Procedure
The following experimental procedures were conducted separately for two groups of 15 and 14 participants, and the second experiment was conducted two weeks after the first experiment.
Study phase. Each participant was given a booklet and explained that the task was to remember one word from each word pair. Subsequently, the task was explained by showing a slide corresponding to each choice condition. The following instructions were provided to each participant.
A familiar Kanji word pair was shown in the middle of each page. For pages corresponding to the self-choice condition, below the word pairs, a question was presented: “Which (of words) do you like better?” in the pleasant criterion, or “Which (of words) do you dislike more?” in unpleasant criterion. For each page like this (corresponding to the self-choice condition), their task was to select one word more pleasant (the word you like better) or unpleasant (the word you dislike more) and to remember it for each pair. For the pages corresponding to the forced-choice condition, a word was underlined, and a question concerning it was presented; ”Do you like this word?” in the pleasantness criterion, or ”Do you dislike this word?” in the unpleasantness criterion.
Examples of these pages are shown in Figure 1. Each participant was also instructed as follows: “As I said before, for each page like this (corresponding to the self-choice condition), your task is to select one word by circling it that is more pleasant or unpleasant and to remember it for each pair. For each slide like this (corresponding to the forced-choice condition), your task is to remember the underlined word while answering the presented question about underlined word by circling ”Yes” or ”No.” Later, each participant was provided five seconds to remember one word on each page. The experimenter sent a signal ”Next page” every five seconds before moving to the next page. Following the signal, the participants turned the page and remembered the chosen or underlined words.
Free recall test. Following the learning phase, the participants were required to recall and write as many words as possible (the chosen or not chosen in the self-choice condition and the underlined or not underlined words in the forced-choice condition). Three minutes were allowed for this test.
Self-choice Condition
Pleasant–Neutral Pairs
Pleasantness Criterion           Unpleasantness Criterion