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J Ostheim

Publications and source records attributed to J Ostheim.

3 recordsLinked to original sources
PubMed1997

Visual sensation during pecking in pigeons.

During the final down-thrust of a pigeon's head, the eyes are closed gradually, a response that was thought to block visual input. This phase of pecking was therefore assumed to be under feed-forward control exclusively. Analysis of high resolution video-recordings showed that visual information collected during the down-thrust of the head could be used for 'on-line' modulations of pecks in progress. We thus concluded that the final down-thrust of the head is not exclusively controlled by feed-forward mechanisms but also by visual feedback components. We could further establish that as a rule the eyes are never closed completely but instead the eyelids form a slit which leaves a part of the pupil uncovered. The width of the slit between the pigeon' eyelids is highly sensitive to both, ambient luminance and the visual background against which seeds are offered. It was concluded that eyelid slits increase the focal depth of retinal images at extreme near-field viewing-conditions. Applying pharmacological methods we could confirm that pupil size and eyelid slit width are controlled through conjoint neuronal mechanisms. This shared neuronal network is particularly sensitive to drugs that affect dopamine receptors.

Animals↗
PubMed1992

Coping with food-limited conditions: feeding behavior, temperature preference, and nocturnal hypothermia in pigeons.

The adaptive response to increasing food scarcity were investigated in a closed economy behavioral procedure. Food-limited conditions were simulated by an increasing fixed ratio (FR) schedule, i.e., an increasing number of keypecks was required to give the pigeons access to a food dispenser. The birds could influence the ambient temperature (Ta) by breaking light beams. The body weight (b.wt.), the deep body temperature (Tb), the selected Ta, the pecks to the food key, and the number of food accesses were continuously recorded. As the FR increased, the pigeons first showed an improvement of the feeding behavior. When this behavioral adaptation failed to maintain a sufficient food intake, the b.wt. of the pigeons gradually decreased and nocturnal hypothermia occurred. Interrelated to nocturnal hypothermia, the birds changed their Ta preference. Only when their b.wt. had reached approximately 70% of its initial value, the birds increased their feeding activity. At all ranges of food scarcity, the pigeons reached a steady state. The work provides evidence about the way adaptive mechanisms interact within the response complex to food-limited conditions.

Animals↗