Classification in well-defined and ill-defined categories: evidence for common processing strategies

Early work in perceptual and conceptual categorization assumed that categories had criterial features and that category membership could be determined by logical rules for the combination of features. More recent theories have assumed that categories have an ill-defined structure and have prosposed probabilistic or global similarity models for the verification of category membership. In the experiments reported here, several models of categorization were compared, using one set of categories having criterial features and another set having an ill-defined structure. Schematic faces were used as exemplars in both cases. Because many models depend on distance in a multidimensional space for their predictions, in Experiment 1 a multidimensional scaling study was performed using the faces of both sets as stimuli, In Experiment 2, subjects learned the category membership of faces for the categories having criterial features. After learning, reaction times for category verification and typicality judgments were obtained. Subjects also judged the similarity of pairs of faces. Since these categories had characteristic as well as defining features, it was possible to test the predictions of the feature comparison model (Smith et al.), which asserts that reaction times and typicalities are affected by characteristic features. Only weak support for this model was obtained. Instead, it appeared that subjects developed logical rules for the classification of faces. A characteristic feature affected reaction times only when it was part of the rule system devised by the subject. The procedure for Experiment 3 was like that for Experiment 2, but with ill-defined rather than well-defined categories. The obtained reaction times had high correlations with some of the models for ill-defined categories. However, subjects' performance could best be described as one of feature testing based on a logical rule system for classification. These experiments indicate that whether or not categories have criterial features, subjects attempt to develop a set of feature tests that allow for exemplar classification. Previous evidence supporting probabilistic or similarity models may be interpreted as resulting from subjects' use of the most efficient rules for classification and the averaging of responses for subjects using different sets of rules.     

Caricature and face recognition

Although caricatures are often gross distortions of faces, they frequently appear to be super-portraits capable of eliciting recognition better than veridical depictions. This may occur because faces are encoded as distinctive feature deviations from a prototype. The exaggeration of these deviations in a caricature may enhance recognition because it emphasizes the features of the face that are encoded. In two experiments, we tested the superportrait hypothesis and the encoding-by-caricature hypothesis. In the first experiment, caricatures were recognized better than faces, and true caricatures of previously seen faces were recognized better than the faces from which the caricatures had been developed. In the second experiment, faces and their caricatures were tachistoscopically presented in a sequential same/different reaction time task. Subjects were slower to distinguish the stimuli when the face preceded its caricature, indicating that caricatures are more similar to the encoded representation of a face than are stimuli in which the distinctive features are deemphasized.     

Does matching of internal and external facial features depend on orientation and viewpoint?

Although it is recognized that external (hair, head and face outline, ears) and internal (eyes, eyebrows, nose, mouth) features contribute differently to face recognition it is unclear whether both feature classes predominately stimulate different sensory pathways. We employed a sequential speed-matching task to study face perception with internal and external features in the context of intact faces, and at two levels of contextual congruency. Both internal and external features were matched faster and more accurately in the context of totally congruent/incongruent facial stimuli compared to just featurally congruent/incongruent faces. Matching of totally congruent/incongruent faces was not affected by the matching criteria, but was strongly modulated by orientation and viewpoint. On the contrary, matching of just featurally congruent/incongruent faces was found to depend on the feature class to be attended, with strong effects of orientation and viewpoint only for matching of internal features, but not of external features. The data support the notion that different processing mechanisms are involved for both feature types, with internal features being handled by configuration sensitive mechanisms whereas featural processing modes dominate when external features are the focus.     

The facilitative effect of positive stimuli on 3-year-olds’ flexible rule use

This study examined the effect of emotional stimuli on 3- to 4-year old children's flexible rule use, as measured by the Dimensional Change Card Sort (DCCS). In Experiment 1, children in two countries (Canada and China) were given 2 versions of the DCCS. The Standard version required children to sort red and blue boats and rabbits first by shape and then by color (or vice versa); the Emotional Faces version required children to sort happy and sad male and female faces first by emotion and then by gender (or vice versa). Children performed significantly better on the Emotional Faces version, and performance on the 2 versions was related. Order in which dimensions were presented had no effect. Experiment 2 examined which aspects of the emotional faces were responsible for the facilitation of children's performance. Performance on the Standard version was compared to performance on three contextual faces versions, in which children were shown happy, sad, or neutral faces and required to sort them by age (child versus adult) and then by gender (or vice versa). Facilitation was only seen in the context of happy faces. Results are consistent with the suggestion that positive stimuli promote cognitive flexibility, perhaps by increasing dopamine levels in prefrontal cortex.     

