Search

A population of individually marked skylarks was studied by Juan D. Delius over four breeding seasons in Ravenglass, Cumbria, England. The original publication of his findings on their behaviour was published in German (Delius, 1963). Here, the article is presented in English for the first time, with updates of the relevant literature. published

The visual control of pecking by pigeons (Columba livia) has latterly been thought to be restricted to the fixation stops interrupting their downward head movements because these stops prevent interference by motion blur. Pigeons were also assumed to close their eyes during the final head thrust of the peck. Here we re-examine their pecking motions using high-speed video recordings and supplementary provisions that permitted a three-dimensional spatial analysis of the movement, including measurements of their pupil diameters and eyelid slit width. The results confirm that pigeons do not close their eyes completely during the presumed optically ballistic phase of pecking. Instead their eyelids are narrowed to a slit. The width of this slit is sensitive to both the ambient illumination levels and the visual backgrounds against which seed targets have to be detected and grasped. There is also evidence of some interaction between pupil diameter and eyelid slit width. We surmise that besides being an eye-protecting reflex, the partial covering of the pupil with the eyelids may increase the depth of focus, enabling pigeons to obtain sharp retinal images of peck target items at very close range and during the beak-gape ‘handling’ of food items and occasional grit particles.

Pigeons learned to discriminate two different patterns displayed with miniature light-emitting diode arrays. They were then tested with 84 interspersed, non-reinforced degraded pattern pairs. Choices ranged between 100% and 50% for one or other of the patterns. Stimuli consisting of few pixels yielded low choice scores whereas those consisting of many pixels yielded a broad range of scores. Those patterns with a high number of pixels coinciding with those of the rewarded training stimulus were preferred and those with a high number of pixels coinciding with the non-rewarded training pattern were avoided; a discrimination index based on this correlated 0.74 with the pattern choices. Pixels common to both training patterns had a minimal influence. A pixel-by-pixel analysis revealed that eight pixels of one pattern and six pixels of the other pattern played a prominent role in the pigeons’ choices. These pixels were disposed in four and two clusters of neighbouring locations. A summary index calculated on this basis still only yielded a weak 0.73 correlation. The individual pigeons’ data furthermore showed that these clusters were a mere averaging mirage. The pigeons’ performance depends on deep learning in a midbrain-based multimillion synapse neuronal network. Pixelated visual patterns should be helpful when simulating perception of patterns with artificial networks. published

Developmental psychologist Paul B. Baltes (1939–2006) was born in Saarlouis, Germany. After studying in Germany he moved to the United States, where he continued the conceptual and methodological quest of his doctoral dissertation to transform developmental psychology into a science that seeks to describe, explain, and modify individual differences in behavioral development across the entire life span. His work was pivotal in establishing life span psychology as a comprehensive and distinct theoretical orientation within contemporary developmental psychology. Paul Baltes' career was characterized by internationality, interdisciplinarity, generativity, societal concern, and institutional prudence and sagacity. One of his central research interests was to explore age-graded changes in the range of plasticity in individual development, with the goal to identify and promote personal and societal conditions that favor successful aging. At the same time, he was not negligent of the negative sides of very old age, and spoke of old age and aging as ‘hope with a mourning band.’