Humans are remarkably good at knowing where to expect relevant stuff, given a particular context. For example, we intuitively know that we should expect a computer mouse next to the keyboard, and below the monitor. It has been claimed that we can learn these patterns of expectations without any explicit awareness of knowing them. Although the existence of this form of learning is undisputed, whether or not it happens outside awareness is hotly debated. Furthermore, the brain mechanisms associated with this form of learning are not well-understood.
In the study that was just published, we investigated both (1) the neural mechanisms underlying the acquisition and exploitation of this type of knowledge and (2) the implicit or explicit nature of the expectations acquired. We discovered that the theta rhythm in the right hippocampus is involved in learning the associations between spatial context and the expected location of target objects. Observer’s behaviour in the experiment was marked by a sudden switch from a learning to an exploitation phase. During the exploitation phase, hippocampal theta activity dropped back to baseline levels, while now the theta rhythm in the prefrontal cortex was clearly elevated for the previously learned contexts. We therefore concluded that prefrontal theta is associated with exploiting the learned knowledge.
We asked our participants whether they subjectively had explicit knowledge about the contextual structure of the experiment, and also probed them objectively for such explicit knowledge. About half of the participants formed explicit knowledge, while the other half did not. We expected the ones who did form explicit knowledge to better have been able to exploit the contextual structure of the experiment, but, intriguingly, we found the opposite pattern! Participants without explicit awareness of the association between context (e.g., the keyboard and monitor) and target (e.g., the mouse) were better able to use this knowledge to guide their perception and behaviour.
Interesting stuff, we’d say. You can find the details in the published paper: Spaak & De Lange (2019) Hippocampal and prefrontal theta-band mechanisms underpin implicit spatial context learning. The Journal of Neuroscience. 1660-19. https://doi.org/10.1523/JNEUROSCI.1660-19.2019