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
