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Howard Hock, Lori Daniels, David Nichols; The Effect of Spatial Attention on Pupil Dynamics. Journal of Vision 2010;10(7):87. doi: https://doi.org/10.1167/10.7.87.
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Although it is well known that the pupil responds dynamically to changes in ambient light levels, we show for the first time that the pupil also responds dynamically to changes in spatially distributed attention. Using a variety of exogenous and endogenous orientating tasks, subjects alternated between focusing their attention on a central stimulus and spreading their attention over a larger area. Fourier analysis of the fluctuating pupil diameter indicated that: 1) pupil diameter changed at the rate of attention variation, dilating with broadly spread attention and contracting with narrowly focused attention, and 2) pupillary differences required changes in attentional spread; there were no differences in pupil diameter between sustained broad and sustained spread attention. Given that broadly spread attention increases the relative activation of large receptive fields and narrowly focused attention increases the relative activation of small receptive fields (Balz & Hock, 1997), the current results indicate that changes in attention spread can be mediated by changes in pupil diameter. Attention is narrowed in order to extract detailed, high spatial frequency information from a stimulus. This information remains available in the retinal image when attention is narrowly focused because the pupil is constricted, minimizing spherical aberration (blur). Attention is broadened in order to attend simultaneously to stimulus information spread over a large region. The pupil is dilated when attention is broadly spread, so spherical aberration (blur) decreases the activation of small receptive fields by reducing the high spatial frequency content of the retinal image. In effect, the large receptive fields that mediate broad spatial attention are “selected” by the dilated pupil.
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