The number of paths and cycles in a digraph

An algorithm is presented for constructing from the adjacency matrix of a digraph the matrix of its simplen-sequences. In this matrix, thei, j entry,i j, gives the number of paths of lengthn from a pointv _i to a pointv _j ; the diagonal entryi, i gives the number of cycles of lengthn containingv _i . The method is then generalized to networks—that is, digraphs in which some value is assigned to each line. With this generalized algorithm it is possible, for a variety of value systems, to calculate the values of the paths and cycles of lengthn in a network and to construct its value matrix of simplen-sequences. The procedures for obtaining the two algorithms make use of properties of a line digraph—that is, a derived digraph whose points and lines represent the lines and adjacency of lines of the given digraph.The research reported here was supported by Grant NSF-G-17771 from the National Science Foundation. We wish to thank Professor Frank Harary for suggesting certain ways of improving an earlier draft of this paper.     

A note on a matrix criterion for unique colorability of a signed graph

A signed graph,S, is colorable if its point set can be partitioned into subsets such that all positive lines join points of the same subset and all negative lines join points of different subsets.S is uniquely colorable if there is only one such partition. Developed in this note is a new matrix, called thetype matrix ofS, which provides a classification of the way pairs of points are joined inS. Such a classification yields a criterion for colorability and unique colorability.The work reported here was supported by Grant MH 10834 from the National Institute of Mental Health.     

An item gains and losses analysis of false memories suggests critical items receive more item-specific processing than list items

In a repeated testing paradigm, list items receiving item-specific processing are more likely to be recovered across successive tests (item gains), whereas items receiving relational processing are likely to be forgotten progressively less on successive tests. Moreover, analysis of cumulative-recall curves has shown that item-specific processing produces a slower, but steadier rate of recall than relational processing. The authors relied on these findings to determine the type of processing that both list items and critical lures receive in the Deese-Roediger-McDermott false memory procedure. The first 2 experiments revealed that critical lures produced more item gains, but only the list items resulted in a decrease in item losses across successive tests. The critical lures also produced slower but steadier cumulative recall. In Experiments 3 and 4, the critical items were physically presented during study, which resulted in the lures producing progressively fewer losses across successive tests. The authors concluded that critical items receive more item-specific processing than list items but that unless they are presented in the list, they do not become part of participants' organized retrieval scheme.     

Chimpanzees (Pan troglodytes) conceal visual and auditory information from others

Chimpanzees (Pan troglodytes) competed with a human for food. The human sat inside a booth, with 1 piece of food to her left and 1 to her right, which she could retract from her chimpanzee competitor's reach as needed. In Experiment 1, chimpanzees could approach either side of the booth unseen but then had to reach through 1 of 2 tunnels (1 clear, 1 opaque) for the food. In Experiment 2, both tunnels were clear and the human was looking away, but 1 of the tunnels made a loud noise when it was opened. Chimpanzees preferentially reached through the opaque tunnel in the first study and the silent tunnel in the second, successfully concealing their taking of the food from the human competitor in both cases. These results suggest that chimpanzees can, in some circumstances, actively manipulate the visual and auditory perception of others by concealing information from them.     

Ovarian steroids enhance object recognition in naturally cycling and ovariectomized, hormone-primed rats

