Participants
A total of 30 right-handed individuals with no history of psychiatric or neurological disorders and normal vision (or vision corrected to normal) were recruited for the study. After providing written informed consent, each participant was compensated with ¥75. Ultimately, 28 participants (18 female, mean age = 21.6 years, SD = 1.5 years) were included in the sample, as two participants were excluded due to excessive EEG artifacts. This study was approved by the local Human Ethics Committee for Human Research, and it was conducted in accordance with the guidelines of the Declaration of Helsinki and its subsequent amendments.
Stimuli, apparatus, andprocedure
Participant completed the experiment in a quiet and soundproof laboratory, individually. They were asked to select pictures in four different choice set sizes, and then fill out a choice overload questionnaire to evaluate their experience (Fig. 1A ). The experiment was managed by E-Prime 2.0 (Psychology Software Tools, Inc., Pittsburgh, PA), which controlled the presentation and timing of the stimuli.
In the choice task, each trial consisted of three main stages: fixation (1s), image presentation stage (10s + 0.5s mask) and response (3s) (Fig. 1B ). During the image presentation stage, participants were shown sets of natural landscape images and were asked to select the one they preferred. The sets size varied, containing 4, 8, 12, or 16 clear images, while non-target images were mosaicked (Fig. 1C and D ). The 10-second duration of the image presentation period was determined based on a pilot experiment, allowing participants enough time to make decisions without feeling rushed, and to make use of the period for information processing. The mask was used to reduce the after effect of image presentation. All pictures were obtained from the free image material website (https://www.pexels.com/zh-cn/) with a total of 800 pictures. These images were standardized to 236 × 177 pixels. Each image was only presented once in the same condition. During the response stage, participants used the mouse to select their preferred image from the current selection set. Each condition contained 50 trials, resulting a total of 200 trials. The order of the four conditions was counterbalanced across participants.
Upon the completion of each condition in the choice task, participants were asked to rate the difficulty of selection on a 7-point scale, together with their positive (including satisfaction with the final choice, pleasure, and satisfaction with the selection process) and negative emotions (including regret, hesitation, and frustration), as well as their inclination to avoid making a choice (for example, delaying or abandoning the choice). Additionally, they were prompted to assess whether the choice sets contained the ”right amount of options” on a 7-point scale.