Supplement to Superior abstract-concept learning by Clark’s nutcrackers (Nucifraga
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Columbiana)
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John F. Magnotti, Jeffrey S. Katz, Anthony A. Wright, & Debbie M. Kelly
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Methods
Subjects. Nine wild-caught Clark’s nutcrackers (5 females) served as experimental
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subjects. Experimental sessions were conducted 5-7 days a week. The nutcrackers were
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maintained at approximately 85-90 % of their ad lib weight and received supplemental feeding
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with a mixture of sunflower seeds, Tradition© turkey starter, mealworms, Lafeber© parrot
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pellets, peanuts, pine seeds and vitamin supplement upon completion of daily sessions The
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nutcrackers were housed individually in cages (71cm high x 47.5cm wide x 48cm deep) within a
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large colony room maintained at a constant temperature of 22º C. A 12-hr light-dark cycle was
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maintained in the colony room.
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Experimental chambers. Nutcrackers were tested in identical (61-cm wide x 31-cm deep
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x 56-cm high) wooden champers. Stimuli were shown on an LCD monitor through a 33-cm
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(wide) x 26-cm (high) cutout. Reinforcers (mealworms) were delivered below the monitor via a
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rotating wheel that advanced on correct responses.
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Stimuli. We used color pictures developed for previous studies of abstract-concept
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learning [1]. For training, the 8 pictures were Apples, Buildings, Cat, Woman’s Face, Flower,
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Glass and Pitcher, Keys, and Orangutan. For transfer testing, novel pictures were tested on
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transfer trials. A picture was only used once during testing. Thus, there were 90 trial-unique
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pictures used over the 6 testing sessions (15 pictures per session). The complete testing set can
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be seen in Figure 4 of [1].
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Stimuli were sized so that the total display (sample and comparison pictures and white
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rectangle) was matched in visual angle to previous work with pigeons and nonhuman primates,
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approximately 69° vertically and 73° horizontally as viewed from the perch (14.5cm from the
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screen) at the average nutcracker height (12 cm). Because the nutcrackers, like pigeons, touch
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the stimuli with their beaks, the visual angle increases as a response is being made. Previous
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studies showing failed transfer by pigeons after 8-item training suggests that this difference in
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response topography cannot guarantee abstract-concept learning [1].
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Experimental Control. Experimental events were controlled and recorded using custom
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Microsoft Visual Basic 6 software running on Microsoft Windows XP. A USB digital I/O panel
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(Phidget) connected the software to the food wheel and chamber lights.
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Supplemental Results
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Acquisition comparison across species. To test the equivalence between species before
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transfer began, we compared accuracy during the last 3 sessions of baseline (Figure S1). A
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repeated-measures analysis of variance (RM ANOVA) on accuracy by Session (3, 2, or 1 session
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before transfer) and Species (nutcracker, rhesus, capuchin, and pigeon) showed moderately
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reliable interaction [F(6, 40) = 2.45, p = 0.04] and session effects [F(2, 40) = 3.10, p = 0.06], but
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a less reliable effect of species [F(3, 20) = 2.05, p = 0.14]. The interaction is driven by small
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increases in performance for pigeons (from 84% to 87%), capuchins (from 82% to 86%), and
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nutcrackers (86% to 87%), but a small decrease for rhesus (from 87% to 82%). Considering only
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the final day before transfer, a one-way ANOVA on accuracy across species yielded no effect of
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species [F(3, 20) = 1.82, p = 0.18]. The total number of trials of baseline training was also
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similar among the nutcrackers (mean = 3300 trials), rhesus (4000), capuchins (3500) and pigeons
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(3000).
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Stability across transfer. To ensure our comparison between baseline accuracy and
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transfer accuracy was conducted during a period of stable performance, we designed a 3-way
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repeated measures analysis of variance to test for the possibility of any bias in responding (e.g.,
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preference for choosing “same”) or change in performance across transfer testing. This 3-way
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RM ANOVA on accuracy by Session (1 to 6), Trial Type (Same/Different) and Stimulus Type
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(Baseline/Transfer) revealed only a main effect of Stimulus Type [F(1, 8) = 46.9, p = 0.0001].
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No other main effects or interactions were significant (all Fs ≤ 4.1, ps ≥ 0.08). The lack of a
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significant effect of trial type (or an interaction with stimulus type) suggests no significant bias
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in responding across birds. The lack of effect due to session suggests no learning occurred during
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transfer testing.
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First session transfer. Although our RM ANOVA results showed no significant change
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in transfer performance across transfer testing, we also analyzed session one transfer
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performance in each nutcracker. For each nutcracker, we compared the number of correct
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responses on transfer trials against baseline performance using the binomial test. Six nutcrackers
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showed transfer performance that was not different from baseline performance (R: baseline =
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83.3% vs. transfer = 100%, p = 0.386; L: 88.8% vs. 90%; p > 0.999; S: 87.8% vs. 80%, p = .350;
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K: 83.3% vs. 80%, p = .677; H: 78.8% vs. 60%, p = 0.235; T: 82.2% vs. 60%, p = 0.085) and
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three showed significantly lower performance on transfer than baseline (B: 82.2% vs. 50%, p =
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0.020; F: 87.8% vs. 50%, p = 0.004; G: 91.1% vs. 60%, p = 0.008). The difference between the
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first-session results and the overall transfer tests is likely due to the lack of sensitivity of the first-
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session binomial tests (low statistical power to reject the null hypothesis of no difference
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between baseline and transfer). We thus take the more conservative results (more likely to show
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a difference between baseline and transfer) from the paired t-tests reported in the main article as
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our test of abstract-concept learning.
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References
[1] Wright, A.A. & Katz, J.S. 2006 Mechanisms of same/different concept learning in
primates and avians. Behavioural Processes 72, 234-254.
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Supplemental Figure
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Figure S1. Percent correct during the final three sessions of 8-item same/different
training for rhesus (N=3; red), nutcrackers (N=9; blue), capuchins (N=3; orange), and pigeons
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(N=9; green). The gray dashed line indicates the 80% acquisition criterion required for transfer
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testing. Error bars are 1 standard error of the mean.