The effects of attention-directing training on recognition memory task performance of three-year-old children

Thirty-eight 3-year-old children served as subjects in an investigation of recognition memory in which schematic faces differing only in the orientation of the eyes were employed as stimuli. A pretest was administered to all children, after which the two experimental groups received training in either attention to the distinctive feature of the training stimuli (also schematic faces) by means of a matching task, or in labeling the faces according to how they looked (sleepy, happy, sad, mad) and in using the labels to perform a matching task. After the training session all children were given a posttest on recognition memory of the faces. The verbally trained group obtained significantly higher scores on the posttest than either the feature or control groups. These results indicate that although the children were able to discriminate the faces, evidenced in their ease of performance on the training tasks, they were not able to use this knowledge unless given training in attaching labels to the stimuli, which enabled them to store the information for later use. Results are discussed in light of Gibson's (1969) theory of the developmental interrelations of cognitive processes.     

Association Learning with Own‐ and Other‐race Faces in three‐ and six‐month old infants – A longitudinal study

This longitudinal study assessed 133 Caucasian German infants at 3 and 6 months of age to investigate the influence of own‐race and other‐race faces as visual stimuli on association learning in the visual expectation paradigm (VExP). The study is related to the findings on the other‐race‐effect (ORE) which is said to emerge at 6 months of age. Caucasian faces were used as stimuli of a familiar ethnic category, whereas African faces were used as stimuli of an unfamiliar ethnic category. There was no significant difference between the two stimulus classes in infants' reaction time (RT) to stimulus shifts at 3 months. At 6 months of age, infants' RT decreased significantly in the Caucasian faces condition but not in the African faces condition. These results indicate that the processing of other‐race versus own‐race faces by the age of 6 months, which is also the relevant age for the onset of the ORE, has an important influence on the performance on the VExP. Copyright © 2011 John Wiley & Sons, Ltd.     

The prototype effect in face recognition: Extension and limits

The prototype effect in face recognition refers to a tendency to recognize the face corresponding to the central value of a series of seen faces, even when this central value or prototype has not been seen. Five experiments investigated the extension and limits of this phenomenon. In all the experiments, participants saw a series of faces, each one in two or more different versions or exemplars, and then performed a recognition test, including seen and unseen exemplars and the unseen prototype face. In Experiment 1, a strong prototype effect for variations in feature location was demonstrated in oldness ratings and in a standard old/new recognition test. Experiments 2A and 2B compared the prototype effect for variations in feature location and variations in head angle and showed that, for the latter, the prototype effect was weaker and more dependent on similarity than for the former. These results suggest that recognition across feature variations is based on an averaging mechanism, whereas recognition across viewpoint variations is based on an approximation mechanism. Experiments 3A and 3B examined the limits of the prototype effect using a face morphing technique that allows a systematic manipulation of face similarity. The results indicated that, as the similarity between face exemplars decreases to the level of similarity between the faces of different individuals, the prototype effect starts to disappear. At the same time, the prototype effect may originate false memories of faces that were never seen.     

An inversion effect modified by expertise in capuchin monkeys

The face inversion effect may be defined as the general impairment in recognition that occurs when faces are rotated 180°. This phenomenon seems particularly strong for faces as opposed to other objects and is often used as a marker of a specialized face-processing mechanism. Four brown capuchin monkeys (Cebus apella) were tested on their ability to discriminate several classes of facial and non-facial stimuli presented in both their upright and inverted orientations in an oddity task. Results revealed significantly better performance on upright than inverted presentations of capuchin and human face stimuli, but not on chimpanzee faces or automobiles. These data support previous studies in humans and other primates suggesting that the inversion effect occurs for stimuli for which subjects have developed an expertise.     

Memory conjunction errors for realistic faces are consistent with configural processing

Conjunction faces are formed from feature sets learned across different faces. In previous studies, false alarms (“old” responses) to conjunctions have been very high, approaching hits to old faces; this is surprising, because, perceptually, upright faces are processed configurally, with strong integration of parts into the whole. We test the idea that the atypical reliance on unrelated parts could be due to using unnatural line drawings as stimuli, and to forming conjunctions across external features (e.g., hair) and internal features (e.g., eyes, mouth). We used realistic face stimuli and conjunctions made entirely from internal features. Results were, as expected, consistent with configural processing for upright faces (hits to old faces much greater than FA to conjunctions) and not for inverted faces (hits to old = FA to conjunctions).     

