The effect of novel distractors on performance in focused attention tasks: A cognitive-psychophysiological approach

In the present study, we examined whether or not novel stimuli affect performance in a focused attention task. Participants responded to a central target while an irrelevant distractor in the visual display was occasionally changed. In Experiment 1, both target and distractor were presented centrally within the focus of attention. In Experiment 2, a central target was presented along with an irrelevant distractor at a peripheral location, outside the focus of attention. Novel distractors were associated with longer latencies and enhanced orienting responses (as measured by skin conductance responses) only when presented at an attended location. In contrast, as is demonstrated in Experiment 3, the same peripheral novel distractors interfered with task performance when they possessed task-relevant information. These results indicate that there is a fundamental difference between novel stimuli and task-relevant stimuli. Whereas the former exert influence only within the focus of attention, the latter affect performance even when positioned in an unattended location. Our findings have important implications for the operation of visual attention.     

Reducing and restoring stimulus-response compatibility effects by decreasing the discriminability of location words

In two experiments, we compared level of activation and temporal overlap accounts of compatibility effects in the Simon task by reducing the discriminability of spatial and non-spatial features of a target location word. Participants made keypress responses to the non-spatial or spatial feature of centrally presented location words. The discriminability of the spatial feature of the word (Experiment 1), or of both the spatial and non-spatial feature (Experiment 2), was manipulated. When the spatial feature of the word was task-irrelevant, lowering the discriminability of this feature reduced the compatibility effect. The compatibility effect was restored when the discriminability of both the task-relevant and task-irrelevant features were reduced together. Results provide further evidence for the temporal overlap account of compatibility effects. Furthermore, compatibility effects when the spatial information was task-relevant and those when the spatial information was task-irrelevant were moderately correlated with each other, suggesting a common underlying mechanism in both versions.     

Dilution of compatibility effects in Simon-type tasks depends on categorical similarity between distractors and diluters

The presence of a distracting stimulus during performance of the Stroop color-naming task leads to dilution of the Stroop effect. Because the automatic activation of word meaning may interfere with the task-relevant stimulus feature (text color; stimulus-stimulus [S-S] interference) and the response (saying the text color; stimulus-response [S-R] interference), it is unclear which of these types of interference is diluted. We introduce a new dilution paradigm using word- and arrow-based Simon tasks, in which only S-R interference is present. Participants made a left or right response to a central color target. A task-irrelevant location-word (Experiment 1) or arrow (Experiment 2) distractor adjacent to the target produced S-R compatibility effects. An additional neutral word or symbol series (diluter) was sometimes presented on the opposite side of the target from the distractor. The compatibility effect was smaller when the distractor and diluter category domains matched than when they mismatched. This result provides evidence that S-R compatibility effects are susceptible to the presence of diluters that are categorically similar to the distractors.     

The cognitive loci of the display and task-relevant set size effects on distractor interference: Evidence from a dual-task paradigm

The congruency effect of a task-irrelevant distractor has been found to be modulated by task-relevant set size and display set size. The present study used a psychological refractory period (PRP) paradigm to examine the cognitive loci of the display set size effect (dilution effect) and the task-relevant set size effect (perceptual load effect) on distractor interference. A tone discrimination task (Task 1), in which a response was made to the pitch of the target tone, was followed by a letter discrimination task (Task 2) in which different types of visual target display were used. In Experiment 1, in which display set size was manipulated to examine the nature of the display set size effect on distractor interference in Task 2, the modulation of the congruency effect by display set size was observed at both short and long stimulus-onset asynchronies (SOAs), indicating that the display set size effect occurred after the target was selected for processing in the focused attention stage. In Experiment 2, in which task-relevant set size was manipulated to examine the nature of the task-relevant set size effect on distractor interference in Task 2, the effects of task-relevant set size increased with SOA, suggesting that the target selection efficiency in the preattentive stage was impaired with increasing task-relevant set size. These results suggest that display set size and task-relevant set size modulate distractor processing in different ways.     

Task-relevance modulates the effects of peripheral distractors

The current study investigated whether task-relevant information affects performance differently from how information that is not relevant for the task does when presented peripherally and centrally. In three experiments a target appeared inside the focus of attention, whereas a to-be-ignored distractor appeared either in the periphery (Experiments 1 and 2) or at the centre (Experiment 3) of attention. In each trial the distractor carried both task-relevant and irrelevant information. The results confirmed the “task relevance” hypothesis: Task-irrelevant information affected performance only when it appeared at the centre of attention, whereas task-relevant information affected performance when it appeared inside as well as outside the main focus of attention. The current results do not support suggestions that spatial stimuli (e.g., arrows) draw attention automatically regardless of task relevance.     

