Distractor Stimuli Research Articles

Preattentive guidance of eye movements during triple conjunction search tasks: the effects of feature discriminability and saccadic amplitude.

Eye movements were monitored during the performance of triple conjunction search tasks. Stimuli varied in color, shape, and orientation. Across trials, the target was either present or absent, and displays consisted of 6, 12, or 24 stimuli. Stimulus discriminability was manipulated for the shape dimension, with half of the participants seeing displays of Es and Fs (low-discriminability [LD] condition) and half seeing displays of Cs and Ts (high-discriminability [HD] condition). Participants in both conditions performed two search tasks. In the single-feature (SF) task, the target stimulus shared one feature with each of the distractors, whereas in the two-feature (TF) task, it shared two features with each distractor. An examination of saccadic endpoints revealed that participants were more likely to fixate on distractor stimuli sharing color (SF task) or color and shape (TF task) with the target. This was a robust finding, being observed across participants, saccades of different amplitudes and sequential position, and following short and long latencies to move. The extent to which participants made use of shape information increased with discriminability.

Influence of Competing Distractors on Response Selection in Huntington's Disease and Parkinson's Disease

Current theories of the basal ganglia suggest a functional role in filtering stimuli that are competing for response selection. We hypothesised that damage to the basal ganglia, as occurs in Huntington's disease (HD) and Parkinson's disease (PD), may alter the effects of distractors on this filtering process. Fourteen HD subjects, 16 PD subjects, and age-matched healthy controls performed an ignored repetition test of negative priming. Negative priming was defined as a significant time cost in responding to a target that shared features with the distractor from the previous trial. Results indicated that whereas healthy controls and PD subjects showed normal negative priming, HD subjects failed to show negative priming. The results indicate that disruption to cells in the neostriatum, but not necessarily to cells in the substantia nigra, may affect selective attention by altering the influence of distractor stimuli competing for action.

Initial development of an auditory continuous performance test for preschoolers

Continuous performance tests, while readily available for school-aged children, are used sparingly with preschoolers. Research assessing auditory sustained attention in preschoolers has had mixed success, partly due to the task difficulty for children under age five. In particular, three-year-old children have shown great difficulty with these tasks because of test length, number of distracter stimuli, and short lnterstimulus intervals. To address these concerns, the Auditory Continuous Performance Test for Preschoolers (ACPT-P) was developed. The ACPT-P is an auditory, computer-based, go no-go, continuous performance test, using one target stimulus and one distracter, presented with a fixed interstimulus interval over a five-minute period.This study examined the psychometric properties and initial validity of the ACPT-P in a sample of 87 typically developing preschoolers. In our sample, children as young as 36 months completed the ACPT-P with few omission or commission errors. Results also indicated a developmental trend, with improved performance with increasing age from age three to six years. Response latency and variability decreased steadily from age three to six years. The ACPT-P variability score was significantly correlated with the Conners' Parent Rating Scale-Revised (Short Form) ADHD Index, while both mean response latency and variability were significantly correlated with measures of motor persistence, praxis, graphomotor skill, and listening vocabulary. The ACPT-P appears to be a developmentally appropriate and potentially useful tool in the assessment of auditory attention in preschool children, especially because of its utility for children as young as 36 months.

Paradigm-dependent modulation of event-related fMRI activity evoked by the oddball task.

We have previously shown that event-related functional magnetic resonance imaging (ER-fMRI) may be used to record responses to the rapid, interleaved presentation of stimuli in the three-stimulus oddball task. The present study examined the sensitivity of ER-fMRI responses to variations in the range of inter-stimulus intervals (ISIs, calculated as the time from the offset of one stimulus to the onset of the next stimulus) and the type of behavioral response task used. ISIs were varied between a wide ISI range (550-2,050 msec) and a narrow ISI range (800-1,200 msec), while maintaining a similar mean ISI (approximately 1 stimulus per sec) between experiments. The response task was varied between button press and subvocal target counting. Gradient echo, echo planar images were acquired for each of three experiments (wide ISI with button press, narrow ISI with button press, and wide-ISI with counting) in five subjects. Target stimuli generated increased fMRI signal in a wide range of brain regions. The use of a narrow ISI range generated a greater volume of subcortical activity and a reduced volume of cortical activity relative to a wide ISI range. The counting task generated a larger amplitude and longer lasting evoked response in brain regions that responded during all three experiments. Rare distractor stimuli evoked fMRI signal change primarily in orbitofrontal, ventral-medial prefrontal and superior parietal cortex. These results illustrate that although ER-fMRI is relatively insensitive as a technique to small variations in the timing of stimulus-evoked responses, it is remarkably sensitive to consequences such variations have for the topographic location and amplitude of neural responses to stimuli.

