Perceptual adaptation to facial asymmetries

Humans and other animals are highly sensitive to deviations from bilateral symmetry and prefer symmetric mates. Fluctuating asymmetries (FAs) are random deviations from perfect symmetry that can result from developmental instability. Human perceptions of facial asymmetry are driven by FAs and insensitive to directional asymmetries (DAs), which have a consistent direction of bias (e.g., left side always larger) across the population and are unrelated to developmental stability. We hypothesized that perceptual adaptation may filter out DAs and provide a proximate mechanism for this perceptual focus on FAs. We created a small population of faces with DAs by applying a unilateral distortion to the same side of each face. After 5 min of adaptation, (new) faces with these DAs looked less asymmetric and the most symmetric-looking distortion shifted toward the adapting asymmetry level. Parallel changes occurred for attractiveness. We suggest that perceptual adaptation may provide the proximate mechanism for an evolutionarily adaptive focus on FAs.     

Not just the norm: Exemplar-based models also predict face aftereffects

The face recognition literature has considered two competing accounts of how faces are represented within the visual system: Exemplar-based models assume that faces are represented via their similarity to exemplars of previously experienced faces, while norm-based models assume that faces are represented with respect to their deviation from an average face, or norm. Face identity aftereffects have been taken as compelling evidence in favor of a norm-based account over an exemplar-based account. After a relatively brief period of adaptation to an adaptor face, the perceived identity of a test face is shifted toward a face with attributes opposite to those of the adaptor, suggesting an explicit psychological representation of the norm. Surprisingly, despite near universal recognition that face identity aftereffects imply norm-based coding, there have been no published attempts to simulate the predictions of norm- and exemplar-based models in face adaptation paradigms. Here, we implemented and tested variations of norm and exemplar models. Contrary to common claims, our simulations revealed that both an exemplar-based model and a version of a two-pool norm-based model, but not a traditional norm-based model, predict face identity aftereffects following face adaptation.     

Distinguishing norm-based from exemplar-based coding of identity in children: evidence from face identity aftereffects

Children's performance on face identification tests improves dramatically between age 4 and adolescence, yet the source of this improvement is controversial. We used face identity aftereffects to examine whether changes in the organization of face-space during childhood could be a source of this improvement. Specifically we tested whether 7- to 9-year-old children, like adults, show patterns of aftereffects predicted by coding facial identity relative to a norm or the patterns predicted by exemplar-based coding. Consistent with use of norm-based coding children's aftereffects were larger (a) for opposite than non-opposite adapt-test pairs equated for perceptual similarity, and (b) for adaptors far from the average than for adaptors closer to the average. In addition, face identity aftereffects were present by age 5, suggesting adult-like face-space properties by 5, though we did not conduct specific tests to distinguish norm-based from exemplar-based coding in this age group. We conclude that children's poor face identification skills cannot be attributed to a failure to use norm-based coding.     

Fitting the child's mind to the world: adaptive norm-based coding of facial identity in 8-year-olds

In adults, facial identity is coded by opponent processes relative to an average face or norm, as evidenced by the face identity aftereffect: adapting to a face biases perception towards the opposite identity, so that a previously neutral face (e.g. the average) resembles the identity of the computationally opposite face. We investigated whether children as young as 8 use adaptive norm-based coding to represent faces, a question of interest because 8-year-olds are less accurate than adults at recognizing faces and do not show the adult neural markers of face expertise. We found comparable face identity aftereffects in 8-year-olds and adults: perception of identity in both groups shifted in the direction predicted by norm-based coding. This finding suggests that, by 8 years of age, the adaptive computational mechanisms used to code facial identity are like those of adults and hence that children's immaturities in face processing arise from another source.     

Aftereffects for face attributes with different natural variability: Children are more adaptable than adolescents

Adults can be adapted to a particular facial distortion in which both eyes are shifted symmetrically (Robbins, R., McKone, E., & Edwards, M. (2007). Aftereffects for face attributes with different natural variability: Adapter position effects and neural models. Journal of Experimental Psychology: Human Perception and Performance, 33, 570–592), but they do not show as great adaptation to an asymmetrical eye distortion. We adapted children and adolescents to symmetrical and asymmetrical eye distortions and measured the aftereffects. Children (aged 6–12, mean age 9 years) showed larger aftereffects than adolescents (aged 13–18, mean age 15 years) and demonstrated aftereffects of a similar magnitude for both asymmetrical and symmetrical distortions. Adolescents only showed aftereffects for symmetrical distortions. We propose that children may have a more flexible face norm and neural responses that allow a broader range of adapted states compared to adolescents.     

