Task Switching and Distractibility

In this thesis I examined the effects of task switching on people’s ability to ignore irrelevant distractors. Load theory proposes that distractor interference critically depends on the availability of executive control to minimise the effects of irrelevant stimuli (e.g. Lavie, 2000). Much work on task switching suggests that task switching demands executive control in order to prepare for and implement a switch between tasks (e.g. Monsell, 2003; Rubinstein, Meyer, & Evans, 2001). I therefore hypothesised that the executive demand of a task switch will result in reduced ability to reject irrelevant distractors in selective attention tasks. The research reported provided support for this hypothesis by showing that task switching results in greater distractor interference as measured with the “flanker task” (e.g. Eriksen & Eriksen, 1974) and with the attentional capture task (e.g. Theeuwes, 1990), even when there was no overlap between the stimuli and responses for the two tasks, and when task-repeated and switch trials were presented within the same block (in AAABBB designs). This research also showed that dissociable executive demands were involved in switching tasks (AAABBB), compared with mixing tasks (ABAB versus AAA), and these executive demands were found to control rejection of distractors in the flanker task and attentional capture task, respectively. In addition, task switching reduced internal distraction by task-unrelated thoughts. The contrast between the effects of task switching on internal versus external sources of distraction further supported the involvement of executive control in task switching. Finally, individual differences in operational span capacity predicted the magnitude of task switching costs and flanker interference effects, suggesting the involvement of executive control in both abilities. Overall, this research highlights a new consequence of task switching on selective attention and distractibility, supporting predictions derived from prevalent views on the role of executive control in task switching and selective attention

Positive emotion broadens attention focus through decreased position-specific spatial encoding in early visual cortex: evidence from ERPs

Recent evidence has suggested that not only stimulus-specific attributes or top-down expectations can modulate attention selection processes, but also the actual mood state of the participant. In this study, we tested the prediction that the induction of positive mood can dynamically influence attention allocation and, in turn, modulate early stimulus sensory processing in primary visual cortex (V1). High-density visual event-related potentials (ERPs) were recorded while participants performed a demanding task at fixation and were presented with peripheral irrelevant visual textures, whose position was systematically varied in the upper visual field (close, medium, or far relative to fixation). Either a neutral or a positive mood was reliably induced and maintained throughout the experimental session. The ERP results showed that the earliest retinotopic component following stimulus onset (C1) strongly varied in topography as a function of the position of the peripheral distractor, in agreement with a near-far spatial gradient. However, this effect was altered for participants in a positive relative to a neutral mood. On the contrary, positive mood did not modulate attention allocation for the central (task-relevant) stimuli, as reflected by the P300 component. We ran a control behavioral experiment confirming that positive emotion selectively impaired attention allocation to the peripheral distractors. These results suggest a mood-dependent tuning of position-specific encoding in V1 rapidly following stimulus onset. We discuss these results against the dominant broaden-and-build theory

Understanding vulnerability for depression from a cognitive neuroscience perspective: a reappraisal of attentional factors and a new conceptual framework

We propose a framework to understand increases in vulnerability for depression after recurrent episodes that links attention processes and schema activation to negative mood states, by integrating cognitive and neurobiological findings. Depression is characterized by a mood-congruent attentional bias at later stages of information processing. The basic idea of our framework is that decreased activity in prefrontal areas, mediated by the serotonin metabolism which the HPA axis controls, is associated with an impaired attenuation of subcortical regions, resulting in prolonged activation of the amygdala in response to stressors in the environment. Reduced prefrontal control in interaction with depressogenic schemas leads to impaired ability to exert attentional inhibitory control over negative elaborative processes such as rumination, leading in turn to sustained negative affect. These elaborative processes are triggered by the activation of negative schemas after confrontation with stressors. In our framework, attentional impairments are postulated as a crucial process in explaining the increasing vulnerability after depressive episodes, linking cognitive and biological vulnerability factors. We review the empirical data on the biological factors associated with the attentional impairments and detail how they are associated with rumination and mood regulation. The aim of our framework is to stimulate translational research

Cholinergic Modulation of Attention.

Rodent studies indicate that cholinergic inputs to frontoparietal cortex play an important role in signal detection, especially in challenging conditions. fMRI studies have likewise shown frontoparietal activity in humans under task conditions parallel to those used in the rodent studies. While these parallels are suggestive, the degree to which the fMRI activation patterns seen in humans reflect cholinergic activity remains unknown. The studies in this dissertation provide stronger evidence for cholinergic influences on the brain systems supporting attention in humans, and begin to delineate how those influences may differ by brain region and interact with other (e.g. dopaminergic) influences to shape cognition and behavior. First, an electroencephalography study showed that gamma synchronization, which previous studies have linked to cholinergic activity and attentional control, increases in response to a distractor challenge. Furthermore, across participants, greater increases in gamma synchronization in parietal cortex were associated with better distractor resistance, whereas greater increases in gamma dispersion in right prefrontal cortex were associated with greater response time variations thought to reflect difficulty in maintaining consistent control. Another series of experiments leveraged variability in cholinergic integrity (measured using PET) in Parkinson’s patients as a natural experiment to determine cholinergic contributions to different aspects of attention and cognitive control. Thalamic cholinergic integrity made the strongest independent contribution to variation in the ability to detect signals under perceptual challenge, whereas cortical cholinergic integrity was the best independent predictor of the ability to resist content-rich distractors likely to draw attention away from the target signal. Exploratory analyses suggested that parietal cholinergic integrity might play an especially important role in resisting these distractors, consistent with the electroencephalography study results. Finally, a secondary data analysis of a larger sample suggested that in conditions making strong demands on executive control, there may be mutual compensation between cholinergic and dopaminergic systems. To summarize, the present findings provide further evidence for cholinergic contributions to frontoparietal brain systems supporting signal detection, attention, and cognitive control, more precisely define the contributions of thalamic, prefrontal, and parietal inputs, and suggest the possibility of mutual compensation with the dopaminergic system in situations of high executive demand.PhDPsychologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111387/1/kaminkim_1.pd

