其他摘要 | Ensemble representation is a process by which people handle a set of stimuli and extract its gist. Previous researches have explored ensemble representation with facial emotion, identity, attractiveness, and other dimensions. However, face is a very informative stimulus, and a set of faces is able to convey certain social information, such as ensemble trustworthiness. Studies on the trustworthiness judgment with individual faces are ample, but studies on the ensemble representation of facial trustworthiness are still very scarce. In this study, using behavioral experiments, event-related potential technologies, and functional magnetic resonance imaging techniques, we investigated mainly three issues: 1) whether trustworthiness could be process within a set, and what kind of relationship existed between set trustworthiness and member trustworthiness, 2) what were the cognitive characteristics of this process and, 3) what were the neural mechanisms characterized by this process.
Study 1 explored whether the trustworthiness of a set of faces could be processed as a whole, and what kind of relationship was between the ensemble trustworthiness of the set and the mean of the members. Experiment 1 found that the scores of the ensemble assessment was significantly higher than the member mean, and there was a positive correlation between the two. The same results were found in Experiment 2. Meanwhile, the D-value between ensemble assessment and member mean differed dependent on set type and participant gender.
Study 2 explored the cognitive characteristics of the ensemble representation of trustworthiness. Experiment 3 to Experiment 5 investigated respectively the impact of member variability, simultaneous presentation-sequence presentation conditions, and reward learning tasks on the ensemble representation of trustworthiness. 1) Experiment 3 found a small effect of variation on ensemble representation, and that the difference between ensemble assessment and member mean, and the interaction between set type and participant gender was no longer significant. 3) Experiment 4 introduced the simultaneous presentation-sequence presentation paradigm, and found that the ensemble representation of trustworthiness may be more in line with parallel processing mechanism. 4) Experiment 5 combined ensemble representation task with reward learning task, and found that sets with higher reward probability gained trustworthiness, and previously high-trustworthy sets with lower reward probability lost trustworthiness. Model comparison further provided different initial expected- values based on trustworthiness and different learning rates based on congruency.
Study 3 used event-related potential technology and functional magnetic resonance imaging technology to explore event-related potential characteristics and brain activation patterns induced by ensemble trustworthiness. 1) Experiment 6 found difference of P1 amplitudes between heterogeneous sets and homogenous sets, and difference of N170 amplitudes between the left hemisphere and the right hemisphere. Meanwhile, the EPN amplitude induced by female medium trustworthiness sets was smaller than high trustworthiness sets, while the LPP amplitude induced was greater than high trustworthiness sets. 2) Experiment 7 found that ensemble trustworthiness processing employed the right angular gyrus, the left temporal middle gyrus and the right frontal middle/superior gyrus.
The results from Study 1 showed that facial trustworthiness could be represented as a whole, but there was a difference between the ensemble estimation and the member mean. Moreover, the size and the direction of the difference would change, dependent on set type and participant gender. The results from Study 2 showed that member variation only had a small effect upon the ensemble representation of trustworthiness, and the process was more in line with the parallel mechanism. Also, ensemble assessment was flexible, and could influence reward learning tasks. The results from Study 3 explored further about the procedure and brain activation of trustworthiness ensemble representation.
This study systematically explored the cognitive characteristics of the ensemble representation of facial trustworthiness, and laid a foundation for the study of ensemble representations of further social information. Also, this study preliminarily explored the neural mechanism of the ensemble representation of facial trustworthiness, and provides experimental evidence for its event-related potential characteristics and relevant brain regions. |
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