Intermittency in human manual tracking tasks

We confirm Craik's (1947) observation that the human manual1y tracking a visual target behaves like an intermittent servo-control1er. Such tracking responses are indicative of "sampled" negative-feedback control but could be the result of other, continuous, mechanisms. Tracking performance therefore was recorded in a task in which visual feedback of the position of the hand-held joystick could be eliminated. Depriving the subjects of visual feedback led to smoother tracking and greatly reduced the signal power of their responses between 0.5-1.8 Hz. Their responses remained intermittent when they used feedback of their own position but not of the target to track a remembered (virtual) target. Hence, intermittency in tracking behavior is not exclusively a signature of visual feedback control but also may be a sign of feedback to memorized waveforms. Craik's (1947) suggestion that the intermittency is due to a refractory period following each movement was also tested. The errors measured at the start of each intermittent response, during tracking of slow waveforms, showed evidence of a small error deadzone (measuring 0.7 cm on the VDU screen or 0.80 degrees at the eye). At higher target speeds, however, the mean size of starting errors increased, and the upper boundary of the distribution of starting error was close to that expected of a refractory delay of approximately 170 ms between responses. We consider a model of the control system that can fit these results by incorporating an error deadzone within a feedback control loop. We therefore propose that the initiation of intermittent tracking responses may be limited by a positional error deadzone and that evidence for a refractory period between successive corrective movements can be satisfied without evoking an explicit timing or sampling mechanism.     

Asymmetries in the regulation of visually guided aiming

An experiment was conducted to examine the contribution of sensory information to asymmetries in manual aiming. Movements were performed in four vision conditions. In the full-vision condition (FV), subjects were afforded vision of both the hand and the target throughout the course of the movement. In the ambient-illumination-off condition (AO), the room lights were extinguished at movement initiation, preventing vision of the moving limb. In the target-off (TO) condition, the target was extinguished upon initiation of the movement. In a no-vision (NV) condition, ambient illumination was removed and the target was extinguished upon initiation of the response movement. Results indicated that accuracy was superior in the full-vision and target-off conditions and when movements were made by the right hand. Movements made by the right hand were also of shorter mean duration. The magnitudes of performance asymmetries were uninfluenced by vision condition. Analyses of movement kinematics revealed that movements made in conditions in which there was vision of the limb exhibited a greater number of discrete modifications of the movement trajectory. On an individual-trial basis, no relationship existed between accuracy and the occurrence of discrete modifications. These data suggest that although vision greatly enhances accuracy, discrete modifications subserved by vision reflect the imposition of nonfunctional zero-order control processes upon continuous higher-order control regimes.     

Is the cerebellum a smith predictor?

The motor system may use internal predictive models of the motor apparatus to achieve better control than would be possible by negative feedback. Several theories have proposed that the cerebellum may form these predictive representations. In this article, we review these theories and try to unify them by reference to an engineering control model known as a Smith Predictor. We suggest that the cerebellum forms two types of internal model. One model is a forward predictive model of the motor apparatus (e.g., limb and muscle), providing a rapid prediction of the sensory consequences of each movement. The second model is of the time delays in the control loop (due to receptor and effector delays, axonal conductances, and cognitive processing delays). This model delays a copy of the rapid prediction so that it can be compared in temporal register with actual sensory feedback from the movement. The result of this comparison is used both to correct for errors in performance and as a training signal to learn the first model. We discuss evidence that the cerebellum could form both of these models and suggest that the cerebellum may hold at least two separate Smith Predictors. One, in the lateral cerebellum, would predict the movement outcome in visual, egocentric, or peripersonal coordinates. Another, in the intermediate cerebellum, would predict the consequences in motor coordinates. Generalization of the Smith Predictor theory is discussed in light of cerebellar involvement in nonmotor control systems, including autonomic functions and cognition.     

