The Joint Effect of Social Comparison and Social Distance on Evaluation of Intertemporal Choice Outcomes in Event-related Potential Studies

Summary

This protocol aims to investigate the neural activity related to social comparison and social distance during the processing of intertemporal decision outcomes. Indifference points will be measured using event-related potentials as part of the study.

Abstract

Intertemporal choice plays a crucial role in our daily lives, influencing decisions related to education, health, consumption, and investment. This research proposes an innovative experimental protocol that examines how social comparison and social distance jointly affect the neural processes involved in outcome assessment for intertemporal choices. The study is based on the theoretical framework of cognitive resource competition. This protocol enables researchers to dynamically establish an indifference point for each participant, effectively eliminating the influence of any biased indifference points on the assessment of intertemporal choices. Consequently, the study solely measures the combined impact of social comparison and social distance on how participants evaluate intertemporal choice outcomes. The findings reveal that individuals are more inclined to opt for immediate outcomes under negative unfair conditions. Moreover, compared to the fair and positive unfair conditions, people tend to undervalue delayed outcomes in the negative unfair condition. The strength of this approach lies in its dynamic indifference point setting, making it an effective method to investigate the influence of various external factors (such as social status and power level) on intertemporal decision-making. While the protocol is designed to measure electrophysiological events like event-related potentials, it can also be tailored for use with fMRI.

Introduction

In daily life, people often face the choice of enjoying the present or investing in the future. This decision, known as intertemporal choice, requires individuals to weigh the value of outcomes at different time points^1,2,3. Over time, the subjective evaluation of outcomes declines hyperbolically or quasi-hyperbolically^4,5,6,7. People tend to prefer small-but-immediate gains over larger-but-later ones⁸.

Previous research has examined various factors influencing intertemporal decision-making. For instance, D. Wang et al.⁹ explored self-other differences in intertemporal decision-making and found that decisions made for oneself or friends tend to prefer delayed larger rewards over immediate smaller rewards compared to decisions made for strangers. The closeness of social relationships affects individuals' perception of time, thereby impacting their intertemporal decision-making. Similarly, Zhao et al.¹⁰ conducted experiments on self-other decision-making in time-based intertemporal choice. The results revealed that participants tend to opt for the smaller immediate option when making decisions for others, but they prefer the large-but-later option for themselves, highlighting the influence of personal interests on the intertemporal decision-making process.

While previous studies have focused on the behavioral and psychological aspects of intertemporal decision-making, they have not provided a direct understanding of the cognitive process or an in-depth analysis of the underlying neural mechanisms. However, an increasing number of recent studies have employed the event-related potentials (ERPs) method to explore intertemporal decision-making and its neurocognitive processes. ERPs refer to the measured brain responses resulting from specific sensory, cognitive, or motor events¹¹. The use of ERPs offers two significant advantages for studying intertemporal decision-making. Firstly, its high temporal resolution enables the differentiation of the temporal sequence of different cognitive processes. Secondly, ERPs components can serve as indicators of specific cognitive processes. For instance, H. Y. Zhang et al.¹² utilized ERPs to investigate the effect of social distance on outcome comparison between individuals and their partners. They concluded that personal closeness moderates individuals' subjective sensitivity during the outcome comparison phase. The study also found that participants expressed greater satisfaction with the loss outcomes of dislikeable players. ERPs components were employed to analyze influential cognitive processes, showing that this higher satisfaction with loss outcomes for dislikeable players resulted from subjects' increased sensitivity to evaluative, motivational, and emotional processes involved in social comparison.

