Gradient effects of within-category phonetic variation on lexical access

In order to determine whether small within-category differences in voice onset time (VOT) affect lexical access, eye movements were monitored as participants indicated which of four pictures was named by spoken stimuli that varied along a 0-40 ms VOT continuum. Within-category differences in VOT resulted in gradient increases in fixations to cross-boundary lexical competitors as VOT approached the category boundary. Thus, fine-grained acoustic/phonetic differences are preserved in patterns of lexical activation for competing lexical candidates and could be used to maximize the efficiency of on-line word recognition.     

Discrimination between host songs by brood parasitic brown-headed cowbirds ( Molothrus ater)

Songbirds can learn both to produce and to discriminate between different classes of acoustic stimuli. Varying levels of auditory discrimination may improve the fitness of individuals in certain ecological and social contexts and, thus, selection is expected to mold the cognitive abilities of different species according to the potential benefits of acoustic processing. Although fine-scale auditory discrimination of conspecific songs and calls has been frequently reported for brood parasitic brown-headed cowbirds (Molothrus ater), it remains unclear why and how they perceive differently the songs of their many host species. Using habituation-dishabituation paradigms and measuring behavioral and physiological (heart-rate) responses, we found that captive female cowbirds consistently discriminated between songs of two host species, the song sparrow (Melospiza melodia) and the red-winged blackbird (Agelaius phoeniceus). Playback experiments with stimuli composed of con-specific followed by heterospecific vocalizations in the field also demonstrated discrimination between these heterospecific songs even though cowbirds were not attracted to playbacks of either host species' songs alone. Our results do not directly support a nest-searching function of heterospecific song discrimination by cowbirds and are most consistent with a function of the parasites' avoidance of attacks by their agressive hosts. These data demonstrate discrimination between heterospecific vocalizations by brown-headed cowbirds and add a novel dimension to the already expansive auditory perceptual abilities of brood parasitic species and other songbirds. Electronic Publication     

Dissociating prelexical and postlexical processing of affective information in the two hemispheres: effects of the stimulus presentation format

Using a lexical decision task, the authors investigated whether brain asymmetries in the detection of emotionally negative semantic associations arise only at a perceptually discriminative stage at which lexical analysis is accurate or can already be found at crude and incomplete levels of perceptual representation at which word-nonword discrimination is based solely on guessing. Emotionally negative and neutral items were presented near perceptual threshold in the left and right visual hemifields. Word-nonword discrimination performance as well as the bias to classify a stimulus as a "word" (whether or not it actually is a word) were assessed for a normal, horizontal stimulus presentation format (Experiment 1) and for an unusual, vertical presentation format (Experiment 2). Results show that while the two hemispheres are equally able to detect affective semantic associations at a prelexical processing stage (both experiments), the right hemisphere is superior at a postlexical, perceptually discriminative stage (Experiment 2). Moreover, the findings suggest that only an unusual, nonoverlearned stimulus presentation format allows adequate assessment of the right hemisphere's lexical-semantic skills.     

More to 3-D vision than meets the eye

Does self-motion affect object recognition? Researchers have long studied how 3-D objects are recognized from different points of view, but have disregarded the observers' own movement by keeping them motionless. A recent study by Simons et al. shows that self-motion cannot be ignored, as it changes the way that objects are recognized.     

Different working memory capacity in normal young adults for visual and tactile letter recognition task

Thirty-nine young adult participants performing the visual and tactile n-back working memory task were compared. In the visual task, letters were presented on a computer screen and in the tactile task, plastic letters embedded on a board were explored tactually. The amount of incorrect responses increased with increasing memory load in both tasks, but was significantly lower in the visual task. Subgrouping the participants with extreme performances into "skilled" and "poor" performers showed that the best performance was found among "skilled" visual performers, and the worst one among "poor" tactile performers. There was more interindividual variation among tactile than visual performance. We conclude that tactile working memory capacity, measured here by letter recognition and letter memory, is generally more limited and shows more variability than visual memory in normal sighted participants.     

Action alters shape categories

Two experiments show that action alters the shape categories formed by 2-year-olds. Experiment 1 shows that moving an object horizontally (or vertically) defines the horizontal (or vertical) axis as the main axis of elongation and systematically changes the range of shapes seen as similar. Experiment 2 shows that moving an object symmetrically (or asymmetrically) also alters shape categories. Previous work has shown marked developmental changes in object recognition between 1 and 3 years of age. These results suggest a role for action in this developmental process.     

A critical boundary to the left-hemisphere advantage in visual-word processing

Two experiments explored boundary conditions for the ubiquitous left-hemisphere advantage in visual-word recognition. Subjects perceptually identified words presented directly to the left or right hemisphere. Strong left-hemisphere advantages were observed for UPPERCASE and lowercase words. However, only a weak effect was observed for AlTeRnAtInG-cAsE words, and a numerical reversal of the typical left-hemisphere advantage was observed for words in a visual prototype font (a very unfamiliar word format). Results support the theory that dissociable abstract and specific neural subsystems underlie visual-form recognition and fail to support the theory that a visual lexicon operates in the left hemisphere.     

