Previous research on the superior temporal sulcus (STS) has shown that it responds more to facial expressions than to neutral faces. Here, we extend our understanding of the STS in two ways. First, using targeted high-resolution fMRI measurements of the lateral cortex and multivoxel pattern analysis, we show that the response to seven categories of dynamic facial expressions can be decoded in both the posterior STS (pSTS) and anterior STS (aSTS). We were also able to decode patterns corresponding to these expressions in the frontal operculum (FO), a structure that has also been shown to respond to facial expressions. Second, we measured the similarity structure of these representations and found that the similarity structure in the pSTS significantly correlated with the perceptual similarity structure of the expressions. This was the case regardless of whether we used pattern classification or more traditional correlation techniques to extract the neural similarity structure. These results suggest that distributed representations in the pSTS could underlie the perception of facial expressions.

The successor representation was introduced into reinforcement learning by Dayan ( 1993 ) as a means of facilitating generalization between states with similar successors. Although reinforcement learning in general has been used extensively as a model of psychological and neural processes, the psychological validity of the successor representation has yet to be explored. An interesting possibility is that the successor representation can be used not only for reinforcement learning but for episodic learning as well. Our main contribution is to show that a variant of the temporal context model (TCM; Howard & Kahana, 2002 ), an influential model of episodic memory, can be understood as directly estimating the successor representation using the temporal difference learning algorithm (Sutton & Barto, 1998 ). This insight leads to a generalization of TCM and new experimental predictions. In addition to casting a new normative light on TCM, this equivalence suggests a previously unexplored point of contact between different learning systems.

Expertise can increase working memory (WM) performance, but the cognitive and neural mechanisms of these improvements remain unclear. Here, we used functional magnetic resonance imaging to assess the degree to which expertise acquisition is supported by tuning of occipitotemporal object representations and tuning of prefrontal and parietal networks that may support domain-specific WM skills. We trained subjects to become experts in a novel category of complex visual objects and examined brain activity while they performed a WM task with objects from the expert category and from an untrained category. Visual expertise training resulted in improved recognition of expert, compared with untrained objects, and this effect was eliminated in a behavioral experiment by stimulus inversion. These behavioral changes were accompanied by increased recruitment of bilateral dorsolateral prefrontal, posterior parietal, and occipitotemporal cortices during WM encoding and maintenance. Across subjects, behavioral measures of expertise reliably predicted increased activation during maintenance of expert objects in all three regions. These neural expertise effects could not be attributed to differences in low-level stimulus characteristics between the two categories, familiarity with features of expert-domain objects, or familiarity with the WM task. These results are consistent with the idea that visual expertise improves WM performance through tuning of occipitotemporal object representations and through development of lateral prefrontal and posterior parietal networks that mediate the application of domain-specific mnemonic skills.

The authors investigated two retrieval-monitoring processes. Subjects studied red words and pictures and then decided whether test words had been studied in red font (red word test) or as pictures (picture test). Memory confusions were lower on the picture test than on the red word test, implicating a distinctiveness heuristic. Memory confusions also were lower when study formats were mutually exclusive (the same item was never studied as both a red word and a picture), compared with a nonexclusive condition, implicating a recall-to-reject process. When the to-be-recollected events were pictures, older adults used each monitoring strategy as effectively as did younger adults.

No abstract