2009-06-25
Have you ever watched a pigeon walking? The head constantly seems to thrust foreward and backward while the rest of body behaves as if being a wind up toy. Scientists know since long that the fore-and-back oscillation of the head is just an illusion: In reality the head quickly thrusts foreward but subsequently stands still while the body moves. Then the head thrusts foreward again, etc. Thus, there is no backward movement of the head. But why is the movement of the head different from the rest of the body? Well, here comes a clever explanation: If the head would move constantly together with the body, the retinal image would be blurred due to movement artefacts. So, a quick foreward thrust (during which the animal should be blind mostly), followed by hold period should be an optimal solution. This explanation was so compelling that it was accepted by almost everybody for decades. Now scientists from Spain, Canada, and Biopsychologists from the Ruhr-University have killed this theory (requiescat in pace as the Romans would say). With a true high-tech approach they managed to flash patterns onto monitors while the pigeons were either just thrusting their head foreward, or were just in their hold phase. To do so, head movements were tracked by means of an optical motion capture system consisting of high-speed cameras which provided the three-dimensional position of a marker mounted on the head of the animal in real time. The job of the pigeons was simple: Tell me which pattern was shown to you. The results were also simple: The pigeons were equally able to perfectly perform the discrimination both in the thrust and in the hold phase. Thus, head-bobbing can not be explained by a temporary blindness during the movement time of the head. Now that the temporary-blindness-theory is dead, what then is the explanation for head bobbing? Well, more research is needed…
Have you ever watched a pigeon walking? The head constantly seems to thrust foreward and backward while the rest of body behaves as if being a wind up toy. Scientists know since long that the fore-and-back oscillation of the head is just an illusion: In reality the head quickly thrusts foreward but subsequently stands still while the body moves. Then the head thrusts foreward again, etc. Thus, there is no backward movement of the head. But why is the movement of the head different from the rest of the body? Well, here comes a clever explanation: If the head would move constantly together with the body, the retinal image would be blurred due to movement artefacts. So, a quick foreward thrust (during which the animal should be blind mostly), followed by hold period should be an optimal solution. This explanation was so compelling that it was accepted by almost everybody for decades. Now scientists from Spain, Canada, and Biopsychologists from the Ruhr-University have killed this theory (requiescat in pace as the Romans would say). With a true high-tech approach they managed to flash patterns onto monitors while the pigeons were either just thrusting their head foreward, or were just in their hold phase. To do so, head movements were tracked by means of an optical motion capture system consisting of high-speed cameras which provided the three-dimensional position of a marker mounted on the head of the animal in real time. The job of the pigeons was simple: Tell me which pattern was shown to you. The results were also simple: The pigeons were equally able to perfectly perform the discrimination both in the thrust and in the hold phase. Thus, head-bobbing can not be explained by a temporary blindness during the movement time of the head. Now that the temporary-blindness-theory is dead, what then is the explanation for head bobbing? Well, more research is needed…
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