Date Published: June 11, 2018
Publisher: Public Library of Science
Author(s): Jianrui Huang, Xianyou He, Xiaojin Ma, Yian Ren, Tingting Zhao, Xin Zeng, Han Li, Yiheng Chen, Cosimo Urgesi.
When people make decisions about sequentially presented items in psychophysical experiments, their decisions are always biased by their preceding decisions and the preceding items, either by assimilation (shift towards the decision or item) or contrast (shift away from the decision or item). Such sequential biases also occur in naturalistic and real-world judgments such as facial attractiveness judgments. In this article, we aimed to cast light on the causes of these sequential biases. We first found significant assimilative and contrastive effects in a visual face attractiveness judgment task and an auditory ringtone agreeableness judgment task, indicating that sequential effects are not limited to the visual modality. We then found that the provision of trial-by-trial feedback of the preceding stimulus value eliminated the contrastive effect, but only weakened the assimilative effect. When participants orally reported their judgments rather than indicated them via a keyboard button press, we found a significant diminished assimilative effect, suggesting that motor response repetition strengthened the assimilation bias. Finally, we found that when visual and auditory stimuli were alternated, there was no longer a contrastive effect from the immediately previous trial, but there was an assimilative effect both from the previous trial (cross-modal) and the 2-back trial (same stimulus modality). These findings suggested that the contrastive effect results from perceptual processing, while the assimilative effect results from anchoring of the previous judgment and is strengthened by response repetition and numerical priming.
When people make judgments of single physical attributes of stimuli presented in a series, sequential effects often occur [1,2] in which judgments of the current stimulus are influenced by the preceeding items. The most widely explored sequential effects are assimilative effects and contrastive effects. A contrastive effect refers to a shift in the response in the direction opposite of the value of the previous item, and an assimilative effect refers to a shift in the response in the direction towards the previous response.
Face attractiveness, which is of great importance in interpersonal interaction, is a holistic visual trait that we often use to make first-pass assessments of people as we associate this feature with romantic viability, sociability, and health (see reviews ). Sequential biases on face attractiveness were prevalent [29–36], but they were little understood. Experiment 1 aimed to primarily find out whether face attractiveness ratings made in sequence were influenced by the true attractiveness values of the previous faces and the ratings given to the previous face. We used the standard sequential judging paradigm in Experiment 1, in which participants judged the attractiveness of a series of faces one by one on a scale of 1 (least attractive) to 8 (most attractive).
When it comes to musical stimuli, sequential bias was also found . That is, musical stimuli are evaluated more positively if they follow bad stimuli than otherwise, vice versa . Whether trial-by-trial sequential biases found in the face attractiveness judgments also occurs in auditory aesthetic can be an interesting issue to be examined. Experiment 2 aimed to characterize sequential biases in auditory stimuli judgments. The same design as Experiment 1 was used, with the exception that auditory stimuli (ringtones) were used instead of visual stimuli (faces).
As mentioned above, some researchers assumed that the contrastive effect resulting from the previous stimulus might be caused by perceptual aftereffect. Then the provision of trial-by-trial feedback (i.e., the attractiveness value), which can mask the perception of the previous stimulus,  can test the assumption. In addition, since the trial-by-trial feedback interferes participants’ tracing of the previous rating , it also indicates whether the assimilative effect is influenced by the reduced chance of numerical priming. Experiment 3 aimed to test the influence of feedback on sequential attractiveness rating bias in a within-subject design. Experiment 3 was identical to Experiment 1 except that participants were told the average rating of each face after they entered their judgments.
Experiment 4 examined whether the assimilative effect is influenced by action repetition. Oral responding rather than key-pressing was applied to avoid participants’ reluctance to change their rating across trials with relatively wide range in traditional key-pressing rating or mouse-clicking rating, which can relatively avoid the tendency of action repetition.
Experiment 5 used an alternative sequential presentation of both visual and auditory stimuli, where the same type of stimulus was presented on every other trial alternatively, to further determine whether sequential rating bias is identifiable under cross-modal situations. If the assimilative effect of the previous response is significant on cross-modal 1-back trials, then it can be explained by the priming of the previous ratings. If the assimilative effect is significant on 2-back trials that are of the same kind of stimulus modality, then it results from the anchoring of the same kind of stimulus. As for contrastive effect, if the value of the stimulus 1-trial back (of different modality) has no effect on the current rating, but the value of the stimulus 2-trial back (of the same modality) does, then we can draw the conclusion that the contrastive effect results from mere visual/auditory perception processing rather than high-level cognitive processing. In this experiment, the oral-responding rating method was applied to avoid the influence of action repetition tendency.
Sequential biases are prevalent in sequential judgment tasks in the domain of psychophysics. However, in the domain of subjective decision making such as facial attractiveness judgments, there is also no consistent conclusion about the sequential biases per se as well as how the sequential biases occur. In this paper, we conducted five experiments to figure out how we made a decision in a sequential subjective judgment task and how the sequential biases came into being.
In the current study, we first demonstrated that our subjective judgment on the current stimulus was biased by both previous stimuli and previous judgments. That is, contrastive and assimilative effects occurred simultaneously on the sequential subjective judgments, and the pattern of the observed sequential biases fit the regression model derived from psychophysical research. We also proved that contrastive effect resulted from low-level perceptual processing of the previous stimuli while the essence of assimilative effect was anchoring of the previous judgments of the same kind of stimulus, which can be strengthened by low-level response repetition as well as numerical priming of the previous rating.