The perception of dynamic visual stimuli relies on two apparently conflicting perceptual mechanisms: rapid visual input must sometimes be integrated into unitary percepts but at other times must be segregated or parsed into separate objects or events. Though they have opposite effects on our perceptual experience, the deployment of spatial attention benefits both operations. Little is known about the neural mechanisms underlying this impact of spatial attention on temporal perception. Here we record magnetoencephalography (MEG) in male and female humans to demonstrate that the deployment of spatial attention for the purpose of segregating or integrating visual stimuli impacts pre-stimulus oscillatory activity in retinotopic visual brain areas where the attended location is represented. Alpha-band oscillations contralateral to an attended location are therefore faster than ipsilateral oscillations when stimuli appearing at this location will need to be segregated, but slower in expectation of the need for i...