Experiment V: Social anxiety and the ultimatum game METHOD

Participants

Twenty-five undergraduates from National Cheng-chi University participated in experiment V. All participants were right-handed and had normal or corrected to normal vision. They were recruited by advertisements, signed an informed consent form and were debriefed at the end of the experiment. Eight participants’

data were excluded for both behavior and ERP data analysis.

Material

The ultimatum task

In the ultimatum game, two players are going to make a deal with how to split 100NT in each round. One player will be the proposer who will propose how to split the money, the other will be the responder with accept or reject the offer to finish the deal. In the present study, all the participants played the role of responders. They were asked to accept or reject the money the proposer offered by press either 7 or 9 in the keyboard. The proposer will only give three different kinds of proposes (responders can either get 10 or get 30 or get 50).

Anxiety manipulations

Two anxieties were manipulated, social vs. non-social. The social anxiety was manipulated by telling the participants while they play the game, the researcher will watch their action through the video camera in the other room.

The non-social anxiety was manipulated by playing the white noise while the participants playing the game.

Subjective Rating Question

After the ultimatum task, the subjects were asked to do some subjective ratings of their anxiety states. The questions were from state-trait anxiety inventory (SATI)(Spielberger, C. D.,2005).

Procedure

The participants were first told to read the confirm consent and sign for it if they all agree with the experiment detail. For the reason to make participants to believe that they are going to play the game with real persons. The researcher told them the proposers in the experiment were all the formal participants and the experiment will keep running, so the researcher will take picture of her/him for the future experiment. After then, they were led to the experiment room and seated in a comfortable chair. The researcher explained about how the brain activity will be recorded and the general purpose of this study then attached the electrodes. Next, participants began to play the ultimatum game, the game was began with one practice block in six practice trials and then three experimental blocks in 60 trials of each. They were allowed to make the decision based on their own pace but were told to try not blink their eyes while the stimuli of offer shows.

In the current experiment, the participants were told they would play the ultimatum game under three different conditions, control, white noise and social anxiety. After the ultimatum game session, the participants were then asked to rating their anxiety state by the questions in SATI. In the end of the experiment they participants were again asked to filled some questions about if they feel any difference under three different conditions. Also their were asked if the

manipulations (ex. White noise and someone is watching them play) have some effects on them.

ERP recording and data analysis

Continuous EEG was recorded during the experiment with a sintered Ag/AgCl 64-electrode Quick-Cap and amplified using Neuroscan Synamps 2 with an A/D conversion rate of 500 Hz. A 0.1-30 Hz band-pass filter was also using during the recording and impedance was kept below 10 kΩ. Moreover, the

EEG was initially referenced to reference point in between CZ and CPZ but converted to an average reference off-line. In the Off-line analysis, the EEG was first filtered with high-pass filter 0.01HZ and then low-pass filter 30HZ. After filtering, the EEG was cut into epochs time-locked to offer presentation (-200 pre-stimulus and 1000ms post-stimulus). Following baseline correction to the 200 ms interval preceding the stimulus, epochs containing excessive noise (60μ V) were rejected and the remaining epochs were averaged to create the

event-related potentials (ERPs). Subjects with fewer than 16 artifact free trials in any conditions were eliminated from ERP analyses in the study. In the average ERP data, FRN amplitude was defined as the difference between the most positive peak within 160–240 ms time window and the most negative potential within 240–320 ms time window.

RESULTS Subjective rating

The SATI scores were test a 3(Anxiety states) ANOVA. However, none of the effect was found significant. It showed participants did not reveal any difference on SATI scores.

Behavior results

Acceptance rate and reaction time

Form the response of the questionnaire at the end of experiment, we found that some of the participants had said that they did not really influence by the

manipulations. In order to decrease the influence of individual difference on the manipulation effect, the acceptance rate and reaction time were both tested by adding the responses of the questionnaire as co-variables. A 3(Anxiety states) x 3(offer) ANOVA was tested. No effect was found significant in reaction time. But the main effect of offer was found significant (F_(2,24)=11.089, p<0.00). It showed that the participants accepted offer 50 higher than offer 30 and offer 10.

Electrophysiological results Feedback Related Negativity

In the ERP results of observation ultimatum game, the ANOVA of 3(Anxiety states)×3(offer)x5(position) were performed on the amplitude of FRN. Because that the maximum FRN amplitudes are observed at frontal sites(Gehring &

Willoughby, 2002; Hajcak, et al., 2006), data from electrode sites Fz, F1, F2, F3 and F4 were tested. The interaction effect of anxiety state and offer was found significant (F_(4,48)=3.305, p<0.05). It showed that under offer 30, the FRN was smaller in white noise condition than social anxiety and control conditions (see Fig 1).

No more effect was found significant.

DISCUSSION

In sum, due to the anxiety effect manipulation has failed on some subjects, the results of this experiment did not really showed any significant effect of anxiety on reaction time and acceptance rate. However, it is interesting to find that under offer 30, the FRN was smaller in white noise condition than social anxiety and control conditions. It might due to the white noise have some effects on the participants while they are playing the ultimatum game, and the reasons should be investigated in the future.

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Search of Homo Economicus: Behavioral Experiments in 15 Small‐Scale 

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