Curved saccade trajectories: voluntary and reflexive saccades curve away from irrelevant distractors.

In this study we examined the impact of irrelevant distractors upon trajectories of reflexive and voluntary saccades. Observers made saccades to visual targets above and below fixation as directed by target appearance (reflexive) or by a central directional cue (voluntary) in the presence of an irrelevant distractor stimulus (a cross) whose appearance was simultaneous with target onset. We recorded saccade latency, amplitude and the magnitude of saccade curvature relative to the direct route from the start-to-end of the saccade. Previous studies of saccades curvature have used distractors to provide information about the saccade task and, as a result, have only examined trajectories of voluntary saccades. However, we have shown that both reflexive and voluntary saccades curved away from irrelevant distractors. The effect of irrelevant distractors indicates that observers do not need to attend to distractors in a voluntary fashion for distractors to modify saccade trajectories. Furthermore, it highlights an important parallel in curvature of saccades and reach trajectories, namely that both curve away from irrelevant distractors. The second important observation was that reflexive, as well as voluntary, saccades curved away from distractors. This suggests that curvature is not solely a consequence of voluntary control. These results have been considered within the context of inhibition-based theories of curvature derived from studies of saccade and manual reach trajectories.

Attention-dependent suppression of distracter visual input can be cross-modally cued as indexed by anticipatory parieto–occipital alpha-band oscillations

Recent studies show that in addition to enhancing neural processing for attentionally relevant stimuli, selective attention also operates by suppressing the processing of distracter stimuli. When subjects are pre-cued to selectively deploy attention during voluntary (endogenous) attentional tasks, these mechanisms can be set up in advance of actual stimulus processing. That is, the brain can be placed in a biased attentional state. Two recent cueing studies have provided evidence for the deployment of such biased attentional states [J.J. Foxe, G.V. Simpson, S.P. Ahlfors, Neuroreport 9 (1998) 3929–3933; M.S. Worden, J.J. Foxe, N. Wang, G.V. Simpson, J. Neurosci. 20:RC63 (2000) 1–6]. Specifically, these studies implicated oscillatory activity in the alpha frequency-band (8–14 Hz) as an anticipatory mechanism for suppressing distracter visual stimulation. The current study extends these findings by showing that this alpha-suppressive effect is also invoked by cross-modal cues. Auditory symbolic cues were used in an intermodal attention task, to direct subjects’ attention to a subsequent task in either the visual or auditory modality. Cueing attention to the auditory features of the imminent task stimuli resulted in significantly higher parieto–occipital alpha amplitude in the period preceding onset of this stimulus than when attention was cued to the visual features. Topographic mapping suggests that this effect is generated in regions of the inferior parietal cortex, areas that have been repeatedly implicated in the engagement and maintenance of visual attention. Taken together, the results of this series of studies suggest that these parietal regions are capable of integrating sensory cues from multiple sensory modalities in order to program the subsequent deployment of visual attention.

Temporal resolution in an interaural temporal difference discrimination task with distracter stimuli

Interaural temporal difference (ITD) thresholds were determined for brief (14-ms) 500-Hz tone bursts in a two-interval forced-choice paradigm in which the interstimulus interval was 36 ms. Preliminary data indicate that the ITD threshold can be affected by the presence of a third (distracter) burst temporally centered between the two primary bursts on each trial: When the distracter has the same ITD as the final burst of the pair, the ITD threshold is unchanged or decreases relative to in the no-distracter condition; when it has the same ITD as the first burst, the threshold increases. The results are consistent with the hypothesis that, when presented with a rapid three-burst triad, the binaural system processes the ITD of the first burst normally (i.e., as if presented in isolation), but confuses or averages the ITDs of the latter two bursts. Follow-up experiments will measure the effects of the discrete nature of the distracter (i.e., by removing the silent gap between the distracter and the burst that shares its ITD), and the frequency of the distracter on the magnitude of its effect. Results will be discussed in terms of binaural temporal resolution of onset versus post-onset information. [Supported by NIDCD.]

