Motion Computation and Visual Orientation In Flies MSc Evolutionary and Adaptive Systems Computer Vision Juan Pablo Calderon

Why study motion? Motion Information plays a prominent role in visual orientation in many animal species. An animal perceives motion whenever an object moves in the environment or either when it moves in the environment. Fly has proven to be suitable to study motion computation since its orientation relies heavily on motion information and has a very simple neural system.

Different types of retinal motion patterns Rotatory Large field motion indicates that the animal is deviating from its course. Image expansion signals indicate that the animal is approaching a target and can be used for landing. Discontinuity and small-field motion activates a fixation system and turning reaction towards objects.

Fly’s Visual System The only information available is given by the time dependent brightness values of the image sensed by the photoreceptors. Nervous system computes a representation of motion information Retinal-motion fields are made by humans, the animal don’t use them.

3 Steps of Computation Motion computed in parallel by a 2-dimensional array of sensors. Retinal-motion patterns are extracted by spatial integration over arrays of appropriately directed local movement detectors. Dynamic properties of the representation are obtained by filtering in time to the needs of the fly in the free flight.

Correlation Type Movement Detector There is preferred and a null direction. At least 4 detectors are needed, for upward, downward, rightward and leftward.

More complex models of Correlation-type motion detectors

Lobula Plate Tangential Cells 3 different types of LPTC cells respond to preferred directions in various ways.

Cells react according to the direction of motion. The neurons hyperpolarizes in response to motion from the back to the front of the animal (null direction, ND). In response to motion along the opposite direction of motion, i.e., from the front to the back, the neuron depolarizes and fires trains of action potentials (preferred direction, PD). Intracellular recording from an equatorial horizontal system cell (HSE-cell).

Some Cells react to stimuli from both eyes

Cells respond differently to different combinations of signals This neuron responds not only to motion in front of its ipsilateral eye, but also to motion in front of the contralateral eye. The contralateral input has such a sign that it leads to a particular sensitivity of the cell for rotational stimuli: translatory stimuli lead to a much smaller response Intracellular recording from a dCH-cell

Different cells respond differently to pattern size Response increases as pattern size increases, but saturates at different levels for different pattern velocities.

Application Natural image sequences as viewed through a 2-dimensional array of correlation-type motion detectors. Joshua Gold and Alexander Borst Natural image sequences as viewed through a 2-dimensional array of correlation-type motion detectors.