The effects of distinctiveness in recognising and classifying faces

In an earlier study it was found that distinctive familiar faces were recognised faster than typical familiar faces in a familiarity decision task. In the first experiment reported here this effect was replicated with the use of celebrities' faces rather than personally familiar faces. In the second and third experiments the effect of distinctiveness was found to reverse if the task was to distinguish between faces and jumbled faces. Subjects took longer to classify distinctive faces as faces than they did to classify typical faces. Thus distinctive faces were recognised faster, but were classified as faces more slowly than were typical faces, both when personally familiar faces and when famous faces were used as stimuli. These results are interpeted as evidence that faces are encoded by reference to a general face prototype.     

Discrimination of artificial categories structured by family resemblances: a comparative study in people (Homo sapiens) and pigeons (Columba livia)

Adult humans (Homo sapiens) and pigeons (Columba livia) were trained to discriminate artificial categories that the authors created by mimicking 2 properties of natural categories. One was a family resemblance relationship: The highly variable exemplars, including those that did not have features in common, were structured by a similarity network with the features correlating to one another in each category. The other was a polymorphous rule: No single feature was essential for distinguishing the categories, and all the features overlapped between the categories. Pigeons learned the categories with ease and then showed a prototype effect in accord with the degrees of family resemblance for novel stimuli. Some evidence was also observed for interactive effects of learning of individual exemplars and feature frequencies. Humans had difficulty in learning the categories. The participants who learned the categories generally responded to novel stimuli in an all-or-none fashion on the basis of their acquired classification decision rules. The processes that underlie the classification performances of the 2 species are discussed.     

Within-category discrimination of musical chords: Perceptual magnet or anchor?

Recent speech research has begun to evaluate the internal structure of categories. In one such study, Kuhl (1991) found that discrimination was poorer for vowel stimuli that were more representative of the category (prototype, or P, set) than it was for less representative stimuli (nonprototype, or NP, set). This finding was interpreted as indicating that a category prototype may function as a “perceptual magnet,” effectively decreasing perceptual distance, and thus discriminability, between stimuli. The present study examines the function of prototypes in a musical category—another natural, but nonspeech category. Paralleling the Kuhl study, representative (P) and less representative (NP) sets of major triad stimuli were constructed, based on equal temperament. Musically experienced subjects rated the stimuli in each set for goodness as a major triad, with the highest rated stimulus serving as a prototype standard for a subsequent discrimination task. Results from the discrimination task demonstrated better performance in the P context than in the NP context. The current nonspeech results indicate that a prototype functions as an anchor rather than a magnet. In addition to providing a natural, nonspeech standard for comparison with speech findings, the results provide some important insights into the nature of musical categories.     

Differential brain responses when applying criterion attribute versus family resemblance rule learning

Subsystems of category learning have been identified on the basis of general domains of content (e.g., tools, faces). The present study examined categories from the standpoint of internal structure and determined brain topography associated with expressing two fundamentally different category rule structures (criterion attribute, CA, and family resemblance, FR). CA category learning involves processing stimuli by isolated features and classifying by properties held by all members. FR learning involves processing stimuli by integral wholes and classifying on overall similarity among members without sharing identical features. fMRI BOLD response to CA and FR categorization was measured with pseudowords as stimuli. Category knowledge for both tasks was mastered prior to brain imaging. Areas of activation emerged unique to the structure of each category and followed from the nature of the rule abstraction procedure. CA categorization was implemented by strong target monitoring and expectation (medial parietal), rule maintenance in working memory, feature selection processes (inferior frontal), and a sensitivity to high frequency components of the stimulus such as isolated features (anterior temporal). FR categorization, consistent with its multi-featural nature, involved word-level processing (left extrastriate) that evoked articulatory rehearsal (medial cerebellar). The data suggest category structure is an important determinant of brain response during categorization. For instance, anterior temporal structures may help attune visual processing systems to high frequency components to support the learning of criterial, highly predictive rules.     

任务类型对面孔联合效应和特征效应的调节

采用特征-联合范式的研究发现, 面孔再认阶段可记录到明显的联合效应和特征效应; 然而, 与再认同属情景记忆的另一任务(来源提取)条件的相应效应尚未报道, 背景信息一致性对联合面孔和特征面孔提取的调节作用以及面孔不同特征对特征效应的影响也未考察。为澄清上述问题, 本文采用特征-联合范式, 并以位置为背景展开研究。实验含一个学习任务和两个测验任务(再认和来源提取)。结果显示, 再认和来源提取阶段均记录到显著的联合效应和特征效应, 且两类效应均在来源提取阶段更强; 任务类型与位置背景一致性交互影响提取绩效; 面孔外部特征和内部特征对特征效应的影响相似。表明联合效应和特征效应具有显著的任务类型敏感性, 这些效应是联合面孔和特征面孔的熟悉性较强且对源面孔的回忆加工相对较弱的结果, 且这两类面孔的提取为背景一致性所调节; 任务类型对两类效应的调节与双重加工理论模型相吻合。     