Previous studies have primarily focused on the competition for cognitive resources between immediate and delayed options in intertemporal decision-making. However, the brain simultaneously processes various tasks, including social comparison and social distance, which further competes for limited cognitive resources. As a result, fewer cognitive resources are allocated to the intertemporal decision-making task. To accurately investigate the influence of external factors on intertemporal decision outcomes, it is crucial to identify the equilibrium state of cognitive resource allocation between immediate and delayed outcome evaluation. In the equilibrium state, individuals assign the same subjective value to the delayed outcome as they do to the immediate outcome. However, if external factors, such as social comparison and social distance, are given more weight in the equilibrium state, it disrupts the cognitive resource balance in intertemporal decision-making. As a result, the cognitive difference between the equilibrium and inequilibrium state can precisely reflect the impact of external factors on the evaluation of intertemporal decision results. The "indifference point" represents the balance point of the delayed outcome on a fixed date in the future, equivalent to the subjective value of the immediate outcome¹³. Some existing studies on intertemporal decision-making have not set the indifference point for each participant in their experimental paradigm. Instead, they calculate the subject's time discount rate in advance using a delay discount task (DDT) and categorize participants into high and low time discount rate groups. Consequently, the results of studies exploring external factors influencing intertemporal decision-making become inconsistent due to the imbalanced allocation of cognitive resources between immediate and delayed option evaluation^14,15,16.

Only a limited number of studies have explored the combined influence of social comparison and social distance on individuals' intertemporal decision-making, and even fewer have utilized the ERPs technique. Consequently, the underlying neural mechanism of intertemporal choice outcome evaluation in the presence of both social factors remains unclear. Existing studies on the impact of external factors on intertemporal decision-making have suffered from inadequate setting of indifference points for delayed outcomes, leading to potential deviations in measuring the effect of these external factors. Different individuals may assign different subjective value evaluations to the same amount of rewards, necessitating the setting of individualized indifference points for each participant to eliminate interference caused by inequitable cognitive resource allocation during intertemporal outcome evaluation. A new experimental paradigm, in which the indifference point for delayed outcomes is determined in advance, is essential to address this issue. A previous study proposed such a paradigm with a fixed one-month delay outcome indifference point, yielding results consistent with expectations from cognitive resource competition theory¹⁷. Though setting an indifference point in advance may introduce bias, it can still effectively influence participants through psychological cues and cognitive reinforcement.

In contrast to prior research where participants merely observed intertemporal choices without direct personal involvement, the current study presents a novel experimental paradigm. Participants are not only engaged in the gambling task but also required to compare their outcomes with others who transition from being strangers to friends. This paradigm explores both individual self-interest in intertemporal choices and the cognitive processing of social comparison, significantly differing from previous investigations. By having participants report their indifference points for one-month delayed outcomes in the DDT task and subsequently using these self-reported indifference points as the delay option's outcome in the upcoming intertemporal decision-making task, this study aims to provide a pure measurement of the joint influence of social comparison and social distance on outcome evaluation in intertemporal decision-making, assuming no glitches occur during the indifference point setting process.

People not only need to perceive interpersonal relationships but also engage in social comparison by comparing their outcomes with others. However, it is unclear whether the interpersonal perceptual task and the social comparison task consume cognitive resources independently or compete for resources during the integrated assessment of the time value of intertemporal choice outcomes. The N100 is a negative deflected brain wave occurring within a 100 ms time window after an event, considered an indicator of attention distribution before comprehensive outcome evaluation. Its amplitude decreases as the number of attention resources increases¹⁸. Liu et al.¹⁹ found a significant effect of social distance during the early N100 stage of outcome processing, suggesting that individuals tend to compare themselves with close people on the ability dimension during the primary stage of outcome processing. Additionally, Mason et al.²⁰ argued that subjects exhibited more negative N100 amplitudes in response to immediate rewards compared to delayed rewards, indicating that temporal delay is encoded in early neural processing.

