A Propensity Score Adjustment for Multiple Group Structural Equation Modeling

In the behavioral and social sciences, quasi-experimental and observational studies are used due to the difficulty achieving a random assignment. However, the estimation of differences between groups in observational studies frequently suffers from bias due to differences in the distributions of covariates. To estimate average treatment effects when the treatment variable is binary, Rosenbaum and Rubin (1983a) proposed adjustment methods for pretreatment variables using the propensity score. However, these studies were interested only in estimating the average causal effect and/or marginal means. In the behavioral and social sciences, a general estimation method is required to estimate parameters in multiple group structural equation modeling where the differences of covariates are adjusted. We show that a Horvitz–Thompson-type estimator, propensity score weighted M estimator (PWME) is consistent, even when we use estimated propensity scores, and the asymptotic variance of the PWME is shown to be less than that with true propensity scores. Furthermore, we show that the asymptotic distribution of the propensity score weighted statistic under a null hypothesis is a weighted sum of independent χ² ₁ variables. We show the method can compare latent variable means with covariates adjusted using propensity scores, which was not feasible by previous methods. We also apply the proposed method for correlated longitudinal binary responses with informative dropout using data from the Longitudinal Study of Aging (LSOA). The results of a simulation study indicate that the proposed estimation method is more robust than the maximum likelihood (ML) estimation method, in that PWME does not require the knowledge of the relationships among dependent variables and covariates.     

Social enrichment improves social recognition memory in male rats

The social environment is thought to have a strong impact on cognitive functions. In the present study, we investigated whether social enrichment could affect rats’ memory ability using the “Different Objects Task (DOT),” in which the levels of memory load could be modulated by changing the number of objects to be remembered. In addition, we applied the DOT to a social discrimination task using unfamiliar conspecific juveniles instead of objects. Animals were housed in one of the three different housing conditions after weaning [postnatal day (PND) 21]: social-separated (1 per cage), standard (3 per cage), or social-enriched (10 per cage) conditions. The object and social recognition tasks were conducted on PND 60. In the sample phase, the rats were allowed to explore a field in which 3, 4, or 5 different, unfamiliar stimuli (conspecific juveniles through a mesh or objects) were presented. In the test phase conducted after a 5-min delay, social-separated rats were able to discriminate the novel conspecific from the familiar ones only under the condition in which three different conspecifics were presented; social-enriched rats managed to recognize the novel conspecific even under the condition of five different conspecifics. On the other hand, in the object recognition task, both social-separated and social-enriched rats were able to discriminate the novel object from the familiar ones under the condition of five different objects. These results suggest that social enrichment can enhance social, but not object, memory span.     

Relative - not absolute - judgments of credibility affect susceptibility to misinformation conveyed during discussion

People remember different details about the same events, and when they discuss events they exchange new – and misleading – information. Discussion can change memory, especially when the source of new information is highly credible. But we do not know whether the effects of credibility are based on absolute judgments – judging a source's credibility independently from our own credibility – or relative judgments – judging a source's credibility only in relation to our own credibility. We addressed this question by manipulating subjects' expectations, leading them to believe that they either had the same, higher or lower “visual acuity” than their partner while they watched a movie together. To create ample opportunities for the pairs to mention misleading details to one another, each member unknowingly saw a different version of the movie. The pairs then discussed some of the critical differences, but not others. Later, everyone took an independent recognition test. Subjects' susceptibility to misinformation depended on their own credibility relative to their partner's, supporting the idea that susceptibility to misinformation depends on relative differences in credibility.     

Acquisition of a same-different discrimination task by pigeons (Columba livia)

Four homing pigeons were trained to discriminate two figures simultaneously presented on an LCD screen. The figure was either a rectangle (A) or a square (B), and four combinations of the two figures, AA, AB, BA, BB, appeared in a pseudo-randomized order. The pigeons' task was to peck one of these figures based upon whether the two figures were identical or not. One pigeon successfully learned this discrimination, with proportions of correct responses above 90% in two consecutive sessions. Of the other birds, two performed above chance level but had difficulty meeting a learning criterion of above 80% in two consecutive sessions. All birds achieved this criterion when the combinations of figures presented were reduced to two. Results suggested that learning the present same-different discrimination is within the capacity of pigeons to a certain extent, although there exists considerable individual variation in the pigeons' skills to acquire complex discrimination.     