Adaptation effects in facial expression recognition

The effect of adaptation on facial expression recognition was investigated by measuring how identification performance of test stimuli falling along a particular expression continuum was affected after adapting to various prototype emotional faces or a control pattern. The results showed that for recognition of fear, happiness, and sadness, inhibition effects were observed on recognition of test expressions following 5 s adaptation to the same emotion, suggesting different neural populations tuned for the encoding of fearful, happy, and sad expressions. Facilitation of recognition of test stimuli differing in emotion to the adapting stimulus was also sometimes observed. The nature of these adaptation effects was investigated by introducing a size transformation or a delay between adapting and test stimuli and was found to survive these changes. The results of a further experiment argued against a criterion effect being the major source by demonstrating the importance of adapting time in generating the effects. Overall, the present study demonstrates the utility of adaptation effects for revealing functional characteristics of facial expression processing.     

Context-produced increase in visibility

Summary It has not been clearly shown that context (e. g., three lines of a square) increases the visibility of a feature (e. g., the fourth line of the same square). To investigate this possibility, four sets of context+feature, context, feature, and BLANK (empty field) stimuli were used. For three out of the four sets, the context+feature stimulus was less likely to be falsely identified as the context and BLANK stimuli (i. e., the stimuli without the feature) than was the feature stimulus. For the same three sets, discriminating between the context+feature and context stimuli produced fewer false identifications (FIs) than discriminating between the feature and BLANK stimuli. The conclusion: the context components of context+feature stimuli increased the visibility of the feature components of the same stimuli.     

Eccentricity biases of object categories are evident in visual working memory

In high-order object areas, face-selective areas prefer centrally presented stimuli, whereas building-selective areas prefer peripherally presented stimuli (Levy et al., 2001). We investigated whether this eccentricity bias was also evident in visual working memory. In Experiment 1, we found that working memory performance for faces decreased towards the periphery while the performance for buildings remained unchanged across different eccentricities. To rule out the possibility that lower level features influence these results, we manipulated the spatial frequency of faces and buildings (Experiment 2) and the spatial layout information of the buildings (Experiment 3). In both of the experiments, we replicated the results of Experiment 1, even when these lower level features of stimuli were controlled. Consistent with previous findings, the current results suggest that each object category is processed in a different manner depending on the eccentricity. This eccentricity bias is likely the result of how the high-order object areas represent different object categories.     

Memory-conjunction errors: Miscombination of stored stimulus features can produce illusions of memory

We demonstrate that subjects will often claim to have previously seen a new stimulus if they have previously seen stimuli containing its component features. Memory for studied stimuli was measured using a "yes"/"no" recognition test. There were three types of test stimuli: target stimuli, which had been presented during study, conjunction stimuli, constructed by combining the features of separate study stimuli, and feature stimuli, in which studied stimulus features were combined with new, unstudied, features. For both nonsense words and faces, the subjects made many more false alarms for conjunction than for feature stimuli. Additional experiments demonstrated that the results were not due to physical similarity between study and test stimuli and that conjunction errors were much more common than feature errors in recall. The results demonstrate that features of stored stimuli maintain some independence in memory and can be incorrectly combined to produce recognition errors.     

Dynamic prototypicality effects in visual search

In recent studies, researchers have discovered a larger neural activation for stimuli that are more extreme exemplars of their stimulus class, compared with stimuli that are more prototypical. This has been shown for faces as well as for familiar and novel shape classes. We used a visual search task to look for a behavioral correlate of these findings regarding both simple geometrical shapes and more complex, novel shape classes. The latter stimulus set enabled us to control for the physical properties of the shapes, establishing that the effects are solely due to the positions of the particular stimuli in a particular shape space (i.e., more extreme versus more central in shape space) and not to specific shape features. The results indicate that finding an atypical instance of a shape class among more prototypical ones is easier and faster than the other way around. The prototypical status of a shape in our experiment could change very quickly, that is, within minutes, depending on the subset of shapes that was shown to the participants. Manipulating the degree of familiarity toward the shapes by selectively increasing familiarity for the extreme shapes did not influence our results. In general, we show that the prototypical status of a stimulus in visual search is a highly dynamic property, depending on the distribution of stimuli within a shape space but not on familiarity with the prototype.