With his memory magnetically erased, a monkey knows he is uncertain.

Although intelligence is associated with what one knows, it is also important to recognize and to respond adaptively when one is uncertain. This competency has been examined developmentally and comparatively, but it is difficult to distinguish between objective versus subjective cues to which organisms may respond. In this study, transcranial magnetic stimulation was used to disrupt cognitive processing by a rhesus monkey (Macaca mulatta) in a computerized divided visual field memory task. When magnetic stimulation disrupted neural activity in the cerebral hemisphere that initially processed the visual images, recognition accuracy declined and use of the uncertain response significantly increased, relative to control conditions. Thus, the monkey tended to respond adaptively when he did not know the answer--where uncertainty was produced by targeted disruption of the neural processing of a stimulus--even in the absence of external, objective cues to corroborate his subjective, metacognitive assessment of uncertainty.