Abstract
In processing a stream of visual information, visual performance is improved by temporal expectation, the timing predictability of sensory events, and by voluntary temporal attention, the prioritization of sensory events at behaviorally relevant time points. Although temporal expectation and attention are usually interchangeably used, they can be dissociated and may be supported by distinct neural mechanisms. Here, we manipulate temporal attention while holding constant expectation and use concurrent MEG to disentangle the effects of temporal attention and expectation on anticipatory visual cortical dynamics. Observers performed an orientation discrimination task. On each trial, two grating targets (T1, T2) appeared for 50 ms sequentially at the fovea, separated by a 300-ms stimulus onset asynchrony. A precue tone (75% validity) instructed observers to attend to T1 or T2. A response cue tone after the targets instructed them to report the orientation (CW/CCW) of either T1 or T2. Thus, on each trial, one target was attended and the other unattended, whereas their expected timing was fixed. The targets were superimposed on 20-Hz flickering noise, which generated a 20-Hz steady state visual evoked response (SSVER) in the visual cortex. We calculated the intertrial phase coherence (ITPC) of the SSVER signal to continuously measure visual cortical sensitivity. Temporal expectation and attention both affected visual cortical sensitivity to visual stimulation in anticipation of the target stimuli. Temporal expectation was accompanied by a ramping increase in ITPC, starting from the precue up to the expected onset of T1, whether attended or not. Temporal attention modulated the slope of the ramp, such that the slope leading up to T1 was steeper when T1 was attended than unattended. These results suggest temporal expectation and attention jointly act on sensory processing, with temporal attention acting over and above expectation in modulating the anticipatory ramping of visual cortical sensitivity.