Task-relevance modulates the effects of peripheral distractors

The current study investigated whether task-relevant information affects performance differently from how information that is not relevant for the task does when presented peripherally and centrally. In three experiments a target appeared inside the focus of attention, whereas a to-be-ignored distractor appeared either in the periphery (Experiments 1 and 2) or at the centre (Experiment 3) of attention. In each trial the distractor carried both task-relevant and irrelevant information. The results confirmed the “task relevance” hypothesis: Task-irrelevant information affected performance only when it appeared at the centre of attention, whereas task-relevant information affected performance when it appeared inside as well as outside the main focus of attention. The current results do not support suggestions that spatial stimuli (e.g., arrows) draw attention automatically regardless of task relevance.     

Does ignoring lead to worse evaluations? A new explanation of the stimulus devaluation effect

Affective evaluation of stimuli just seen in visual search tasks has been shown to depend on task-relevant stimulus configuration (Raymond, Fenske, & Tavassoli, 2003): Whereas targets and novel stimuli were evaluated similarly, distractors were devaluated. These results were explained by an inhibition-based account of the influence of selective attention on emotion. In the present experiments, we demonstrated that stimulus devaluation might not be a consequence of attentional inhibition. By simply instructing participants to react to an accepted or rejected stimulus in the visual search task of Experiment 1, we found distractor devaluation in the first case and target devaluation in the second case. We conclude that devaluation of stimuli is mediated by the affective connotation implied by response labels and instructions. This was confirmed in Experiment 2: To-be-ignored stimuli were not devaluated when participants knew that those stimuli would become task-relevant during the experiment.     

Taking a bright view of negative priming in the light of dim stimuli: further evidence for memory confusion during episodic retrieval.

A same-different letter-matching task was used to examine the effects of stimulus intensity on negative priming, which is poorer performance when target letters have been presented as distractor letters on the immediately preceding trial. In Experiment 1, stimulus intensity was manipulated between-participants, whereas in Experiment 2, it varied randomly from trial-to-trial within-participants. In Experiment 1, negative priming was equivalent for both stimulus intensities. In Experiment 2, negative priming effects were larger for repeated intensity stimuli than for nonrepeated intensity stimuli, when stimulus intensity was dim. Furthermore, for repeated intensity stimuli, negative priming effects were enhanced when the overt response required to the stimulus was repeated from prime to probe trial. These results are consistent with the hypothesis that negative priming may be due to memory confusion, rather than to inhibition of the distractor stimuli.     

Attention switching between global and local elements: Distractor category and the level repetition effect

When selecting information at global and local levels of hierarchical stimuli, there is a robust effect of level repetition in which performance is more efficient when a target is presented at the same level as the previous target. Moreover, the effect is symmetrical; it affects global and local processing equally. Evidence exists to suggest the effect may be automatic; however, we show here that the level repetition effect requires some amount of competition from the ignored level, and that the nature of the irrelevant information can determine whether the level-repetition effect is symmetrical (global and local responses are affected equally) or asymmetrical (global responses are more greatly affected than local responses). In Experiment 1, the level-repetition effect was eliminated when information at the distracting level was invariant across trials; effects of hemisphere bias and level repetition were observed only when suppression or filtering of distractor information was required. Experiment 2 demonstrated that simple featural variance is sufficient to produce the level repetition effect and that the symmetry of the level-repetition effect is sensitive to Garner-type interference that affects global processing to a greater extent than local processing. In Experiment 3, we showed that the absence of a level-repetition effect in the invariant distractor condition persists when the position of relevant stimuli is random within a block, a manipulation which should greatly reduce the contribution of controlled attention. We conclude that simple featural variance at the ignored level is critical to produce the advantage of level repetition, and that the size of the effect can be asymmetrical.     

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.     

