing in spatial localization

Using a dual-task methodology, this study examined the involvement of selective attention in spatial localization. Thirty participants located a single, briefly presented, peripheral target stimulus, appearing in one of 50 positions on either side of a central fixation point, with or without the requirement to identify a simultaneously presented central distractor stimulus. Results revealed a robust interference effect in localization performance at short target durations that depended on the number of the to-be-identified distractor items. This outcome provides convergent support for the role of the attentional system in spatial localization.     

Can attentional control settings be maintained for two color–location conjunctions? Evidence from an RSVP task

Previous investigations of the ability to maintain separate attentional control settings for different spatial locations have relied principally on a go/no-go spatial-cueing paradigm. The results have suggested that control of attention is accomplished only late in processing. However, the go/no-go task does not provide strong incentives to withhold attention from irrelevant color–location conjunctions. We used a modified version of the task in which failing to adopt multiple control settings would be detrimental to performance. Two RSVP streams of colored letters appeared to the left and right of fixation. Participants searched for targets that were a conjunction of color and location, so that the target color for one stream acted as a distractor when presented in the opposite stream. Distractors that did not match the target conjunctions nevertheless captured attention and interfered with performance. This was the case even when the target conjunctions were previewed early in the trial prior to the target (Exp. 2). However, distractor interference was reduced when the upcoming distractor was previewed early on in the trial (Exp. 3). Attentional selection of targets by color–location conjunctions may be effective if facilitative attentional sets are accompanied by the top-down inhibition of irrelevant items.     

On varying the span of visual attention: Evidence for two modes of spatial attention

Three experiments investigated whether subjects could selectively attend to a target item presented in close spatial proximity to a distractor element. Typically, the display consisted of two curved lines, one a target and the other a distractor. The task was to judge the direction of curvature of the target. When subjects attended to a target away from fixation, performance was affected by the presence of a distractor within an area of 1° around the target. In contrast, the distractor did not influence target processing when subjects fixated on the target location. Two modes of visual attention are proposed. When a target is located away from fixation, a “wide” attentional span is employed. With the present stimuli, this led to the detailed processing of items within 1° of the attended position. However, when targets are at fixation a “narrow” span can be adopted, with the result that there is differential processing of attended items even within the formerly critical area.     

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.     

Distractor familiarity leads to more efficient visual search for complex stimuli

Previous reports suggest that distractor familiarity plays an important role in determining visual search efficiency. However, the specific tasks used in those studies limit the extension of their findings to real-world situations and everyday images. In the present study, subjects engaged in a prolonged period of search experience as a control of their level of familiarity with a large set of target and distractor images. Reaction times and search slopes decreased dramatically over this period, especially for trials with a large target eccentricity and many distractors. Following extended practice, search among familiar distractors was more efficient than search among unfamiliar distractors. Furthermore, we found that familiar targets were located more efficiently than unfamiliar targets and that subjects were faster at locating targets that they had experienced in the majority of the search trials. These results show that prolonged visual experience facilitates processing of both target and distractor items during search.     

Multiple attentional sets while monitoring rapid serial visual presentations

The present study examined whether observers are able to establish multiple attentional sets to concurrently monitor two different spatial locations. Observers identified a target letter in red or cyan among nontarget letters of other heterogeneous colours during a temporal feature search. A peripheral distractor display consisted of one item of either the same colour as the current target, and the other potential target colour, or an irrelevant colour that could never be the target. They identified an odd-ball colour letter among homogenous colours during a singleton search. The results revealed that observers maintained multiple attentional sets for detecting two singletons or for targets involving two (or three) features. However, they were unable to maintain a mixture of sets. Moreover, exposure to a distractor containing feature that corresponded to a feature of the current target was advantageous for target identification. The presence or absence of this set-specific capture depended on top-down knowledge and did not occur automatically in the singleton-detection stream. These results demonstrate a limitation in the flexibility of attentional sets. Although two singleton detections were possible, multiple attentional templates for a more complex attentional set could not be maintained concurrently when monitoring multiple rapid serial visual presentations.     

Emotional devaluation of distracting patterns and faces: a consequence of attentional inhibition during visual search?

Visual search has been studied extensively, yet little is known about how its constituent processes affect subsequent emotional evaluation of searched-for and searched-through items. In 3 experiments, the authors asked observers to locate a colored pattern or tinted face in an array of other patterns or faces. Shortly thereafter, either the target or a distractor was rated on an emotional scale (patterns, cheerfulness; faces, trustworthiness). In general, distractors were rated more negatively than targets. Moreover, distractors presented near the target during search were rated significantly more negatively than those presented far from the target. Target-distractor proximity affected distractor ratings following both simple-feature and difficult-conjunction search, even when items appeared at different locations during evaluation than during search and when faces previously tinted during search were presented in grayscale at evaluation. An attentional inhibition account is offered to explain these effects of attention on emotional evaluation.     

