Visual guidance of action

How does perception start

starts with static pattern of light intensity on the retina

The outcome of perception is the formation of an

internal representation of objects in the environment

Our actions towards objects in the real world are informed by

internal representations

Explain the work of J.J. Gibson (1966, 1979)

• stimulation by light in itself does not lead to perception

  • e.g. eyes covered with halves of table tennis balls

• light energy is affected by the medium that it traverses

  • e.g. water, glass, air

• different surfaces reflect light in different ways depending on their textures, opacity, slant, etc.

  • e.g. light reflected by polished or textured surfaces

Describe the Visual cliff (Gibson & Walk, 1960) study

goal: perception of depth from texture

• 6-14 month old infants and variety of animal species

the experiment used a glass-covered table with a checkerboard pattern, creating a "shallow" and a "deep" side to test if depth perception is innate

What was found from the Visual cliff (Gibson & Walk, 1960) study

demonstrated that infants (6–14 months) possess depth perception, as most refused to crawl over an apparent drop-off

What is optic array

it represents the arrangement of light at a specific point of observation, structured by surfaces in the surrounding environment. It is not just retinal images, but the light available to an observer from all directions

What is optic flow

the constant, changing pattern of visual information on the retina caused by relative motion between an observer and their environment, which allows the brain to perceive self-motion, speed, and direction

What is structural invariants

patterns of relationships that remain constant despite changes in the retinal image

• e.g. a possible invariant specifying size constancy ratio of an object’s height to the distance between its base and the horizon

What are the four transformational invariants

• flow - locomotion (moving)

• non flow - stasis (lack of change or movement)

• outflow - approach

  • centre of outflow - direction

  • shift of the centre change of direction

• inflow - retreat from

What is the role of the perceiver in direct perception

• pick-up information in optic array and optic flow

• no need to process the retinal image and internal representations

Is perception direct or indirect

direct

What two things provide all the information needed for perception

optic array and optic flow

What is Gibson’s theory of Affordances

proposes that organisms perceive their environment not just in terms of shapes and spatial properties, but in terms of action possibilities - what the environment "affords" them

• bridge the gap between perception and action

  • e.g. a mail-box affords positing letters

Describe the methods of Micro-affordances (Ellis & Tucker, 2000)

• participants required to make a power or precision grip in response to a high or low pitch tone

• if an object present in the background (irrelevant to the task) affords a grip compatible with the response, then response is faster and more accurate

What is the purpose of the Micro-affordances (Ellis & Tucker, 2000) study

to describe how seeing objects automatically activates specific motor components - like grip type or wrist rotation - associated with interacting with them

What are the four key findings of Micro-affordances (Ellis & Tucker, 2000)

• action potentiation: the study showed that viewing objects automatically activates motor components (like gripping or rotating)

• compatibility effects: participants were faster to respond (e.g., press a button) when the required action matched the affordance of the object (e.g., handle orientation matching the hand)

• micro-level analysis: unlike Gibson's general affordances, these focus on specific, small-scale, neural-based "micro-affordances" (e.g., a power vs. precision grip)

• experimental evidence: two experiments showed that holding or rotating a tool is influenced by the visual input of its functional part (e.g., a handle), causing a "compatibility effect"

What do the findings of the Micro-affordances (Ellis & Tucker, 2000) study show

these findings suggest the brain constantly maps visual, graspable objects into potential motor actions

What do the neo-gibsonians argue

that perception and action are directly coupled and continuous, with the environment providing all necessary information for behaviour

What does exteroceptive mean

information from the environment

• e.g. spatial relationship between landmarks to guide navigation

What does proprioceptive mean

information from the body

• e.g. maintain balance with eyes closed

What does exproproceptive (Lee, 1977) mean

position of the body relative to the environment

• e.g. obstacle avoidance

What was the method of the Swinging room (Lee & Aronson, 1974)

• suspended bottomless box

• wallpaper provides texture

• movements of the room produce optic flow

  • expanding optic flow

    • subject sways backwards

    • creates an expanding visual pattern, simulating that the subject is falling forward

  • contracting optic flow

    • subject sways forward

    • creates a contracting visual pattern, simulating that the subject is falling backward

• visual information overrides proprioceptive information

How did toddlers (13-16 months) react in the swinging room

• show the same behavioural pattern

• visual information overrides proprioceptive information early in development

The swinging room (Lee & Aronson, 1974) experiment showed that

vision dominates over other senses in maintaining posture and balance.

• when the surrounding walls moved, creating "optic flow," participants (including toddlers) swayed or fell to compensate, even though their feet remained on a stationary floor

What does time-to-contact mean

to an observer's ability to estimate the remaining time before a moving object reaches a specific point or hits them

• it is a crucial aspect of visual perception and motor control, allowing humans to initiate necessary actions, such as catching a ball, breaking in traffic, or avoiding a collision

What are the behaviours that might be regulated by using time to contact

• long jumping (Lee et al., 1982)

• catching a bus

• jumping over puddles

• avoiding obstacles

• fishing gannets (Lee and Reddish, 1981)

Describe the study of Time to contact in fishing gannets (Lee and Reddish, 1981)

• dive from height of 30m

• reach speed of 24m/sec

• wings streamlined just before reaching the water

• predictions based on corrected tau values

• predictions based on height, velocity, and acceleration

• observation of bird’s behaviour

• predictions based on tau fit the data