perception and action

• Perception happens all the time as you move
• Inferential perspective

  Presuming you're trying to create a 3-dimensional, realistic representation of the world around you
• The retinal image is not sufficient, you have to add inferences to it
• Purpose of perception

  Ensure survival --> we need action (without action, perception is worthless, and vice versa)
• Motion is cheaper than detail for the frog, so it will starve to death in a room full of dead flies (can't see them)
• Can't perceive without movement and vice versa
• Affordance perception


  Ability to perceive our possibilities for action within the environment e.g., throwing, grasping
• Vision is highly important for affordance perception
• We perceive relationships within the environment, not realism - relationships shape our experience of the world
• Affordances exist whether you perceive them or not
• Perception is expensive
• Optic flow


  Sufficient to understand the world, along with the rate of change of the retinal image
• If you move, you have different visual angles (proxy for retinal image) from different objects - the angle changes based on distance from the object (if closer, the angle is bigger)
• 90% of the world thinks the perceptual system is correct
• The stimulus is not impoverished if you move
• As you move, the point of expansion in the horizon is determined by your eye level (if you get closer to something above eye height, it moves upwards as you get closer to it)
• When trying to keep our balance, we try to keep our visual field still
• As you walk, the speed of the rate of change changes
• Motion parallax


  A way of telling how far things are - objects that are closer to you appear to move faster than objects that are farther away, because the angular change in your visual field is greater for closer objects
• Perceptual-motor couplings


  We learn to couple relevant visual information with given motor output
• Babies practice perceptual-motor couplings a lot - they walk roughly 39 football fields a day, fall about 15 times per hour, and have 100-210 spontaneous independent hand movements every 15 minutes when alert
• We take it for granted, but we need visual feedback to make certain movements
• The passive kittens in the kitten carousel experiment (Held & Hein, 1963) struggled with depth perception and coordination of vision with movement even if they were exposed to the same visual stimuli - bc they did not actively engage with environment
• Babies don't understand that 3D objects are the same if they change perspective (shape constancy) until they can sit up and use their hands to rotate the object back and forth, getting tactile, motor, and visual information to learn that the object hasn't changed
• You can walk to a target by making the angle between your direction of movement and the target 90 degrees
• The focus of expansion is the center of the visual field and specifies where you're going, with its height defined by eye height
• Optic flow calibration

  You calibrate your speed perception by optic flow and your own movements
• If walking very slowly through a constant environment or landscape, it feels like walking on quicksand
• If the world is inverted, it's very hard, like a baby again, and would take about 2 weeks to recalibrate
• Bees use optic flow to determine how far food is, and update their dance depending on changes in the sun
• Visual control heuristics


  Using optical angular information (rates of change) to successfully perform actions, rather than converting it into environment-specifying meanings
• When catching a fly ball, if you keep your eyes on the ball, you don't see where you're going, which can lead to accidents
• Self-optimisation


  Minimising energetic cost when moving through the environment, allowing energy conservation to get food
• Nepalese porters walk for 15 seconds then rest for 45 seconds, which is a "natural adoption of a movement pattern that minimises movement expenditure"
• Gait transition


  Automatically adjusting our gait (walking/running) to achieve metabolic efficiency
• Experience with a behaviour does lead to novel faster and higher levels of self-optimisation, while those without experience tend to be more variable and take longer to achieve self-optimisation
• When running at a fixed stride rate and speed, we naturally adopt the most energetically efficient stride length
• Gait is modulated by optic flow
• The kitten carousel experiment (Held & Hein, 1963) investigated the role of self-produced movement in the development of visual perception