Week 6-Perception, Motion & Action

Question 1

Who is James Gibson (1904 – 1979)?

Answer 1

-He developed his theory by investigating the effect flying an
aircraft had on visual perception.

-He used his findings to help develop training films describing the problems experienced while taking off and landing and visual aptitude tests for screening out pilot applicants.

Question 2

How does Gibson (1979)’s theory challenge
the traditional approach to vision perception?

Answer 2

The Traditional Approach:
The central function of vision is to identify and recognise objects
-It involves expensive cognitive processing:
representation, interpretation, decision making

The Direct Perception Approach:
-Perception is holistic and is about picking up
information directly from the environment.
-No need for interpretation
-Allows for a more direct interaction between
the individual and the environment

Question 3

Define Direct Perception

Answer 3

-Humans perceive the environment directly.

-Direct perception is the activity of getting information from the ambient array of
light. I call this a process of information pickup that
involves . . . looking around, getting around, and looking at

Question 4

What is Gibson’s (1979) theory of ecological perception?

Answer 4

LIGHT IS THE KEY TO VISION
-Light illuminates the surfaces of objects in different degrees, depending on how they are in relation to the source of illumination.

-Objects absorb light and reflect it. There are differing degrees of illumination and shade.

-Depending on their surfaces (e.g. be smooth or irregular) objects will reflect light differently.

-As a result of being reflected off of objects,
LIGHT IS STRUCTURED

-This structure directly provides information about the objects, their relative position and their behaviour (e.g. motion)

Question 5

Gibson’s (1979) theory of ecological perception: What is Optic Array? (ambient array of light)

Answer 5

-All the information from the environment that
reaches the eye = Reflected (solid) angles of light
from objects

■ Optic Array is SUBJECTIVE – it depends on the observer’s position and orientation (ambient vision – looking around) and motion in the environment (ambulatory vision –sampling light by moving about)

Question 6

Gibson’s (1979) theory of ecological perception: How does he criticise the traditional approach and what does he emphasise?

Answer 6

-He criticizes the traditional psychophysics approach of testing vision through static displays. e.g., classic tests of depth perception using static 2D stimulus presentations failed to predict student pilots’ performances

-Changes taking place in the surrounding field of light provide an important form of information that static displays miss.

-He emphasises that organisms are seldom passive. Stimulation is often acquired through personal action, obtained rather than imposed.

-Due to such active engagement with the world, stimulus input can be modified through both motor movement and movement of the sensory organs

Question 7

Gibson’s (1979) theory of ecological perception: What is Information Pick-Up?

Answer 7

-The brain “picks up” information about objects directly = BOTTOM-UP process

-The act of picking up information, moreover, is a
continuous act, an activity that is ceaseless and unbroken. The sea of energy in which we live flows and changes without sharp breaks (Gibson, 1979/1986, p.240).

Question 8

What does light provide us with?

Answer 8

-The information lies in the structure of ambient light, that is, in its having an arrangement or being an array (Gibson, 1966, p. 208).

LIGHT PROVIDES US WITH HIGHER-ORDER VARIABLES, OR INVARIANTS
-These are characteristic of the optic array that remain unaltered as observers move around the
environment.

INVARIANTS ARE PICKED-UP BY DIRECT PERCEPTION
-Invariants are patterns in sensory information that are revealed when an organism engages in motor interaction with the environment (Mossio & Taraborelli, 2008, p. 1328)

Question 9

What are invariants?

Answer 9

■ Single lines, are a basis for considerable information:
■ Inform of edges, corners, horizons, outlines,
borders, and other phenomena
■ Lines do not inform of texture, shade, or reflectance,
■ but that information is also available in structured light.

Question 10

What are invariants? Part 2

Answer 10

The so-called “perceptual cues”, rather than being deductions of the brain, are also directly available in
structured light, e.g:
■ occlusion,
■ linear perspective,
■ distance from the horizon,
■ Texture gradients,
■ Motion parallax (or Relative Motion)
■ vanishing points

Question 11

What are motion invariants?

Answer 11

■ Movement (from self and other objects) provides
further information.

■ This information is critical to guide our motion and interactions within the environment

-Objects (light) appear and disappear as one moves about.

• Looming tells of an object’s approach.
• Motion gradients relate objects in the visual field with each other with respect to a point of fixation (or
  “Focus of expansion”)

Question 12

Motion Invariants: What is Optic Flow?

Answer 12

Changes in the pattern of light that reaches the over of an observer created

Question 13

What are second-order properties in Gibson’s invariants?

Answer 13

That is, what is invariant in an optic array, is the relationship between two of its varying components - the components vary, but the relationship does not.

Question 14

What must we do whilst we navigate the world?

Answer 14

1. We must continually plan where we want to move
2. We must try to avoid colliding with obstacles on our path.
3. We must check that we are following the planned path.

-To do so we determine our direction accurately and efficiently.

