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Individuals with developmental dyslexia have been characterized by problems with attentional orienting. In the current study, we specifically focused on possible changes in endogenous visual orienting that may be reflected in the electroencephalogram. A variant of the Posner cuing paradigm was employed with valid or invalid central cues that preceded target stimuli that were presented in the left or right visual field. The target stimuli consisted of vertical or horizontal stripes with low (two thick lines) or high (six thin lines) spatial frequencies. We examined lateralized alpha power in the cue-target interval as recent studies revealed that a contra vs. ipsilateral reduction in alpha power relates to the orienting of attention. An initial orienting effect in the lower alpha band was more pronounced for dyslexic individuals than for controls, suggesting that they oriented at an earlier moment in time. However, in contrast with controls, at the end of the cue-target interval no clear contralateral reduction in the upper alpha band was observed for dyslexic individuals. Dyslexic individuals additionally displayed slower responses, especially for invalidly cued high spatial frequency targets in the left visual field. The current data support the view that dyslexic individuals orient well to the cued location but have a problem with sustaining their attention.

Voluntary orienting of visual attention is conventionally measured in tasks with predictive central cues followed by frequent valid targets at the cued location and by infrequent invalid targets at the uncued location. This implies that invalid targets entail both spatial reorienting of attention and breaching of the expected spatial congruency between cues and targets. Here, we used event-related functional magnetic resonance imaging (fMRI) to separate the neural correlates of the spatial and expectancy components of both endogenous orienting and stimulus-driven reorienting of attention. We found that during endogenous orienting with predictive cues, there was a significant deactivation of the right Temporal-Parietal Junction (TPJ). We also discovered that the lack of an equivalent deactivation with nonpredictive cues was matched to drop in attentional costs and preservation of attentional benefits. The right TPJ showed equivalent responses to invalid targets following predictive and nonpredictive cues. On the contrary, infrequent-unexpected invalid targets following predictive cues specifically activated the right Middle and Inferior Frontal Gyrus (MFG-IFG). Additional comparisons with spatially neutral trials demonstrated that, independently of cue predictiveness, valid targets activate the left TPJ, whereas invalid targets activate both the left and right TPJs. These findings show that the selective right TPJ activation that is found in the comparison between invalid and valid trials results from the reciprocal cancelling of the different activations that in the left TPJ are related to the processing of valid and invalid targets. We propose that left and right TPJs provide "matching and mismatching to attentional template" signals. These signals enable reorienting of attention and play a crucial role in the updating of the statistical contingency between cues and targets.

In this study, we investigate how exogenous and endogenous orienting of spatial attention affect visuospatial working memory (VSWM). Specifically, we focused on two attentional effects and their consequences on storage in VSWM, when exogenous (Experiment 1) or endogenous (Experiment 2) orienting cues were used. The first effect, known as the meridian effect, is given by a decrement in behavioural performance when spatial cues and targets are presented in locations separated by vertical and/or horizontal meridians. The second effect, known as the distance effect, is given by a decrement in the orienting effects as a function of the spatial distance between cues and targets. Our results revealed a dissociation between exogenous and endogenous orienting mechanisms in terms of both meridian and distance effects. We found that meridian crossing affects performance only when endogenous cues were used. Specifically, VSWM performance with endogenous cueing depended more on the number of meridian crossings than on distance between cue and target. By contrast, a U-shaped distance dependency was observed using exogenous cues. Our findings therefore suggest that exogenous and endogenous orienting mechanisms lead to different forms of attentional bias for storage in VSWM.

In everyday life, the allocation of spatial attention typically entails the interplay between voluntary (endogenous) and stimulus-driven (exogenous) attention. Furthermore, stimuli in different sensory modalities can jointly influence the direction of spatial attention, due to the existence of cross-sensory links in attentional control. Using fMRI, we examined the physiological basis of these interactions. We induced exogenous shifts of auditory spatial attention while participants engaged in an endogenous visuospatial cueing task. Participants discriminated visual targets in the left or right hemifield. A central visual cue preceded the visual targets, predicting the target location on 75% of the trials (endogenous visual attention). In the interval between the endogenous cue and the visual target, task-irrelevant nonpredictive auditory stimuli were briefly presented either in the left or right hemifield (exogenous auditory attention). Consistent with previous unisensory visual studies, activation of the ventral fronto-parietal attentional network was observed when the visual targets were presented at the uncued side (endogenous invalid trials, requiring visuospatial reorienting), as compared with validly cued targets. Critically, we found that the side of the task-irrelevant auditory stimulus modulated these activations, reducing spatial reorienting effects when the auditory stimulus was presented on the same side as the upcoming (invalid) visual target. These results demonstrate that multisensory mechanisms of attentional control can integrate endogenous and exogenous spatial information, jointly determining attentional orienting toward the most relevant spatial location.

Specific increases of reaction times (RTs) were found in normal subjects, when endogenous spatial cues and targets were separated by the vertical visual meridian (VM) or by the vertical auditory (AM) meridian, when targets were either visual or auditory. The aim of this study was to assess if this effect could be attributed to longer RTs needed to shift activation between the hemispheres, or rather to different spatial maps underlying visual and auditory attention.We tested the VM effect in deaf subjects. If the shifting of activation from one hemisphere to the other causes the increase in RTs, then no differences between normal and sensory disabled people should take place, as the incoming perceptual information in the residual modality uses the same neural pathways while crossing the vertical meridian. Conversely, if the vertical meridian effects are related to the spatial representation systems underlying endogenous orienting mechanisms, then the lack of the auditory perceptual system in deaf people may have determined different organization processes in the brain circuits, strongly affecting the orienting mechanisms of spatial attention.Compared with a control group of hearing subjects, we found no evidence of the VM effect in deaf subjects.This finding, jointly with those of a previous experiment which showed no AM effect on blind subjects (Olivetti BelardinelliSantangelo 2005) supports the idea of different spatial maps underlying visual and auditory attention, and suggests that their co-existence may induce interference effects in space processing, giving rise to the anisotropic representation of visual and auditory spaces, observed in normal subjects.