The semantics ofR4

The LogicR4 is obtained by adding the axiom (A vB(AvB) to the modal relevant logicNR. We produce a model theory for this logic and show completeness. We also show that there is a natural embedding of a Kripke model forS4 in eachR4 model structure.We are indebted to several people for discussions relating to the topic of this paper, in particular, Kit Fine, John Slaney, J. M. Dunn, Jacques Riche, M. A. McRobbie, and Jill LeBlanc. We would also like to thank the Automated Reasoning Project for material assistance. Mares would like to thank The Social Sciences and Humanities Research Council of Canada for fellowships 456-89-0128 and 457-90-0081, which supported him while writing this paper.     

The rationing of health care: A doctor's dilemma

Physicians are currently presented with very difficult ethical issues regarding who receives what level of medical care and for how long. A meaningful response to these perplexing issues necessitates a collaboration of doctors with others steeped in religious and ethical traditions. This paper addresses the complicated issue of the rationing of health care, and this issue is then addressed by responses from representatives of the religious community. This symposium took place at the New York Hospital—Cornell Medical Center in March 1991.The Rev. Curtis W. Hart, M.Div. is Director of Pastoral Care and Education at the New York Hospital—Cornell Medical Center.The Rev. Paul Conner, O.P., is Associate Professor and Director of the Master's Program in Public Health Care Ethics at New York Medical College. Larry Rasmussen, Th.D., is Reinhold Niebuhr Professor of Social Ethics at Union Theological Seminary in New York. Dr. Harlan J. Wechsler is Rabbi of Congregation Or Zarua and Visiting Professor of Philosophy at Jewish Theological Seminary in New York.     

From denial to hope: A systemic response to clergy sexual abuse

This article offers a definition of sexual abuse in the ministerial relationship and describes a systemic approach for intervening that cares for the needs of victims and perpetrators, and provides an opportunity for congregations to move from denial to hope both spiritually and organizationally.He is the author of many articles on organizational structure and Christian social action.     

The imp of the reverse: A phenomenology of the unconscious

The debate regarding the unitary versus multiple nature of the human person is examined with special attention to the division between conscious and unconscious. The roots of the unconscious are traced to the experience of alienation or feeling divided within. An existential analysis is provided in order to shed light on the nature of the unconscious. The experience of feeling divided within is explained as a metaphor that is taken literally. An existential-phenomenological explanation of the unconscious is provided which preserves the essential unity of the human person.     

Transitional phenomena as evidenced in prayer

In this paper, we demonstrate that the study of prayer facilitates understanding of the deeply personal object related nature of religious experience. Within prayer, individuals enter the transitional sphere and meet their God representation. Both conscious and unconscious aspects of prayer can be made available through the use of a projective test developed by the authors, known as STARR: Spiritual Themes and Religious Responses test. The data obtained suggest the usefulness of Winnicottian concepts of transitional phenomena, playing, communicating, and capacity to be alone as a contemporary psychoanalytic framework for interpreting religious experience.     

Art,logotherapy, and the unconscious God

In this article the author outlines how art can be used in Logotherapy and Existenzanalyse to help the client uncover, discover, and make use of the meaning and spiritual potentials in his or her life. In Logotherapy and Existenzanalyse art can be used to help over-come fear of verbal communication, to help overcome fear of the spiritual and meaning potentials in the client's life, and to help the client gain awareness and contact with the unconscious God.     

The mormon health traditions: An evolving view of modern medicine

The Mormon church has long been seen as an unusual group in relation to its health practices. But its health traditions and practices go much further than the ban on tobacco, coffee, and alcohol for which it is so well known. Church teachings and influences pervade the entire Mormon existence. This paper briefly discusses these traditions, first by examining their roots in the teachings of its first two prophet/presidents, Joseph Smith and Brigham Young. Then, how these ideas have evolved into the church's current thought is examined; and finally, the church's responses to many modern-day health care issues are presented.The author wishes to thank Dr. John King at Eastern Virginia Medical School in Norfolk, for his assistance and encouragement.