The different roles of category- and feature-specific attentional control settings on attentional enhancement and inhibition

Contingent attentional capture suggests that top-down attentional control settings (ACS) can enhance attentional processing of task-relevant properties and inhibit attentional processing of task-irrelevant properties. However, it remains unclear how ACS operates when a distractor has both task-relevant and task-irrelevant characteristics. In the present study, two lateralized ERP components, N2pc and distractor positivity (Pd), were employed as markers of attentional enhancement and inhibition, respectively. The degree of matching between a distractor and a conjunctively defined target was manipulated to illustrate attentional guidance by category-specific ACS (cACS) and feature-specific ACS (fACS), and the relative position between the distractor and the target was manipulated to isolate the processing of the distractor and the target. Experiment 1 showed that, with a long display duration for searching, a reliable N2pc component was elicited by a distractor that was feature-matched but category-mismatched (C-F+) relative to the target-defined properties, suggesting an enhancing effect of fACS. In contrast, Experiment 2 demonstrated that, with a short display duration, a Pd component was elicited by a distractor that was feature-mismatched but category-matched (C+F-) relative to the target-defined properties, suggesting an inhibitory effect of fACS. Moreover, both attentional enhancement and inhibition were only triggered by fACS but not by cACS. In summary, ACS can enhance target-relevant properties or inhibit target-irrelevant properties in response to the display duration, and fACS affects both enhancement and inhibition more than cACS.     

Interference From Multi-dimensional Objects During Feature and Conjunction Discriminations

Feature discrimination performance within an attended object and interference from irrelevant, multi-dimensional objects (distractors) were examined in a two-choice, response compatibility paradigm. Results showed that the amount of interference by multi-dimensional distractors was dependent on three factors: (1) the discriminability of the incompatible, task-relevant distractor features; (2) the number of incompatible, task-relevant distractor features; and (3) whether the task-relevant, incompatible features matched the task goals. The most interesting finding was that additive priming effects were found for multiple, task-relevant features that matched the task goals, whether these features were present in the attended object or in the ignored object. Models that assume that each task-relevant feature primes its corresponding decision/response asynchronously and that this priming is combined to meet a decision/response criterion (at least when attended) can account for distractor interference during conjunction discriminations. Implications of these findings for feature integration models, template models, and a response selection model are discussed.     

The inability to ignore auditory distractors as a function of visual task perceptual load

Using a response competition paradigm, we investigated the ability to ignore target response-compatible, target response-incompatible, and neutral visual and auditory distractors presented during a visual search task. The perceptual load model of attention (e.g., Lavie & Tsal, 1994) states that task-relevant processing load determines irrelevant distractor processing in such a way that increasing processing load prevents distractor processing. In three experiments, participants searched sets of one (easy search) or six (hard search) similar items. In Experiment 1, visual distractors influenced reaction time (RT) and accuracy only for easy searches, following the perceptual load model. Surprisingly, auditory distractors yielded larger distractor compatibility effects (median RT for incompatible trials minus median RT for compatible trials) for hard searches than for easy searches. In Experiments 2 and 3, during hard searches, consistent RT benefits with response-compatible and RT costs with response-incompatible auditory distractors occurred only for hard searches. We suggest that auditory distractors are processed regardless of visual perceptual load but that the ability to inhibit cross-modal influence from auditory distractors is reduced under high visual load.     

Attentional selection: A salience-based competition for representation

The role of salience in localized attentional interference (LAI) was examined. In two experiments, target discrimination performance was measured as a function of the spatial separation between the target and a salient distractor item. In Experiment 1, both the salience of the distractor and that of a target were manipulated. Distractor salience was manipulated via size changes to the distractor, and target salience was manipulated by using unmasked or onset targets. When the target was of low salience, the magnitude of interference from the distractor increased with distractor salience. However, when the target had an abrupt onset, the distractor had no impact on target performance. In Experiment 2, the attentional salience of the distractor was manipulated using a probability manipulation. Displays contained both a target and a color singleton distractor. The color singleton produced LAI when it was predictive of the target location but not when it was unpredictive of the target location. The results of both experiments are consistent with models of competition-based attentional selection.     

The role of selection in generating auditory negative priming

The importance of selecting between a target and a distractor in producing auditory negative priming was examined in three experiments. In Experiment 1, participants were presented with a prime pair of sounds, followed by a probe pair of sounds. For each pair, listeners were to identify the sound presented to the left ear. Under these conditions, participants were especially slow to identify a sound in the probe pair if it had been ignored in the preceding prime pair. Evidence of auditory negative priming was also apparent when the prime sound was presented in isolation to only one ear (Experiment 2) and when the probe target was presented in isolation to one ear (Experiment 3). In addition, the magnitude of the negative priming effect was increased substantially when only a single prime sound was presented. These results suggest that the emergence of auditory negative priming does not depend on selection between simultaneous target and distractor sounds.     

