Problem 7 2.4
Changes in your environment
The ecological approach to perception
Gibson – perception evolved so that we can move within, and act upon, the world
A better approach is to study perception in situations where people move through
and interact with the environment
Gibson's approach focused on perception in natural contexts and so was called the
ecological approach to perception
A major goal of this approach is to determine how movement creates perceptual
information that both guides further movement and helps observers perceive the
environment
The moving observer
Optic flow – movement of an observer (e.g. you sitting
in a moving car) creates movement of objects and the
scene (trees moving past you and the road coming
towards you) relative to the observer. It has two
important characteristics:
1. It is more rapid near the moving observer (longer
arrows indicate more rapid flow).
- The gradient of flow - the different speed of flow i.e. fast near the observer and
slower further away.
- Provides information about how fast the observer is moving
- The observer uses the information provided by the gradient of flow to determine
their speed of movement
2. There is no flow at the destination toward which they are moving (white dot in
the centre)
- Focus of expansion (FOE) – the absence of flow at the destination points
Invariant information – information that remains constant regardless of what the
observer is doing or how the observer is moving
- Optic flow provides invariant information because the same flow information is
present each time the observer is moving through the environment in a
particular way
- The focus of expansion always occurs at the point toward which they are moving.
If they change direction, the FOE shifts to a new location, but the FOE is still there
- Even when specific aspects of a scene change, optic flow and the FOE continue to
provide info about how fast a person is moving and where
they are heading
Self-produced information
Self-produced information – when a person makes a movement,
this movement creates information, this information then is used
to guide further movement
- E.g. if a person is driving, movement of the car provides optic
flow information, and the observer then uses this flow
information to help steer the car
, Senses do not work in isolation
Gibson felt that we should consider how
each of the senses provides information for
the same behaviours
- E.g. balance – this includes the vestibular
canals of your inner ear and the receptors
in the joints and muscles + information
provided by vision
Vision provides a frame of reference that
helps the muscles constantly make
adjustments to help maintain balance
- Swinging room experiment - stationary
floor but swinging walls and ceiling
- Oscillating the room through as little as 6
mm caused subjects to sway
approximately in phase with this
movement
- Shows vision can override the traditional
sources of balance information provided
by the inner ear and the receptors in the
muscles and joints
Staying on course: walking and driving
Walking
Optic flow can provide invariant information regarding a person’s trajectory and
speed
As well as this, various strategies can play a role in maintaining one’s heading
Visual direction strategy – observers keep their body pointed toward a target
- If they go off course, the target will drift to the left or right
- When this happens, the walker can correct their course by realigning his or her
body with the target
Optic flow information is not always necessary for navigation – we can find our way
even when flow information is minimal e.g., at night or in a snowstorm
- Experiments show that people are able to walk directly toward the target and
stop within a fraction of a meter of it
- This was found even when they were told to walk in a different direction first
Shows people are able to navigate short distances accurately in the absence of any
visual stimulation at all
- Subjects accomplished this by mentally combining knowledge of
their own movements with their memory for the position of the
target throughout their walk
Spatial updating – the process by which we keep track of our
position within a surrounding environment while we move
The optic flow however does provide important information about
direction and speed when walking
- this information can be combined with the visual direction
strategy and spatial updating process to guid walking behaviours
Changes in your environment
The ecological approach to perception
Gibson – perception evolved so that we can move within, and act upon, the world
A better approach is to study perception in situations where people move through
and interact with the environment
Gibson's approach focused on perception in natural contexts and so was called the
ecological approach to perception
A major goal of this approach is to determine how movement creates perceptual
information that both guides further movement and helps observers perceive the
environment
The moving observer
Optic flow – movement of an observer (e.g. you sitting
in a moving car) creates movement of objects and the
scene (trees moving past you and the road coming
towards you) relative to the observer. It has two
important characteristics:
1. It is more rapid near the moving observer (longer
arrows indicate more rapid flow).
- The gradient of flow - the different speed of flow i.e. fast near the observer and
slower further away.
- Provides information about how fast the observer is moving
- The observer uses the information provided by the gradient of flow to determine
their speed of movement
2. There is no flow at the destination toward which they are moving (white dot in
the centre)
- Focus of expansion (FOE) – the absence of flow at the destination points
Invariant information – information that remains constant regardless of what the
observer is doing or how the observer is moving
- Optic flow provides invariant information because the same flow information is
present each time the observer is moving through the environment in a
particular way
- The focus of expansion always occurs at the point toward which they are moving.
If they change direction, the FOE shifts to a new location, but the FOE is still there
- Even when specific aspects of a scene change, optic flow and the FOE continue to
provide info about how fast a person is moving and where
they are heading
Self-produced information
Self-produced information – when a person makes a movement,
this movement creates information, this information then is used
to guide further movement
- E.g. if a person is driving, movement of the car provides optic
flow information, and the observer then uses this flow
information to help steer the car
, Senses do not work in isolation
Gibson felt that we should consider how
each of the senses provides information for
the same behaviours
- E.g. balance – this includes the vestibular
canals of your inner ear and the receptors
in the joints and muscles + information
provided by vision
Vision provides a frame of reference that
helps the muscles constantly make
adjustments to help maintain balance
- Swinging room experiment - stationary
floor but swinging walls and ceiling
- Oscillating the room through as little as 6
mm caused subjects to sway
approximately in phase with this
movement
- Shows vision can override the traditional
sources of balance information provided
by the inner ear and the receptors in the
muscles and joints
Staying on course: walking and driving
Walking
Optic flow can provide invariant information regarding a person’s trajectory and
speed
As well as this, various strategies can play a role in maintaining one’s heading
Visual direction strategy – observers keep their body pointed toward a target
- If they go off course, the target will drift to the left or right
- When this happens, the walker can correct their course by realigning his or her
body with the target
Optic flow information is not always necessary for navigation – we can find our way
even when flow information is minimal e.g., at night or in a snowstorm
- Experiments show that people are able to walk directly toward the target and
stop within a fraction of a meter of it
- This was found even when they were told to walk in a different direction first
Shows people are able to navigate short distances accurately in the absence of any
visual stimulation at all
- Subjects accomplished this by mentally combining knowledge of
their own movements with their memory for the position of the
target throughout their walk
Spatial updating – the process by which we keep track of our
position within a surrounding environment while we move
The optic flow however does provide important information about
direction and speed when walking
- this information can be combined with the visual direction
strategy and spatial updating process to guid walking behaviours
