Debi Roberson

Colour categories in a stone-age tribe

The Dani of Irian Jaya are a stone-age Melanesian people who have provided an empirical basis for the study of cross-cultural perception and cognition. Although they had only two terms for describing colour, the Dani memory for colour seemed to be much like that of modern English speakers. We have investigated another stone-age culture, the Berinmo of Papua New Guinea, for the way in which they categorize colours, but the results do not support the idea that colour categories could be universal.

The categorical perception of colors and facial expressions: The effect of verbal interference

A series of five experiments examined the categorical perception previously found for color and facial expressions. Using a two-alternative forced-choice recognition memory paradigm, it was found that verbal interference selectively removed the defining feature of categorical perception. Under verbal interference, there was no longer the greater accuracy normally observed for cross-category judgments relative to within-category judgments. The advantage for cross-category comparisons in memory appeared to derive from verbal coding both at encoding and at storage. It thus appears that while both visual and verbal codes may be employed in the recognition memory for colors and facial expressions, subjects only made use of verbal coding when demonstrating categorical perception.

Color categories: Evidence for the cultural relativity hypothesis

The question of whether language affects our categorization of perceptual continua is of particular interest for the domain of color where constraints on categorization have been proposed both within the visual system and in the visual environment. Recent research (Roberson, Davies, & Davidoff, 2000; Roberson et al., in press) found substantial evidence of cognitive color differences between different language communities, but concerns remained as to how representative might be a tiny, extremely remote community. The present study replicates and extends previous findings using additional paradigms among a larger community in a different visual environment. Adult semi-nomadic tribesmen in Southern Africa carried out similarity judgments, short-term memory and long-term learning tasks. They showed different cognitive organization of color to both English and another language with the five color terms. Moreover, Categorical Perception effects were found to differ even between languages with broadly similar color categories. The results provide further evidence of the tight relationship between language and cognition.

Similarity and categorisation: neuropsychological evidence for a dissociation in explicit categorisation tasks

A series of experiments are reported on a patient (LEW) with difficulties in naming. Initial findings indicated severe impairments in his ability to freesort colours and facial expressions. However, LEWs performance on other tasks revealed that he was able to show implicit understanding of some of the classic hallmarks of categorical perception; for example, in experiments requiring the choice of an odd-one-out, the patient chose alternatives dictated by category rather than by perceptual distance. Thus, underlying categories appeared normal and boundaries appeared intact. Furthermore, in a two-alternative forced-choice recognition memory task, performance was worse for within-category decisions than for cross-category decisions. In a replication of the study of Kay and Kempton [Kay, P., Kempton, W., 1984. What is the Sapir-Whorf hypothesis? American Anthropologist 86, 65-78], LEW showed that his similarity judgements for colours could be based on perceptual or categorical similarity according to task demands. The consequences for issues concerned with perceptual categories and the relationship between perceptual similarity and explicit categorisation are considered; we argue for a dissociation between these kinds of judgements in the freesort tasks. LEWs inability to make explicit use of his intact (implicit) knowledge is seen as related to his language impairment.

Color Categories Are Culturally Diverse in Cognition as Well as in Language

Categorization is a fundamental property of human cognition. This article presents a summary of recent research that has reexamined the nature of linguistic and nonlinguistic color categories and the relationship between them. Improvements in experimental paradigms combined with a better understanding of the relationship between physiology and higher level cognition have led to a clearer understanding of the complexities of the relationship between culture, language, cognition, and perception. It is concluded that possession of linguistic color categories facilitates recognition and influences perceptual judgments, even in languages with terms that are less abstract than English. Cognitive categories for color appear to be tightly tied to the linguistic terms used to describe them.

