A framework for understanding the relationship between externally and internally directed cognition.

Externally directed cognition (EDC) involves attending to stimuli in the external environment, whereas internally directed cognition (IDC) involves attending internally to thoughts, memories and mental imagery. To date, most studies have focused on the competition or trade-offs between these modes of cognition. However, both EDC and IDC include a variety of cognitive states that differ along multiple dimensions. These dimensions may influence the way in which EDC and IDC relate to each other. In this review, we present a novel framework that considers whether cognitive resources are oriented externally or internally, and also whether a given cognitive state involves intentional (i.e., voluntary) or spontaneous (i.e., involuntary) processing. Within this framework, we examine the conditions under which EDC and IDC are expected to either compete, or co-occur without interference. We argue that EDC and IDC are not inherently antagonistic, but when both involve higher levels of intentionality they are increasingly likely to compete, due to the capacity limitations of intentional processing. In contrast, if one or both involve spontaneous processing, EDC and IDC can co-occur with minimal interference given that involuntary processes are not subject to the same capacity constraints. A review of the brain regions implicated in EDC and IDC suggests that their neural substrates are partially segregated and partially convergent. Both EDC and IDC recruit the lateral prefrontal cortex (PFC) during intentional processing, and may therefore compete over the processes and representational space it supports. However, at lower levels of intentionality, EDC and IDC rely on largely distinct neural structures, which may enable their co-occurrence without interference. The proposal that EDC and IDC can in some cases co-occur, provides a framework for understanding the complex mental states that underlie theory of mind, creativity, the influence of self-evaluative processing on cognitive control, and memory-guided attention.