1. Neuroscience
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Tracking prototype and exemplar representations in the brain across learning

  1. Caitlin R Bowman  Is a corresponding author
  2. Takako Iwashita
  3. Dagmar Zeithamova  Is a corresponding author
  1. Department of Psychology, University of Oregon, United States
  2. Department of Psychology, University of Wisconsin-Milwaukee, United States
Research Article
Cite this article as: eLife 2020;9:e59360 doi: 10.7554/eLife.59360
10 figures, 3 tables and 1 additional file

Figures

Category-learning task.

Conceptual depiction of (A) exemplar and (B) prototype models. Exemplar: categories are represented as individual exemplars. New items are classified into the category with the most similar exemplars. Prototype: categories are represented by their central tendencies (prototypes). New items are classified into the category with the most similar prototype. (C) Example stimuli. The leftmost stimulus is the prototype of category A and the rightmost stimulus is the prototype of category B, which shares no features with prototype A. Members of category A share more features with prototype A than prototype B, and vice versa. (D) During the learning phase, participants completed four study-test cycles while undergoing fMRI. In each cycle, there were two runs of observational study followed by one run of an interim generalization test. During observational study runs, participants saw training examples with their species labels without making any responses. During interim test runs, participants classified training items as well as new items at varying distances. (E) After all study-test cycles were complete, participants completed a final generalization test that was divided across four runs. Participants classified training items as well as new items at varying distances.

Regions of interest from a representative subject.

Regions were defined in the native space of each subject using automated segmentation in Freesurfer.

Behavioral accuracy for interim and final tests.

(A) Mean generalization accuracy across each of four interim tests completed during the learning phase. Source data can be found in Figure 3—source data 1. (B) Mean categorization accuracy in the final test. Source data can be found in Figure 3—source data 2. In both cases, accuracies are separated by distance from category prototypes (0–3) and old vs. new (applicable to distance two items only). Error bars represent the standard error of the mean. 

Behavioral model fits.

Scatter plots indicate the relative exemplar vs. prototype model fits for each subject. Fits are given in terms of negative log likelihood (i.e., model error) such that lower values reflect better model fit. Each dot represents a single subject and the trendline represents equal prototype and exemplar fit. Dots above the line have better exemplar relative to prototype model fit. Dots below the line have better prototype relative to exemplar model fit. Pie charts indicate the percentage of individual subjects classified as best fit by the prototype model (in blue), the exemplar model (in red), and those similarly fit by the two models (in grey). Model fits were computed separately for the 1st half of the learning phase (interim tests 1–2, A,D), the 2nd half of the learning phase (interim tests 3–4, B,E), and the final test (C,F). Source data for all phases can be found in Figure 4—source data 1.

Neural prototype and exemplar model fits.

Neural model fits for each region of interest for (A) the first half of the learning phase, (B) the second half of the learning phase, (C) the overall learning phase (averaged across the first and second half of learning), and (D) the final test. Prototype fits are in blue, exemplar fits in red. Neural model fit is the effect size: the mean/SD of ß-values within each ROI, averaged across appropriate runs. VMPFC = ventromedial prefrontal cortex, ahip = anterior hippocampus, phip = posterior hippocampus, LO = lateral occipital cortex, IFG = inferior frontal gyrus, and Lat. Par. = lateral parietal cortex. Source data for interim tests is in Figure 5—source data 1 and Figure 5—source data 2 for the final test.

Author response image 1
Author response image 2
Author response image 3
Author response image 4
Author response image 5

Tables

Table 1
ANOVA results for model-based fMRI during the learning phase.
EffectdfFPηp2
ROI3.4,95.6 GG3.90.002.12
Model1,282.60.12.09
Learning half1,282.18.15.07
ROI x Model2.9,80.3 GG5.91.001.17
ROI x Learning half3.1,86.9 GG0.53.67.02
Model x Learning half1,280.09.76.003
ROI x Model x Learning Half3.2,89.6 GG2.31.08.08
Table 2
Dimension values for example prototypes and training stimuli from each category.
Dimension values
Stimulus12345678
Prototype A11111111
A111111100
A201110111
A310101111
A411011011
Prototype B00000000
B100000011
B210001000
B301010000
B400100100
Author response table 1
PhaseModelFeature weights (w)Sensitivity
(C)
NeckTailFeetNoseEarsColorBodyPattern
Immediate tests 1-2Exemplar.12.15.16.18.10.11.10.0836.6
Prototype.13.13.15.17.09.12.10.0924.7
Immediate tests 3-4Exemplar.09.15.15.11.15.08.14.1356.1
Prototype.10.15.16.11.12.10.14.1349.3
Final testExemplar.11.16.14.15.13.06.14.1257.9
Prototype.11.15.16.13.11.09.17.0949.7

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