Preserved thematic and impaired taxonomic categorisation: a case study

The present paper seeks to understand more about categorisation and its relation to naming. A patient with language impairments (LEW) was examined in a three-part investigation of his ability to make classification decisions. The first part demonstrated LEW’s inability to make taxonomic classifications of shape thus confirming his previously documented impaired perceptual categorisation. The second part demonstrated that, despite LEW’s inability to perform simple taxonomic classifications, he could reason analogically as well as a 4/5 year-old child. It is therefore argued that taxonomic classifications cannot be driven by the development of analogical reasoning. The third part more directly contrasted thematic and taxonomic classification. LEW showed a preference for thematic classification. In fact, there was no evidence of any substantial ability to make taxonomic colour classifications despite evidence for good preservation of the associated object-colour knowledge.

Categorical perception of facial expressions: Evidence for a "category adjustment" model

Four experiments probed the nature of categorical perception (CP) for facial expressions. A model based on naming alone failed to accurately predict performance on these tasks. The data are instead consistent with an extension of thecategory adjustment model (Huttenlocher et al., 2000), in which the generation of a verbal code (e.g., “happy”) activated knowledge of the expression category’s range and central tendency (prototype) in memory, which was retained as veridical perceptual memory faded. Further support for a memory bias toward the category center came from a consistently asymmetric pattern of within-category errors. Verbal interference in the retention interval selectively removed CP for facial expressions, under blocked, but not under randomized presentation conditions. However, verbal interference at encoding removed CP even under randomized conditions and these effects were shown to extend even to caricatured expressions, which lie outside the normal range of expression categories.

Cultural Relativity in Perceiving Emotion From Vocalizations

A central question in the study of human behavior is whether certain emotions, such as anger, fear, and sadness, are recognized in nonverbal cues across cultures. We predicted and found that in a concept-free experimental task, participants from an isolated cultural context (the Himba ethnic group from northwestern Namibia) did not freely label Western vocalizations with expected emotion terms. Responses indicate that Himba participants perceived more basic affective properties of valence (positivity or negativity) and to some extent arousal (high or low activation). In a second, concept-embedded task, we manipulated whether the target and foil on a given trial matched in both valence and arousal, neither valence nor arousal, valence only, or arousal only. Himba participants achieved above-chance accuracy only when foils differed from targets in valence only. Our results indicate that the voice can reliably convey affective meaning across cultures, but that perceptions of emotion from the voice are culturally variable.

What’s in the name? Categorical perception for unfamiliar faces can occur through labeling

The conditions under which categorical perception (CP) occurs for unfamiliar faces are unclear. Although CP is generally found only for familiar faces, it has been reported for unfamiliar faces after brief training (Levin & Beale, 2000) or even without any learning of the original faces (Campanella, Hanoteau, Seron, Joassin, & Bruyer, 2003). Three experiments investigated whether CP can be observed for an unfamiliar morphed face continuum without preexposure to the endpoints of the continuum (Experiment 1); with brief exposure to the endpoints (Experiment 2); or with exposure to named endpoints (Experiment 3). CP was always observed for matched pairs of famous faces. However, CP for unfamiliar faces was induced only when participants observed names paired with the endpoint faces before the start of the experiment. The results suggest that CP effects for unfamiliar faces can be observed extremely rapidly when clear category labels are presented.

Categorical perception effects reflect differences in typicality on within-category trials

Many studies have shown better discrimination of two stimuli that cross a category boundary than of two stimuli belonging to the same category. This finding, known as categorical perception, is generally assumed to reflect consistently good performance on cross-category trials, relative to within-category trials. However, Roberson, D., Damjanovic, L., and Pilling, M. (Memory & Cognition, 35, 1814–1829, 2007) revealed that performance on within-category pairs of morphed facial expressions matched performance on cross-category trials when the target was a good exemplar of its category. Here, we investigate the generality of that finding by conducting new analyses of data from a series of studies of categorical perception in facial identity and color domains with speakers of different languages. Consistent with Roberson et al. (2007), the new analyses demonstrate that performance for central targets on within-category trials is as good as performance on cross-category trials. Participants perform badly on within-category items only when the target is closer to the category boundary than is the distractor. These results provide no support for the view that categorical perception is associated with increased perceptual sensitivity at category boundaries.