We initiated our analysis by examining whether the pre-treatment attitudes toward internal combustion engine cars (ICE-cars) and electric cars (E-cars) varied among the experimental groups. A one-way ANOVA revealed no significant differences between the groups for both attitude objects (ICE-cars: F(1,318) = 0.0, p = .965; E-cars: F(1,318) = 0.28, p = .600). Therefore, we can confidently assume that the subsequent results are not influenced by disparities in prior attitudes across the groups.
To investigate the influence of prior attitudes on the assessment of information sources and subjectively perceived attitude changes, we utilized Pearson correlations. In Fig. 1 (A-D), we present separate correlations between prior attitudes toward conventional and electric cars and each vignette's ratings, categorized into positively and negatively framed messages. It's important to note that these analyses are aggregated across the three message types. The level of agreement with the statements displayed a strong association with participants' prior attitudes (positive: ICE-car: r = .58, p = .001; E-car: r = .66, p = .001; negative: ICE-car: r = .49, p = .001; E-car: r = .43, p = .001). These results reveal robust instances of motivated reasoning for both types of transport modes and message framings (positive/negative). Authors of messages that align closely with participants' pre-existing attitudes are evaluated as more likable and competent compared to authors of information that diverges significantly from those pre-existing attitudes. Interestingly, we observed evidence of a backfire effect. Attitude polarization (Fig. 1D), which signifies the shift and reinforcement of attitudes among individuals with strong pre-existing attitudes in the opposite direction of message valence, was notably stronger for positive information (ICE-car: r = .30, p = .001; E-car: r = .47, p = .001). In contrast, negative messages about cars did not yield significant results (ICE-car: r = .07, p = n.s.) and showed a weaker relationship (E-car: r = 0.15, p = 0.01). Overall, the correlations between prior attitudes and message evaluations were more pronounced for positive statements than for negative ones. This pattern was consistent for positively valenced messages about E-cars compared to ICE-cars, with a contrasting tendency observed for negative statements about the two vehicle types.
Subsequently, we conducted a separate analysis of the effects of positive and negative persuasive messages. In Fig. 2 (A-D), we present the average responses to all vignette-related measures, categorized by condition and valence. Consistent with the notion that positive messages tend to be more appealing and persuasive than negatively valenced ones 38, participants' ratings, on average, were significantly higher for positive information. Separate dependent t-tests revealed substantial differences across all three conditions concerning: agreement with the statements (rational: t(159) = 6.50, p < .001; emotional: t(159) = 4.56, p < .001; combined: t(159) = 6.88, p < .001), perceived competence of the sender (rational: t(159) = 5.88, p < .001; emotional: t(159) = 4.83, p < .001; combined: t(159) = 7.76, p < .001), likability of the sender (rational: t(159) = 6.06, p < .001; emotional: t(159) = 6.96, p < .001; combined: t(159) = 8.69, p < .001), and perceived attitude shift in response to the information (rational: t(159) = 5.69, p < .001; emotional: t(159) = 2.60, p < .01; combined: t(159) = 4.24, p < .001).
When comparing the impact of different types of persuasive appeals on perceived attitude changes (Fig. 2D), we employed one-way ANOVA followed by Tukey's HSD post-hoc tests (p < .05). Surprisingly, we observed no significant differences either among the groups or in any pairwise comparisons between groups, whether for positive or negative messages (F(2,477) = 0.15, p = .8590, ηp2 = .0003), nor for negative messages alone (F(2,477) = 1.80, p = .166, ηp2 = .0006). Conversely, when assessing evaluations regarding sender characteristics, we detected notable effects across all types of persuasive appeals. For rational statements, participants indicated the highest levels of agreement (positive: F(2,477) = 8.85, p = .001; negative: F(2,477) = 13.45, p = .001), sender competence (positive: F(2,477) = 7.23, p = .0001, ηp2 = .029; negative: F(2,477) = 19.40, p = .001, ηp2 = .075), and likability (positive: F(2,477) = 2.36, p = .10, ηp2 = .009; negative: F(2,477) = 20.04, p = .001, ηp2 = .077), regardless of whether the message was positively or negatively framed. Responses to emotional information were slightly, though not significantly, more positive than those to the combined condition, as indicated by the post-hoc test.
However, a more detailed analysis of covariance (ANCOVA), with control variables for perceived dissonance (i.e., agreement), prior attitudes, and their two-way interactions with the treatment, painted a nuanced picture for all dependent variables. The main effect of message type on perceived attitude change showed slight significance (positive: F(2,477) = 3.29, p = .0379, ηp2 = 0.014; negative: F(2,477) = 3.80, p = .0231, ηp2 = .016). Notably, covariates, such as prior attitude towards E-cars (positive: F(1,478) = 9.32, p = .0024, ηp2 = .019; negative: F(1,478) = 11.34, p = .0008, ηp2 = .019), and agreement with the statement, had a significant effect on perceived attitude change (positive: F(1,478) = 215.83, p = .0001, ηp2 = 0.312; negative: F(1,478) = 45.23, p = .0001, ηp2 = .087). However, prior attitudes toward ICE-cars showed no significant influence on perceived attitude change (positive: F(1,478) = 0.76, p = .7829, ηp2 = .018; negative: F(1,478) = 0.93, p = .3352, ηp2 = .017). Furthermore, the results revealed a small yet significant interaction between message type and agreement for negatively framed statements (F(2,477) = 3.80, p = .0023, ηp2 = .018), and a non-significant interaction for positively valenced statements (F(2,477) = 2.15, p = .117, ηp2 = .009). When participants exhibited more dissonance with the information, they perceived combined messages as the most persuasive. In contrast, when respondents showed greater agreement with the statements, rationally and emotionally framed messages led to stronger perceived attitude changes.
A second ANCOVA examining the perceived competence of the message sender, with prior attitudes, agreement, and their interactions as covariates, showed that the effect of message type became non-significant for positively framed statements (F(2,477) = 0.58, p = .5595, ηp2 = .002). However, it remained significant for negatively framed statements (F(2,477) = 5.12, p = .0063, ηp2 = .021), with rational messages leading to the highest perceived competence. No significant interaction between message type and agreement was found, but the main effect of agreement was strongly associated with attributed competence (positive: F(1,478) = 680.07, p = .0001, ηp2 = .588; negative: F(1,478) = 807.27, p = .0001, ηp2 = .629). Additionally, prior attitudes towards E-cars significantly influenced competence attribution for negatively framed messages (positive: F(1,478) = 0.39, p = .5278, ηp2 = .001; negative: F(1,478) = 25.12, p = .0001, ηp2 = .050). This finding aligns with previous research indicating the impact of motivated reasoning on expertise perception and suggests that competence attribution to the sender was primarily driven by perceived dissonance with persuasive appeals rather than the type of argumentation or prior attitudes.
In summary, the empirical results demonstrate the influence of prior attitudes and dissonance on information evaluation, providing support for the proposed motivated reasoning processes. This effect was most pronounced for negatively valenced combined statements, resulting in more negative judgments about senders' characteristics and lower persuasiveness compared to positive rational or emotional messages. The impact of different message types was primarily moderated by the level of dissonance or disagreement with the statements.