Caricaturing facial expressions

The physical differences between facial expressions (e.g. fear) and a reference norm (e.g. a neutral expression) were altered to produce photographic-quality caricatures. In Experiment 1, participants rated caricatures of fear, happiness and sadness for their intensity of these three emotions; a second group of participants rated how 'face-like' the caricatures appeared. With increasing levels of exaggeration the caricatures were rated as more emotionally intense, but less 'face-like'. Experiment 2 demonstrated a similar relationship between emotional intensity and level of caricature for six different facial expressions. Experiments 3 and 4 compared intensity ratings of facial expression caricatures prepared relative to a selection of reference norms - a neutral expression, an average expression, or a different facial expression (e.g. anger caricatured relative to fear). Each norm produced a linear relationship between caricature and rated intensity of emotion; this finding is inconsistent with two-dimensional models of the perceptual representation of facial expression. An exemplar-based multidimensional model is proposed as an alternative account.     

THREE-DIMENSIONAL BILATERAL SYMMETRY BIAS IN JUDGMENTS OF FIGURAL IDENTITY AND ORIENTATION

Abstract— The two experiments reported explored a bias toward symmetry in judging identity and orientation of indeterminate two-dimensional shapes. Subjects viewed symmetric and asymmetric filled, random polygons and described, "what each figure looks like" and its orientation. Viewers almost universally interpreted the shapes as silhouettes of bilaterally symmetric three-dimensional (3-D) objects. This assumption of 3-D symmetry tended to constrain perceived vantage of the identified objects such that symmetric shapes were interpreted as straight-on views, and asymmetric shapes as profile or oblique views. Because most salient objects in the world are bilaterally symmetric, these findings are consistent with the view that assuming 3-D symmetry can be a robust heuristic for constraining orientation when identifying objects from indeterminate patterns.     

A unified account of the effects of distinctiveness, inversion, and race in face recognition

A framework is outlined in which individual faces are assumed to be encoded as a point in a multidimensional space, defined by dimensions that serve to discriminate faces. It is proposed that such a framework can account for the effects of distinctiveness, inversion, and race on recognition of faces. Two specific models within this framework are identified: a norm-based coding model, in which faces are encoded as vectors from a population norm or prototype; and a purely exemplar-based model. Both models make similar predictions, albeit in different ways, concerning the interactions between the effects of distinctiveness, inversion and race. These predictions were supported in five experiments in which photographs of faces served as stimuli. The norm-based coding version and the exemplar-based version of the framework cannot be distinguished on the basis of the experiments reported, but it is argued that a multidimensional space provides a useful heuristic framework to investigate recognition of faces. Finally, the relationship between the specific models is considered and an implementation in terms of parallel distributed processing is briefly discussed.     

Distinctiveness and expertise effects with homogeneous stimuli: towards a model of configural coding

Recent studies using Brennan's computerized caricature generator have demonstrated distinctiveness effects consistent with the idea that faces are coded in terms of their individual distinctive properties. Based on these findings it is suggested that, for homogeneous classes whose members share a common configuration, distinctive configural information may be coded as metric deviations from a spatial norm. Experiments are described which demonstrate similar distinctiveness effects in bird identification. Transformations that increase distinctiveness (caricatures) produced faster identification and a higher recognition proportion, for both experts and nonexperts, than transformations that reduce distinctiveness (anticaricatures). This distinctiveness advantage is consistent with the norm-based coding idea. Furthermore, within certain limits, increasing distinctiveness did not impair performance relative to that for veridical drawings. For experts there was also a caricature advantage, such that 50% caricatures of birds in a highly homogeneous and familiar class (passerines) were identified more quickly, provided that they were recognized at all, than uncaricatured veridical drawings. The significance of a caricature advantage for the visual coding of configural information is discussed.     

