Jules Davidoff

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.

Hemispheric sensitivity differences in the perception of colour.

Signal detection analysis was performed on data obtained from discrimination tasks using lateralized coloured stimuli. It was found that there was a right hemisphere superiority in discriminability to both hue and saturation.

Language and perceptual categorisation

In a pioneering set of experiments, Rosch investigated the colour processing of a remote traditional culture. It was concluded that colours form universally natural and salient categories. However, our own cross-cultural research, backed up by neuropsychological data and interference studies, indicates that perceptual categories are derived from the words in the speakers language. The new data support a rather strong version of the Whorfian view that perceptual categories are organized by the linguistic systems of our mind.

The Mental Representations of Faces and Houses: Issues Concerning Parts and Wholes

We explore the integration of facial features and house parts to form holistic representations of complete objects. In Experiments 1, 2, and 3, we test for evidence of the holistic representation of houses and faces. We do so by testing for a complete over part probe advantage (CPA) in 2AFC recognition and matching tasks. We present evidence consistent with holistic features being represented for both types of stimuli. In Experiments 4 and 5, we examine further theeffect with faces. Experiment 4 shows thatfacial features used in the matching task contribute differentially to CPAs across varying probe delays but with a similar pattern to that found in the recognition task (Experiment 1). Experiment5 shows thatCPAs are mandatory and cannot be removed by precueing with the probe type or the name of the feature to be probed.

The bare bones of object recognition: implications from a case of object recognition impairment

Three experiments were designed to investigate the performance of a patient (RK) who could name objects when presented in conventional views but showed catastrophic failures in identification from unconventional views. The aim of all three experiments was to assess the properties of the central representations that allow recognition of objects presented in conventional but not unconventional views. All three experiments showed that RK had problems in object identification not apparent from his naming performance. In the first experiment, RK was found to be extremely impaired at recognising the parts of objects even though he could name the whole object. In the second experiment, alterations in colour, shape and parts of objects were undetected in stimuli that he could name. In the third experiment, RK showed considerable difficulty with mirror-images and inversion tasks. The explanation for RKs impaired object recognition could not be attributed to defects to his early visual processing. We argue that RKs recognition is achieved through abstract (object-centred) representations that are global rather than local, and quite independent of their spatial framework. These abstract representations we take to be the essential bare bones for object recognition.

More Accurate Size Contrast Judgments in the Ebbinghaus Illusion by a Remote Culture

The Ebbinghaus (Titchener) illusion was examined in a remote culture (Himba) with no words for geometric shapes. The illusion was experienced less strongly by Himba compared with English participants, leading to more accurate size contrast judgments in the Himba. The study included two conditions of inducing stimuli. The illusion was weaker when the inducing stimuli were dissimilar (diamonds) to the target (circle) compared with when they were similar (circles). However, the illusion was weakened to the same extent in both cultures. It is argued that the more accurate size judgments of the Himba derive from their tendency to prioritize the analysis of local details in visual processing of multiple objects, and not from their impoverished naming.

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.