Detection of the intrinsic size of Sagittarius A* through closure amplitude imaging.

We have detected the intrinsic size of Sagittarius A*, the Galactic center radio source associated with a supermassive black hole, showing that the short-wavelength radio emission arises from very near the event horizon of the black hole. Radio observations with the Very Long Baseline Array show that the source has a size of 24 +/- 2 Schwarzschild radii at 7-millimeter wavelength. In one of eight 7-millimeter epochs, we also detected an increase in the intrinsic size of 60(-17)(+25)%.

Activity anorexia: An interplay between basic and applied behavior analysis.

The relationship between basic research with nonhumans and applied behavior analysis is illustrated by our work on activity anorexia. When rats are fed one meal a day and allowed to run on an activity wheel, they run excessively, stop eating, and die of starvation. Convergent evidence, from several different research areas, indicates that the behavior of these animals and humans who self-starve is functionally similar.

Levels of stimulus control: a functional approach.

This paper surveys some illustrative experiments on categorization of visual stimuli by animals other than human. The results suggest a classification of categorical powers in five steps from simple discrimination to rote and open-ended categorization, to concepts and the use of abstract relations. Nonhuman animals evidently readily categorize up to the fourth level as here defined, which is the level of concepts.

Teaching pigeons an abstract relational rule: insideness.

In 49 sessions, pigeons failed to learn to sort a collection of 80 stimuli composed of a closed curve and a dot, divided into two categories, according to whether the dot was or was not inside the curve. Next, the pigeons were successfully trained, first with the insides of the curves shown in bright red, then with a darker red, and finally with a black matching the background outside the curve. After this stepwise procedure, the pigeons displayed a limited ability to sort novel curves and dot locations according to whether the dot was or was not inside the curve.