During locomotion, animals employ visual and mechanical cues in order to establish the orientation of their head, which reflects the orientation of the visual coordinate system. However, in certain situations, contradictory cues may suggest different orientations relative to the environment. We recorded blowflies walking on a horizontal or tilted surface surrounded by visual cues suggesting a variety of orientations. We found that the different orientations relative to gravity of visual cues and walking surface were integrated, with the orientation of the surface being the major contributor to head orientation, while visual cues and gravity also play an important role. In contrast, visual cues did not affect body orientation much. Cue integration was modeled as the weighted sum of orientations suggested by the different cues. Our model suggests that in the case of lacking visual cues, more weight is given to gravity.

A group of gibbons (Hylobates lar) has been maintained in the seminatural, designed environment of Hall island, Bermuda, since 1970, demonstrating the feasability of long term, experimental studies of animals instrumented with intracerebral electrodes and a shoulder harness to carry radio stimulators and telemetric units for recording of mobility. Observations of spontaneous behavior were synchronized using 5 sec units, broadcast to experimenters in the field.The following conclusions are derived from our study:(1) Daytime gibbon mobility showed a periodicity related to basic biological clocks and not to mutual behavioral influences.(2) Periodicities were consistent for the same animal on different days and homogeneous intervals, validating observations made during relatively brief periods.(3) Caudate nucleus stimulation produced inhibition while central gray stimulation induced escape. Neither effect modified spontaneous rhythms.(4) Behavioral categories such as SITS, HANGS, and SWINGS remained within specific limits of occurrence on different days but showed clear oscillations, suggesting the existence of ultradian rhythms. CLIMBS had one daily peak while FORAGES had two peaks.(5) Biological mechanisms regulating cyclic activity may be similar in the Laboratory and in open field situations.(6) We propose a mathematical treatment for the analysis of behavioral data, considering the animal as a stochastic generator of random sequences. The model provides a description of basic states versus time facilitating a probabilistic prediction of primate social behavior with greater accuracy than in the past.

P ermanent implantation of electrodes within the brain is a widely used method to investigate neurological functions and electrophysiological correlates of behavior. We know that perception, decision making, learning, and other activities may be accompanied by detectable electrical phenomena; we also know that electrical stimulation of the brain may induce or modify a variety of autonomic,

Flies are often observed to approach dark objects. To a naïve observer they seem to pay selective attention to one out of several objects although previous research identified as a possible underlying mechanism a reflex-like fixation behavior integrating responses to all objects. In a combination of behavioral experiments and computational modelling, we investigated the choice behavior of flies freely walking towards an arrangement of two objects placed at a variable distance from each other. The walking trajectories were oriented towards one of the objects much earlier than predicted by a simple reactive model. We show that object choice can be explained by a continuous control scheme in combination with a mechanism randomly responding to the position of each object according to a stochastic process. This may be viewed as a special form of an implicit attention-like mechanism, for which the model does not require an explicit decision mechanism or a memory for the drawn decision.

Flies are often observed to approach dark objects. To a naïve observer they seem to pay selective attention to one out of several objects although previous research identified a reflex-like fixation behavior integrating responses to all objects as possible underlying mechanism. In a combination of behavioral experiments and computational modelling, we investigate the choice behavior of flies freely walking towards an arrangement of two objects placed at a variable distance from each other. The walking trajectories are oriented towards one of the objects much earlier than predicted by a simple reactive model. We show that object choice can be explained by a continuous control scheme in combination with a mechanism randomly responding to the position of each object according to a stochastic process. Although this may be viewed as a special form of an attention-like mechanism, the model does not require an explicit decision mechanism or a memory for the drawn decision.Summary StatementWalking blowflies apparently choose one of two objects to approach. In model simulations, a fixation scheme combined with random attention replicates this behavior without an explicit decision mechanism.