A symmetric and an asymmetric model for the equal-sensation function in olfaction

Data from various intramodel matching experiments in olfaction were analyzed with regard to a symmetric and an asymmetric model for the equal-sensation function. The asymmetric model was discussed in relation to the symmetric model. In all, 11 equal-sensation functions were investigated, and of these 9 were with different pairs of odorants. The following odorants were investigated: hydrogen sulfide, pyridine, dimethyl disulfide, and five odorants obtained by different combustion procedures of animal manure. It was found that the equal-sensation function can be written in the following asymmetric form: $$\varphi _i = b_{ik} \lambda \cdot \varphi _k ^{b_{ik} } ,\psi _i = \psi _k $$ or symmetric form: $$\varphi _i = C^{I - b_{ik} } \cdot \varphi _k ^{b_{ik} } ,\psi _i = \psi _k ,$$ where ?_i and ?_k are stimuli expressed in multiples of respective absolute thresholds, λ and C are general constants invariant of experimental matching method and matched attribute (perceived unpleasantness or intensity). The constants λ and C were calculated both for group data and individual data. The asymmetric form of the equal-sensation function was interpreted in terms of relativity and the symmetric form in terms of measurement.     

Facial-expression affective attributes and their configural correlates: components and categories

The present study investigates the perception of facial expressions of emotion, and explores the relation between the configural properties of expressions and their subjective attribution. Stimuli were a male and a female series of morphed facial expressions, interpolated between prototypes of seven emotions (happiness, sadness, fear, anger, surprise and disgust, and neutral) from Ekman and Friesen (1976). Topographical properties of the stimuli were quantified using the Facial Expression Measurement (FACEM) scheme. Perceived dissimilarities between the emotional expressions were elicited using a sorting procedure and processed with multidimensional scaling. Four dimensions were retained in the reconstructed facial-expression space, with positive and negative expressions opposed along D1, while the other three dimensions were interpreted as affective attributes distinguishing clusters of expressions categorized as "Surprise-Fear," "Anger," and "Disgust." Significant relationships were found between these affective attributes and objective facial measures of the stimuli. The findings support a componential explanatory scheme for expression processing, wherein each component of a facial stimulus conveys an affective value separable from its context, rather than a categorical-gestalt scheme. The findings further suggest that configural information is closely involved in the decoding of affective attributes of facial expressions. Configural measures are also suggested as a common ground for dimensional as well as categorical perception of emotional faces.     

A multi-attribute extension of the secretary problem: Theory and experiments

We present a generalization of a class of sequential search problems with ordinal ranks, referred to as “secretary” problems, in which applicants are characterized by multiple attributes. We then present a procedure for numerically computing the optimal search policy and test it in two experiments with incentive-compatible payoffs. With payoffs dependent on the absolute ranks of the attributes, we test the optimal search model with both symmetric (Experiment 1) and asymmetric (Experiment 2) search problems. In both experiments we find that, relative to the optimal search policy, subjects stop the search too early. Our results show that this bias is largely driven by a propensity to stop prematurely on applicants of intermediate (relative) quality.     

Emotions as signals of normative conduct

Social interactions are heavily norm-based and these norms need to be learned. For this, the emotional reactions of other's in response to a norm transgression can serve as signals. We were able to show that when a group responds with anger to a norm transgressing behaviour, participants were better able to correctly infer the norm than when the group responded with sadness or emotional neutrality. We further tested a process-model showing that this inference is based on the participants' understanding of the groups' appraisals of the behaviour. That is, participants who were able to reverse engineer the underlying appraisal of norm-incompatibility from the emotion expressions inferred the norm more readily. Humans as a social species, require efficient means to quickly adapt to new situations and to perform flawlessly in social contexts. Emotion information is one of the instruments that can be used in this quest.     

Asymmetric preferences for road safety: Evidence from a stated choice experiment among car drivers

Recent research has proposed fitting responses from discrete choice experiments to asymmetric value functions consistent with prospect theory, taking into account respondents’ reference points in their valuation of choice attributes. Previous studies have mainly concentrated on travel time and cost attributes, while evidence regarding road safety attributes is very limited.This paper investigates the implicit utility of a road safety attribute, defined as the number of casualties per year in alternative car trip choices, when safety improves or deteriorates. Using appropriate statistical tests we are able to reject symmetric preferences for losses and gains in the level of safety and estimate a sigmoid value function that exhibits loss aversion and diminishing sensitivity. This adds an interesting psychological dimension to the preference of road safety. Possible implications of this finding for policy making are discussed.     

