SD; Standard Deviation, M; Mean
To examine the effect of congruity eliminating the encoding difficulty, this study first examined if the chosen word by the pleasantness criterion is recalled more often than those selected by the unpleasantness criterion in pleasant–neutral pairs and those chosen by the unpleasantness criterion are recalled more often than those chosen by the pleasantness criterion in unpleasant–neutral pairs. The words chosen following the pleasantness criterion were recalled as much as those chosen by the unpleasantness criterion in pleasant–neutral pairs; however, those chosen by the unpleasantness criterion were recalled more often than those chosen by the pleasantness criterion in unpleasant–neutral pairs. This result confirmed the hypothesis of the unpleasantness criterion and indicated that the congruity between the criterion of choosing and the type of word pair was critical for the self-choice effects on memory.
According to the integration hypothesis (Toyota et al., 2007), chosen words in the congruous contexts were more effectively integrated into a cognitive structure than those in incongruous contexts. In this study, the words chosen by the unpleasantness criterion were more congruous with unpleasant–neutral pairs than those chosen by the pleasantness criterion. In other words, the words chosen by the pleasantness criterion were incongruous to unpleasant-neutral pairs. The congruity between the chosen word and the context (the word pair in this study) facilitated the integration of the chosen word into one’s cognitive structure. As mentioned above, previous studies (Toyota et al., 2007; Toyota & Kobayashi, 2009; Toyota, 2013) have indicated that an apparent criterion of choice is the determinant of self-choice effects. According to these studies, congruity makes the criterion apparent to facilitate the integration of chosen words into participants’ cognitive structure. Previous studies (Toyota et al., 2007; Toyota & Kobayashi, 2012) have indicated robust self-choice effects and the superiority of the self-choice condition to the forced-choice condition; however, this effect was not observed in this study. The inconsistency between the studies may be because of some differences in the procedure. Specifically, the number of word pairs in a list may be critical. In this study, the number of word pairs assigned to each condition (e.g., pleasant-neutral pairs in the pleasantness criterion in the self-choice condition) was only two, whereas, in previous studies, the number was four. The smaller the number of word pairs, the harder to discriminate the differences between the conditions.
Second, this study examined the hypothesis regarding the negativity bias; the chosen unpleasant words in unpleasant–neutral pairs would be recalled more often than the chosen pleasant words in pleasant–neutral pairs. This hypothesis was confirmed; the words chosen by the unpleasant criterion in unpleasant–neutral pairs were recalled more often than those chosen by the pleasant criterion in pleasant–neutral pairs. Toyota (2014), using the incidental memory procedure, indicated the “negativity bias” in participants with a low ability to manage and regulate emotions. This study also showed the bias in the self-choice effect procedure. However, the difference in the strength of emotion between pleasant and unpleasant words used in this study must be noted. There is a possibility that unpleasant words elicited stronger emotions than pleasant ones. As it is difficult to discriminate the quality and the strength between pleasant and unpleasant emotions, further research is required to control the above possibility.