Sensory gain control (amplification) as a mechanism of selective attention: electrophysiological and neuroimaging evidence

Hillyard, Steven A.; Vogel, Edward K.; Luck, Steven J. · 1998 · OpenAlex-citations

DOI: 10.1098/rstb.1998.0281

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Summary

This review paper investigates the neural mechanisms underlying selective attention, specifically proposing that sensory gain control (amplification) serves as a primary mechanism for enhancing attended stimuli. The authors address the theoretical debate regarding whether attention operates at early sensory stages or late post-perceptual stages. They distinguish between two potential neural mechanisms: "amplification," which increases the magnitude of stimulus-evoked neural responses, and "tonic bias," which elevates baseline neural firing rates independent of stimulus presence. The paper synthesizes evidence from electrophysiological recordings (event-related potentials, or ERPs) and neuroimaging (PET) to argue that early sensory amplification is a distinct and critical component of visual-spatial attention. The authors analyze data from multiple experimental paradigms, including single-unit recordings in macaque monkeys and human ERP/PET studies. In monkey studies, researchers recorded neural activity in area V4 while subjects attended to locations inside or outside a neuron’s receptive field. These experiments revealed that attention could modulate baseline firing rates (bias) without affecting stimulus-evoked responses, or it could amplify the transient sensory response when both attended and unattended locations fell within the receptive field. In human studies, subjects performed spatial attention tasks where they attended to specific visual field locations while ignoring others. ERPs were recorded to measure the timing and amplitude of sensory-evoked components, particularly the early P1 (80–100 ms) and N1 (140–190 ms) waves. To localize these effects, researchers combined ERP source localization with PET imaging, which measures regional cerebral blood flow (rCBF). The findings demonstrate that directing spatial attention to a location significantly increases the amplitude of early visual ERP components, specifically the P1 wave, without altering its latency or scalp topography. This pattern indicates a pure gain control mechanism rather than the activation of separate neural populations. Crucially, the earliest component, C1 (50–60 ms), which originates in primary visual cortex (V1), remained unaffected by attention. In contrast, the P1 enhancement was localized to extrastriate cortical areas, particularly the fusiform gyrus and ventral-lateral extrastriate cortex. Combined ERP-PET studies confirmed that the cortical regions showing increased rCBF during attention corresponded precisely with the neural generators of the amplified P1 component. Furthermore, these activations were retinotopically organized, appearing in dorsal extrastriate cortex for lower visual field stimuli and ventral regions for upper field stimuli. The significance of these results lies in their strong support for "early selection" theories of attention. The data indicate that attentional modulation occurs at an early stage of visual processing in extrastriate cortex, prior to full stimulus identification. This early amplification improves the signal-to-noise ratio of attended inputs, facilitating more efficient perceptual processing. The paper concludes that sensory gain control is a fundamental mechanism of selective attention, distinct from tonic biasing mechanisms. By separating amplification from suppression and bias, the authors provide a refined framework for understanding how the brain prioritizes relevant sensory information.

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• attention selective divided