Independent visual threshold measurements in the two eyes of freely moving rats and mice using a virtual-reality optokinetic system.

Slow horizontal head and body rotation occurs in mice and rats when the visual field is rotated around them, and these optomotor movements can be produced reliably in a virtual-reality system. If one eye is closed, only motion in the temporal-to-nasal direction for the contralateral eye evokes the tracking response. When the maximal spatial frequency capable of driving the response ("acuity") was measured under monocular and binocular viewing conditions, the monocular acuity was identical to the binocular acuity measured with the same rotation direction. Thus, the visual capabilities of each eye can be measured under binocular conditions simply by changing the direction of rotation. Lesions of the visual cortex had no effect on the acuities measured with the virtual optokinetic system, whereas perceptual thresholds obtained previously with the Visual Water Task are. The optokinetic acuities were also consistently lower than acuity estimates from the Visual Water Task, but contrast sensitivities were the same or better. These data show that head-tracking in a virtual optokinetic drum is driven by subcortical, lower frequency, and contralateral pathways.

Developments and prospects for population statistics in countries of the former Soviet Union.

"This paper examines recent developments and prospects for population statistics in the former Soviet Union, whose dissolution provides both opportunities and problems. It is important for scholars to be aware of past limitations of Soviet data, since the formation of independent states has neither removed bureaucratic impediments to the production of high-quality data, nor has it led to a population more ready to answer questions fully. Temporarily at least, there is a decrease in the amount and comparability of available information, and in some instances, in its quality. We begin with an overview of the system used to gather population statistics in the former Soviet Union and its inherent problems. We then discuss the challenges faced by the newly independent countries and the changes they need to make to achieve global comparability, including a shift toward the use of standard international definitions and away from political restrictions on data availability."

The validity of survey responses on abortion: evidence from Estonia.

This paper presents results of a validation survey of abortion conducted in Tallinn, Estonia in April and May 1992. The sample was drawn from patient records in a maternity hospital. Women who had an abortion in that hospital in 1991 were asked about recent abortions as part of a survey about women's health. More than 80% of the respondents reported having a recent abortion. Some respondents misreported their abortion as a miscarriage. Moreover, some variation in reporting was associated with respondents' characteristics. Ethnic Estonians were less likely to report their abortion than were Russians, women over age 40 were less likely to report the abortion than younger women, and women who had the abortion late in the first trimester were less likely to report that abortion. There was some evidence that unmarried women were less likely than married women to report their abortion, and that women who had borne three or more children were less likely to report their abortion than women who had borne fewer children. These differences probably stem from the extent to which pregnancy or abortion is considered stigmatizing for women in different situations.

A simple measure of fertility control.

We describe a simple measure of fertility control: the proportion of all births from the age-specific fertility schedule that occurs among women by age 35. This measure has broad applicability because it does not require information on marital fertility rates. When both the proportion of births by age 35 and the most commonly used measure of fertility control, m, are calculated for a population over time, they are correlated very highly. Because of increasing levels of nonmarital fertility in several developed countries, measures of fertility control that are based on marital fertility are less appropriate now than in the past.

Trends in mortality of the Soviet population.

A review of current mortality trends in the Soviet Union is presented. "Discussed are variations (by republic and over time) in life expectancy, infant mortality, and mortality in the working ages. Analyzing trends since 1959, the authors highlight problems relating to the quality and interpretation of pertinent statistical data of Soviet origin. Distinguishing real trends from pseudotrends, they evaluate mortality differences among regions and illustrate a more favorable long-term trend in mortality than suggested by official figures...."