5.7.2 Directionality for both perception and action

Think of noticing a penny on the sidewalk on your right, verifying that it is a penny and not a glob of gum, and then bending to pick it up. For chicks it would be a kernel of corn rather than a penny.

Relativity in vision (in space, but without Einstein).

• We would like perception to be invariant to the position of the head and the inclination of the body
• The 2D pixellated image on the retina is relative to our point of view which is determined by distance and by how the head is angled relative to the objects being looked at.
• One can easily experiment with a camera by turning and tilting it to explore this kind of relativity.
• Chicks vision must be relatively unaffected by the angle of the head, and therefore the viewpoint of the eye. Their heads of chicks move side to side as well as forward and back while following the hen or pecking at food.

The next challenge is to get our fingers into the right place, withou missing or stubbing them against the sidewalk. For chicks it is pecking the corn without missing or striking against the ground.

Relativity in action.

• We need to bend our knees, bend our waist, and angle our are in the right direction.

For accurate action coordination, such as in ballet or in sports, it would be ideal if perception could yield 3 dimensional descriptions of limb positions in space and time that could readily be converted into instructions for action.

• For sake of coordination, the space and time coordinates should be relative to a shared reality rather than being individualistic or subjective
• We will come back to this notion of a shared reality in later sections

Minimal context and history dependence.

• We would like the action specification to be invariant to our physical states such as tiredness, or the weight we might be carrying in a bag
• The precise muscle tension requirements are relative to the weight we carry and our state of exhaustion
• One can easily experiment by going up a long flight of stairs in the morning, after breakfast, or going up the same stairs after a long work day carrying a heavy bag.
• A precisely choreographed ballet requires the male dancer to be in position and in time to catch the ballerina.
• Listening to the music accompanying the ballet movements, this would be roughly a beat by beat accuracy.
• Both our ballet example and the imprinting 'follow the target' example would lead us to speculate that it is more relevant to specify action relative to the environment rather than in terms of repeatable sequences of muscle tension specifications

Directionality will reappear in the next two sections for action and perception respectively.