Distraction by task-irrelevant stimuli: the effects of endogenous spatial attention and visual working memory load

Salient stimuli, like sudden changes in the environment or emotional stimuli, generate a priority signal that captures attention even if they are task-irrelevant. However, to achieve goal-driven behavior, we need to ignore them and to avoid being distracted. It is generally agreed that top-down factors can help us to filter out distractors. A fundamental question is how and at which stage of processing the rejection of distractors is achieved. Two circumstances under which the allocation of attention to distractors is supposed to be prevented are represented by the case in which distractors occur at an unattended location (as determined by the deployment of endogenous spatial attention) and when the amount of visual working memory resources is reduced by an ongoing task. The present thesis is focused on the impact of these factors on three sources of distraction, namely auditory and visual onsets (Experiments 1 and 2, respectively) and pleasant scenes (Experiment 3). In the first two studies we recorded neural correlates of distractor processing (i.e., Event-Related Potentials), whereas in the last study we used interference effects on behavior (i.e., a slowing down of response times on a simultaneous task) to index distraction. Endogenous spatial attention reduced distraction by auditory stimuli and eliminated distraction by visual onsets. Differently, visual working memory load only affected the processing of visual onsets. Emotional interference persisted even when scenes occurred always at unattended locations and when visual working memory was loaded. Altogether, these findings indicate that the ability to detect the location of salient task-irrelevant sounds and identify the affective significance of natural scenes is preserved even when the amount of visual working memory resources is reduced by an ongoing task and when endogenous attention is elsewhere directed. However, these results also indicate that the processing of auditory and visual distractors is not entirely automatic

When, Why and How Do Attentional Control Settings Influence Reflexive Capture?

Most models of selective attention acknowledge the role of both goal-driven and saliency-driven factors (Itti & Koch, 2001). An important ongoing debate asks when and to what extent top-down task settings prevent distraction by salient but irrelevant stimuli. Some studies suggest that reflexive orienting of spatial attention occurs only when distractors are congruent with task-relevant properties of the target (Folk, Remington, & Johnston, 1992); while others argue that the initial capture of attention is entirely stimulus-driven (Theeuwes, 1991). The present study tested whether attentional control settings always mediate capture, whether capture changes over time, and whether individual differences predict attentional capture. The first set of experiments tested whether a non-predictive and non-congruent cue captures attention when subjects are required to make a "target-absent" button-press response on catch trials. Results indicated reflexive spatial attentional capture to the distractor’s location, even when the stimulus shared no critical features with the target, but only when a behavioral response to catch trials was required. These findings provide new evidence that the ability of a stimulus to capture attention goes beyond the contingency of congruency between cue and target, and demonstrate that top-down set mediates capture through suppression, which is disabled when participants must attend to the temporal order of events. A second set of experiments extended these results with evidence that the novel capture found in the first experiment diminished over time as a function of experience with the task; whereas capture in the classic contingent case remained present throughout the experiment, suggesting that capture was initially stimulus-driven in both cases, followed by top-down suppression of irrelevant stimuli. Results from a third experiment demonstrated capture to a congruent cue despite its low validity (16%), supporting the contingent capture hypothesis. However, we also found evidence that experience with the cue’s probability may have induced more efficient disengagement over time, suggesting another way in which attentional control settings may be disabled. Overall these studies contribute to our understanding of the complex influences of internal and external factors on attentional capture, as well as the ways in which we can study them both experimentally and analytically.Doctor of Philosoph

Reward- and attention-related determinants of color selection in human visual cortex