-We rely on several visual cues to achieve
this goal. (And according to Gibson, these are
changing patterns of light that our brain directly picks up)

Question 15

What is the Radial Outflow Hypothesis?
(Gibson, 1950)

Answer 15

■ When we want to reach some goal we use visual
information to move directly towards it

■ Radial Outflow Hypothesis: the overall or global
outflow pattern (Optic Flow + Focus of Expansion) specifies an observer’s heading

Question 16

Define optic flow

Answer 16

Describes the characteristic distribution of
local motion directions across the visual field (appearance of objects as the observer moves past
them)

Question 17

Define the gradient of flow

Answer 17

The difference in flow as a function of distance from the observer:
–Objects at different distances move at different speeds on the retina of the eye

Question 18

Define the focus of expansion

Answer 18

The point in a distance where there is no
flow
■ With the aid of optic flow, the brain calculates answers to motion-relevant questions

Question 19

What is Global Outflow?

Answer 19

■ Invariant information

■ Self-produced – flow is created by the movement of the observer

Question 20

What is the Retinal Flow Field?

Answer 20

Changes in the pattern of light on the retina

-Optic flow is highly unstable due to the complex, phasic head and eye movements the observer makes.

-The observer also rarely moves on a straight line to reach the target (e.g. avoid obstacles)

Question 21

Define Linear Retinal Flow

Answer 21

Contains a focus of expansion (= optic flow)

Question 22

Define Rotary Retinal Flow

Answer 22

Rotation in the retinal image produced by non-
linear changes in the path, eye and head movements

Question 23

Do people use Flow Information? Land & Lee (1994). Nature

Answer 23

■ Car fitted with instruments to measure:
* Angle of the steering wheel
* Speed of vehicle
* Direction of gaze of driver

■ When driving straight, driver looks straight ahead, but not at focus of expansion

■ When driving around a curve, driver looks at tangent point on the inside of the bend

■ This suggests drivers use other information in addition to optic flow to determine their heading

Question 24

How are Scene-based cues are also
used to estimate heading? (Hahn et al., 2003) (START RECORDING FROM HERE)

Answer 24

-Motion is not essential for accurate perception of heading.

-Observers can determine the path
of motion from two sequentially
presented views when apparent
motion is absent.

-Using static scene-based information, which specifies the scene layout and egocentric distance.

-If ISI (time between showing 2 pictures) is short, participants perceived motion (almost like an animation).

-Motion is not essential for the perception of heading and direction.

Question 25

What 2 systems provides heading estimation? (Snyder & Bischof, 2010)

Answer 25

1. One uses motion information (motion-based cues): provides navigational mechanisms and is fast and automatic (fast processing; unlimited capacity)
2. One uses retinal displacement (scene-based cues): objects nearer the observer show stronger retinal displacement and are more informative (Provides navigational planning and re-orienting. This is slower and requires attentional resources (i.e.
   cognitive load; limited capacity) (system would struggle with providing info on the nearest object).

Question 26

What Brain area is tuned to Optic Flow?

Answer 26

■ Medial Superior Temporal area is part
of the ‘motion system’ in dorsal
extrastriate cortex - area V5/MT.

■ Britten & van Wezel (1998) electrically microstimulated MST while trained monkeys performed a visual heading discrimination task (i.e. determine whether right or left direction for heading optic flow).

■ Microstimulation induced a significant shift of responses in the direction of the stimulated neuron (if they simulated left hemisphere neurons with a preference for the right side of peripheral vision, the monkeys were worse at determining the head of direction. Vice versa showed an impairment in the task demonstrating the role of MST in motion).

Smith et al. (2006, EJN):
-Arrows coming forward in different directions

■ Reduced proportions of right choices during micro-stimulation of neurons with leftward heading preference.

■ Human MST is strongly responsive to
coherent optic flow (i.e. large patterns of dots moving with global flow motion).

-The global motion in optic flow has the MST playing a role in perceiving actions that way but not when it has random moving patterns.

Question 27

What are affordances?

Answer 27

■ Information about the potential
use of objects e.g., the use of a ladder is to go up and down on it.

■ Intrinsic characteristics of the objects, which allow for human interaction

■ “affordances are opportunities for action
that exist in the environment and do not
depend on the animal’s mind” (Withagen et al., 2012, p.251)

Question 28

How are affordances perceived directly?

Answer 28

■ Gibson argued that an object’s affordances are perceived directly.

PAPPAS & MACK (2008, Visual Cognition):
-Presented participants with a focus point, then presented a tool e.g., a hammer wuickly so it was outside the visual conscious perception showing a scrambled image afterwards.
-Still, participants made a grasping movement towards the tool
■ Briefly seen objects (that afford a motor response) activate the visuomotor system automatically, without conscious perception and potentiate a subsequent motor response.

Wilf et al. (2013, Front Psychol)
-Interested in Gibsons idea
-Presented objects which were graspable compared to ones you couldn’t
-Looked at whether objects with a metal handle from a graspable distance activated the motor system
■ Affordance of graspability triggers rapid activity in the motor system THEREFORE, the affordances are perceived directly from the environment

Question 29

What determines how affordance is perceived?

