Memory Image Completion: Establishing a task to behaviorally assess pattern completion in humans

Abstract

For memory retrieval, pattern completion is a crucial process that restores memories from partial or degraded cues. Neurocognitive aging models suggest that the aged memory system is biased toward pattern completion, resulting in a behavioral preference for retrieval over encoding of memories. Here, we built on our previously developed behavioral recognition memory paradigm-the Memory Image Completion (MIC) task-a task to specifically target pattern completion. First, we used the original design with concurrent eye-tracking in order to rule out perceptual confounds that could interact with recognition performance. Second, we developed parallel versions of the task to accommodate test settings in clinical environments or longitudinal studies. The results show that older adults have a deficit in pattern completion ability with a concurrent bias toward pattern completion. Importantly, eye-tracking data during encoding could not account for age-related performance differences. At retrieval, spatial viewing patterns for both age groups were more driven by stimulus identity than by response choice, but compared to young adults, older adults' fixation patterns overlapped more between stimuli that they (wrongly) thought had the same identity. This supports the observation that older adults choose responses perceived as similar to a learned stimulus, indicating a bias toward pattern completion. Additionally, two shorter versions of the task yielded comparable results, and no general learning effects were observed for repeated testing. Together, we present evidence that the MIC is a reliable behavioral task that targets pattern completion, that is easily and repeatedly applicable, and that is made freely available online.

Keywords: cognitive aging; eye-tracking; pattern completion bias; recognition memory.

Conflict of interest statement

The authors declared that they have no conflict of interest.

© 2018 The Authors. Hippocampus published by Wiley Periodicals, Inc.

Figures

Figure 1

Experiment 1. (a) Learned stimulus library in all possible levels of completeness (percentages indicate portions of the image that are still visible through the mask) and new stimulus office. (b)Left: performance for both age groups (green: young adults and gray: older adults), separately for learned and new stimuli for the five different levels of stimulus completeness (mean); right: bias measure (see methods for a detailed explanation)—difference in accuracy scores for learned minus new stimuli calculated separately for each participant (mean); positive values indicate a bias toward pattern completion, significant differences from 0 are indicated with * separately for each age group as indicated by color. (c) Exemplary false alarm distribution for new stimulus office showing that older adults chose one particular false response option (library) most often rather than guessed more overall, which would have led to similar frequencies for all five response options. (d) Exemplary fixation heatmaps, warmer colors indicate higher fixation numbers; lower panel: fixation heatmaps for correctly identified stimuli (exemplary: library identified as library) for each masking level (100–5%); top left: fixation heatmap for a response‐matching erroneous response (exemplary: office 21% identified as library), top right: fixation heatmap for a stimulus‐matching erroneous response (exemplary: library 21% identified as new); top middle: fixation overlap—fixation heatmaps for correctly identified stimuli were correlated with heatmaps for stimulus‐matching erroneous responses (stim match), or with response‐matching erroneous responses (resp match). Pearson's correlation coefficients were Fisher's z‐transformed and averaged across stimuli and completeness levels, separately for both age groups (correlation values in the figure were back‐transformed for better comprehensibility), significant differences are indicated with *: stim‐match correlations were overall higher than resp‐match correlations suggesting that the viewing patterns were driven by the stimulus rather than by the response choice, but older adults' fixation patterns for resp‐match stimuli correlated more than those of young adults (and these fixation overlap scores correlated with the response bias in older adults; see Section 3 for details) suggesting that the more likely a participant is to falsely recognize the office as the library, the more the fixation patterns for library and office overlap [Color figure can be viewed at wileyonlinelibrary.com]

Figure 2

Experiment 1. Fixation numbers and durations (mean). Left, during encoding, significant effects are indicated with *; middle, during retrieval in the whole image; right, during retrieval within specific IAs (the parts of the image that still carry information). Data are presented for both age groups (green: young adults and gray: older adults) and all stimulus completeness levels, but collapsed over learned and new stimuli as there were no differences between them; sum of durations in ms [Color figure can be viewed at wileyonlinelibrary.com]

Figure 3

Experiment 2. (a) Exemplary learned stimuli for versions 3 (black) and 4 (orange). (b) Performance for learned stimuli separately for all tested versions (blue: version 1, magenta: version 2, black: version 3, and orange: version 4) and the five different levels of stimulus completeness (mean ± standard error). (c) Performance and bias measures at initial (top) and second testing (bottom) for comparable versions 3 and 4; left: performance separately for learned and new stimuli for the five different levels of stimulus completeness (mean); right, bias measure (see Section 2.5 for a detailed explanation)—difference in accuracy scores for learned minus new stimuli calculated separately for each participant (mean); positive values indicate a bias toward pattern completion [Color figure can be viewed at wileyonlinelibrary.com]