Categorical and dimensional perceptions in decoding emotional facial expressions

We investigated whether categorical perception and dimensional perception can co-occur while decoding emotional facial expressions. In Experiment 1, facial continua with endpoints consisting of four basic emotions (i.e., happiness-fear and anger-disgust) were created by a morphing technique. Participants rated each facial stimulus using a categorical strategy and a dimensional strategy. The results show that the happiness-fear continuum was divided into two clusters based on valence, even when using the dimensional strategy. Moreover, the faces were arrayed in order of the physical changes within each cluster. In Experiment 2, we found a category boundary within other continua (i.e., surprise-sadness and excitement-disgust) with regard to the arousal and valence dimensions. These findings indicate that categorical perception and dimensional perception co-occurred when emotional facial expressions were rated using a dimensional strategy, suggesting a hybrid theory of categorical and dimensional accounts.     

Retrieval-induced forgetting in rats

“Retrieval-induced forgetting” in rats was evaluated using a modified spontaneous object recognition test. The test consisted of a sample phase, retrieval or interference phase, and a test phase with 60-min delay period inserted between the phases. Rats were randomly assigned to one of three groups (control, retrieval and interference) and allowed to explore the field in which two different objects (A, B) were placed in the sample phase. In the retrieval phase, two identical objects (B, B), which were the same as one of the objects presented in the sample phase, were placed again. In the interference phase, two identical objects (C, C), which were novel for animals, were placed. In the test phase, two different objects (A, D), one of which was identical to that presented in sample phase (familiar object) and the other was novel, were placed and the time spent exploring each object was analyzed. While the exploration of the novel object was significantly longer than that of the familiar object in rats subjected to the interference phase, rats subjected to the retrieval phase could not discriminate between the familiar and the novel objects at the test phase. These results demonstrate the “retrieval-induced forgetting” phenomenon in a spontaneous object recognition test in rats.     

Do squirrel monkeys (<Emphasis Type="Italic">Saimiri sciureus</Emphasis>) and capuchin monkeys (<Emphasis Type="Italic">Cebus apella</Emphasis>) predict that looking leads to touching?

Squirrel monkeys (Saimiri sciureus) and capuchin monkeys (Cebus apella) were tested using an expectancy violation procedure to assess whether they use an actors gaze direction, signaled by congruent head and eye orientation, to predict subsequent behavior. The monkeys visually habituated to a repeated sequence in which the actor (a familiar human or a puppet) looked at an object and then picked it up, but they did not react strongly when the actor looked at an object but then picked up another object. Capuchin monkeys responses in the puppet condition were slightly more suggestive of expectancy. There was no differential responding to congruent versus incongruent look–touch sequences when familiarization trials were omitted. The weak findings contrast with a strongly positive result previously reported for tamarin monkeys. Additional evidence is required before concluding that behavior prediction based on gaze cues typifies primates; other approaches for studying how they process attention cues are indicated.This revised version was published online in March 2004 with corrections to Fig. 2. The number 1 in the bottom left panel should be a cross and was, moreover, misaligned.     

Performance of pigeons (Columba livia) on maze problems presented on the LCD screen: in search for preplanning ability in an avian species

The authors examined how pigeons (Columba livia) perform on 2-dimensional maze tasks on the LCD monitor and whether the pigeons preplan the solution before starting to solve the maze. After training 4 pigeons to move a red square (the target) to a blue square (the goal) by pecking, the authors exposed them to a variety of detour tasks having lines as a barrier. A preview phase was introduced, during which the pigeons were not allowed to peck at the monitor. Results of a set of experiments suggest that our pigeons successfully learned to solve these tasks, that they came to take an efficient strategy as the barriers became complex, and that they possibly preplan its solution, at least on familiar, well-practiced tasks.     

Elicitation of spontaneous mirror reversal drawing on the forehead

32 Japanese participants drew symmetrical and asymmetrical letters on their own foreheads. By observing their drawing strokes, it was judged that 29 of them drew symmetric letters in reverse, that is, as if these were viewed from inside the head. However, 14 of these 29 seemed to have noticed their reversed perception because they drew asymmetric letters intentionally reversed so they would appear correct when viewed from outside. Only three participants drew the letters in a normal way irrespective of the letter symmetry.     

Speech perception by budgerigars(Melopsittacus undulatus): The voiced-voiceless distinction

Discrimination of synthetic speech sounds from the bilabial, alveolar,and velar voice onset time (VOT) series was studied in 5 budgerigars. The birds were trained, using operant conditioning procedures, to detect changes in a repeating background of sound consisting of a synthetic speech token. Response latencies for detection were measured and were used to construct similarity matrices. Multidimensional scaling procedures were then used to produce spatial maps of these speech sounds, in which perceptual similarity was represented by spatial proximity. The results of these experiments suggest that budgerigars discriminate among synthetic speech sounds from these three VOT continua, especially between those from the bilabial and alveolar series, in a categorical fashion.