Magdeburg, Univ., Fak. für Naturwiss., Diss., 2015von Antje Buschschult

Magnocellular and parvocellular influences on reflexive attention

There is currently disagreement in the visual attention literature regarding the stimulus features capable of triggering a reflexive shift of attention. One theory posits that features activating the magnocellular (M) visual stream, such as abruptly appearing objects with luminance contrast and low spatial frequencies, are responsible for activating the reflexive attention system (e.g. Steinman et al., 1997; Yantis and Egeth, 1997). However, recent experiments suggest stimuli activating the parvocellular (P) stream, such as isoluminant colors with high spatial frequencies, may be equally important for initiating reflexive shifts of attention (e.g. Lu, 2006; Yeshurun, 2004). Using behavioral and eventrelated potential (ERP) measures, we designed stimuli to stimulate either the M or P system to test whether the predominate activation of these systems trigger similar reflexive attention mechanisms, or if mechanisms of attentional capture are engaged differently depending on M or P activation. We predicted that similar attention effects would be observed if both pathways triggered automatic attentional orienting. However, if only magnocellular activation engages the reflexive attention system then we hypothesized that attention effects would only be seen when stimuli activated this system and not the P system. The present findings support the view that both systems are capable of triggering reflexive visual orienting. Specifically, reaction times (RTs) to target stimuli were speeded and the P1 and P300 components enhanced when spatially preceded by both M and P cues at short interstimulus intervals (ISI's), but these findings were characteristically different at long ISIs where inhibition of return (IOR) typically occurs. Further evidence supporting attention capture from M and P activation was evidenced by a greater negativity to uncued compared to cued trials at short ISIs, i.e. the IIN component. However, we also found evidence that M and P stimulation produced different effects depending on whether the target stimulus activated the M or P system. Together these results are consistent with the basic processing characteristics of the M and P pathways and show that activation either pathway can trigger a reflexive shift of visual attention

The role of multisensory integration in the bottom-up and top-down control of attentional object selection

Selective spatial attention and multisensory integration have been traditionally considered as separate domains in psychology and cognitive neuroscience. However, theoretical and methodological advancements in the last two decades have paved the way for studying different types of interactions between spatial attention and multisensory integration. In the present thesis, two types of such interactions are investigated. In the first part of the thesis, the role of audiovisual synchrony as a source of bottom-up bias in visual selection was investigated. In six out of seven experiments, a variant of the spatial cueing paradigm was used to compare attentional capture by visual and audiovisual distractors. In another experiment, single-frame search arrays were presented to investigate whether multisensory integration can bias spatial selection via salience-based mechanisms. Behavioural and electrophysiological results demonstrated that the ability of visual objects to capture attention was enhanced when they were accompanied by noninformative auditory signals. They also showed evidence for the bottom-up nature of these audiovisual enhancements of attentional capture by revealing that these enhancements occurred irrespective of the task-relevance of visual objects. In the second part of this thesis, four experiments are reported that investigated the spatial selection of audiovisual relative to visual objects and the guidance of their selection by bimodal object templates. Behavioural and ERP results demonstrated that the ability of task-irrelevant target-matching visual objects to capture attention was reduced during search for audiovisual as compared to purely visual targets, suggesting that bimodal search is guided by integrated audiovisual templates. However, the observation that unimodal targetmatching visual events retained some ability to capture attention indicates that bimodal search is controlled to some extent by modality-specific representations of task-relevant information. In summary, the present thesis has contributed to our knowledge of how attention is controlled in real-life environments by demonstrating that spatial selective attention can be biased towards bimodal objects via salience-driven as well as goal-based mechanisms

The role of multisensory integration in the bottom-up and top-down control of attentional object selection

Selective spatial attention and multisensory integration have been traditionally considered as separate domains in psychology and cognitive neuroscience. However, theoretical and methodological advancements in the last two decades have paved the way for studying different types of interactions between spatial attention and multisensory integration. In the present thesis, two types of such interactions are investigated. In the first part of the thesis, the role of audiovisual synchrony as a source of bottom-up bias in visual selection was investigated. In six out of seven experiments, a variant of the spatial cueing paradigm was used to compare attentional capture by visual and audiovisual distractors. In another experiment, single-frame search arrays were presented to investigate whether multisensory integration can bias spatial selection via salience-based mechanisms. Behavioural and electrophysiological results demonstrated that the ability of visual objects to capture attention was enhanced when they were accompanied by noninformative auditory signals. They also showed evidence for the bottom-up nature of these audiovisual enhancements of attentional capture by revealing that these enhancements occurred irrespective of the task-relevance of visual objects. In the second part of this thesis, four experiments are reported that investigated the spatial selection of audiovisual relative to visual objects and the guidance of their selection by bimodal object templates. Behavioural and ERP results demonstrated that the ability of task-irrelevant target-matching visual objects to capture attention was reduced during search for audiovisual as compared to purely visual targets, suggesting that bimodal search is guided by integrated audiovisual templates. However, the observation that unimodal targetmatching visual events retained some ability to capture attention indicates that bimodal search is controlled to some extent by modality-specific representations of task-relevant information. In summary, the present thesis has contributed to our knowledge of how attention is controlled in real-life environments by demonstrating that spatial selective attention can be biased towards bimodal objects via salience-driven as well as goal-based mechanisms

