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Supplementary Material
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Relative contributions of goal representation and kinematic information in self-monitoring
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by chimpanzees and humans
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Takaaki Kaneko and Masaki Tomonaga
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Primate Research Institute, Kyoto University, Inuyama, Aichi, 484-8506, Japan
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Corresponding author (Present Address):
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Takaaki Kaneko
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Department of Psychology, Kyoto University, Yoshida-Honmachi, Kyoto 606-8501, Japan
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E-mail: [email protected], Tel: +81-75-753-2442
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Four Supplementary Figures
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Supplementary References
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Supplementary Movie
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Figure S1. Goal-overlap effect across blocks in chimpanzees
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The mean self-cursor detection times across participants as a function of block order.
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Shaded areas represent 95% confidence intervals (CIs) for the comparison between single
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and multiple conditions. Darker shades indicate where CIs overlap between conditions.
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The results reveal that performance was relatively stable over time. Chimpanzee
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participants performed eight test blocks, whereas human participants performed only one
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test block. This was due to the limited number of available chimpanzees. We increased the
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number of test blocks for each chimpanzee to increase data stability. Here we analyzed the
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temporal changes in chimpanzee behavior across blocks. We performed a three-way mixed-
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model analysis of variance in which block order was included as a fixed factor for the
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analysis in Figure 3. The results showed neither an interaction including block order
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(F(7,35)= 2.0, p = .083, ηp2 = .28 for the interaction with distractor action; F(7,35)= 1.98, p
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= .086, ηp2 = .29 for the interaction with target number; F(7,35)= 0.93, p = .495, ηp2 = .16
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for the two-way interaction with distractor action and target number) nor a main effect of
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block order (F (1,7)= 1.26, p = .297, ηp2 = .20). Therefore, the behavior of chimpanzees was
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relatively stable across blocks during the current task, and the expertise effect could not
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explain the species difference observed in Experiment 1.
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Figure S2. The effect of manipulation accuracy on cursor discrimination. We elimiated the
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possiblity that the accuracy with which the trackball device was manipulated affected our
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results. a). To quantify trackball accuracy, manipulation efficiency was calculated using
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the following fomula: D/T, where D is the direct distance between the initial cursor location
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and the target and T is the actual cursor trajectory. Thus, a value close to one indicates
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very accurate manipulation, whereas imprecise manipulation leads to a lower value. b)
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and c) The mean effciencies of chimpanzees and humans with/without distortion are
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shown. Humans were more efficient than chimpanzees when distortion was absent, but
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the two species performed comparably when distortion was applied for humans. Error bars
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represent 95% confidence intervals (CIs). d) Mean time for cursor discrimination in human
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participants in the presence of distortion. The results are consistent with those for humans
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in the absence of distortion. Error bars represent 95% CIs for comparisons between single
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and multiple conditions. The overall results suggest that the accuracy of trackball
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manipulation is unlikely to explain the species difference in the goal-overlap effect on
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cursor discrimination.
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Figure S3. Mean time for cursor discrimination in eye-tracking experiment (Experiment 2).
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Error bars represent 95% CIs for the comparison between single and multiple conditions.
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The results were consistent with those of Experiment 1. Goal overlap was associated with
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decreased cursor discrimination in chimpanzees, but this effect was absent in humans.
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Figure S4. Temporal changes in relative fixation position.
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The mean distance between the fixation point and the object (target and cursor) is shown
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as a function of fixation order under conditions with/without the distractor. Error bars
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indicate 95% CIs for species comparisons. The species difference in gaze behavior was
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constant across fixation order even during the latter part of a trial, in which the cursors
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had already been discriminated. The mean distance between fixation point and object
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under the distractor condition was analyzed with a mixed-model analysis of variance with
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species, object, and fixation order as fixed factors and participant as a random factor
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nested in species. A similar fixation-pattern tendency was observed from the beginning of a
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trial to the latter part of the trial. An interaction was observed between species and object
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(F(4,44 )= 23.6, p =.001, ηp2 = .68) but no interaction was observed between species and
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order (F(4,44 )= 0.3, p = .87, ηp2 = .03) or among species, order, and object (F(4,44 ) = 0.4, p
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= .79, ηp2 = .04). Cursor discrimination should have been completed in the latter part of
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the trial; however, the species difference in fixation patterns remained from the beginning
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of the trial to the end. Thus, the species difference in gaze behavior cannot be attributed
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solely to the difference in strategy used to perform the task. A clear explanation of why the
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distance between fixation point and object decreased with fixation order remains unknown,
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but it may be partially due to the phenomenon known as the saccadic global effect; that is,
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early fixation (just after stimulus onset) tends to rest between several objects rather than
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directly on one of them (Findlay, 1982).
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Movie S1
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This video shows a chimpanzee performing a test trial.
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Supplementary Reference
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Findlay, J. M. (1982). Global visual processing for saccadic eye movements. Vision
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Research, 22(8), 1033–1045.