SAM Model Research Articles

Cardiological aging in SAM model: effect of chronic treatment with growth hormone

The purpose of this study was to investigate the effect of aging on different parameters related to inflammation, oxidative stress and apoptosis in hearts from two types of male mice models: senescence-accelerated mice (SAM-P8) and senescence-accelerated-resistant (SAM-R1), and the influence of chronic administration of Growth Hormone (GH) on old SAM-P8 mice. Forty male mice were used. Animals were divided into five experimental groups: two 10 month old untreated groups (SAM-P8/SAM-R1), two 2 month old young groups (SAM-P8/SAM-R1) and one 10 month old group (SAM-P8) treated with GH for 30 days. The expression of tumor necrosis factor-alpha, interleukin 1, interleukin 10, heme oxygenases 1 and 2, endothelial and inducible nitric oxide synthases, NFkB, Bad, Bax and Bcl-2 were determined by real-time reverse transcription polymerase chain reaction (RT-PCR). Results were submitted to a two way ANOVA statistical evaluation using the Statgraphics program. Inflammation, as well as, oxidative stress and apoptosis markers were increased in the heart of old SAM-P8 males, as compared to young controls and this situation was not observed in the old SAM-R1 mice. Exogenous GH administration reverted the effect of aging in the described parameters of old SAM-P8 mice. Our results suggest that inflammation, apoptosis and oxidative stress could play an important role in the observed cardiovascular alterations related to aging of SAM-P8 mice and that GH may play a potential protective effect on the cardiovascular system of these animals.

Using latent class modeling to detect bimodality in spacing effect data

A recently proposed theory of the spacing effect [Raaijmakers, J. G. W. (2003). Spacing and repetition effects in human memory: application of the SAM model. Cognitive Science, 27, 431–452.] suggests that the spacing effect is conditional on study-phase retrieval leading to two groups of students showing different magnitudes of the spacing effect. This bimodality was also observed in histograms of spacing-effect data. In this study, we used latent class regression analysis to investigate whether these groups can be detected in existing datasets (Experiment 1). Specific hypotheses about the magnitude of the spacing effect in the latent classes were assessed in Experiment 2. Latent class regression analysis in both experiments showed that the fit of the two-class model was considerably better than the (1-class) ANOVA model. Moreover, the results of Experiment 2 showed, in line with our predictions, that when the presentation rate changed from 1 s to 4 s the increase in spacing effect was larger for the low-performing class than for the high-performing class.

Sexual Abuse of Males: The SAM Model of Theory and Practice

Sexual Abuse of Males: The SAM Model of Theory and Practice

Book Review: Sexual Abuse: Sexual Abuse of Males: The SAM Model of Theory and Practice

Book Review: Sexual Abuse: Sexual Abuse of Males: The SAM Model of Theory and Practice

Inaccuracies of a Plastic “Pinna” SAM for SAR Testing of Cellular Telephones Against IEEE and ICNIRP Safety Guidelines

A 2-mm-thick plastic shell with 5-10-mm-thick tapered plastic spacer in the shape of a pinna-specific anthropomorphic mannequin (SAM) head model is being used for determination of the specific absorption rate (SAR) of cellular telephones for compliance testing against IEEE and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) Safety Guidelines used in the U.S. and Europe, respectively. We have used three-dimensional computer-aided design files of the SAM Model with 1-mm resolution to calculate peak 1- and 10-g SAR for cheek and 15/spl deg/-tilted positions of some typical telephones for comparison with those for three anatomic models of the head to show that the SAR obtained for SAM is up to two or more times smaller than for anatomic models. This is due to the shift of the high SAR locations to a low radiated fields region away from the antenna, particularly at 835 MHz, and a substantial physical separation from the absorptive phantom at 1900 MHz. Due to the use of lossless plastic for the pinna, another handicap of the SAM model is the total lack of knowledge of 1- or 10-g SAR in the pinna tissues required by all safety guidelines (current or proposed). To remedy this situation, we propose a modified SAM with a lossy pinna, for which 1- and 10-g SARs are relatively close to those for anatomic models, provided we use a fluid of higher conductivity than that currently used for compliance testing at 835 MHz. Lastly, we compare the implications of the current IEEE and ICNIRP guidelines and the newly proposed IEEE guidelines with a relaxed limit of 4.0 W/kg for any 10-g of tissue of the pinna for maximum allowable powers for cellular telephones at 835 and 1900 MHz to show that the newly proposed relaxed IEEE limits will allow radiated powers that may be 8-16 times those permitted by the current IEEE Standard and up to two times higher than those permitted under ICNIRP guidelines used in over 30 countries.

