perceptual organisation, gestalt psychology and face perception Flashcards
Low level vision
Extracts local information about lines, bars and edges
Mid level vision
Joins together isolated features into larger groups
High level vision
Forms the basis for object recognition
Ventral stream
What stream
Object identification
Dorsal stream
Where stream
Viso-spatial information processing
No strict separation in visual processing
Complex connectivity in the visual system
No strict anatomical or functional separation of what and where streams (Konen & Kaster, 2008)
Overcoming ambiguity in grouping
We need constraining principles
We use prior knowledge and assumptions about the input
Gestalt principles of perceptual organisation
Described a set of laws or principles of perceptual organisation
Relationships between elements are critical for perception and that’s what’s important
Early Gestalt psychologists recognised the easy ones, newer ones are less easy to understand intuitively
Principle of proximity
Group things based on where they are
Pieces of information that are close together in space are bound together
Principle of similarity
Pieces of information that are similar in some way are bound together
Can see when principle of proximity takes over, in the case of the different coloured dots
Principle of common fate
Things that move together are bound together as a concept
Assumes that features that move together come from same object
Principle of good continuation
Most natural objects smooth continuation in orientation
Our brain assumes that smooth lines mean they are connected
Face perception
Many factors found in the face tell us lot about an individual
Face is important in telling us about characteristics that can change quickly
Gaze direction particularly important in understanding how we interact with the environment
Faces processed very efficiently
Brain areas of face processing
Have specific brain areas that are relatively dedicated to facial processing
Three main areas
Inferior occipital gyri
(Also known as occipital face area - specifically dedicated for facial processing)
Superior temporal sulcus
Lateral fusiform gyrus
Domain specific account for face perception
Mechanisms operate independently of general object perception
We only use certain areas just for faces, nothing else
Expertise account for face perception
Mechanisms derive from general object perception but have become finely tuned due to extensive experience
We are good at detecting faces because we have used the skills so much
Exposed to faces so much that our object processing system can become an expert
Holistic processing
Representing features and their relationship as one unit
Part-whole effect
Features are easier to identify when presented as part of a face (Tanaka & Fara, 1993)
Face inversion effect
Inversion disrupts processing of fine details and relationships between features
Specialised mechanisms only kick in when we see a configuration we recognise
Thatcher illusion (Thompson, 1980)
Holistic processing won’t kick in if the face with swapped eyes and mouth are upside down
Prosopagnosia
Failure to identify or distinguish between faces despite otherwise normal visual and cognitive ability
Patients can identify other object categories
Prosopagnosia patients will still be able to identify that a familiar individual is familiar but be unable to identify
Opposite of prosopagnosia?
Capgras syndrome
Norm-Based Code
Facial features are represented as deviations from the average face
In our brain, we have stored the average face
We judge all of the other faces based on that average face
Further away from the norm, the easier it should be to recognise the face
After-effects in High level vision
If we change the way we think about the norm, the way in which we perceive faces would be very different
1. Change your norm by looking at one face in the Bush/Obama illusion
2. Neurons that code for facial features adapt to specific characteristics of adaptor face
3. As a consequence, perception of subsequent faces are biased away from adaptor characteristics