Executive attention, task selection and attention-based learning in a neurally controlled simulated robot

We describe the design and implementation of an integrated neural architecture, modelled on human executive attention, which is used to control both automatic (reactive) and willed action selection in a simulated robot. The model, based upon Norman and Shallice's supervisory attention system, incorporates important features of human attentional control: selection of an intended task over a more salient automatic task; priming of future tasks that are anticipated; and appropriate levels of persistence of focus of attention. Recognising that attention-based learning, mediated by the limbic system, and the hippocampus in particular, plays an important role in adaptive learning, we extend the Norman and Shallice model, introducing an intrinsic, attention-based learning mechanism that enhances the automaticity of willed actions and reduces future need for attentional effort. These enhanced features support a new level of attentional autonomy in the operation of the simulated robot. Some properties of the model are explored using lesion studies, leading to the identification of a correspondence between the behavioural pathologies of the simulated robot and those seen in human patients suffering dysfunction of executive attention. We discuss briefly the question of how executive attention may have arisen due to selective pressure

Sensory ERP effects in auditory distraction: did we miss the main event?

Event-related potentials (ERPs) offer unique insights into processes related to involuntary attention changes triggered by rare, unpredictably occurring sensory events, that is, distraction. Contrasting ERPs elicited by distracters and frequent standard stimuli in oddball paradigms allowed the formulation of a three-stage model describing distraction-related processing: first, the distracting event is highlighted by a sensory filter. Second, attention is oriented towards the event, and finally, the task-optimal attention set is restored, or task priorities are changed. Although this model summarizes how distracting stimulus information is processed, not much is known about the cost of taking this exceptional route of processing. The present study demonstrates the impact of distraction on sensory processing. Participants performed a Go/NoGo tone-duration discrimination task, with infrequent pitch distracters. In the two parts of the experiment the duration-response mapping was reversed. Contrasts of distracter and standard ERPs revealed higher P3a- and reorienting negativity amplitudes for short than for long tones, independently from response type. To understand the cause of these asymmetries, short vs. long ERP contrasts were calculated. The ERP pattern showed that short standards elicited an attention-dependent offset response, which was abolished for short distracters. That is, the apparent P3a- and RON enhancements were caused by the removal of a task-related attentional sensory enhancement. This shows that the disruption of task-optimal attention set precedes the elicitation of the P3a, which suggests that P3a does not reflect a process driving the initial distraction-related attention change

Oscillatory Control over Representational States in Working Memory

In the visual world, attention is guided by perceptual goals activated in visual working memory (VWM). However, planning multiple-task sequences also requires VWM to store representations for future goals. These future goals need to be prevented from interfering with the current perceptual task. Recent findings have implicated neural oscillations as a control mechanism serving the implementation and switching of different states of prioritization of VWM representations. We review recent evidence that posterior alpha-band oscillations underlie the flexible activation and deactivation of VWM representations and that frontal delta-to-theta-band oscillations play a role in the executive control of this process. That is, frontal delta-to-theta appears to orchestrate posterior alpha through long-range oscillatory networks to flexibly set up and change VWM states during multitask sequences

Preparatory Template Activation during Search for Alternating Targets

Visual search is guided by representations of target-defining features (attentional templates). We tracked the time course of template activation processes during the preparation for search in a task where the identity of color-defined search targets switched across successive trials (ABAB). Task-irrelevant color probes that matched either the upcoming relevant target color or the previous now-irrelevant target color were presented every 200 msec during the interval between search displays. N2pc components (markers of attentional capture) were measured for both types of probes at each time point. A reliable probe N2pc indicates that the corresponding color template is active at the time when the probe appears. N2pcs of equal size emerged from 1000 msec before search display onset for both relevant-color and irrelevant-color probes, demonstrating that both color templates were activated concurrently. Evidence for color-selective attentional control was found only immediately before the arrival of the search display, where N2pcs were larger for relevant-color probes. These results reveal important limitations in the executive control of search preparation in tasks where two targets alternate across trials. Although the identity of the upcoming target is fully predictable, both taskrelevant and task-irrelevant target templates are coactivated. Knowledge about target identity selectively biases these template activation processes in a temporally discrete fashion, guided by temporal expectations about when the target template will become relevant