Ten-Month-Old Infants' Reaching Choices for "more": The Relationship between Inter-Stimulus Distance and Number.

Animals and human infants discriminate numerosities in visual sets. Experiments on visual numerical judgments generally contrast sets in which number varies (e.g., the discrimination between 2 and 3). What is less investigated, however, is set density, or rather, the inter-stimulus distance between the entities being enumerated in a set. In this study, we investigated the role of set density in visual sets by 10-month-old infants. In Experiment 1, infants were offered a choice between two sets each containing four items of the exact same size varying in the distance in between the items (ratio 1:4). Infants selected the set in which the items are close together (higher density). Experiment 2 addressed the possibility that this choice was driven by a strategy to "select all in one go" by reducing the size and distance of items. Ten-month-olds selected the sets with higher density (less inter-stimulus distance) in both experiments. These results, although bearing replication because of their originality, seem consistent with principles in Optimal Foraging in animals. They provide evidence that a comparable rudimentary capacity for density assessment (of food items) exists in infants, and may work in concert with their numerical representations.

Quantity discrimination in salamanders.

We investigated discrimination of large quantities in salamanders of the genus Plethodon. Animals were challenged with two different quantities (8 vs 12 or 8 vs 16) in a two-alternative choice task. Stimuli were live crickets, videos of live crickets or images animated by a computer program. Salamanders reliably chose the larger of two quantities when the ratio between the sets was 1:2 and stimuli were live crickets or videos thereof. Magnitude discrimination was not successful when the ratio was 2:3, or when the ratio was 1:2 when stimuli were computer animated. Analysis of the salamanders' success and failure as well as analysis of stimulus features points towards movement as a dominant feature for quantity discrimination. The results are generally consistent with large quantity discrimination investigated in many other animals (e.g. primates, fish), current models of quantity representation (analogue magnitudes) and data on sensory aspects of amphibian prey-catching behaviour (neuronal motion processing).

Social-cognitive beliefs, alcohol, and tobacco use: a prospective community study of change following a ban on smoking in public places.

OBJECTIVE: To examine social-cognitive change associated with behavior change after the introduction of a smoke-free public places policy. DESIGN: Adults (N = 583) who use public houses licensed to sell alcohol (pubs) completed questionnaires assessing alcohol and tobacco consumption and social-cognitive beliefs 2 months prior to the introduction of the smoking ban in England on July 1, 2007. Longitudinal follow-up (N = 272) was 3 months after the introduction of the ban. MAIN OUTCOME MEASURES: Social-cognitive beliefs, daily cigarette consumption, and weekly alcohol consumption. RESULTS: Smokers consumed considerably more alcohol than did nonsmokers at both time points. However, a significant interaction of Smoking Status x Time showed that while smokers had consumed fewer units of alcohol after the ban, nonsmokers showed an increase over the same period. There was a significant reduction in number of cigarettes consumed after the ban. Subjective norms concerning not smoking, and perceived severity of smoking-related illness increased across time. Negative outcomes associated with not smoking were reduced among former smokers and increased across time among smokers. Regression analyses showed that changes in subjective norm and negative outcome expectancies accounted for significant variance in change in smoking across time. CONCLUSION: Results suggest that the smoking ban may have positive health benefits that are supported by social-cognitive change.

Horses (Equus caballus) select the greater of two quantities in small numerical contrasts.

The ability to select the greater numerosity over another in small sets seems to stem from the calculation of which set contains more, and has been taken as evidence of a primordial representation at the roots of the primate numerical system. We tested 56 horses (Equus caballus) in a paradigm previously used with human infants and nonhuman primates. Horses saw two quantities paired in contrasts-2 versus 1, 3 versus 2, 6 versus 4 and a control for volume, 2 versus 1 big-and had to make a choice by snout touching the container holding the numerosity selected. The horses spontaneously selected the greater of the two quantities when the numerosities were small. These results add to evidence showing spontaneous quantity assessment in a variety of species.

Disposition to recognize goals in infant chimpanzees.

Do nonhuman primates attribute goals to others? Traditional studies with chimpanzees provide equivocal evidence for "mind reading" in nonhuman primates. Here we adopt looking time, a methodology commonly used with human infants to test infant chimpanzees. In this experiment, four infant chimpanzees saw computer-generated stimuli that mimicked a goal-directed behavior. The baby chimps performed as well as human infants, namely, they were sensitive to the trajectories of the objects, thus suggesting that chimpanzees may be endowed with a disposition to understand goal-directed behaviors. The theoretical implications of these results are discussed.

Salamanders ( Plethodon cinereus) go for more: rudiments of number in an amphibian.

Techniques traditionally used in developmental research with infants have been widely used with nonhuman primates in the investigation of comparative cognitive abilities. Recently, researchers have shown that human infants and monkeys select the larger of two numerosities in a spontaneous forced-choice discrimination task. Here we adopt the same method to assess in a series of experiments spontaneous choice of the larger of two numerosities in a species of amphibian, red-backed salamanders ( Plethodon cinereus). The findings indicate that salamanders "go for more," just like human babies and monkeys. This rudimentary capacity is a type of numerical discrimination that is spontaneously present in this amphibian.