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Perirhinal cortex (PrC) has long been implicated in familiarity assessment for objects and concepts. However, extant studies have mostly focused on changes in familiarity induced by recent exposure in laboratory settings. There is an increasing appreciation of other types of familiarity signals, in particular graded familiarity of object concepts accumulated throughout one’s lifetime. In prior work (Duke et al., 2017, Cortex, 89, 61–70) that investigated neural correlates of lifetime familiarity, PrC has been shown to track familiarity ratings when participants make related judgements. A theoretically important characteristic of familiarity is its automaticity. Support for this idea comes from documented modulation of behavioural performance, and of PrC signals, by recent exposure under conditions in which this exposure is not task relevant. In the current fMRI study, we aimed to determine whether PrC also tracks lifetime familiarity of object concepts automatically, and whether this type of familiarity also influences behavior when it is not task relevant. During scanning, neurotypical participants (N=30, age range 18-40, 7 males) provided animacy judgement about concrete object concepts presented at differing frequencies in an initial study phase. In a subsequent test phase, they made graded judgements of recent or lifetime familiarity. Behavioural performance showed sensitivity to both types of familiarity even when it was not relevant for the task at hand. Across five sets of fMRI analyses, we found that PrC consistently tracks recent and lifetime familiarity of object concepts regardless of the task at hand. Critically, while several other temporal-lobe regions also showed isolated familiarity effects, none of them tracked familiarity with the same consistency. These findings demonstrate that PrC automatically tracks multiple types of familiarity. They support models that assign a broad role in the representation of information about object concepts to this structure. |
