Internal selective attention is delayed by competition between endogenous and exogenous factors

External selective attention is mediated by competition between endogenous (voluntary) and exogenous (involuntary) factors, with the balance of competition determining which stimuli are selected. Occasionally, exogenous factors “win” this competition and drive the selection of salient but task-irrelevant stimuli. Endogenous and exogenous selection mechanisms may also compete to control the selection of internal representations (e.g., those stored in working memory), but how this competition manifests and whether it is resolved in the same way as external attention is unknown. Here, we leveraged the high temporal resolution of human EEG to determine how competition between endogenous and exogenous factors influences the selection of internal representations. Unlike external attention, competition between endogenous and exogenous factors did not prompt a selection of salient-but-task-irrelevant working memory content. Instead, it simply delayed the endogenous selection of task-relevant content by several hundred milliseconds. Thus, competition between endogenous and exogenous factors influence the allocation of attention in the external environment and within working memory, but through different mechanisms. Significance Statement Sensory inputs can be selected based on endogenous (voluntary) or exogenous (involuntary) factors. During perception, conflict between endogenous and exogenous selection mechanisms can produce attention capture, i.e., an involuntary shift of attention to a salient but otherwise irrelevant stimulus. Endogenous and exogenous factors may also compete to control the selection of internal representations, for example, those stored in working memory. We show that - unlike external attention - competition between endogenous and exogenous factors during the selection of working memory content does not produce a capture-like phenomenon, but instead delays the endogenous selection of task-relevant memory content. This result points to a fundamental difference in how competition between voluntary and involuntary factors shape the selection of external and internal information.