How western scrub-jays (Aphelocoma californica) select a nut: effects of the number of options, variation in nut size, and social competition among foragers

Western scrub-jays (Aphelocoma californica) often visually assess and handle several whole (unshelled) peanuts before selecting one to transport and cache; this behavior is a search for a preferred heavy nut. I repeatedly video-taped individually identifiable jays as they landed on a feeding platform and chose from presentations of peanuts that varied in the number of items or in the distribution of sizes. I examined how differences among these presentations and a bird’s social status affected the amount of assessment and the economic consequences of choice. I also examined the specific patterns of handling peanuts, called sampling, to quantify the degree to which sampling sequences were typified by repeated comparisons among sampled peanuts (retrospective sampling), or sequential assessment and rejection of peanuts (prospective sampling). Peanut assessment was more extensive and prospective when there were many options from which to choose than when there were few. Peanut assessment was more extensive and retrospective when options were similar in size than when they varied. Scrub-jays were more likely to make repeated comparisons immediately before selecting a peanut than elsewhere in a sampling sequence. Subordinate scrub-jays, who were at the greatest risk of pre-emption by competitors, assessed peanuts less extensively and were more prospective in their sampling than dominants. Unless peanuts were very similar in size, jays were more accurate at selecting a high-quality peanut and achieved a higher rate of food storage than if they had not assessed. These results show that scrub-jays can adaptively modify how they search to improve their rate of food storage, and also suggest some of the specific search tactics used by jays when assessing peanuts. Received: 26 April 1999 / Accepted after revision: 10 October 1999     

On the locus of the divided-attention effects

Reaction times in a choice reaction task were used to localize the livided-attention effect (less proficient performance under dual than under ingle-taks conditions) in a sequential-stage model of human information processing. Experiment 1 eliminated a central (memory-dependent) processing tage, while Experiment 2 suggested that a stimulus sampling process within the hitial encoding stage was the locus of the effect. Thus, the effect was localized in the input, not the central or an output stage of processing. A slower stimulus ampling rate was indicated under dual-than under single-task conditions.     

青少年网络成瘾人格特征研究

本研究采用问卷调查法,对某初级中学363名初中生的网络成瘾状况与人格特征进行研究。结论表明:初中生网络成瘾检出率为5.79%;初中生在网络成瘾存在性别差异,男生比女生更易成瘾。网络成瘾学生与非成瘾学生在《卡特尔十四种人格因素问题》中的忧虑性、自律性、适应性与焦虑性、孤独倾向、身体症状和冲动倾向等因子上差异显著。与非成瘾学生相比,成瘾学生的自制能力较差,成瘾学生可能更经常体验到孤独、焦虑和不满,并且在生活中较容易出现适应不良现象。     

The distribution matters: two types of sample-size tasks

Different studies on how well people take sample size into account have found a wide range of solution rates. In a recent review, Sedlmeier and Gigerenzer (1997) suggested that a substantial part of the variation in results can be explained by the fact that experimenters have used two different types of sample-size tasks, one involving frequency distributions and the other sampling distributions. This suggestion rested on an analysis of studies that, with one exception, did not systematically manipulate type of distribution. In the research reported in this paper, well-known sample-size tasks were used to examine the hypothesis that frequency distribution versions of sample-size tasks yield higher solution rates than corresponding sampling distribution versions. In Study 1, a substantial difference between solution rates for the two types of task was found. Study 2 replicated this finding and ruled out an alternative explanation for it, namely, that the solution rate for sampling distribution tasks was lower because the information they contained was harder to extract than that in frequency distribution tasks. Finally, in Study 3 an attempt was made to reduce the gap between the solution rates for the two types of tasks by giving participants as many hints as possible for solving a sampling distribution task. Even with hints, the gap in performance remained. A new computational model of statistical reasoning specifies cognitive processes that might explain why people are better at solving frequency than sampling distribution tasks. Copyright© 1998 John Wiley & Sons, Ltd.     

Understanding the effects of sample size on the variability of the mean

In the first three experiments, we attempted to learn more about subjects' understanding of the importance of sample size by systematically changing aspects of the problems we gave to subjects. In a fourth study, understanding of the effects of sample size was tested as subjects went through a computerassisted training procedure that dealt with random sampling and the sampling distribution of the mean. Subjects used sample size information more appropriately for problems that were stated in terms of the accuracy of the sample average or the center of the sampling distribution than for problems stated in terms of the tails of the sampling distribution. Apparently, people understand that the means of larger samples are more likely to resemble the population mean but not the implications of this fact for the variability of the mean. The fourth experiment showed that although instruction about the sampling distribution of the mean led to better understanding of the effects of sample size, subjects were still unable to make correct inferences about the variability of the mean. The appreciation that people have for some aspects of the law of large numbers does not seem to result from an in-depth understanding of the relation between sample size and variability.     

