Perception, motion and action- Lecture 2 Flashcards
James Gibson (1904-1979) Theory of direct perception
The perceived environment is not a construct of the brain- information is picked up from the environment and processed in a one way system
accounts
for recognition of objects, their position in the space, their movement and direction and their
relation to the observer. T
Affordances
Important concept in Gibson’s theory (1979)
an object is perceived not only by its visual features, but also by the potential
motor actions it affords
Pappas & Mack (2008)
Unseen objects that afford motor response activate the visuomotor system automatically without conscious perception- THE AFFORDANCE EFFECT
Will et al (2013)
affordance of graspability triggers rapid activity in the motor cortex (compatible images would be able to grasp-correct orientated object)
Visually guided action-
Optic flow
Gibson (1950)
How the objects and surfaces in the environment flow when you move through the world- due to changes in the pattern of light that reaches the eyes of the observer
Focus of expansion
Target point towards which the observer is moving towards- appears to be motionless
Smith et al (2006)
Medial superior temporal area is strongly responsive to coherent optic flow- fMRI shows high activity in MST area to moving
Optic array
is all the information
from the environment that reaches the eyes
It is subjective- depends on our position and orientation in the environment
Flaw in Affordances
Oversimplified, as the same object may have a range of affordances- actually learning, practise, mood, psychological state and creativity may influence the perceived use- no longer bottom up approach
Invariant
higher order of the opric array that remains unaltered as observers move around the environment
e.g. focus of expansion, texture gradients, parallel lines that converge to a point
Flaw in Gibsons notion of Optic flow
If we can’t move directly to our goal then things become more complicated
Retinal Flow field
it is the changes in the pattern of light that reaches the retina produced by the
observer moving in environment as well as eye and head movements
Linear Retinal Flow + Rotary Retinal Flow.
Linear Retinal Flow
contains a focus of expansion (= optic flow of Gibson),
Rotary Retinal Flow
Produced by non-linear changes in the path with eye and head movements
Snyder and Bischof (2010)
2 systems in which we use to make judgements of heading when there is rotary flow disrupting the linear flow:
- Using motion
- Retinal Displacement
Retinal Displacement
the objects that are nearer to the direction of heading show less retinal
displacement, whilst those nearer the observer show stronger retinal displacement and are
more informative.
Why not just retinal displacement system as a guide for heading?, but also uses motion
It is not useful for curved pathways (complex motion direction)
-The first
system uses motion information quickly and automatically
-The second system uses displacement information more slowly
Evidence for 2 part system of heading
MST are not
only responsive to expansion, but also to rotation, and even more to a combination of the
two…. So probably this area can compensate for distorted flow fields and decode
information from retinal displacement and factor it in to adjust the visual flow perception.
Curved pathway- Point of Heading
2 Potential strategies
Future Path strategy
Tangent-point strategy
Future path strategy
The observer identifies a number of point along the future path
Tangent-point strategy
the point on the inside edge of the road at which its
direction appears to reverse
Lappi et al (2013)
drivers tend to switch from fixating the tangent point to fixating the future path ahead as they negotiate curves. Probably the tangent point provides
relatively precise information. As a result, drivers may use it when uncertainty about the
precise nature of the curve or bend is maximal (i.e., when approaching and entering it).
Thereafter, drivers may revert to focusing on the future path.
Visually guided action- TIME TO CONTACT
Information that allows us to predict the moment in which there will be contact between us and some objects
David Lee (1976) Professor of perception
Developed the General Tau Theory
General Tau Theory
Provided we are approaching an object at constant velocity, we can use Tau to predict TIME TO CONTACT.