Establishing visual category boundaries between objects: a PET study

Individuals with Alzheimer's disease (AD) often have problems in recognizing common objects. This visual agnosia may stem from difficulties in establishing appropriate visual boundaries between visually similar objects. In support of this hypothesis, showed that AD subjects have difficulties in establishing visual category boundaries between continuously graded shapes. In an attempt to investigate the neural basis of these impairments, the current study required a group of neurologically healthy elderly participants to categorically classify a series of ellipses varying in width while regional blood flow changes were measured using positron emission tomography (PET). Two categorization conditions were compared in order to isolate changes in cortical activity that dissociated the categorization of shapes situated either near or far from a category boundary that divided the width continuum. The participants produced a discontinuity in the probability and speed of categorizing the shapes at some point along the continuum, suggesting that the objects were classified into distinct categories. Moreover, a comparison of the PET scans obtained while the subjects were categorizing the shapes situated near vs. far form the category boundary revealed significant differences in cortical activity in the parietal and frontal brain areas. These findings suggest that both visuo-spatial and decision making mechanisms may be involved in establishing categorical distinctions between continuously graded stimuli. It is proposed that the functional role of the parietal and frontal cortical regions in establishing visual boundaries between categories of objects may be relevant for understanding object recognition impairments in AD.     

Event-related brain potential correlates of the other-race effect: A review

People are better at remembering own-race relative to other-race faces. Here, we review event-related brain potential (ERP) correlates of this so-called other-‘race’ effect (ORE) by discussing three critical aspects that characterize the neural signature of this phenomenon. First, difficulties with other-race faces initially emerge during perceptual processing, which is indexed by an increased N170. Second, as evidenced by ‘difference due to subsequent memory’ effects, more effortful processing of other-race faces is needed for successful encoding into long-term memory. Third, ERP old/new effects reveal that a stronger engagement of processing resources is also required for successful retrieval of other-race faces from memory. The ERP evidence available to date thus suggests widespread ethnicity-related modulations during both perceptual and mnemonic processing stages. We further discuss how findings from the ORE compared with potentially related memory biases (e.g. other-gender or other-age effects) and how ERP findings inform the ongoing debate regarding the mechanisms underlying the ORE. Finally, we outline open questions and potential future directions with an emphasis on using multiple, ecologically more valid ‘ambient’ images for each face to assess the ORE in paradigms that capture identity rather than image recognition.     

Differential ordering of objects and attributes

By reference to nominated attributes, a genus, being a population of objects of one specified kind, may be partitioned into species, being subpopulations of different kinds. A prototype is an object representative of its species within the genus. Using this framework, the paper describes how objects can be relatively differentiated with respect to attributes, and how attributes can be relatively differentiating with respect to objects. Methods and rationale for such differential ordering of objects and attributes are presented by example, formal development, and application.For a genus comprisingn species of object there is a subsetP ofn distinct prototypes. With respect tom nominated attributes, each object in has anm-element characterization. Together these determine ann ×m objects × attributes matrix, the rows of which are the characterizations of the prototypical objects. Over then species in , an associated relative frequency vector gives the distribution of objects (and of their characterizations). The matrix and vector associate the objects in with points in a metric space (P, ); and it is with respect to various sums of distances in this attribute space that one can differentially order objects and attributes.The definition of the distance function is generalized across kinds of difference, types of characterization, scale-types of measurement, Minkowskiindex 1, and any form of distribution of objects over species. Explanatory and taxonomic applications in psychology and other fields are discussed, with focus on classification, identification, recognition, and search. The Braille code and the identification of its characters provide illustration.An anticipation and some preliminary indications were given in Sutcliffe and Bristow (1966), Sutcliffe (1972, 1973), and Nowakowska (1975). Subsequently the ideas have been extended and their applications realized in a computer program which, in its development, has so far gone through many minor and three major revisions to its present form in Sutcliffe (1985). The foregoing provided the foundation for the empirical applications and for the presentation in this paper of the ideas in their general form. the research has been supported by funds from the University of Sydney Research Grant and from the Australian Research Grants Scheme. In the working out and exposition of the ideas I have very much benefited from constructive critical comment given by C. R. Latimer, J. B. Michell, G. Oliphant, and E. Seneta, and from the professional programming skills of Michael Wilson and David Shillito. I am grateful for the invitation and the facilities for writing extended during 1983 by Georges Noizet, Laboratoire de Psychologie Expérimentale, Université René Descartes, Paris V, and by Samuel Messick, Vice President for Research, E.T.S. Princeton, N.J. Finally, I acknowledge the improvements in presentation of this paper which have arisen from the editor's and reviewers' comments.