Environmental toxicants and developmental disabilities: a challenge for psychologists

Developmental, learning, and behavioral disabilities are a significant public health problem. Environmental chemicals can interfere with brain development during critical periods, thereby impacting sensory, motor, and cognitive function. Because regulation in the United States is based on limited testing protocols and essentially requires proof of harm rather than proof of lack of harm, some undefined fraction of these disabilities may reflect adverse impacts of this "vast toxicological experiment" (H. L. Needleman, as quoted in B. Weiss & P. J. Landrigan, 2000, p. 373). Yet the hazards of environmental pollutants are inherently preventable. Psychologists can help prevent developmental disabilities by mobilizing and affecting public policy, educating and informing consumers, contributing to interdisciplinary research efforts, and taking action within their own homes and communities to reduce the toxic threat to children.     

On the limits of infants' quantification of small object arrays

Recent work suggests that infants rely on mechanisms of object-based attention and short-term memory to represent small numbers of objects. Such work shows that infants discriminate arrays containing 1, 2, or 3 objects, but fail with arrays greater than 3 [Feigenson, L., & Carey, S. (2003). Tracking individuals via object-files: Evidence from infants' manual search. Developmental Science, 6, 568-584; Feigenson, L., Carey, S., & Hauser, M. (2002). The representations underlying infants' choice of more: Object files versus analog magnitudes. Psychological Science, 13(2), 150-156]. However, little is known about how infants represent arrays exceeding the 3-item limit of parallel representation. We explored possible formats by which infants might represent a 4-object array. Experiment 1 used a manual search paradigm to show that infants successfully discriminated between arrays of 1 vs. 2, 2 vs. 3, and 1 vs. 3 objects. However, infants failed to discriminate 1 vs. 4 despite the highly discriminable ratio, providing the strongest evidence to date for object-file representations underlying performance in this task. Experiment 2 replicated this dramatic failure to discriminate 1 from 4 in a second paradigm, a cracker choice task. We then showed that infants in the choice task succeeded at choosing the larger quantity with 0 vs. 4 crackers and with 1 small vs. 4 large crackers. These results suggest that while infants failed to represent 4 as “exactly 4”, “approximately 4”, “3”, or as even as “a plurality”, they did represent information about the array, including the existence of a cracker or cracker-material and the size of the individual objects in the array.     

Never getting to zero: Elementary school students' understanding of the infinite divisibility of number and matter

Clinical interviews administered to third- to sixth-graders explored children's conceptualizations of rational number and of certain extensive physical quantities. We found within child consistency in reasoning about diverse aspects of rational number. Children's spontaneous acknowledgement of the existence of numbers between 0 and 1 was strongly related to their induction that numbers are infinitely divisible in the sense that they can be repeatedly divided without ever getting to zero. Their conceptualizing number as infinitely divisible was strongly related to their having a model of fraction notation based on division and to their successful judgment of the relative magnitudes of fractions and decimals. In addition, their understanding number as infinitely divisible was strongly related to their understanding physical quantities as infinitely divisible. These results support a conceptual change account of knowledge acquisition, involving two-way mappings between the domains of number and physical quantity.     

It was the best of times, it was the worst of times: doctoral students' experiences of family therapy research training through alternative forms of data representation

In this study, we interviewed 14 doctoral students from 10 COAMFTE-accredited doctoral programs to learn more about how they experienced their research training and what they might suggest to strengthen the research culture in their training programs. We solicited somewhat unconventional data--metaphors, poetry, free associations, critical experiences--to (a) tap into our participants' underlying thought processes, (b) capture the multifaceted nature of their doctoral research training, and (c) represent the richness of our participants' subjective experiences. The themes we identified reflect both positive and negative research training experiences and suggest several ways that family therapy program faculty might improve their programs' research training and culture.     