Learning and memory processes may be influenced by fluctuations in steroid hormones, such as estrogens and progestins. In this study, we have used an animal model to investigate the effects of endogenous fluctuations in ovarian steroids in intact female rats and effects of administration of ovarian steroids to ovariectomized rats for non-spatial, working memory using the object recognition task. Performance in this task relies on cortical and hippocampal function. As such, serum, cortical, and hippocampal concentrations of estradiol (E2), progesterone (P4), and P4's metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), were measured by radioimmunoassay. Experiment 1: Rats in behavioral estrus, compared to those in diestrus or estrus, spent a greater percentage of time exploring a novel object concomitant with increases in serum E2, P4, and 3alpha,5alpha-THP levels. Regression analyses revealed that there was a significant positive relationship between E2 levels in the hippocampus and 3alpha,5alpha-THP levels in the hippocampus and cortex and performance in this task. Experiment 2: Administration of E2 and/or P4 immediately post-training increased the percentage of time spent exploring the novel object and produced levels of E2, P4, and 3alpha,5alpha-THP akin to that of rats in behavioral estrus. Experiment 3: Post-training administration of selective estrogen receptor modulators, including 17beta-E2, propyl pyrazole triol, and diarylpropionitrile increased the percentage of time spent exploring the novel object compared to vehicle-administration. Experiment 4: Post-training P4 or 3alpha,5alpha-THP administration, compared to vehicle, increased the percentage of time spent exploring the novel object and produced P4 and/or 3alpha,5alpha-THP levels within the physiological range typically observed for rats in behavioral estrus. Experiment 5: If post-training administration of E2 and/or P4 was delayed one hour, no enhancement in object recognition was observed. Together, these results suggest that E2 and progestins can have mnemonic effects through actions in the cortex and/or hippocampus.     

The effects of conducting behavioral observations on the behavior of the observer

Behavior-analytic approaches to occupational safety are often effective for improving safety in organizations, and have been successful in a wide variety of settings. The effects of these safety processes are thought to arise primarily from the behavioral observation process and the delivery of feedback. Typically, supervisors or employee observers involved in behavioral safety implementations conduct observations. The present study was an attempt to assess the effects of conducting observations on an observer's safety performance. An ABC multiple baseline counterbalanced across two sets of behaviors was conducted in a simulated office. The target behaviors involved knee and back positions during lifts; back, shoulder, and feet positions while sitting; neck and wrist positions while typing; and neck position during phone use. Substantial improvements in safety performance occurred after participants conducted observations on a videotape of a confederate's performance. The possible behavioral functions responsible for this change, and the implications of these findings for applied settings, are discussed.     

Acquired surface alexia in Spanish: a case report

This paper reports a case study of acquired surface alexia in Spanish and discusses the most suitable tests to detect this syndrome in a writing system that is very regular for reading at the segmental and supra-segmental levels. Patient MM has surface alexia characterized by quantitatively good performance in reading words and pseudowords; accurate but slow and syllabic reading of words, nonwords and sentences; good performance in lexical decision tasks including words and nonwords; errors in lexical decision with pseudohomophones; and homophone confusions. This pattern of reading can be interpreted as a disorder in the lexical reading route and overdependence on the non-lexical route. We discuss nonlexical impairments and the interpretation of alexia and suggest tasks to identify surface alexia in a shallow orthography.     

Changing Beliefs About Corporal Punishment: Increasing Knowledge About Ineffectiveness to Build More Consistent Moral and Informational Beliefs

Although the effectiveness of corporal punishment (CP) has received little empirical support, public support for this disciplinary method continues despite calls for its abandonment by researchers. Even among educators, favorable attitudes toward the use of CP are prevalent. We measured education majors beliefs about CP before and after they read about CP research on its effectiveness and side effects. Students who changed their behavioral intent regarding whether they would use CP as a parent increased their knowledge about its ineffectiveness, resulting in greater consistency between their moral and informational beliefs (Wainryb, 1998). Persons who are likely to change from defending to opposing CP regard it as being similar to bad-tasting medicine—not very pleasant but nonetheless necessary. Recommendations concerning implementation and changing other beliefs are discussed.     

Race/ethnicity and sexual orientation: intersecting identities

Racial/ethnic minority women who come to identify as lesbian must confront the norms and expectations of both the majority and minority cultures in which they live. This article reports findings from a diverse sample of nearly 450 women and examines the effects of race/ethnicity on sexual identity development in African American, Latina, and White lesbians. African American and Latina respondents differed little in the timing and disclosure of lesbian identity; comparisons between women of color and White women revealed substantial variability. Findings are discussed in terms of their implications for practice with lesbians of color.