Decreased perceptual sensitivity during attention shifts

Both saccades and attention shifts are cognitive mechanisms for relocating the focus of information processing to different spatial locations. While it is known that visual sensitivity decreases during saccades (i.e., saccadic suppression) to support stable visual experience, here we asked whether attention shifts would also cause reduced perceptual sensitivity. In Experiment 1, we measured phases of the rhythmic spontaneous shift of attention between two task-relevant locations. To estimate the perceptual sensitivity at different attention states, a task-irrelevant visual probe was presented in the background at varying phases of attention oscillation, and the amplitudes of pupil constrictions induced by the probe were measured. Results showed a reduction in pupil constriction during attention shifts, indicating a decrease in perceptual sensitivity. Additional tests with a single-location attention task revealed an absence of modulation of pupil constriction, confirming that the reduced sensitivity was due to attention shifts and not to rhythmic attention sampling. In Experiment 2, instead of relying on pupil constriction, MEG responses to the probe stimulus were used to estimate the perceptual sensitivity during attention shifts. The experimental design was similar to that used in Experiment 1, and the results showed a decrease in MEG responses in the occipital region during attention shifts. Further analysis identified that the modulation of MEG response peaked around 150-200 ms after the probe onset, indicating that the modulation occurs at a late stage compared to that in the saccadic suppression. Additionally, a whole-brain analysis revealed that the decreased response was primarily located in the parietal region. Taken together, our findings suggest that attention shifts over space are accompanied by decreases in visual sensitivity, likely due to suppressive top-down modulation from the parietal attention network to the early visual cortex.