Quantifying social asymmetric structures

Many social phenomena involve a set of dyadic relations among agents whose actions may be dependent. Although individualistic approaches have frequently been applied to analyze social processes, these are not generally concerned with dyadic relations, nor do they deal with dependency. This article describes a mathematical procedure for analyzing dyadic interactions in a social system. The proposed method consists mainly of decomposing asymmetric data into their symmetric and skew-symmetric parts. A quantification of skew symmetry for a social system can be obtained by dividing the norm of the skew-symmetric matrix by the norm of the asymmetric matrix. This calculation makes available to researchers a quantity related to the amount of dyadic reciprocity. With regard to agents, the procedure enables researchers to identify those whose behavior is asymmetric with respect to all agents. It is also possible to derive symmetric measurements among agents and to use multivariate statistical techniques.     

Egocentric Interpretations of Fairness in Asymmetric,Environmental Social Dilemmas: Explaining Harvesting Behavior and the Role of Communication

This research explores the effects of egocentric interpretations of fairness, expectations about other actors’ harvesting decisions, and communication on the focal actor's harvesting decisions in asymmetric social dilemmas. We found support for the predictions that egocentrism exists in perceptions of fairness in asymmetric dilemmas, overharvesting is positively related to the amount of egocentrism, and egocentrism is stronger before discussion than after discussion. Furthermore, in a comparison between asymmetric and symmetric dilemmas, we found that egocentrism and overharvesting were greater in asymmetric dilemmas than in symmetric dilemmas. Finally, the results indicate that among certain actors, overharvesting in asymmetric dilemmas is positively related to the amount of harvesting expected from the other parties. This study contributes to the social dilemma literature by (1) introducing the idea of egocentric interpretations of fairness as an explanation for overharvesting behavior, (2) demonstrating that egocentrism is more pronounced in asymmetric versus symmetric dilemmas, (3) suggesting that the reduction of egocentric interpretations of fairness is another reason why communication enhances cooperative behavior, and (4) demonstrating that beliefs about what others will do is related to harvesting decisions in asymmetric as well as symmetric dilemmas.     

The judgment of covariation between binary variables: Some conditions that influence the process

Two hundred subjects made decisions based on the data of two binary variables, ethnic origin and employment status. They were asked to specify the information necessary and sufficient for making the decision before doing so. Variables studied were: (1) Type of question. Five questions were used, four of which focused on one of the four instances involved (e.g., Which information is necessary to find out if there is a connection between Asian immigrants and unemployment?). Question five was unbiased. (2) Type of variable. Half of the subjects found two symmetric variables, and half found one symmetric and one asymmetric variable. (3) Level of correlation. Five different correlations were used, three favoring Asians, one favoring Europeans, and one representing a zero correlation. Subjects made logical decisions that were not influenced by any of the experimental conditions. The selection of information before and after making choices was influenced by all variables except level of correlation. The biased questions produced deviations from normative reasoning; the two symmetrical variables and the process of making decisions encouraged normative reasoning.     

Dyadic Power Profiles: Power‐Contingent Strategies for Value Creation in Negotiation

Using a simulated employment negotiation, we tested the conditional relationships among dyadic power profiles (symmetric high, symmetric low, and asymmetric), the choice and sequencing of strategies, and value creation. We showed that negotiators in symmetric high, symmetric low, and asymmetric power dyads took distinctly different paths to value creation. Value creation was associated with increased mutual accommodation in high‐power dyads but with increased contentiousness in low‐power dyads. Asymmetric power dyads maximized value creation when they adopted a neutral stance, neither overusing nor underusing any one strategy. Although strategy use was a better predictor of value creation than strategy sequencing, sequences played an increasingly important role in value creation as the level of total power within the negotiation increased.     

Attractiveness of Facial Profiles Is a Function of Distance From Archetype

The term archetype is used here to refer to a facial structure defined by certain geometric relationships that occur as a result of normal growth and that guarantee efficient mastication. Two experiments are reported that test whether or not facial attractiveness is related to this functional ideal. Attractiveness of female profiles was found to be related strongly to distance from archetype, and this relationship held at different age levels (but it was not mediated by apparent age level). In contrast, attractiveness was not related to the degree to which a given face conformed either to the golden section or to a cephalometric norm. Arguments are presented for defining attractiveness for a given individual rather than in terms of an absolute standard for all faces.