Spacing and repetition effects in human memory: application of the SAM model

AbstractSpacing between study trials of an item increases the probability that item will be recalled. This article presents a new model for spacing based on the SAM theory of memory developed by Raaijmakers and Shiffrin (1980, 1981). The model is a generalization of the SAM model as applied to interference paradigms (Mensink & Raaijmakers, 1988, 1989) and may be viewed as a mathematical version of the Component‐Levels theory proposed by Glenberg (1979). It is assumed that on a second presentation of an item, information is added to an existing trace if the episodic memory image corresponding to that item is retrieved. If it is not retrieved, a new image is stored. It is shown that the model predicts many standard findings including the lack of a spacing effect for the recall of at least one of two items each presented once (Ross & Landauer, 1978).

Spacing and repetition effects in human memory: application of the SAM model

Spacing between study trials of an item increases the probability that item will be recalled. This article presents a new model for spacing based on the SAM theory of memory developed by Raaijmakers and Shiffrin (1980, 1981). The model is a generalization of the SAM model as applied to interference paradigms (Mensink & Raaijmakers, 1988, 1989) and may be viewed as a mathematical version of the Component-Levels theory proposed by Glenberg (1979). It is assumed that on a second presentation of an item, information is added to an existing trace if the episodic memory image corresponding to that item is retrieved. If it is not retrieved, a new image is stored. It is shown that the model predicts many standard findings including the lack of a spacing effect for the recall of at least one of two items each presented once (Ross & Landauer, 1978).

From snapshot information to long-term population dynamics of Acacias by a simulation model

The African Acacia species A. raddiana is believed to be endangered in the Negev desert of Israel. The ecology of this species is not well understood. The main idea of our study is to learn more about the long-term population dynamics of these trees using snapshot information in the form of size frequency distributions. These distributions are highly condensed indices of population dynamics acting over many years. In this paper, we analyse field data on recruitment, growth, and mortality and use an existing simulation model of the population dynamics of A. raddiana (SAM) to produce contrasting scenarios of these live history processes that are based on the analysed field evidence. The main properties of simulated as well as observed tree size frequency distributions are characterised with Simpson's index of dominance and a new permutation index. Finally, by running the SAM model under the different scenarios, we study the effect of these different processes on simulated size frequency distributions (pattern) and we compare them to size distributions observed in the field, in order to identify the processes acting in the field. Our study confirms rare recruitment events as a major factor shaping tree size frequency distributions and shows that the paucity of recruitment has been a normal feature of A. raddiana in the Negev over many years. Irregular growth, e.g., due to episodic rainfall, showed a moderate influence on size distributions. Finally, the size frequency distributions observed in the Negev reveal the information that, in this harsh environment, mortality of adult A. raddiana is independent of tree size (age).

The Spatial Diffusion of Secondary Impacts: Rural-Urban Spillovers in Grampian, Scotland

The paper analyzes rural-urban spillover effects using a bi-regional SAM model which allows for flows of commodities and factor incomes between the two areas. Multiplier decomposition is used to investigate the nature of spillovers. The results indicate stronger spillover effects from urban to rural Grampian, than viceversa. In contrast, results from a restricted, input output version of the model suggest that the effects are more consistent with nodal response. Input-output an alysem say produce biased results and studies of contemporary rural-urban relationships should look beyond production linkages to the broader range of relationships within a SAM framework

False recognition of associates: How robust is the effect?

