Visual attention and metacontrast modify latency to perception in opposite directions.

In human observers, cue-induced visual attention ('bottom-up' transient focal attention) shortens the latency of perception. Metacontrast reduces the intensity of perception and can even obliterate it. We show that a close relationship exists between both, but that their effects are reversed: cue-induced visual attention not only shortens latency but also intensifies perception, and metacontrast not only lowers intensity of perception but also prolongs latency. A common neurophysiological mechanism for both is possible. Indirect evidence suggests that this could be a subthreshold modulation of neuronal thresholds by de- and hyperpolarization.