Near-field visual acuity of pigeons: effects of head location and stimulus luminance.

Two pigeons were trained to discriminate a grating stimulus from a blank stimulus of equivalent luminance in a three-key chamber. The stimuli and blanks were presented behind a transparent center key. The procedure was a conditional discrimination in which pecks on the left key were reinforced if the blank had been present behind the center key and pecks on the right key were reinforced if the grating had been present behind the center key. The spatial frequency of the stimuli was varied in each session from four to 29.5 lines per millimeter in accordance with a variation of the method of constant stimuli. The number of lines per millimeter that the subjects could discriminate at threshold was determined from psychometric functions. Data were collected at five values of stimulus luminance ranging from--0.07 to 3.29 log cd/m2. The distance from the stimulus to the anterior nodal point of the eye, which was determined from measurements taken from high-speed motion-picture photographs of three additional pigeons and published intraocular measurements, was 62.0 mm. This distance and the grating detection thresholds were used to calculate the visual acuity of the birds at each level of luminance. Acuity improved with increasing luminance to a peak value of 0.52, which corresponds to a visual angle of 1.92 min, at a luminance of 2.33 log cd/m2. Further increase in luminance produced a small decline in acuity.     

Roll vection analysis of suggestion-induced visual field narrowing

Instructions to simulate visual field narrowing resulted in apparently narrow visual fields when these were evaluated by means of conventional perimetry. However, when a pattern of stripes moving around the visual axis was viewed, the magnitude of the induced change in the subjective horizontal or vertical (roll vection) was unaffected. These results demonstrate that conventional perimetric techniques may in some instances be inadequate to demonstrate functional peripheral vision. Evaluation of the peripheral visual field in perimetry, the role of peripheral vision in visually guided behavior, and the effect of stressors on peripheral visual functions are discussed.     

Bayesian theories of conditioning in a changing world

The recent flowering of Bayesian approaches invites the re-examination of classic issues in behavior, even in areas as venerable as Pavlovian conditioning. A statistical account can offer a new, principled interpretation of behavior, and previous experiments and theories can inform many unexplored aspects of the Bayesian enterprise. Here we consider one such issue: the finding that surprising events provoke animals to learn faster. We suggest that, in a statistical account of conditioning, surprise signals change and therefore uncertainty and the need for new learning. We discuss inference in a world that changes and show how experimental results involving surprise can be interpreted from this perspective, and also how, thus understood, these phenomena help constrain statistical theories of animal and human learning.     

The “Big Tent” of Community Psychology: Reactions to Paul Toro’s 2004 Presidential Address

This article summarizes discussions that took place following Paul Toros presidential address for the Society for Community Research and Action (SCRA). Toro argued that community psychology and SCRA are big tents. He suggested growth through increasing the involvement of ethnic minorities, community practitioners, international colleagues, students and early career professionals and individuals from allied disciplines. Themes in the discussions included: the founding values of community psychology, diversity, and social action. Those present felt that the field was facing a mid-life crisis and needed to re-establish its identity. Newer professionals looked to their seasoned colleagues to help define and establish that identity, and involve them in the process. Respondents were supportive of increased involvement of individuals from oppressed groups and practitioners in SCRA. Less attention was paid to increasing the role of international colleagues, professionals from allied disciplines, and members of the community.     

The Systematicity of Davidson’s Anti-skeptical Arguments

Topoi - Donald Davidson contributed more deeply to our understanding of language, thought, and reality than perhaps any other recent philosopher. His discussions of skepticism are sometimes seen as...