Results

Behavioral data

Purchase rate
Only trials that registered responses in <4 s after stimulus onset were included for behavioral analyses. The one-way repeated-measure ANOVA revealed a significant main effect of price frame on purchase rate, F(2, 56) = 7.793, p = 0.007, ηp2 = 0.218. As illustrated in Figure 2A, subsequent pairwise comparison indicated that participants made buy decisions more often in ZP (M = 0.550, S.E. = 0.033) compared to NP (M = 0.440, S.E. = 0.036, p = 0.009). But the contrast between ZP and LP (M = 0.529, S.E. = 0.032, p = 0.241), as well as the contrast between NP and LP (p = 0.065), was not significant.
Figure 2  Behavioral results. (A) The purchase rate for each condition and (B) the RT for each condition. The error bars indicate standard error of the mean. **p < 0.01.

Reaction time
The ANOVA showed a significant main effect of price frame on reaction time (RT), F(2, 56) = 7.030, p = 0.004, ηp2 = 0.201. As illustrated in Figure 2B, pairwise comparison indicated shorter RT for ZP (M = 1,387.390 ms, S.E. = 86.931) than NP (M = 1,484.370 ms, S.E. = 95.516, p = 0.004). However, the contrast between ZP and LP (M = 1,406.854 ms, S.E. = 79.764, p = 1.000), as well as that between NP and LP (p = 0.073), was not significant.

ERP data
As shown in Figure 3, the two-way repeated-measure ANOVA for LPP amplitude demonstrated a significant main effect of price frame, F(2, 56) = 4.220, p = 0.020, ηp2 = 0.131, and electrode, F(2, 56) = 56.792, p = 0.000, ηp2 = 0.670. The LPP amplitude elicited by ZP (M = 5.627 μV, S.E. = 0.696) was more positive than that by NP (M = 4.730 μV, S.E. = 0.725, p = 0.013). But similar to the behavioral results, there was neither statistically significant difference of LPP amplitudes between ZP and LP (M = 4.979 μV, S.E. = 0.687, p = 0.279), nor between NP and LP (p = 1.000). Furthermore, the LPP amplitudes at Cz (M = 2.687 μV, S.E. = 0.652), CPz (M = 5.448 μV, S.E. = 0.724), and Pz (M = 7.202 μV, S.E. = 0.783) differed from each other (ps < 0.05). However, the interaction between price frame and electrode was not significant, F(4, 112) = 1.932, p = 0.110, ηp2 = 0.065.
Figure 3  ERP results. Grand-averaged ERP waveforms from three central electrodes (Cz, CPZ, and Pz) time-locked to the onset of price stimulus. The gray rectangles denote the time window for LPP analysis. Positive voltage is plotted downwards.

Correlation analyses results
Two-tailed Pearson correlation analyses between the mean amplitude of LPP and RT were performed at the group level in order to explore if there were functional connections between one's brain activity and behavioral performance. It showed significant negative correlation between LPP amplitude and RT in NP (r = −0.381, p = 0.041), but no significant correlations between them in ZP (r = −0.102, p = 0.600), and LP (r = −0.320, p = 0.091).