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. 2019 Jul 11;10:1610. doi: 10.3389/fpsyg.2019.01610

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Copyright © 2019 Mei, Chen and Dong.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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The schematic description of the trial sequences for the two-interval forced choice (2IFC) task and trial types in Experiment 1. The sad-previous trial (A) and happy-previous trial (B) were displayed separately. In each trial, the first facial expression was presented for 1000 ms, followed by a 1000 ms noise mask and a 250 ms fixation cross. Then the second facial expression was presented for 500 ms, and after a 1000 ms noise mask, the question “which facial expression was more sad” (Experiment 1a) or “which facial expression was more happy” (Experiment 1b) appeared until participants made a response by pressing “1” or “2” on the keypad. The next trial started after a 1500 ms intertrial interval. We classified the trial types based upon the position of the n-back first emotional expression in the morph continuum (see Analysis for details).