Attention mediated by synchrony of neurons

Using electrophysiological recordings in area V4 of monkeys attending to one stimulus and ignoring others, researchers at the National Institutes of Mental Health (NIMH) found that groups of neurons devoted to the attended stimulus synchronize their activity, whereas neurons devoted to the distracting stimulus do not. The researchers suggest that coordination in firing amplifies the signal of the attended stimulus to stress importance over the distracting stimuli to higher brain processing areas. The exact mechanism by which these high-frequency oscillations are generated and enhanced is not yet known. The full report is published in the February 23 issue of Science.

Asymmetries in visual search: an introduction.

In visual search tasks, observers look for a target stimulus among distractor stimuli. A visual search asymmetry is said to occur when a search for stimulus A among stimulus B produces different results from a search for B among A. Anne Treisman made search asymmetries into an important tool in the study of visual attention. She argued that it was easier to find a target that was defined by the presence of a preattentive basic feature than to find a target defined by the absence of that feature. Four of the eight papers in this symposium in Perception & Psychophysics deal with the use of search asymmetries to identify stimulus attributes that behave as basic features in this context. Another two papers deal with the long-standing question of whether a novelty can be considered to be a basic feature. Asymmetries can also arise when one type of stimulus is easier to identify or classify than another. Levin and Angelone's paper on visual search for faces of different races is an examination of an asymmetry of this variety. Finally, Previc and Naegele investigate an asymmetry based on the spatial location of the target. Taken as a whole, these papers illustrate the continuing value of the search asymmetry paradigm.

Hand-centered attentional and motor asymmetries in unilateral neglect

On several accounts of ‘selection for action’, acting on a target object among distractors requires that irrelevant inputs and responses to these inputs are inhibited, and relevant inputs and responses selected. In unilateral neglect associated with right-hemisphere lesions, selection processes may be biased toward stimuli on the right, as right is usually defined by head and body hemispace. In normal subjects performing reaching-to-target tasks, selection may be ‘hand-centered’ (Tipper S., Lortie C., Baylis G.C., Journal of Experimental Psychology: Human Perception and Performance 18(4) (1992) 891–905) in that distractor stimuli close to the hand compete strongly with the target for the control of action, causing greater interference than distractors far from the hand. We reasoned that in the context of a reaching task, a left–right asymmetry in unilateral neglect may be defined with respect to the position of the hand. This predicts that target and distractor stimuli to the left of hand (i.e. requiring leftward movements for contact) should compete less strongly for the control of action than stimuli to the right of the hand. We tested this hypothesis by asking eight patients with unilateral neglect (and 12 healthy controls) to reach to central targets presented alone and with surrounding distractors from left or right start positions. Patients with neglect, but not controls, were slower to initiate reaches from right start as compared to left start positions. In this context, patients showed interference from distractors to the right of the hand and facilitation from distractors to the left of the hand. This indicates that a left–right selection asymmetry in neglect may be hand-centered. These data can be explained on a model of damage to the portion of a distributed neuronal population coding movement vectors to stimuli in relatively leftward locations.

Bilateral field interactions and hemispheric asymmetry in number comparison

We investigated bilateral field interactions and hemispheric asymmetry in number comparison. A numerical comparison task with three different stimulus notations (Arabic numerals, word numerals and bar graphs) was used. In all conditions, a target was displayed in one visual field, simultaneously with a distractor of the same format in the other visual field. Participants had to indicate manually whether the magnitude of the target was small or large, ignoring the distractor stimulus. Only in the condition with Arabic numerals did we obtain some evidence for a LVF advantage, which argues against a strong laterality of number magnitude representations. Significant interactions between target and distractor values were observed, indicating rich interhemispheric interactions. The interactions were mainly situated at the response stage, but the presence of a bilateral identity effect also points to interactions at the input level.

Is attentional focusing an inhibitory process at distractor location?

This study investigated whether attentional focusing is an inhibitory mechanism of lateral distractor stimuli. Attentional focusing is defined as the visual system capacity to vary the spatial extent of the attended area without shifting attention. A two-choice-reaction time task with compatible and incompatible flankers was used. Results were interpreted on the basis of the time course of attentional focusing.

