Visual evoked potentials and selective attention to points in space

Van Voorhis, Steven; Hillyard, Steven A. · 1977 · Crossref

DOI: 10.3758/bf03206080

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Summary

This study investigates the neural correlates of selective visual attention by examining how Visual Evoked Potentials (VEPs) change when subjects focus attention on specific spatial locations. The research was motivated by methodological criticisms of earlier studies, particularly regarding stimulus randomness and eye fixation control, which may have confounded attention effects with anticipatory arousal. The authors aimed to replicate previous findings of early VEP enhancement while strictly controlling for these variables and comparing visual attention effects to well-established auditory findings. The experiment involved 12 subjects who viewed flashes presented in the left or right visual fields under three stimulus schedules: a replication of a previous quasi-independent sequence, a slow random (Bernoulli) sequence, and a fast random sequence. Subjects performed under four attention conditions: passive viewing, focused attention on one field, focused attention on the opposite field, and divided attention on both fields. VEPs were recorded from occipital (O2) and vertex (Cz) electrodes, with strict monitoring of eye position to ensure fixation. Data analysis excluded trials with eye movements or blinks, and components were defined by specific latency windows. The results demonstrated that attending to a specific visual field significantly enhanced VEP amplitudes compared to unattended or passive conditions. However, the specific components affected differed by recording site. At the vertex (Cz), the N1 component (120–200 msec) showed the most consistent and dramatic enhancement with attention, analogous to auditory attention effects. At the occipital site (O2), the P1 and P2 components were more sensitive to attention shifts, while N1 was less affected. The P3 component (300–500 msec) was enhanced at both sites for attended stimuli. Crucially, these attention effects persisted even when stimuli were presented in a completely random Bernoulli sequence, refuting the hypothesis that earlier findings were due to anticipatory states. Additionally, faster stimulus rates caused amplitude depression, particularly at the vertex, but did not eliminate the attention effects. The study concludes that selective visual attention modulates distinct neural generators depending on the scalp recording site. The vertex N1 enhancement likely reflects general attentional processes similar to those in the auditory modality, whereas occipital P1 and P2 enhancements may reflect modality-specific visual processing. By controlling for fixation and stimulus randomness, the authors provide robust evidence that early VEP components are genuine physiological correlates of spatial selective attention, distinct from later, modality-nonspecific components like P3.

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Topics

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• attention selective divided
• useful field of view