The P300 is a positive deflected brain wave appearing around 300 ms after an event, serving as a direct index of outcome evaluation. A larger P300 amplitude indicates a higher attentional allocation and more exhaustive outcome assessment¹². H. Y. Zhang et al.¹² demonstrated that the P300 was larger during the outcome evaluation phase of gambling with dislikeable players, reflecting participants' stronger motivation to outperform dislikeable players. Moreover, anxious individuals may struggle with concentrating or focusing on anything beyond their present worries due to their avoidance of future uncertainties²¹. An ERP study on the influence of anxiety levels on intertemporal choice outcomes showed that highly anxious individuals exhibited a significantly more positive P300 amplitude when seeing the immediate option compared to the delayed option²². According to resource allocation theory, cognitive resources allocated to the intertemporal decision-making task are reduced during the comprehensive outcome assessment phase. Hypothesis 1 proposes competition for cognitive resources between the interpersonal perceptual task, social comparison task, and intertemporal decision-making task at different cognitive stages. At the electrophysiological level, there are main or interaction effects for social distance and time delay on the N100 component, and for social comparison and time delay on the P300 component.

Based on cognitive resource competition theory, when additional tasks such as social comparison and interpersonal perceptual tasks are introduced, they compete for limited cognitive resources with the intertemporal decision-making task. As a result, fewer cognitive resources are available for the intertemporal decision-making task, leading to a lack of elaborate processing of the time effect on outcome evaluation. This results in individuals having a reduced sensitivity to time and a smaller time discounting rate. In light of this theory, hypothesis 2 is proposed for the present study: when participants face both social comparison and interpersonal perceptual tasks simultaneously, they will have a higher evaluation for delayed outcomes. Specifically, compared to immediate rewards, delayed rewards will elicit a more positive P300 amplitude at the EEG level. This effect is expected due to the increased competition for cognitive resources, leading to a stronger attentional allocation and more exhaustive evaluation of delayed outcomes.

According to D. Kahneman²³, attention is divisible, and the allocation of attention is a matter of degree. When faced with multiple parallel tasks, individuals prioritize them based on their relevance to self-interest and allocate cognitive resources accordingly²⁴. However, numerous studies have indicated that an inferior task with limited cognitive resources may be susceptible to interference and have negligible effects on other tasks. This could be due to a significant disparity in cognitive resource allocation between tasks of different priorities. In the present experimental paradigm, the intertemporal decision-making task is considered a superior task directly linked to self-interest, thus receiving the highest priority in cognitive resource allocation. Compared to the social comparison task and the interpersonal perceptual task, the intertemporal decision-making task is allocated cognitive resources at least one order of magnitude higher. Hypothesis 3 proposes that despite the simultaneous processing of the social comparison task and the interpersonal perceptual task, individuals will rate the immediate and delayed outcomes equally. This means that there will be no significant difference in the P300 component of neural activities between immediate and delayed outcome conditions. This hypothesis is based on the premise that the intertemporal decision-making task receives significantly more cognitive resources due to its higher priority, making the cognitive resource competition between immediate and delayed outcomes less pronounced. As a result, individuals would evaluate the two outcomes equally at the neural activity level.

When individuals perceive that their reward is less than what others receive, they often experience feelings of dissatisfaction and anger. This realization can motivate them to either seek changes in the current situation or withdraw from comparisons altogether to establish a perceived sense of fairness²⁵. In an unfairly disadvantaged circumstance, a significant disparity in rewards can negatively impact an individual's self-esteem, leading them to avoid comparing themselves with others and redirecting cognitive resources to a less challenging task²⁶. As a psychological defense mechanism, individuals facing an unfair disadvantage comparison condition will reallocate cognitive resources from the social comparison task to the intertemporal decision-making task. Higher time discounting rates are associated with greater cognitive resource allocation. Based on the above understanding, the present article proposes hypothesis 4: in comparison to both fair or unfair advantage conditions, subjects will assign lower evaluations to delayed rewards in the unfair disadvantage condition. At the electrophysiological level, this is expected to be reflected in a smaller P300 component elicited by delayed rewards in the unfair disadvantaged condition. This effect occurs due to the reallocation of cognitive resources to the intertemporal decision-making task, leading to reduced attentional allocation and a less exhaustive evaluation of delayed outcomes.

