One major question toward understanding selective attention regards the efficiency of selection. One theory contends that this efficiency in vision is determined primarily by the perceptual load (PL) imposed by the relevant stimuli; if this load is high enough to fill attentional capacity, irrelevant stimuli will be excluded before they interfere with task performance, but if this load is lower the spare capacity will be directed automatically to the irrelevant information, which will then interfere with task performance. The current study attempts to test and extend this theory in order to understand better the role of PL by examining its effects on event-related brain potentials (ERPs), voltage fluctuations recorded at the scalp that reflect underlying cognitive operations. Stimuli were presented one at a time, and subjects were instructed to respond to rare deviant stimuli that appeared within a relevant stimulus channel and to ignore stimuli in an irrelevant channel, where channel was defined by either spatial (left, right) or nonspatial (red, blue) attributes in separate tasks. PL was manipulated by varying the similarity between the target/deviant and standard stimulus, and increases in PL were found to increase the magnitude of the relevant-irrelevant difference waveforms in both tasks at predicted temporal windows. These findings suggest that PL affects attentional selection that is tonically maintained across many experimental trials, and does so not only when selection is spatially based but also when it is based upon nonspatial cues.
"Instead, it shares more similarities with the original construct of perceptual load (i. e., primarily taxing processing capacities), put forward previously (Lavie, 1995, 2005), and similarly implemented in previous studies (e.g., Barnhardt et al., 2008; Erthal et al., 2005; Handy and Mangun, 2000, experiment 1). Therefore, we label our attention manipulation perceptual load throughout the manuscript. "
[Show abstract][Hide abstract] ABSTRACT: Converging electrophysiological and brain-imaging results show that sensory processing in V1 can be modulated by attention. In this study, we tested the prediction that this early filtering effect depends on the current affective state of the participant. We recorded visual evoked potentials (VEPs) to visual peripheral distractors while participants performed a demanding task at fixation, whose perceptual load was manipulated in a parametric fashion. Crucially, levels of negative affect were either increased or decreased independently of changes in perceptual load. Concurrent psychophysiological measurements and self-report scales confirmed that changes in emotional state were effective. In the control condition, ERP results showed that the C1 component generated in response to the exact same peripheral distractors systematically varied in amplitude with the amount of perceptual load imposed at fixation, being larger when perceptual load decreased. However, this early modulatory effect in V1 was disrupted when participants transiently experienced increased state anxiety, resulting in a decreased C1 amplitude even though task load at fixation remained low. These results suggest that early bottom-up processing in V1 is not only influenced by the amount of attention resources available, but also by the current internal state of the participant.
"Modulation of the P1 by attentional load has been observed previously in spatial selection tasks when comparing processing at attended versus unattended locations (Handy et al. 2001; Fu et al. 2008), but the earliest reported load effects within the focus of attention have been at the latency of the later N1 component (Barnhardt et al. 2008). A distinguishing feature of the present study was that attention was diffusely distributed across the visual field in anticipation of a peripheral target event, whereas the study of Barnhardt et al. (2008) employed a paradigm in which participants were required to monitor a single spatial location. The relative amount of attentional resources available to be devoted to that single location is likely to have been very high, perhaps raising the threshold above that at which attentional load manipulations take effect. "
[Show abstract][Hide abstract] ABSTRACT: Recent behavioral studies suggest that asymmetries in visuospatial orienting are modulated by changes in the demand on nonspatial components of attention, but the brain correlates of this modulation are unknown. We used scalp-recorded event-related potentials to examine the influence of central attentional load on neural responses to lateralized visual targets. Forty-five participants were required to detect transient, unilateral visual targets while monitoring a stream of alphanumeric stimuli at fixation, in which the target was defined either by a unique feature (low load) or by a conjunction of features (high load). The earliest effect of load on spatial orienting was seen at the latency of the posterior N1 (190-240 ms). The commonly observed N1 enhancement with contralateral visual stimulation was attenuated over the right hemisphere under high load. Source analysis localized this effect to occipital and inferior parietal regions of the right hemisphere. In addition, we observed perceptual enhancement with increasing load within the focus of attention (fixation) at an earlier stage (P1, 90-140 ms) than has previously been reported. These data support the view that spatial asymmetries in visual orienting are modulated by nonspatial attention due to overlapping neural circuits within the right hemisphere.
"That is, the discrimination task at target presentation was quite difficult as estimated by an average subject accuracy of 75% correct. Previous studies have demonstrated that increases in perceptual load lead to a greater taxing of resource-limited attentional mechanisms, whereby significantly greater behavioral (Lavie & Tsal, 1994) and perceptual consequences (Barnhardt, Ritter, & Gomes, 2008; Handy & Mangun, 2000) of attention are observed under conditions of greater target processing difficulty. Thus, if WM and attention share a common capacity-limited resource, the demonstrated significant association between individual's WMC and attention may be specific to conditions of difficult target discrimination. "
[Show abstract][Hide abstract] ABSTRACT: A growing literature suggests that working memory and attention are closely related constructs. Both involve the selection of task-relevant information, and both are characterized by capacity limits. Furthermore, studies using a variety of methodological approaches have demonstrated convergent working memory and attention-related processing at the individual, neural and behavioral level. Given the varieties of both constructs, the specific kinds of attention and WM must be considered. We find that individuals' working memory capacity (WMC) uniquely interacts with feature-based attention when combined with spatial attention in a cuing paradigm (Posner, 1980). Our findings suggest a positive correlation between WM and feature-based attention only within the spotlight of spatial attention. This finding lends support to the controlled attention view of working memory by demonstrating that integrated feature-based expectancies are uniquely correlated with individual performance on a working memory task.
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