Each encoding run was followed by a non-scanned recognition test. Participants were tested on the directly learned (16 AB, 16 BC) and inference (16 AC) associations for each triad type (Figure 1C). On each self-paced test trial, a cue was presented on the top of the screen (e.g., an A stimulus)
and two choice probes were presented at the bottom of the screen (e.g., two B stimuli from different triads). Participants indicated which of the two choice stimuli was associated with the cue. Participants were instructed that on inference trials, the association between the cue click here (A) and the correct choice (C) was indirect, mediated through a third stimulus (B) that shared an association with both the cue and the correct choice during encoding. To control for familiarity, the incorrect choice was a familiar item, but one that was not [directly or indirectly] associated with the cue. The order of test trials was pseudorandom, with the constraint that individual inference trials were tested before the corresponding AB and BC associations to ensure that an AC association was not formed during the test. Because of the repeated study-test nature of the design, participants were instructed prior to scanning that they would be tested on the directly learned associations as well as the indirect relationships.
Participants practiced the encoding and test phases prior to scanning using stimuli different from those Ku-0059436 mw used during fMRI data collection. In a separate scanning session (separated by 1–7 days), an and object/scene encoding localizer and guided recall task was collected for multivoxel pattern classifier training and validation (see Supplemental Experimental Procedures). Whole-brain imaging data were acquired on a 3.0T GE Signa MRI system (GE Medical Systems). During each session, structural images were acquired using
a T2-weighted flow-compensated spin-echo pulse sequence (TR = 3 s; TE = 68 ms; 256 × 256 matrix, 1 × 1 mm in-plane resolution) with thirty-one 3-mm-thick oblique axial slices (0.6 mm gap), approximately 20° off the AC-PC line. Functional images were acquired using a GRAPPA parallel echo-planar imaging (EPI) sequence using the same slice prescription as the structural images (TR = 2 s; TE = 30 ms; flip angle = 90°; 64 × 64 matrix; 3.75 × 3.75 mm in-plane resolution, interleaved slice acquisition). For each functional scan, the first six EPI volumes were discarded to allow for T1 stabilization. An additional high-resolution T1-weighted SPGR scan (sagittal plane, 1.3 mm slice thickness, 1 mm2 in-plane resolution) was acquired during the first scanning session. Head movement was minimized using foam padding. Data were preprocessed and analyzed using SPM5 (Wellcome Department of Cognitive Neurology) and custom MATLAB routines.
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