Sample selection and inductive generalization

In two experiments with adults (N=126), we examined the influence of sampling procedure on inductive generalization. In predicate sampling, participants learned the category identity of individuals known to possess some property. In subject sampling, individuals selected for category identity were discovered to possess a novel property. In both experiments, sampling procedure influenced induction. Predicate sampling resulted in very narrow generalization, whereas subject sampling yielded a fairly high and constant rate of projection. Differences in confidence of generalizations were also observed. Conditions in which evidence was described as randomly sampled from a collection of animals yielded a consistent decrease in projections as predicted by similarity-based models. The results are presented as support for an evidence-based view of induction.     

Methods of time sampling: A reappraisal of momentary time sampling and partial interval recording

We compared the accuracy of momentary time sampling (MTS) and partial interval recording (PIR) in estimating both absolute behavioral levels and relative change. A computer randomly generated runs of pseudobehavior varying in duration and rate and simulated MTS and PIR of each run. Results indicated that when estimating absolute behavioral levels, duration rather than rate should be used as the dependent measure, and MTS is more accurate than PIR. In contrast, PIR is the more sensitive method for detecting relative changes in behavioral levels, although, at high rates, PIR tends to underestimate the degree of change.     

Subjective sampling distributions and the additivity of estimates

Abstract.— Previous studies of sampling distributions have been conducted almost exclusively under the assumption that persons behave in accordance with the "fundamental convention" of probability, i.e. that the sum of all probability estimates will equal 1. When this assumption was tested by asking subjects to give "unrestricted" probability estimates of all possible outcomes of samples from a given population, a general tendency of overestimation made the sum of all probabilities exceed 1 to a considerable extent. The subjective sampling distributions appeared to be unaffected by sample size ( N=5 or 10) and number of outcomes, and were flatter than the corresponding "objective" sampling distributions.     

Using three-dimensional graphics in neuropsychological hypothesis testing

This paper presents the application of an overlapping sampling technique used with a fast Fourier transform on electroencephalographic data. The use of this sampling and analysis technique is demonstrated on data in which steady state, rate of change, and critical event hypotheses are tested. The benefit of applying computer-generated three-dimensional graphics to the results of using this innovative sampling and analysis technique is emphasized.     

Sampling distributions of the entropy in visual scanning

Identifying true statistical dependencies in visual-scanning data involves showing that the observed scanning pattern is significantly more ordered than that which would be produced by a stratified random-sampling model. In the past, entropy has been used as the index to measure statistical order or dependency. Due to the unknown nature of the underlying sampling distributions of entropy, however, researchers have had to use relatively less powerful nonparametric statistical tests to determine significance. In this paper we present relevant portions of the family of sampling distributions of entropy and show that they are sufficiently normally distributed to allow the use of a more powerful parametric statistical test when attempting to distinguish among the different models of sampling.     

大连市171名中老年人两周患病及用药调查

为了解中老年人群患病和用药情况及其影响因素,在大连市某社区随机抽取171名50岁以上的居民进行问卷调查。结果发现,患病人群中80.6%患的是慢性病,以高血压、其他心血管疾病、糖尿病为主,应当加强中老年人的自我保健意识,真正做到以"预防为主",减少中老年人的发病率,根据处方用药,减少自我用药,并避免不良反应的发生。     

Reinforcer sampling: a technique for increasing the behavior of mental patients

Mental hospital patients in a motivating ward environment were using the available reinforcers less than was desired. A procedure for increasing the frequency of using reinforcers was developed: all patients were required to engage in the reinforcing event each time it was available but the duration of this required participation was limited so that the event was merely sampled. The effect of this required sampling was experimentally evaluated for three different reinforcers: going for a walk, watching a movie, and attending a music session. More patients used each of the three reinforcers and to a greater extent when the sampling procedure was used. Participation was increased even for those patients who had already been using the reinforcers, demonstrating that the technique did more than provide simple familiarization. Some familiarization was involved since the participation was slightly increased even after the sampling procedure was discontinued. The technique appears to be especially applicable when reinforcers are being delivered infrequently.     

Differences Between Minority,Majority, and Unanimous Group Members in the Communication of Information

This article integrates research on minority influence and information sampling in groups. The traditional information‐sampling paradigm implies that the discussion bias for common over unique information affects all types of groups universally. We proposed an alternative in which information sampling depends on the composition of opinions. We proposed that groups with a minority opinion may focus more on unique information and that a minority opinion may lead majority members to consider more preference‐inconsistent information. In a study that tested how minority, majority, and unanimous group members differ in their discussion of information, results lent no support for the alternative conception of information sampling. However, when the minority prevailed, minority members repeated significantly more common information than when the majority prevailed.     

