Abstract
Many flying insects, such as flies, wasps and bees, pursue a saccadic flight and gaze strategy. This behavioral strategy is thought to separate the translational and rotational components of self-motion and, thereby, to reduce the computational efforts to extract information about the environment from the retinal image flow. Because of the distinguishing dynamic features of this active flight and gaze strategy of insects, the present study analyzes systematically the spatiotemporal statistics of image sequences generated during saccades and intersaccadic intervals in cluttered natural environments. We show that, in general, rotational movements with saccade-like dynamics elicit fluctuations and overall changes in brightness, contrast and spatial frequency of up to two orders of magnitude larger than translational movements at velocities that are characteristic of insects. Distinct changes in image parameters during translations are only caused by nearby objects. Image analysis based on larger patches in the visual field reveals smaller fluctuations in brightness and spatial frequency composition compared to small patches. The temporal structure and extent of these changes in image parameters define the temporal constraints imposed on signal processing performed by the insect visual system under behavioral conditions in natural environments.
Highlights
While moving through a cluttered environment, animals need to gather information about their own movements as well as the spatial structure of their surroundings
It is important to know the typical input received during behavior in natural environments, i.e. the image statistics of natural sceneries and the dynamics of changes caused by behavioral actions, to understand the mechanisms underlying vision
Visual systems have to cope with the peculiarities of the image statistics encountered in behavioral situations, i.e. the brightness, contrast and textural features of the retinal input, as well as their characteristic temporal changes during behavior in natural environments
Summary
While moving through a cluttered environment, animals need to gather information about their own movements as well as the spatial structure of their surroundings. The mechanisms for extracting spatial information from the retinal image flow were concluded to have evolved in insects to optimally handle the information available in the natural input. This information is generated by an active flight and gaze strategy that is characterized by sequences of alternating saccadic turns and straight flight segments [2]–[13]. The saccadic flight and gaze strategy is thought to already separate the translational and rotational components of retinal image motion to a large extent at the behavioral level This simplifies the extraction of spatial information from the retinal image flow
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