exogenous

Meaning: Exogenous means caused by something outside the individual or system being studied; endogenous means arising from within. In attention research, an exogenous cue is a sudden, salient external event, such as a flash, a loud noise or abrupt movement, that tends to draw attention to its location quickly and reflexively, even when the person was not trying to look there. This is bottom-up processing, driven by the stimulus. Endogenous attention is guided by goals, instructions or expectations (top-down) and is usually slower to deploy and easier to sustain. In biology, an exogenous substance, such as a hormone given as a supplement, comes from outside the body.

On the MCAT: A passage describes a cueing task. A cue appears, then a target appears at the cued or an uncued location, and reaction times are compared. A peripheral flash is the typical exogenous cue; a central arrow telling the participant where to look is the typical endogenous cue. Reaction times are generally faster when the cue correctly predicts the target location. Other questions ask you to classify a scenario: turning toward a fire alarm is exogenous, while scanning a crowd for a friend is endogenous.

Common confusion: Students mix up exogenous and endogenous. Exogenous is linked to the external stimulus and bottom-up processing; endogenous is linked to internal goals and top-down processing. The word describes what triggers the shift in attention, not whether the environment is involved at all.