In the context of the unfairly disadvantaged circumstance, the reallocation of increased cognitive resources to the intertemporal decision-making task may not significantly impact the assessment of immediate outcomes. This is because the immediate outcome's time value may not require extensive processing, leading to a lesser influence of cognitive resource reallocation on this aspect. Therefore, hypothesis 5 is proposed, suggesting that in the unfairly disadvantaged circumstance, people are more likely to opt for an immediate reward. At the neural activity level, there will be a distinct difference in the P300 component between the immediate and delayed outcomes due to the different sensitivity of time perception.

Additionally, when individuals are engaged in a gambling task with a friend and face an unfair outcome, fewer cognitive resources will be allocated to the evaluation of the intertemporal choice's outcome due to the demands of perceiving and processing social relationships. Consequently, as a result of reduced cognitive resources, individuals become less sensitive to time in this situation. Hence, hypothesis 6 is raised: compared to interactions with strangers, people will express more satisfaction with delayed rewards in the unfairly disadvantaged condition. This means that delayed rewards will produce a larger P300 component at the neural activity level in the context of interactions with friends compared to strangers.

Protocol

This research scheme was approved by the local and institutional ethics committee and complies with the latest version of the Declaration of Helsinki. All participants provided written informed consent before participating. The participants had normal vision or normal correction and no psychiatric or neurological disorders. The participants did not have drug or psychotropic medication using experience and no perm or hair dyeing history within six months. If subjects had excessive artifacts in the EEG data, they were not included in the subsequent data analysis.

1. Experimental stimuli

1. Stimuli of the Delay Discounting Task (DDT) task
   1. In the DDT task, divide 34 paper cards into an immediate reward card group and a delayed reward card group.
      NOTE: There are two cards printed: '10 CNY now' and '20 CNY now,' respectively, in the immediate reward card group. These cards represent that participants will gain the amount of the reward shown on the card immediately. In the delayed reward card group, the remaining 32 cards are printed with 'X CNY 1 month later,' meaning the participant will receive X CNY one month later. There is a group of 16 cards incrementing from 10 to 25 CNY at 1 CNY intervals, each paired with a '10 CNY now' immediate reward card. Another 16-card group ranges from 20 to 35 CNY, increased by 1 CNY, and paired with a '20 CNY now' immediate reward card. In each trial, an immediate reward card and a delayed reward card, e.g., the '10 CNY now' card and the '11 CNY 1 month later' card, will be presented to the subject at the same time to choose. If an immediate card is chosen, the existing delayed reward card will be replaced by a larger amount delayed one to set a new pair of two cards in the next trial.
2. Stimuli of the gambling task
   1. In the cue phase, ensure that the name of the other participant (in Chinese), Song style, 72 pounds, is displayed in the center of the screen.
   2. In the gambling decision-making phase, ensure that two cards are presented symmetrically on the left and right sides of the fixation in the center of the screen. The card (4.76° × 4.76°) has a blue diamond pattern on the back.
   3. In the feedback phase, ensure that the outcome of the gambling task (in Chinese), Song style, 72 pounds, black, is shown in the center of the screen. Check that the player's outcome is displayed in an upper position while the other's outcome is in a lower position (Figure 1).
      NOTE: For the present study, a 2 (time delay: now vs. 1 month) × 4 (social comparison: small fair, large fair, negative unfair, positive unfair) set of gamble results was designed. The gain conditions are analyzed simply to establish a comparative effect because of the existence of the sign effect in intertemporal choices^27,28. When presented with an immediate reward, the amount of a small outcome is 10 CNY, and a large one is 20 CNY. When shown a delayed reward, the delayed amount is set according to the indifference points of the previous DDT task. The amount of a small outcome is X1 CNY, and a large one is X2 CNY (see step 2.1 for more details). For example, the negative unfair condition in the immediate reward situation means one gets 10 CNY now, while the other participant gets 20 CNY now. The negative unfair condition in the delayed reward situation means one gets a smaller X1 CNY after 1 month, while the other participant gets a larger X2 CNY after 1 month. The other three conditions are the small fair condition, the large fair condition, and the positive unfair condition. The total of 8 outcomes is provided in Table 1.

