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Eccentricity Differentially Modulates Electrophysiological Indices of Saliency (Ppc) and Attention (N2pc) in Visual Search.

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Title: Eccentricity Differentially Modulates Electrophysiological Indices of Saliency (Ppc) and Attention (N2pc) in Visual Search.
Authors: Kerzel, Dirk (AUTHOR), Oxner, Matt (AUTHOR), Müller, Matthias M. (AUTHOR)
Source: Psychophysiology. Jul2026, Vol. 63 Issue 7, p1-12. 12p.
Subjects: Electrophysiology, Attention, Visual perception, Visual cortex
Abstract: This study systematically investigated how visual eccentricity and placement relative to the vertical and horizontal meridians modulate the earliest electrophysiological markers of visual selection: the Ppc (saliency registration) and the N2pc (attentional selectivity). While previous research has largely employed stimuli on the horizontal midline, we employed three experiments to map these components across varying eccentricities (0.8°, 2°, and 6°) and spatial configurations (diagonal vs. horizontal), utilizing cortical magnification scaling to ensure comparable visibility. The results reveal a robust functional dissociation between the two components. The N2pc exhibited a significant reduction in amplitude at 6° eccentricity across all experiments, regardless of behavioral performance, suggesting that focused spatial attention is shaped by the retinotopic architecture of the central visual field. In contrast, the Ppc remained relatively stable in the periphery (2.0° and 6.0°) but showed inconsistent presence at the near‐foveal 0.8° eccentricity, suggesting that early saliency maps are less affected by eccentricity than subsequent attentional deployment. Additionally, a post‐N2pc positivity (PNP) component emerged in the far periphery and for near‐foveal horizontal targets; however, its functional significance remains unclear. These findings demonstrate that electrophysiological indices of saliency and attentional selection are differentially affected by visual field position. On a practical note, small eccentricities and diagonal placements are preferable for maximizing the N2pc. Conversely, these same parameters should be avoided to maximize the Ppc. Impact Statement: Electrophysiological indices of saliency (Ppc, 80–120 ms) and attention (N2pc, 180–300 ms) are recorded at electrodes PO7/PO8, yet they require different stimulus placements for optimal results. We found the Ppc to be unreliable at small eccentricities (0.8°), particularly on the diagonals, whereas the N2pc was significantly reduced at large eccentricities (6.0°). While horizontal stimuli showed consistent results at small distances (0.8° vs. 2.0°), diagonal stimuli caused notable N2pc variations. Consequently, researchers should avoid central placement to capture the Ppc and avoid the (far) periphery to elicit the N2pc. [ABSTRACT FROM AUTHOR]
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Database: Psychology and Behavioral Sciences Collection
Description
Abstract:This study systematically investigated how visual eccentricity and placement relative to the vertical and horizontal meridians modulate the earliest electrophysiological markers of visual selection: the Ppc (saliency registration) and the N2pc (attentional selectivity). While previous research has largely employed stimuli on the horizontal midline, we employed three experiments to map these components across varying eccentricities (0.8°, 2°, and 6°) and spatial configurations (diagonal vs. horizontal), utilizing cortical magnification scaling to ensure comparable visibility. The results reveal a robust functional dissociation between the two components. The N2pc exhibited a significant reduction in amplitude at 6° eccentricity across all experiments, regardless of behavioral performance, suggesting that focused spatial attention is shaped by the retinotopic architecture of the central visual field. In contrast, the Ppc remained relatively stable in the periphery (2.0° and 6.0°) but showed inconsistent presence at the near‐foveal 0.8° eccentricity, suggesting that early saliency maps are less affected by eccentricity than subsequent attentional deployment. Additionally, a post‐N2pc positivity (PNP) component emerged in the far periphery and for near‐foveal horizontal targets; however, its functional significance remains unclear. These findings demonstrate that electrophysiological indices of saliency and attentional selection are differentially affected by visual field position. On a practical note, small eccentricities and diagonal placements are preferable for maximizing the N2pc. Conversely, these same parameters should be avoided to maximize the Ppc. Impact Statement: Electrophysiological indices of saliency (Ppc, 80–120 ms) and attention (N2pc, 180–300 ms) are recorded at electrodes PO7/PO8, yet they require different stimulus placements for optimal results. We found the Ppc to be unreliable at small eccentricities (0.8°), particularly on the diagonals, whereas the N2pc was significantly reduced at large eccentricities (6.0°). While horizontal stimuli showed consistent results at small distances (0.8° vs. 2.0°), diagonal stimuli caused notable N2pc variations. Consequently, researchers should avoid central placement to capture the Ppc and avoid the (far) periphery to elicit the N2pc. [ABSTRACT FROM AUTHOR]
ISSN:00485772
DOI:10.1111/psyp.70357