Experience sampling reveals the role that covert goal states play in task-relevant behavior

Cognitive neuroscience has gained insight into covert states using experience sampling. Traditionally, this approach has focused on off-task states. However, task-relevant states are also maintained via covert processes. Our study examined whether experience sampling can also provide insights into covert goal-relevant states that support task performance. To address this question, we developed a neural state space, using dimensions of brain function variation, that allows neural correlates of overt and covert states to be examined in a common analytic space. We use this to describe brain activity during task performance, its relation to covert states identified via experience sampling, and links between individual variation in overt and covert states and task performance. Our study established deliberate task focus was linked to faster target detection, and brain states underlying this experience-and target detection-were associated with activity patterns emphasizing the fronto-parietal network. In contrast, brain states underlying off-task experiences-and vigilance periods-were linked to activity patterns emphasizing the default mode network. Our study shows experience sampling can not only describe covert states that are unrelated to the task at hand, but can also be used to highlight the role fronto-parietal regions play in the maintenance of covert task-relevant states.

Increasing stimulus similarity drives nonmonotonic representational change in hippocampus

Studies of hippocampal learning have obtained seemingly contradictory results, with manipulations that increase coactivation of memories sometimes leading to differentiation of these memories, but sometimes not. These results could potentially be reconciled using the nonmonotonic plasticity hypothesis, which posits that representational change (memories moving apart or together) is a U-shaped function of the coactivation of these memories during learning. Testing this hypothesis requires manipulating coactivation over a wide enough range to reveal the full U-shape. To accomplish this, we used a novel neural network image synthesis procedure to create pairs of stimuli that varied parametrically in their similarity in high-level visual regions that provide input to the hippocampus. Sequences of these pairs were shown to human participants during high-resolution fMRI. As predicted, learning changed the representations of paired images in the dentate gyrus as a U-shaped function of image similarity, with neural differentiation occurring only for moderately similar images.

Integrating words that refer to typical sequences of events

The organisation and processing of event concepts in semantic memory is an important issue in language processing and memory research. The present study tested whether pairs of words denoting events that can plausibly occur in sequence (marinate-grill) generate expectancies for a target that denotes a subsequently occurring event (chew). In Experiment 1, two events that tend to occur sequentially primed the third. In Experiment 2, the individual primes (i.e., marinate and grill separately) did not prime their related event targets. Experiments 1 and 2 used a lexical-decision task on the target. Therefore, information from both primes must be integrated to sufficiently activate knowledge of the subsequently occurring target. This is the first study to demonstrate priming among words denoting sequentially occurring events. In Experiment 3, a relatedness decision task, processing of these event triplets was facilitated when the first two event words were presented in a temporally correct order compared with when their order was reversed. These findings are not predicted by spreading activation theory and cannot be simulated by corpus-based models that do not include order-sensitive measures. We interpret the results as evidence for the role of situation models and the use of world knowledge during online language comprehension, even in the absence of sentential contexts.