Tau= the size of object s retinal image/ rate of expansion
Tau
Tau= the size of object s retinal image/ rate of expansion
The faster the rate of expansion…
less time there is to contact
Limitations of Tau Theory
May provide simple and elegant framework to explain observers’ time-to-contact judgments
BUT…
-Speed must be constant
-Tau provides information about time to contact with the eyes
-Tau can only be applied to spherical symmetrical objects
Cues that observers use to predict time-to-contact
- Object familiarity -Hosking & Crassini (2010)
- Binocular Disparity- steroscopic vision- perceprion of depth
- Relative size- De Lucia (2013)
- Emotional value of approaching object- Brendel et al. (2012)
Summation point about factors influencing Time to contact
Lack of a comprehensive theory that integrates/combines all of the factors influencing time to contact judgements
Scott Glover (2004) Control model
2 systems that enable humans to perform an action, which partially overlap:
Planning system and control system
Planning system- Control model
Intuitively starts before control system- relatively slow
Involves processes prior to movement:
-T arget identified (e.g. coffee mug)
-A ffordances analysed
-M ovement - how this should be carried out
-T imings worked out using metrical properties
Planning system- control model
Influenced by…
bottom up factors- visual info, affordances, visual context
top down factors- individuals goals, cognitive load
Brain areas involved in Planning system
Inferior parietal lobule- processing sensory info, visual representation of object and visual context
Prefrontal cortex, motor cortex, basal ganglia- Planning and selection of the correct motor tools
Control system- Control model
Starts during execution of movement- faster circuit as not susceptible to conscious influence
-Ensures movement is accurate
3 components of control system
EFFERENCE COPY=copy of the efferent signal sent to muscles from primary motor cortex- used by the brain to compare actual with desired movement.
PROPRIOCEPTION=sensation relating to position of ones body
VISUAL PERCEPTION=target object’s spatial characteristics
Brain areas involved in Control system
Superior parietal lobe- visual representation formed
Cerebellum and basal ganglia- control of motor processes
Glover (2012)
fMRI study defining planning and control systems
contrast of brain activation across tasks
Results confirm the existence of separate neural systems for
the planning and control of reaching and grasping
Glover (2005)
the control process was disrupted when TMS was applied to the superior parietal lobe- confirming what model proposed
Streiemer et al (2011)
TMS applied to inferior and superior parietal lobes - planning process was more greatly disrupted when applied to the inferior parietal lobe- in line with the control model
Evidence for control model from Lesion patients
Ideomotor apraxia- inferior parietal lobe damage- poor at initiating movements in direction of target
Optic ataxia- superior and posterior parietal lobe damage- difficulties making accurate movements to perform action
Perception of human motion
Humans are very tuned to interpreting other people’s movements and actions
Gunnar johansson (1998)
Studied perception of the human body in motion
Point Light Sequencing
Johansson (1973)- used point lights on human model and found that a figure can be perceived even when it is masked by irrelevant noise dots.
Images contained just the few light dots but ppts were still able to identify a figure
Mather & Murdoch (1994)
Gender discrimination as a function of view angle.
Participants were very accurate at identify gender-specific differences.
Biological motion as innate?
May prove as ontogenic and phlogenic foundation for humans higher order social cognition
Simion et al (2008)
Showed pointlight display of chickens to newborns (0 – 3 days) who had
no previous experience of them, as well as non-biological motion.
Preferred to look at a display showing biological motion
experience and human motion perception
- Humans can become increasingly sensitive to human motion due to increased exposure
- Also exposure helps develop a better dedicated internal cortical representation of the spatial organisation of the body parts
Pinto (2006)
3 month olds = equally sensitive to point-light humans, cats and spiders
By 5 months= more sensitive to displays of human motion
Influence of own repertoire of actions on human motion perception
Cohen (2002)- point light displays used of humans dogs and seals
- performance best with human motion
- tested on dog and seal trainers and human motion still better
- must be that we recognise motion most similar to that of our own, not just having experience with a type (e.g. seal motion)
Specific brain region for human motion?
Superior Temporal Sulcus seems to be of particular importance
Thompson et al (2005) –
fMRI- STS strongly responds to moving bodies even through
occlusion, but not to disconnected moving parts.
Gilaie-Dotan et al. (2013a)
Grey matter volume in the
superior temporal sulcus on motion detection correlated positively with the
detection of biological motion but not non-biological motion.