False recognition of nonpresented words that were strong associates of 12 words in a study list was examined. Six lists were read to subjects; each list contained the 12 strongest associates to a critical nonpresented word. False-alarm rates to the 6 critical nonpresented words were obtained under several different conditions. The manipulations included varying the level of processing done to the study lists, varying the recognition-test procedure, repeating each of the study lists three times, and mixing the words from the six study lists together. A reliable false-recognition effect for critical nonpresented words was obtained in all conditions. However, the effect was not impervious to all of the manipulations. Significantly lower false recognition was obtained when learning was incidental as well as when the words on the six lists were mixed together. Neither level of processing nor repetition significantly influenced false recognition. This last result is inconsistent with Hintzman’s (1988) MINERVA 2 global memory model, but agrees with predictions from Shiffrin, Ratcliff, and Clark’s (1990) SAM model.

Human and management factors in probabilistic risk analysis: the SAM approach and observations from recent applications

Most severe industrial accidents have been shown to involve one or more human errors and these are generally rooted in management problems. The objective of this paper is to draw some conclusions from the experience that we have acquired from three different studies of this phenomenon: (1) the Piper Alpha accident including problems of operations management and fire risks on-board offshore platforms, (2) the management of the heat shield of the NASA space shuttle orbiter, and (3) the roots of patient risks in anaesthesia. This paper describes and illustrates the SAM approach (System-Action-Management) that was developed and used in these studies to link the probabilities of system failures to human and management factors. This SAM model includes: first, a probabilistic risk analysis of the physical system, second, an analysis of the decisions and actions that affect the probabilities of its basic events, and third, a study of the management factors that influence those decisions and actions. In the three initial studies, the analytical links (conditional probabilities) among these three submodels were coarsely quantified based on statistical data whenever available, or most often, on expert opinions. This paper describes some observations that were made across these three studies, for example, the importance of the informal reward system, the difficulties in the communication of uncertainties, the problems of managing resource constraints, and the safety implications of the short cuts that they often imply.

The SAM model of senescence

The SAM model of senescence

Process dissociation, single-process theories, and recognition memory.

According to the assumptions of L. L. Jacoby's (1991) process dissociation method, performance in recognition memory is determined by the combination of an unconscious familiarity process and a conscious intentional recollection process. The process dissociation method is used to produce estimates of the contributions of the 2 components to recognition performance. This article investigates whether the method provides the correct estimates of components if performance actually depends on only a single process or on 2 processes different from those assumed by the method. The SAM model (G. Gillund & R. M. Shiffrin, 1984) was used to produce simulated data based on a single process. Variants of SAM with 2 processes and R. C. Atkinson and J. F. Juola's (1973) 2-process model were used to produce data based on 2 processes.

The First International Conference on Senescence: The SAM Model Kyoto, Japan, 1994

The First International Conference on Senescence: The SAM Model Kyoto, Japan, 1994

Word frequency effects in associative and item recognition.

The word frequency effect (WFE) has been taken as evidence that recall and recognition are in some way fundamentally different. Consequently, most models assume that recall and recognition operate via very different retrieval mechanisms. Experiment 1 showed that the WFE reverses for associative recognition, which requires discrimination between intact test pairs and recombinations of study list words from different study pairs. Experiment 2, in which word triples were used, revealed an interaction between word frequency and test type: for item recognition, performance was better for low-frequency words; however, for associative recognition and free recall, performance was better for high-frequency words. In Experiment 3, item recognition was tested: although overall performance was better for low-frequency words, the recognition advantage for items in intact pairs was larger for high-frequency words, suggesting two components in recognition memory. These results imply common mechanisms in recall and recognition. Theoretical implications are discussed within the framework of the SAM model.

List-strength effect: I. Data and discussion.