Answer 29

■ The theory that affordance is intrinsic in the object is oversimplified (because what acts as a modifier/regulator?).

Determinants on how affordance is perceived?
■ mood – psychological state
■ Creative processes – art and
design (e.g., using objects in ways not typically used).
■ Learning and practice – People use an object in different ways adding a new dimension of affordances.

Question 30

What are affordances for locomotion? (Adolph Joh & Eppler, 2010)

Answer 30

• Surface Friction vs. Slant
• Infants rely primarily on information
  for slant
• Touching and hesitation not increased by the sight of slippery surface

-Manipulated the friction of surfaces (i.e., high friction vs low friction)

■ Perhaps information for surface layout is
more reliable
■ Perhaps affordance for friction is learned
more slowly through experience

Question 31

Why do young children make errors in judging accordance?

Answer 31

1. Errors may stem from less accurate perception – some affordances require more perceptual precision which are not fully developed yet in young children).
2. Errors may stem from liberal response criterion – e.g. what is judged as risky.
3. Errors may stem from less sophisticated executive functions – low inhibitory control
   to refrain from exploring and attempting and can’t stop themselves from doing something risky (doesn’t develop until 4 or 5).
4. Errors may stem from haptic exploration – need to learn to better use haptic and visual information.

Question 32

What is Glover’s (2004) Model for Action Planning and Control?

Answer 32

-Planning largely influenced by a large array of visual and cognitive information
-Control is influenced solely by the spatial characteristics of the target

2 systems interplay to enable humans
to perform the action:
1. Planning System
2. Control System

Planning system:
* Operates prior to a movement
* Selects the best motor program to reach a certain goal given the environment

Control System:
* Operates during execution of movement
* Must minimize the spatial error of the movement by constantly analysing the target and actor. Updates the goal as more information is acquired.

Question 33

What is the planning system? (Glover, 2004)

Answer 33

■ Activated before the initiation of movement.

■ Selects the target and plans movement type and timing.

■ Both “Bottom-up” influence1 – e.g., visual information, object’s affordances, visual context and “Top-down” influence2 -
conscious processes e.g., individual’s goals, cognitive load etc.

Brain areas - different processes:
– inferior parietal lobule1: integrates visual representation of the object + visual context = “Slow” process.
– Inferotemporal Lobe: object recognition
– prefrontal cortex2: planning and selection of correct motor tools
– Motor Cortex: Motor execution
– Basal Ganglia: Motor programs

Question 34

What is the Control system? (Glover, 2004)

Answer 34

• During the execution of the movement (online)
• Uses accuracy and adjustments – use of somatosensory feedback.
• Faster - uses little information (no context – only target)
• Not need for conscious influence.

Brain areas:
 Superior Parietal Lobe: Control
 Cerebellum: Fine movements
 Basal ganglia: Motor programs

• Relies on:
   Efference copy (internal copy of a motor command i.e., the mental representation of the command you are planning to execute before you execute).
   Proprioception (sensation relating to the position of body i.e., how we perceive that object in comparison to the position of our body).
   Visual perception (target object’s spatial characteristics)

Question 35

Are there different brain areas for the 2 systems? (Glover et al., 2012)

Answer 35

■ planning and control of simple reaching and grasping actions.

■ fMRI study w 4 tasks (involved tasks relating to reaching and grasping).

■ different regions of the Posterior Parietal
Cortex (PPC) are involved in either the
planning (middle/posterior intraparietal lobe) or online control (superior parietal lobe) of the action.

■ TMS research can tell if the brain area is causally/necessarily involved.

■ TMS over superior parietal lobe disrupted control on adjusting action to changing size of object (Glover et al., 2005)

• TMS over inferior parietal lobe did not cause large disruption on a task where sbjs planned to reach out and touch target (Striemer et al., 2011).
• Perhaps IPL may be required for some functions of the planning process (e.g., selecting the goal of the action, selecting the target for the action).
• However, it may not have causal role in programming the action.

Question 36

What is Ideomotor apraxia?

Answer 36

Planning system compromised:
– damage to the (left) inferior parietal lobe (but also other areas of the parietal lobe)

– poor at initiating purposeful movements towards a target (e.g. reaching/grasping object) – BUT control of the action is
accurate.

– Also deficits in properly performing tool-use pantomimes (e.g., pretending to use a
hammer), imitation; communicative gestures (e.g., waving goodbye), response to
verbal command.

Question 37

What is Optic ataxia?

Answer 37

Control system compromised:
– Also known as Bálint syndrome

– Patient is not able to guide her hand towards object with the help of visual information.

– all aspects of visual guidance over reaching with the hand and arm get gradually lost (despite visual perception remains intact) (can visually perceive object it is the manipulation that is difficult to them).

– damage to the superior and posterior parietal cortex.

– Patients IG (Grea et al., 2002) and CF (Blangero et al., 2008) – could perform task well, but poor control if the target suddenly moved location.