Attentional Load Asymmetrically Affects Early Electrophysiological Indices of Visual Orienting

The University of Queensland, School of Psychology and Queensland Brain Institute, Brisbane, Queensland 4072, Australia.
Cerebral Cortex (Impact Factor: 8.67). 05/2011; 21(5):1056-65. DOI: 10.1093/cercor/bhq178
Source: PubMed


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.

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    • "Based on the findings of O'Connell et al. (2011), who implemented a detection task while load was manipulated within the visual modality, we expected a significant reduction of the contralateral N1 amplitude under load. We predicted similar effects of visual and auditory load on the basis of our previous clinical finding: in the presence of brain damage spatial awareness was modulated by dual-tasking regardless of the nature (i.e., sensory modality) of the stimuli that had to be concurrently processed [19]. "
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    • "2.1.2. Spatial attention (RSVP) task Full details of this visual attention task are described elsewhere (O'Connell et al., 2011). A schematic of a single trial is illustrated in Fig. 1. "
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    • "The TPJ represents a key node in the ventral frontoparietal attention network implicated in both the orienting of visuospatial attention and the maintenance of arousal (Corbetta and Shulman, 2002, 2011). De-regulation of RH TPJ activity is thought in turn to reduce activation of the bihemispheric dorsal frontoparietal network (implicated in the distribution of visuospatial attention across the visual field) and has been linked to rightward shifts in visuospatial bias in healthy participants (O’Connell et al., 2011; Newman et al., 2013; Benwell et al., 2013b). We posit that these neural correlates may also underlie the length effect observed here in the elderly, over and above any age-related changes in task processing. "
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