Extra items added to a list cause memory for the other items to decrease (the list-length effect). In one of the present studies we show that strengthening (or weakening) some items on a list harms (helps) free recall of the remaining list items. This is termed the list-strength effect. However, in seven recognition studies the list-strength effect was either absent or negative. This held whether strengthening was accomplished by extra study time or extra repetitions. The seven studies used various means to control rehearsal strategies, thereby providing evidence against the possibility that the findings were due to redistribution of rehearsal or effort from stronger to weaker items within a list. Current models appear unable to predict these results. We suggest that different retrieval operations underlie recall and recognition, as in the SAM model of Gillund and Shiffrin (1984), which can be made to fit the results with certain relatively minor modifications.

List-strength effect: II. Theoretical mechanisms.

Ratcliff, Clark, and Shiffrin (1990) examined the list-strength effect: the effect of strengthening (or weakening) some list items upon memory for other list items. The list-strength effect was missing or negative in recognition, missing or positive in cued recall, and large and positive in free recall. We show that a large number of current models fail to predict these findings. A variant of the SAM model of Gillund and Shiffrin (1984), involving a differentiation hypothesis, can handle the data. A variant of MINERVA 2 (Hintzman, 1986, 1988) comes close but has some problems. Successful variants of a variety of composite and network models were not found (e.g., Ackley, Hinton, & Sejnowski, 1985; Anderson, 1972, 1973; Metcalfe Eich, 1982; Murdock, 1982; Pike, 1984). The results suggest constraints on the future development of such models.

The distribution of personal income at the sectoral level in Italy: A SAM model

This paper applies a SAM multiplier decomposition to investigate the impact of the structure of consumption demand on the inequality in the distribution of personal income in Italy in 1980. The household sector is divided into socioeconomic groups by income size. The results show a low capacity on the part of the poorest deciles to generate income for the household sector. The decomposition shows that the benefits originating from an intially equal increase in disposable income across population deciles increasingly favor the upper-middle income deciles.

Memory for information about persons: the effect of encoding operations on subsequent retrieval

Three experiments designed to test the hypothesis that list length effects are a function of encoding as well as retrieval processes are reported. Subjects in Experiment 1 were presented with a list of behaviors, each of which had been ostensibly performed by one of two target persons. Subjects attempting to learn the information as well as possible manifested strong between-category and within-category list length effects. However, subjects who expected to interact with one of the targets at a later time manifested only within-category list length effects. Experiment 2 demonstrated that when the list contained two categories (nouns and adjectives), but all of the informatioin pertained to a single target person, both orienting tasks produced both types of list length effects. Experiment 3 demonstrated that the two types of list length effects are also affected by encoding operations when subjects learn unrelated lists of words. The results are discussed in terms of their implications for the recent SAM model.

Hypermnesia as determined by level of recall

The results of three experiments provide converging evidence for the conclusions that hypermnesia (increased recall with repeated testing) does not depend on encoding of material in an imaginal format, but is related to the level of recall across conditions within an experiment. In Experiment 1 subjects performed orthographic, phonological, or semantic operations on words and then recalled them on three successive free recall tests. Orienting tasks affected the level of recall (semantic > phonological > orthographic), and the level of recall was correlated with hypermnesia. In Experiment 2 subjects studied nonsense syllables presented either once or three times and were then given three tests. Recall improved across tests, and the improvement was reliably greater for items studied three times. In both Experiments 1 and 2 subjects who received three tests recalled no more total items than did subjects given a single long test of equivalent duration. In Experiment 3 subjects repeatedly recalled instances of categories from semantic memory. Hypermnesia was observed and was again related to level of recall. The results help delineate the necessary and sufficient conditions for observing hypermnesia on repeated tests, and are in general agreement with the account of the phenomenon provided by J. G. W. Raaijmakers and R. M. Shiffrin's (In The psychology of learning and motivation: Advances in research and theory . New York: Academic Press, 1980, Vol. 14.) SAM model.