Concurrent processing of saccades in visual search

We provide evidence that the saccadic system can simultaneously program two saccades to different goals. We presented subjects with simple visual search displays in which they were required to make a saccade to an odd-colored target embedded in an array of distractors. When there was strong competition between target and distractor stimuli (due to color priming from previous trials), subjects were more likely to make a saccade to a distractor. Such error saccades were often followed, after a very short inter-saccadic interval (∼10–100 ms), by a second saccade to the target. The brevity of these inter-saccadic intervals suggests that the programming of the two saccades (one to a distractor and one to the target) overlapped in time. Using a saccade-contingent change in the search display, we show that new visual information presented during the initial saccade does not change the goal of the second saccade. This supports the idea that, by the end of the first saccade, programming of the second saccade is already well underway. We also elicited two-saccade responses (similar to those seen in search) using a double-step task, with the first saccade directed to the initial target step and the second saccade directed to the second target step. If the two saccades are programmed in parallel and programming of each saccade is triggered by one of the two target steps, the second saccade should occur at a relatively fixed time after the onset of the second target step, regardless of the timing of the initial saccade. This prediction was confirmed, supporting the idea that the two saccades are programmed in parallel. Finally, we observed that the shortest inter-saccadic intervals typically followed hypometric initial saccades, suggesting that the initial saccade may have been interrupted by the impending second saccade. Using predictions from physiological studies of interrupted saccades, we tested this hypothesis and found that the hypometric initial saccades did not appear to be interrupted in mid-flight. We discuss the significance of our findings for models of the saccadic system.

Competition for Infants' Attention: The Interactive Influence of Attentional State and Stimulus Characteristics.

The interactive effects of stimulus characteristics and attentional state on infants' distraction latency were studied. As 7-month-old infants explored initial stimuli that were composed of either a single nonmoving component or multiple moving components, one of several types of distractors was presented in the periphery. Infants' distraction latencies (the amount of time they took to turn from the initial stimulus to the distractor) varied as a function of the interaction between the infants' attentional state at distractor onset and the characteristics of the stimuli. Variations in the visual characteristics of the distractor stimulus (solid rectangle vs. checkerboard) had a larger effect on distraction latency when infants were in a focused attentional state than when they were in a casual attentional state. Similarly, variations in the auditory characteristic of the distractor stimulus (1 intermittent tone vs. 2 alternating tones) had a larger effect when infants were engaged in a focused attentional state toward the multicomponent toys. Thus, infants' distractibility in this context reflects an interaction between the infants' attentional state and the competition between external stimuli for their attentional focus.

Visual filtering and covert orienting in persons with Down syndrome

A forced-choice reaction time (RT) task was used to examine the efficiency of visual filtering (the inhibition of processing of irrelevant stimuli) and covert orienting (shifts of visual attention independent of eye movement) components of attention in persons with Down syndrome ( n = 20) and children of average intelligence ( n = 20) matched for mental age (MA) (average MA = approximately 5.4 years). Conditions varied with regard to presence or absence of distractors, and the validity (valid, invalid, or neutral) of location cues. Contrary to expectations, persons with Down syndrome and MA-matched children of average intelligence at approximately age 5 showed similar patterns of performance on a task that required filtering distracting stimuli and searching for relevant information in the visual field. Both groups responded more efficiently to a target preceded by a valid cue as compared to a target preceded by an invalid or neutral cue. In addition, performance was more efficient with a target that was presented without irrelevant information as compared to one that was flanked on either side by extraneous, nontarget information and therefore necessitated filtering for efficient performance. These two findings indicate that: (1) disengaging from the location of an incorrect cue, and then searching for, locating, and responding to a target requires more time and attention than simply locating and responding to a target that has been validly cued; and (2) processing and responding to a target flanked by extraneous information entails filtering, and therefore requires more time and resources than simply responding to a target without distractors. In general, the development of visual reflexive, covert orienting, and filtering are intact in persons with Down syndrome relative to their level of functioning at an MA level of approximately 5 years, a period that is critical in the development of attentional processes.

Increases in cortical acetylcholine release during sustained attention performance in rats

Acetylcholine (ACh) efflux in the frontoparietal cortex was studied with in vivo microdialysis while rats performed in an operant task designed to assess sustained attention. Transferring animals from the baseline environment into the operant chambers elicited a robust increase in cortical ACh efflux that persisted throughout the 18-min pre-task period. Subsequent performance in the 36-min sustained attention task was associated with further significant increases in frontoparietal ACh efflux, while the termination of the task resulted in a delayed decline in ACh levels. Upon the 12-min presentation of a visual distracter (flashing houselight, 0.5 Hz) during task performance, animals initially developed a significant response bias to the left lever in the first 6-min distracter block, reflecting a reduction of attentional effort. Under continued conditions of increased attentional demand, performance recovered during the second 6-min distracter block. This return to attentional processing was accompanied by an increase in cortical ACh efflux, suggesting that the augmentation of attentional demand produced by the distracter elicited further increases in ACh release. The enhancement of cortical ACh efflux observed prior to task performance implies the presence of complex relationships between cortical ACh release and anticipatory and/or contextual factors related to operant performance and attentional processing. This finding, along with the further increases in cortical ACh efflux associated with task performance, extends hypotheses regarding the crucial role of cortical cholinergic transmission for attentional functions. Furthermore, the effects of the distracter stimulus provide evidence for a direct relationship between attentional effort and cortical ACh release.