	Small Fair condition	Negative Unfair condition	Positive Unfair condition	Large Fair Condition
Now	10  Vs  10	10  Vs  20	20  Vs  10	20  Vs  20
1 month	X1  Vs  X1	X1  Vs  X2	X2  Vs  X1	X2  Vs  X2

Table 1: The collection of gambling results. The table depicts the set of 8 social comparison results.

Figure 1: Stimuli of the feedback interface for gambling task. Please click here to view a larger version of this figure.

2. Experimental procedure

1. Perform the first stage task, a DDT task (Figure 2), to measure the participants' indifference points²⁹, before participants perform Electroencephalogram(EEG) recordings.
   1. Give the participant two cards to choose, one of which is a fixed amount of 10 CNY (or 20 CNY) that they could get immediately, and the other card is a variable amount of money which means the participant could obtain after 1 month, and the variable amount is gradually increased 1 CNY for each trial from 10 CNY to 25 CNY (or 20 CNY to 35 CNY). If the participant chooses the card with the immediate reward, he/she continues to the next trial.
   2. Change the variable amount card to set a new pair of two cards and ask the participant to make a new choice.
      NOTE: The experiment is stopped when the participant chooses the delayed reward card. Then, the amount of the delayed reward card X₁ (or X₂) is regarded as the indifference point for 1 month later of this participant.
2. Perform the second stage task, a gambling ERPs task (Figure 3), to explore the joint effect of social comparison and social distance on evaluating intertemporal choice outcomes.
   1. Display the fixation in the center of the screen, with a random duration from 400-600 ms.
   2. Display the opponent's name in the cue interface for 1000 ms, to inform the player who will complete the forthcoming gambling task.
   3. Present two cards symmetrically on the left and right sides of the fixation in the center of the screen. Ask the player to choose a card with an external numeric keypad. Press 1 on the keypad to choose the left card, and press 3 to choose the right card.
   4. Highlight the selected card with a red rim for 1000 ms after the participant makes the decision.
   5. Display the outcomes of both the participant and the opponent for 1000 ms.
   6. Display a blank screen for 500 ms.
      NOTE: Participants were instructed to engage in a gambling game with either a friend or a stranger. At the start of the game, the participants were presented with the opponent's name to play with. Subsequently, two poker cards appeared on the screen, each capable of winning a certain amount of money, with the value varying over time. The participants were then asked to press a specific button on an external keyboard to select either the left or right card. Once chosen, the selected card would be circled with a red border. Finally, the gambling results of both the participants and their respective matchmakers were presented.

Figure 2: The process of the Delay Discounting Task (DDT). Please click here to view a larger version of this figure.

Figure 3: Time course of a single trial. The figure depicts the procedure of a single trial for the gambling task. Please click here to view a larger version of this figure.

