Behavioral and event-related potential (ERP) studies have shown that spatial attention is gradually distributed around the center of the attentional focus. The present study compared uni- and crossmodal gradients of spatial attention to investigate whether the orienting of auditory and visual spatial attention is based on modality specific or supramodal representations of space. Auditory and visual stimuli were presented from five speaker locations positioned in the right hemifield. Participants had to attend to the innermost or outmost right position in order to detect either visual or auditory deviant stimuli. Detection rates and event-related potentials (ERPs) indicated that spatial attention is distributed as a gradient. Unimodal spatial ERP gradients correlated with the spatial resolution of the modality. Crossmodal spatial gradients were always broader than the corresponding unimodal spatial gradients. These results suggest that both modality specific and supramodal spatial representations are activated during orienting attention in space.
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Intermodal attention effects consisting of larger amplitudes of ERPs to stimuli when their modality was attended compared to when their modality was unattended were observed in the present experiment for auditory and visual stimuli (see Figs. 2, 3); we report the significant Attended Modality effects of the overall ANOVAs in Tables 1 and 3 but, due to space limitations, we do not discuss them in detail. Nevertheless, intermodal attention effects confirm that participants were indeed selectively attending one modality only.
ERP effects of spatial and intermodal attention were significant at the peripheral speaker as well. Since the main focus of the present study was on attention gradients, we do not report ERPs to peripheral stimuli in the present paper.
From Fig. 4c, the impression might emerge that the amplitude of the spatial attention effect decreases linearly across speakers both in the unimodal and crossmodal condition. We explicitly tested for a linear trend by fitting linear regression lines for each participant. While the linear trend was significant in the unimodal condition (t(13) = 3.23, P = 0.007), it failed to reach significance level in the crossmodal condition (t(13) = 1.36, P = 0.198).
From Fig. 4d, the impression might emerge that the amplitude of the spatial attention effect decreases linearly across speakers both in the unimodal and crossmodal condition. We explicitly tested for a linear trend by fitting linear regression lines for each participant. While the linear trend was significant in the unimodal condition (t(13) = 3.64, P = 0.003), it failed to reach significance level in the crossmodal condition (t(13) = 1.19, P = 0.254).
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Föcker, J., Hötting, K., Gondan, M. et al. Unimodal and Crossmodal Gradients of Spatial Attention: Evidence from Event-related Potentials. Brain Topogr 23, 1–13 (2010). https://doi.org/10.1007/s10548-009-0111-8
- Spatial attention
- Event-related brain potentials
- Spatial representation