Effects of target and distractor heterogeneity on search for a color target.

Experiments were designed to investigate the effects of target and distractor heterogeneity on the threshold for detection of a color target in a search task. In the first two experiments stimuli were chosen so that the target and distractor stimuli varied along one Cardinal axis in color space, while the target differed from distractors along another Cardinal axis. The Cardinal axis signaling the relevant target-distractor difference was consistent from trial to trial within an experiment. When observers searched for a color target among homogeneous distractors but the color of the target and distractors changed from trial to trial there was a small increase in threshold. When the distractors within a display were heterogeneous, and the target color varied from trial to trial there was a larger and more consistent increase in threshold. Varying stimuli along a Cardinal axis other than the Cardinal axis that differentiates target and distractors can impair performance in visual search tasks. Further experiments showed that the presence of heterogeneous distractors had little or no effect on thresholds when location or color cues indicated that these stimuli were irrelevant to the task. Results suggest that the effect of heterogeneity in these experiments is attentional in nature rather than sensory.

Color mechanisms used in selecting stimuli for attention and making discriminations.

Previous work (Nagy & Thomas, 2003) showed that signals in different Cardinal color mechanisms could be combined to facilitate search for a color target. Further investigation (Nagy et al., 2003) suggested that signals in one Cardinal color mechanism were used to select a subset of stimuli to be attended, while signals in second Cardinal mechanism were used to discriminate the stimuli within the selected subset. In the studies described below, we asked if observers could use color mechanisms tuned to directions other than the Cardinal directions to select and discriminate stimuli. Observers searched for a single target stimulus that differed in chromaticity from nine distractor stimuli. A two-alternative forced-choice procedure was used to estimate thresholds. Results were consistent with the hypothesis that color mechanisms tuned to many different directions in color space mediate discrimination, but suggest that only signals in Cardinal mechanisms can be used to select stimuli for attention. Results imply that the selection of stimuli for attention on the basis of color may be mediated at the level of the lateral geniculate nucleus (LGN).

Social preferences of developing guinea pigs (Cavia porcellus) from the preweaning to the periadolescent periods.

Preference tests in a novel environment (Experiment 1) and unobtrusive observations in a specialized living environment (Experiment 2) examined the attractiveness of various classes of conspecifics for maturing guinea pigs (Cavia porcellus). It was found that (a). the young continued to remain near the mother well beyond weaning; (b). there was increased time spent with unrelated adult females, but not males, after weaning; (c). male and female offspring behaved similarly; and (d). littermates spent considerable time with each other. These results provide no evidence that guinea pigs approaching sexual maturity begin to associate preferentially with novel animals or potential breeding partners. Choices were largely predictable from earlier findings of the ability of various classes of conspecifics to reduce hypothalamic-pituitary-adrenal activity of the young.

Effects of a program of human interaction and alterations in diet composition on activity of the hypothalamic-pituitary-adrenal axis in dogs housed in a public animal shelter.

OBJECTIVE: To determine whether a program of human interaction or alterations in diet composition would alter activity of the hypothalamic-pituitary-adrenal (HPA) axis in dogs housed in an animal shelter. DESIGN: Prospective study. ANIMALS: 40 dogs. PROCEDURE: Dogs were (n = 20) or were not (20) enrolled in a program of regular supplemental human interaction (20 min/d, 5 d/wk, for 8 weeks) involving stroking, massaging, and behavioral training. In addition, half the dogs in each group were fed a typical maintenance-type diet, and the other half were fed a premium diet. Plasma cortisol and ACTH concentrations were measured during weeks 0, 2, 4, and 8 and before and after exposure to a battery of novel situations during weeks 0 and 8. RESULTS: Plasma cortisol concentration was significantly decreased by week 2, but plasma ACTH concentration was not significantly decreased until week 8 and then only in dogs fed the premium diet. Following exposure to novel situations, plasma cortisol and ACTH concentrations were significantly increased. However, during week 8, dogs enrolled in the program of human interaction had significantly lower increases in cortisol concentration than did dogs not enrolled in the program. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that both a program of human interaction and alterations in diet composition have moderating effects on activity of the HPA axis in dogs housed in an animal shelter and that activity of the HPA axis may be increased for a longer period during shelter housing than measurement of plasma cortisol concentration alone would suggest.

Exploring human interaction and diet effects on the behavior of dogs in a public animal shelter.

This study examined the effects of 2 manipulations--a brief, regular period of human contact and diet--on the behavior of dogs confined in a public animal shelter. A behavioral battery designed to assess reactions to novel situations, and a test of responsiveness to an unfamiliar human were administered both prior to (pretest) and immediately following (posttest) the 8-week intervention period. Overall, the regular periods of increased human contact together with a diet that contained augmented levels of digestible protein, fat, calories, and animal-derived ingredients reduced signs of behavioral reactivity from pretest to posttest. In some cases, the comparison diet appeared more effective, but only for dogs receiving minimal human interaction. The results indicate that a combination of human interaction and high quality diet may positively affect the behavior of dogs in animal shelters.