Selective attention influences sensory processing such that relevant information is preferentially encoded at the expense of irrelevant information. Over the last several decades, multiple electrophysiological and neuroimaging studies in humans and nonhuman primates have shown that attention selectively increases the amplitude, or the gain, of visual responses evoked by attended stimuli compared to responses evoked by unattended stimuli.

Multicellular eukaryotes rose to prominence around the Proterozoic–Phanerozoic transition coupled to evolving ecological interactions between megascopic autotrophs and heterotrophs. Animals in particular are thought to have had a pivotal role as—for example—predators, grazers, and filterers in expanding the food web through interactive processes not available to microbial life.