Psychologists in secondary schools: Training and present patterns of service

Psychologists serving randomly selected secondary schools were surveyed regarding actual and preferred patterns of service and training. Though a small sample was employed, the random sampling procedure and high response rate attained were viewed by the investigators as effective means for controlling the sampling error that often occurs in survey research. As a group, respondents indicated little specialized training for working with the secondary school population. Traditional assessment and report writing activities occupied the main portion of respondents' working time although nearly all reported involvement in the design and implementation of intervention plans for a variety of client groups. The psychologist-to-student ratio was found to be 1:6180, and more than 60% of those surveyed reported plans for a career change out of school psychology. One-fourth of the districts surveyed reported that psychological services were not regularly available.     

Continuous time modelling with individually varying time intervals for oscillating and non‐oscillating processes

When designing longitudinal studies, researchers often aim at equal intervals. In practice, however, this goal is hardly ever met, with different time intervals between assessment waves and different time intervals between individuals being more the rule than the exception. One of the reasons for the introduction of continuous time models by means of structural equation modelling has been to deal with irregularly spaced assessment waves (e.g., Oud & Delsing, 2010). In the present paper we extend the approach to individually varying time intervals for oscillating and non‐oscillating processes. In addition, we show not only that equal intervals are unnecessary but also that it can be advantageous to use unequal sampling intervals, in particular when the sampling rate is low. Two examples are provided to support our arguments. In the first example we compare a continuous time model of a bivariate coupled process with varying time intervals to a standard discrete time model to illustrate the importance of accounting for the exact time intervals. In the second example the effect of different sampling intervals on estimating a damped linear oscillator is investigated by means of a Monte Carlo simulation. We conclude that it is important to account for individually varying time intervals, and encourage researchers to conceive of longitudinal studies with different time intervals within and between individuals as an opportunity rather than a problem.     

Campus Student Suicide Rates: Fact or Artifact?

A review of all English-language studies (14 foreign and 17 American) on campus student suicides was undertaken. Only studies reporting original data and containing sufficient demographic information to compute standard mortality rates (SMR) or crude suicide rates were analyzed and organized into single-site studies. Only 4 single-site studies had a higher suicide rate than the comparable populations. Multiple-site collaborative studies done in the United States since 1960 strongly suggest a campus student suicide rate significantly less than in the matched control population. However, deficiencies in case finding, case definition, sampling bias, and statistical techniques may place these conclusions in doubt. The author outlines research methods that might be applied to future multiple-site studies to resolve questions related to late adolescent and young adult suicidal behavior on campus and in other similar educational settings.     

Development of infant prehension handedness: A longitudinal analysis during the 6- to 14-month age period

Handedness is a developmental phenomenon that becomes distinctively identifiable during infancy. Although infant hand-use preferences sometimes have been reported as unstable, other evidence demonstrates that infant hand-use preference for apprehending objects can be reliably assessed during the second half of the infant's first year of life. The current study provides further insight into the stability of prehension preferences. We modeled individual and group level patterns of prehension handedness during the period from 6 to 14 months of age. We examined the developmental trajectories for prehension handedness in relation to the sampling rate at which preferences are assessed. The results revealed interesting developmental changes in prehension handedness that can only be identified when using monthly sampling intervals. We conclude that using non-linear multilevel models of infant handedness with monthly sampling intervals permit us to accurately capture the developmental changes in manual skills that occur during this period of infancy.     

Sampling Development

Research in developmental psychology requires sampling at different time points. Accurate depictions of developmental change provide a foundation for further empirical studies and theories about developmental mechanisms. However, overreliance on widely spaced sampling intervals in cross-sectional and longitudinal designs threatens the validity of the enterprise. This article discusses how to sample development in order to accurately discern the shape of developmental change. The ideal solution is daunting: to summarize behavior over 24-hour intervals and collect daily samples over the critical periods of change. We discuss the magnitude of errors due to undersampling, and the risks associated with oversampling. When daily sampling is not feasible, we offer suggestions for sampling methods that can provide preliminary reference points and provisional sketches of the general shape of a developmental trajectory. Denser sampling then can be applied strategically during periods of enhanced variability, inflections in the rate of developmental change, or in relation to key events or processes that may affect the course of change. Despite the challenges of dense repeated sampling, researchers must take seriously the problem of sampling on a developmental time scale if we are to know the true shape of developmental change.     

Further evaluating the conditional decision rule for comparing two independent means

Many books on statistical methods advocate a ‘conditional decision rule’ when comparing two independent group means. This rule states that the decision as to whether to use a ‘pooled variance’ test that assumes equality of variance or a ‘separate variance’ Welch t test that does not should be based on the outcome of a variance equality test. In this paper, we empirically examine the Type I error rate of the conditional decision rule using four variance equality tests and compare this error rate to the unconditional use of either of the t tests (i.e. irrespective of the outcome of a variance homogeneity test) as well as several resampling‐based alternatives when sampling from 49 distributions varying in skewness and kurtosis. Several unconditional tests including the separate variance test performed as well as or better than the conditional decision rule across situations. These results extend and generalize the findings of previous researchers who have argued that the conditional decision rule should be abandoned.