Biology of elderly suicide.

Most studies of suicide in younger patients have demonstrated significant alterations in the serotonin system. Although a high percentage of completed suicides occur in late-life, to date very few studies of the biology of suicide have focused on this age group. This chapter describes age-related changes in the central nervous system pertinent to the biology of suicide, then reviews post-mortem biological studies of the brains of suicides and suicide attempters. As suicide attempts in the elderly are characterized by the use of violent means, biologic studies of impulsive violence are discussed. Finally we describe data on the effect of degenerative diseases on the serotonin system and the possible link to increased suicidal behavior in affected patients. This review underscores the need for further study of the biology of suicide in the geriatric age group.     

A comparison of the effects of partial reinforcement schedules using a within-subject serial autoshaping procedure

Three experiments, each using a single group of pigeons, are reported. In Experiment 1 subjects were initially trained with two stimuli, one of which was always followed by food, the other being reinforced according to a 50% partial reinforcement schedule. Subsequently a serial procedure was adopted in which an additional stimulus, C, was consistently followed by the partially reinforced CS. A second additional stimulus, A, was followed on half of its occurrences by the continuously reinforced CS, its remaining presentations being followed by nothing. The rate of autoshaped keypecking was substantially greater during A than during C. In the remaining experiments subjects received first-order conditioning with a single stimulus that was either partially (Experiment 2) or continuously (Experiment 3) reinforced. The stimuli A and C were then again introduced for serial autoshaping. Stimulus A was occasionally paired with the CS and occasionally followed by nothing, whereas stimulus C was always followed by the CS. As in Experiment 1, the rate of responding during A was greater than during C. It is proposed that one influence on the rate of autoshaped keypecking during a CS is the accuracy with which the immediate consequences of that CS are predicted.     

Homosexuality and Nature: happiness and the law at stake

ABSTRACT In this essay the argument set forth by Michael Levin regarding the abnormality of homosexual behaviour is reviewed and criticized. Against his argument which holds that homosexual behaviour is abnormal because it constitutes an evolutionary aberration, I argue that Levin's and all similarly constructed arguments fail to show that evolutionary origins of sexual behaviour have any significant normative force. I contend that his notion of homosexuality is confused and that he fails to consider alternative methods of how homosexuality might have indeed served evolutionary adaptive purposes or been the result of surplus adaptations. I argue, too, that Levin's linking of unhappiness with homosexual behaviour is spurious and ill-supported. Consequently, I reject Levin's claims that public policy ought to do what it can to minimize the incidence of such behaviour. I argue by contrast that if happiness is the end of public policy decisions, then society ought to take what measures it can to protect persons in respect of their homosexual behaviour and identities.     

Are rats short-sighted? Effects of stimulus distance and size on visual detection

Behavioural evidence concerning short-sightedness in rats is apparently conflicting: in some experiments rats have performed poorly with visual stimuli further than about 60 cm distant, while in others they have made efficient use of more distant cues, for example to find their way through mazes. However, in the experiments suggesting short-sightedness, the physical size of the stimuli was not varied, so that stimulus distance and visual angle were confounded. In the present experiment, therefore, the size and distance of the stimuli to be detected were varied independently. Over the range tested (30-160 cm), distance was found to produce relatively slight effects on the smallest detectable visual angle, and these tended to diminish with practice. Thus, no good evidence was found for short-sightedness in rats up to 160 cm, a finding consistent with current views of the structure and image-forming capacities of the rat's eye. The smallest detectable targets were, however, surprisingly large in view of the rat's visual acuity (which is about 1c/deg): at the distances tested, animals required considerable training to run reliably to targets subtending less than 5-10° of visual angle. Difficulties in responding to stationary stimuli of this size are likely to restrict severely the use that rats make of vision both in the laboratory and in their natural surroundings.     

The recovery of structure from motion: no evidence for a special link with the convergent disparity mechanism

Convergent and divergent stereo mechanisms were compared in their ability to recover structure from motion. Contrary to a recent result reported by Richards and Lieberman, no difference in their performance was found; both mechanisms appeared equally capable of supporting the perception of good structure from motion. Possible reasons for the disparate results are discussed.