Visual discrimination of spectral distributions

Human observers seem to be able to use different features that classify materials with a large degree of accuracy. In this paper, we look at human perception of statistical properties of the spectral distribution in a scene. We investigated whether human observers can discriminate just as accurately between coloured textures that have a spectral distribution due either to shading only or to both shading and specular reflectance as between uniform colours. Thresholds for the discrimination of coloured textures are about 15 times as high as thresholds for the discrimination of uniform colours, provided there is a sharp transition between the two colours. However, the coloured texture thresholds are only 1.5 times higher when we introduce a gradual transition between the two colours. There are also distinct qualitative differences in discrimination thresholds for different base colours. These differences cannot be predicted from discrimination thresholds for uniform colours. Human observers are surprisingly good at discriminating between a material edge and a shadow edge in complex scenes. Statistical differences in the orientation of the colour distributions in colour space might be used to accomplish this. In a second experiment we investigated how well observers can discriminate between two linear distributions in colour space that have the same base colour but different orientations. When we vary the line-length in R, G, B space, thresholds cannot be predicted completely by the conservation of the average distance between the two distributions. This means that observers use not only the maximum colour difference in the stimulus to do the task, but other cues are also involved.     

Neuroreceptor imaging of stress and mood disorders

Techniques such as positron emission tomography and single photon emission computed tomography allow for the imaging of neurotransmitter receptors and transporters in the brain. These tools have been used to investigate serotonergic, dopaminergic, and opioidergic function in healthy subjects as well as in patients with major depressive disorder, bipolar disorder, and other mood disorders. Pharmacologic challenges, such as amphetamine challenge, and physiologic stressors, such as pain challenge, have been used to further examine the function of these neurotransmitter systems. Neuroimaging of patient populations before and after medication treatment may be useful to understand changes in neurotransmission that accompany disease remission. As new radiotracers with higher selectivity for the various receptors and transporters are developed, imaging techniques may provide new insights into the pathophysiology of mood disorders, leading to improved diagnosis and treatment.     

Infants' attribution of a goal to a morphologically unfamiliar agent

How do infants identify the psychological actors in their environments? Three groups of 12‐month‐old infants were tested for their willingness to encode a simple approach behavior as goal‐directed as a function of whether it was performed by (1) a human hand, (2) a morphologically unfamiliar green object that interacted with a confederate and behaved intentionally, or (3) the same unfamiliar green object that behaved in a matched, but apparently random manner. Using a visual habituation technique, only infants in the first two conditions were found to encode the approach behavior as goal‐directed. Thus infants appear able to attribute goals to non‐human, even unfamiliar agents. These results imply that by the end of the first year of life infants have a broad notion of what counts as an agent that cannot easily be reduced to humans, objects that are perceptually similar to humans, or objects that display self‐propulsion.     

Preference and performance measures of handedness

Handedness cannot be predicted using a single performance measure, and preference measures of handedness are unreliable because of their subjectivity. This report was designed to examine the relationship between hand performance and hand preference using six different measures: the Waterloo Handedness Questionnaire (a measure of hand preference), the Wathand Box (a performance-based indicator of hand preference), two pegboard tasks, finger tapping, and grip strength and to determine the most accurate performance-based predictor of hand preference as measured by the Waterloo Handedness Questionnaire. Multiple linear regression analysis showed that together, the Wathand Box score and the lateralized place phase of the grooved pegboard task were the most accurate predictors of hand preference.     

Encoding context and false recognition memories

False recognition of an extralist word that is thematically related to all words of a study list may reflect internal activation of the theme word during encoding followed by impaired source monitoring at retrieval, that is, difficulty in determining whether the word had actually been experienced or merely thought of. To assist source monitoring, distinctive visual or verbal contexts were added to study words at input. Both types of context produced similar effects: False alarms to theme-word (critical) lures were reduced; remember judgements of critical lures called old were lower; and if contextual information had been added to lists, subjects indicated as much for list items and associated critical foils identified as old. The visual and verbal contexts used in the present studies were held to disrupt semantic categorisation of list words at input and to facilitate source monitoring at output.