Event-related potential correlates of visual identity negative priming unbiased by trial-by-trial effects

Negative priming (NP) refers to slowed reaction times and/or less accurate responses in people responding to a target that was ignored on a previous trial. Although extensive research with behavioral measures has been conducted, little is known about the electrophysiological mechanisms underlying this effect. The few previous studies carried out have led to contradictory results, supporting either episodic-retrieval or inhibition-based theoretical perspectives. In this study, we analyzed the ERP correlates of negative priming by using an experimental global context which, similar to the NP standard context, included Attended repetition trials. In addition, we presented relevant stimuli in separate blocks instead of the more usual randomized design. The NP effect can be biased by strategies adopted by participants when attended and ignored repetition trials are presented randomly. Specifically, we observed an enhanced N2 when a distractor from the previous trial became the target in the next trial. It is supposed that this finding reflects the involvement of additional attentional resources in the selection of a previously inhibited distractor as the new target stimuli.     

When do irrelevant visual stimuli impair processing of identical targets?

Three experiments investigated whether the repeated-letter inferiority effect (RLIE) and repetition blindness (RB) are identical phenomena or not and how the RLIE can be reconciled with the flanker compatibility effect (FCE). Participants reported a masked target and ignored an unmasked distractor. We manipulated the type of distractor (identical, alternative target, or neutral), the order of presenting distractor and target, and the predictability of target location. When distractors preceded the targets, distractors identical to the target always caused deficits in target processing (i.e., RB). With simultaneous presentation, identical distractors caused deficits (i.e., an RLIE) for unpredictable target locations only. Yet the RLIE was significantly smaller than RB. This result suggests that simultaneously presented stimuli are identified serially, in random order, if target position is unpredictable. As a result, RB arises only in the 50% of all trials with identical distractors in which the distractor is identified before the target. With simultaneous presentation and predictable target location, however, parallel processing of targets and distractors was possible that gave rise to an FCE in recognition accuracy. Analyses of false alarm rates revealed no evidence of significant response biases.     

Conflict-induced perceptual filtering

In a variety of conflict paradigms, target and distractor stimuli are defined in terms of perceptual features. Interference evoked by distractor stimuli tends to be reduced when the ratio of congruent to incongruent trials is decreased, suggesting conflict-induced perceptual filtering (i.e., adjusting the processing weights assigned to stimuli associated with the target and with the distractor features). In search of evidence for such a mechanism, we administered a flanker task, in which targets and distractors were defined in terms of stimulus location (Experiment 1) or color (Experiment 2). The efficiency of processing stimuli associated with target and distractor features was assessed in intermixed trials of a visual search task, in which a target had to be detected irrespective of these features. In both experiments search times were shorter for stimuli associated with the target feature than with the distractor feature of the flanker task. This effect was increased under conditions of a reduced congruent/incongruent ratio, thereby providing evidence for conflict-dependent perceptual filtering.     

Viewers prefer predictive cues

Devaluation-by-inhibition hypothesis demonstrated that previously ignored items are judged more negatively than previously attended and novel items. Based on this view, the present study investigated the evaluation of preceding stimuli that presumably elicit attentional processes to task-relevant stimuli. Accordingly, we employed a Posner-type cueing task followed by evaluation of the preceding cues indicating left and right directions. The important manipulation is predictability of two different preceding cues which predict the target location with high or with low probability. In Experiment 1 with two different arrows, a low predictive arrow was judged more negatively than a high predictive cue. Experiment 2 using gaze cues of two persons instead of two different arrows supported the findings of Experiment 1. These findings are consistent with devaluation-by-inhibition, suggesting that cue items triggering attention to the target are devaluated when they have less predictability.     

Retinal location and its effect on the spatial distribution of visual attention

A series of studies tested for distractor compatibility effects across wide target/distractor distances (0.6 degree to 20 degrees of visual angle). The effects of precue condition, constant/varied target location, horizontal/vertical distractor distance, and foveal/peripheral presentation were studied. Results show strong compatibility effects across wide distances when distractors are at peripheral retinal locations. When both stimuli were presented at the same peripheral location in opposite hemifields, compatibility effects were evident within an area of at least 2.5 degrees of visual angle. In contrast, when foveally placed distractors were used, compatibility effects were found primarily with target letters positioned near. The findings suggest that distance effects are not homogeneous across retinal location.