Brain responses to biological relevance

Abstract & This study examines whether orienting attention to biologically based social cues engages neural mechanisms distinct from those engaged by orienting to nonbiologically based nonsocial cues. Participants viewed a perceptually ambiguous stimulus presented centrally while performing a target detection task. By having participants alternate between viewing this stimulus as an eye in profile or an arrowhead, we were able to directly compare the neural mechanisms of attentional orienting to social and nonsocial cues while holding the physical stimulus constant. The functional magnetic resonance imaging results indicated that attentional orienting to both eye gaze and arrow cues engaged extensive dorsal and ventral frontoparietal networks. Eye gaze cues, however, more vigorously engaged two regions in the ventral frontal cortex associated with attentional reorienting to salient or meaningful stimuli, as well as lateral occipital regions. An event-related potential study demonstrated that this enhanced occipital response was attributable to a higher-amplitude sensory gain effect for targets appearing at locations cued by eye gaze than for those cued by an arrowhead. These results endorse the hypothesis that differences in attention to social and nonsocial cues are quantitative rather than qualitative, running counter to current models that assume enhanced processing for social stimuli reflects the involvement of a unique network of brain regions

Isolating the Neural Substrates of Visually Guided Attention Orienting in Humans

The neural processes that enable healthy humans to orient attention to sudden visual events are poorly understood because they are tightly intertwined with purely sensory processes. Here we isolated visually guided orienting activity from sensory activity using event-related potentials (ERPs). By recording ERPs to a lateral stimulus and comparing waveforms obtained under conditions of attention and inattention, we identified an early positive deflection over the ipsilateral visual cortex that was associated with the covert orienting of visual attention to the stimulus. Across five experiments with male and female adults participants, this ipsilateral visual orienting activity (VOA) could be distinguished from purely sensory-evoked activity and from other top-down spatial attention effects. The VOA was linked with behavioral measures of orienting, being significantly larger when the stimulus was detected rapidly than when it was detected more slowly, and its presence was independent of saccadic eye movements towards the targets. The VOA appears to be a specific neural index of the visually guided orienting of attention to a stimulus that appears abruptly in an otherwise uncluttered visual field

Conjunction search is relational: Behavioral and electrophysiological evidence

Attention selects behaviorally relevant stimuli for further capacity-limited processing and gates their access to awareness. Given the importance of attention for conscious perception, it is important to determine the factors and mechanisms that drive attention. A widespread view is that attention is biased to the specific feature values of a conjunction target (e.g., vertical, red, medium). By contrast, the results of the present study show that attention is tuned to the 2 relative features that distinguish a conjunction target from the irrelevant nontargets (e.g., larger and bluer). Moreover, an irrelevant conjunction cue that is briefly presented prior to the target can automatically attract attention, even in the absence of any feature contrasts. Importantly, automatic orienting to the conjunction cue was completely independent of the physical similarity between cue and target, and depended only on whether the conjunction cue matched the relative features of the target. These results demonstrate that attentional orienting is determined by a mechanism that can rapidly extract information about feature relationships and guide attention to the stimulus that best matches the relative attributes of the target. These results are difficult to reconcile with extant feature-specific accounts or object-based accounts of attention and argue for a relational account of conjunction search. (PsycINFO Database Recor