3. Experimental preparation and electrophysiological recording

1. Recruit a pair of participants who are friends and gender-matched. Recruit an extra participant who is completely unfamiliar with either of the other two and gender-matched.Ask only one of the pair of friends to make a response to the task and wear the electrode cap (see Table of Materials); the rest of the two other participants are not required to make any reactions and just observe the screen.
   NOTE: 10 pairs of subjects (19 males and 1 female) were recruited from the undergraduate and graduate students of Harbin Engineering University to participate in the experiment, ranging in age from 18 to 28 years old (M = 22.35, SD = ±3.21). Due to excessive artifacts, the data of 2 subjects (1 female) were discarded.
2. Introduce the equipment and materials required for the experiment and the relevant procedures (including the experimental task and required time) to the participants after arriving at the lab. Help participants understand the basic situation of the experimental process and remove their worries.
3. Ask participants to read and sign the informed consent form before the experiment.
4. Guide participants to clean their hair with neutral shampoo and dry it completely.
5. Instruct participants to enter the experimental room and sit in a comfortable chair ~1 m far from the screen.
6. Start the DDT task (step 2.1) to record the indifference points (X₁ and X₂) of the participant.
7. After the DDT task, use the alcohol and facial scrub, respectively, to scrub the participant's skin gently for corresponding electrodes on the tip of the nose, as reference electrodes, on the above and below of the left eye about 10 mm, near the outer canthus of both sides and on the left and right mastoids.
8. Put the electrode caps with 64 Ag/AgCl electrodes (see Table of Materials) on the participant's head. Ensure that the midline electrodes of the electrode cap coincide with the extension line of the subject's nasal tip.
   1. Position the CZ electrode at the top of the head. Confirm the position of the cap. FP1 and FP2 position is located 2 cm above the root of the participant's nose, and T3, T4 electrodes are placed 2 cm above the ear tip.
9. Fill the conductive gel and tighten the external electrodes with an adhesive bandage, i.e., the vertical electrooculography electrodes, the horizontal electrooculography electrodes, the mastoid electrodes of M1 and M2, and the reference electrode.
10. Tighten the strap of the electrode cap on the chin to prevent the electrodes from shifting during the experiment with moderate tightness.
11. Reduce all electrodes' impedances to below 10 kΩ (the commonly used impedance threshold is 5 kΩ or 10 kΩ). Follow the mentioned procedure:
    1. Switch the recording software (see Table of Materials) to the impedance monitoring interface.
    2. Fill the internal cylindrical space of all electrodes in the cap with conductive gel with a blunt-tipped syringe to ensure that the scalp is properly connected to the electrode.
    3. Observe the real-time impedance value on the display until the impedance falls below the threshold.
12. Inform the participants that the experiment will be conducted in a closed and quiet environment, make the participants relax, and avoid excessive blinking and body movement during the experiment.
13. Display a guide on the screen prior to the beginning of the experiment to keep the participants aware of experimental procedures and appropriate responses.
14. Start the gambling task (step 2.2) in the E-prime software (see Table of Materials). Execute 10 practice trials to help the participants understand the experimental procedures.
15. Implement the formal experiment session, including 480 trials, and record the EEG signals. Divide all trials into 6 blocks, allowing the participants to take a break of 2 min at the end of each block.
16. Save the recorded EEG data and assist the participants in removing the electrode cap. Help the participants wash the conductive gel residue from hair or skin.
17. Use the IOS scale³⁰ to measure each participant's degree of self-inclusion in friends or strangers and test the social distance manipulation.
18. Thank the participants for participating in the experiment and pay them a reward.
    NOTE: Each participant was paid 40 Chinese yuan (CNY) for this experiment.

Results

IOS scale result
The IOS scale score³⁰ was used to examine the social distance and self-relevance of the participants to friends and strangers, and it was found that the social distance of the participants to friends (6.20 ± 0.696) was higher than the social distance of the participants to strangers (1.45 ± 0.605), t(19) = 21.978, p < 0.001, 95%, Cl = (4.30 - 5.20), revealing that the social distance manipulation is effective.

Discussion

Experimental results and significance
Generally, additional tasks, such as social distance perception and social comparison, compete for cognitive resources with the intertemporal decision-making task at different cognitive stages. Firstly, both social distance and time delay have main effects on N100 amplitude, respectively. The present results indicate that gambling with friends induces a greater N100 amplitude than with strangers. Moreover, immediate outcomes elicit greater N100 amplitude than d...

Materials

Name	Company	Catalog Number	Comments
Electrode caps	Neurosoft Labs, Inc, USA	64 Ag/AgCl electrodes	with a configuration of the international 10–20 system of electrode
E-Prime software	Psychology Software Tools, Inc, USA	2	Experimental generation system for computerized behavior research
Liquid Crystal Display Monitor	ROYAL PHILIPS, Netherlands		Display experimental procedure
NeuroScan Synamp2 Amplifier	Neurosoft Labs, Inc, USA		bandpass filter 0.05-100 Hz, sampling rate 1000 Hz