Selectively ignoring locations does not modulate contingent involuntary orienting,but selectively attending does

Attending to a location in the visual field facilitates processing of objects in that location, and numerous studies have revealed processing benefits by precuing target locations. Recent studies have also demonstrated that precuing a location to ignore reduces distraction by items in that location; however, precuing a feature (colour) to ignore increases distractor interference, at least before a template for rejection is established. Thus, locations, not features, can be selectively ignored. The present study used a spatial cuing task to examine whether featurally-relevant items are selected when they appear in ignored locations. The results revealed contingent attentional capture by target-relevant cues (red cue when searching for red targets, but not for onset targets), even when the cue appeared in a location that was ignored. Importantly, this was equivalent to contingent capture elicited by cues in non-ignored locations. However, when observers were precued to the target location, contingent capture was largely eliminated. The results suggest salient items with target-relevant features are selected from selectively ignored locations, but focusing attention onto a location can preclude capture by salient and target-relevant items.     

Target objects defined by a conjunction of colour and shape can be selected independently and in parallel

It is generally assumed that during search for targets defined by a feature conjunction, attention is allocated sequentially to individual objects. We tested this hypothesis by tracking the time course of attentional processing biases with the N2pc component in tasks where observers searched for two targets defined by a colour/shape conjunction. In Experiment 1, two displays presented in rapid succession (100 ms or 10 ms SOA) each contained a target and a colour-matching or shape-matching distractor on opposite sides. Target objects in both displays elicited N2pc components of similar size that overlapped in time when the SOA was 10 ms, suggesting that attention was allocated in parallel to both targets. Analogous results were found in Experiment 2, where targets and partially matching distractors were both accompanied by an object without target-matching features. Colour-matching and shape-matching distractors also elicited N2pc components, and the target N2pc was initially identical to the sum of the two distractor N2pcs, suggesting that the initial phase of attentional object selection was guided independently by feature templates for target colour and shape. Beyond 230 ms after display onset, the target N2pc became superadditive, indicating that attentional selection processes now started to be sensitive to the presence of feature conjunctions. Results show that independent attentional selection processes can be activated in parallel by two target objects in situations where these objects are defined by a feature conjunction.     

The depth of distractor processing in search with clutter

Some search tasks involve looking for a category target in clutter. This is the task faced, for example, by a baggage screener looking for weapons in a suitcase. Such tasks presumably involve the segmentation and recognition of the target object, but it is unknown whether they also involve the segmentation and recognition of the distractor objects. To examine the depth of distractor processing in this task, we had observers search through cluttered displays composed of normal and chimerical distractors. The normal distractors were photographs of recognizable objects, while the chimerical distractors were created by interchanging parts between the normal objects. The obsever's task was to identify the display quadrant that contained an animal or a vehicle target. We varied the difficulty of the search task by varying target and distractor discriminability, target uncertainty, and target occlusion. Only when the target was partially occluded did we find an effect of distractor type. In this case, observers may have found the target through a process of mentally eliminating whole distractor objects. When the target was unoccluded, we found no evidence that observers selected and rejected whole distractors during search. This second result supports our previous claim that often the items for search in clutter are not whole objects.     

The striking similarities between standard,distractor-free,and target-free recognition

It is often assumed that observers seek to maximize correct responding during recognition testing by actively adjusting a decision criterion. However, early research by Wallace (Journal of Experimental Psychology: Human Learning and Memory 4:441–452, 1978) suggested that recognition rates for studied items remained similar, regardless of whether or not the tests contained distractor items. We extended these findings across three experiments, addressing whether detection rates or observer confidence changed when participants were presented standard tests (targets and distractors) versus “pure-list” tests (lists composed entirely of targets or distractors). Even when observers were made aware of the composition of the pure-list test, the endorsement rates and confidence patterns remained largely similar to those observed during standard testing, suggesting that observers are typically not striving to maximize the likelihood of success across the test. We discuss the implications for decision models that assume a likelihood ratio versus a strength decision axis, as well as the implications for prior findings demonstrating large criterion shifts using target probability manipulations.     

Unique sudden onsets capture attention even when observers are in feature-search mode

Two sources of attentional capture have been proposed: stimulus-driven (exogenous) and goal-oriented (endogenous). A resolution between these modes of capture has not been straightforward. Even such a clearly exogenous event as the sudden onset of a stimulus can be said to capture attention endogenously if observers operate in singleton-detection mode rather than feature-search mode. In four experiments we show that a unique sudden onset captures attention even when observers are in feature-search mode. The displays were rapid serial visual presentation (RSVP) streams of differently coloured letters with the target letter defined by a specific colour. Distractors were four #s, one of the target colour, surrounding one of the non-target letters. Capture was substantially reduced when the onset of the distractor array was not unique because it was preceded by other sets of four grey # arrays in the RSVP stream. This provides unambiguous evidence that attention can be captured both exogenously and endogenously within a single task.     

Repetition blindness in priming in perceptual identification: Competitive effects of a word intervening between prime and target

University students named a 72-ms masked target word that was preceded by two 120-ms consecutively presented words, a prime word followed by a distractor. In Experiment 1, all words were in lowercase letters, whereas in Experiment 2, the target word was changed to uppercase letters. In both experiments there was an accuracy and latency cost (repetition blindness: RB) when the prime was the same word as the target, with the cost much less severe in Experiment 2 than in Experiment 1. A low-frequency distractor impaired target identification compared with a high-frequency distractor. Distractor frequency interacted with target frequency such that high-frequency targets preceded by low-frequency distractors had the lowest accuracy. The results are consistent with a frequency-dependent competition for access to working memory among briefly displayed words. However, there was no clear evidence that effects of target repetition on interword competition play a role in RB. The effects of a letter case change for the target are consistent with a contribution of token distinctiveness to word-order recovery in the intervening-word priming task.