A Comparison Between Adults With Conduct Disorder And Normal Controls on a Continuous Performance Test: Differences in Impulsive Response Characteristics

Continuous Performance Test (CPT) responding was compared between 15 adults with a history (childhood/adolescent) of Conduct Disorder (CD) and 15 normal controls. Of particular interest was whether response latencies and commission errors, which have been suggested to be measures of impulsivity, would differ between the groups. The CPT procedure used included two conditions: Immediate Memory Task and Delayed Memory Task (IMT/DMT; Dougherty et al., 1998). Both the IMT (0.5-s delay) and DMT (3.5-s delay with distracter stimuli at 0.5-s intervals) required the subject to respond if a briefly displayed number was identical to the one presented before it. Stimuli included target (identical match), catch (four of five digits matched), and novel (no match). Participants completed six 22-min testing sessions scheduled across a single day. The most significant findings were that the CD group (compared to the control group) had (a) elevated commission errors (responses to catch stimuli); (b) lower stimulus discriminability (between target and catch stimuli); and (c) shorter response latencies. These results are consistent with the few previous studies indicating that these parameters are related to impulsive behaviors.

Anticipatory Biasing of Visuospatial Attention Indexed by Retinotopically Specific α-Bank Electroencephalography Increases over Occipital Cortex

Alpha-band (8-14 Hz) oscillatory EEG activity was examined with high-density scalp electrical recording during the cue-stimulus interval of an endogenous spatial cueing paradigm. In different blocks, cued spatial locations (left or right) were in either the upper or lower visual field, and attended stimuli were either oriented Ts or moving dots. Distractor stimuli were equally likely in the uncued hemifield. Sustained focal increases of alpha-band activity were seen over occipital cortex contralateral to the direction of the to-be-ignored location (ipsilateral to the cued direction of attention) before onset of the to-be-attended stimulus. The focus of alpha-band activity also moved depending on whether cued locations were in the upper or lower field. Results are consistent with active gating of uncued spatial locations.

The achromatic mechanism and mechanisms tuned to chromaticity and luminance in visual search.

The purpose of the study was to determine whether visual search can be mediated by an achromatic, or luminance, mechanism in which signals are independent of the chromaticity of the stimuli. Experiments were designed to determine whether variability in the chromaticity of distractor stimuli made it more difficult to search for a target that differed from the distractor stimuli in luminance. Variability in the chromaticity of the distractors had little or no effect on search times when the target stimulus was white. Variability in the chromaticity of the distractors increased search times when the target was a reddish or bluish chromaticity. Results obtained with white targets suggest that these searches are mediated by an achromatic mechanism in which the signals are independent of the chromaticity of the stimuli. Results obtained with reddish and bluish targets suggest that searches for those targets may be mediated by mechanisms tuned to both chromaticity and luminance. Further experiments in which observers searched for targets that differed from distractors in both chromaticity and luminance provided additional support for the second conclusion.

A Study on Search Processing in Early Vision by Visual Angle and Stimuli Heterogeneity

This study aims at confirming the significance of search asymmetry, which appears under the condition of the exchange of target stimulus to distractor items with simple features, and at proposing some new arrangements of the stimuli presented in terms of visual angle and stimuli heterogeneity for examining search processing in early vision. The results obtained were as follows: (1) Search time depended on visual angle, for example, target position of stimuli presentation among distractors, and on heterogeneity in distractor stimuli presentation-search time also depended on the serial self-terminating effect, which appeared in participants when they could not find a target in parallel processing; (2) significant search asymmetry was confirmed by search time under the conditions of applying visual stimuli of lines in 2 kinds of arrangements, parallel and converging; (3) for the evaluation of search processing performance, correct ratio was an important index in addition to search time. Search time reflected a self-terminating effect depending on the condition of stimuli presentation, whereas correct ratio reflected performance accuracy in visual search. The former represents the total processing of human visual search performance and the latter represents human perception accuracy in early vision.