Lecture 3- Object and face perception Flashcards
What is object perception?
We don’t see features we automatically put them together into meaningful parts and we see them as the whole object
What is object perception needed for?
Survival
What is detection and recognition?
We group objects together in different senses and then we use the memory to decide what it is
What is feature detection?
Part of the brain is selective for different features for example contrast boundaries
What are examples for features?
Colour, orientation and spatial frequency
What does low spatial frequency do in object recognition?
Convey rapidly to higher order brain areas by fast magnocellular pathways
What does high spatial frequency do in object recognition?
Convey slowly by parvocellular pathways
What is low level analysis?
Encoding features such as brightness, colour contrast, spatial detail, orientation and texture
What is high level analysis?
Understanding of the meaning
What does the presentation of visual stimuli lead to in feature processing?
Detailed processing of basic features to identify cortical cells involved in processing
Who studied cortical cells?
Hubel and Wiese
What did Hubel and Wiese do?
Studied the cells in the part of the occipital cortex in early stages of visual processing
What did Hubel and Wiesel find?
There are two types of neurones in the primary visual cortex: simple cell and complex cell
What does simple and complex cells do?
Provide ambiguous information and respond in the same way to different stimuli
We combine info from many neurones to remove ambiguities
What is grouping?
When the brain has automatic rules for deciding how to organise features to form an object
What are the three groupings found by Zanker?
Law of proximity, law of similarity and common fate
What is law of proximity?
Grouping of object close together
What is law of similarity?
Grouping of those similar
What is common fate?
Humans perceive visual elements that move in the same speed or direction
What is the most powerful cues from grouping?
Proximity when decide which contours belong to which objects
Who looked at grouping by uniform connectedness?
Palmer and Roch
What did Palmer and Roch find?
Grouping by uniform connectedness dominated proximity and similarity
What is contour for visual object?
Extracting objects for different spatial scales, neurones will respond at low and high spatial frequencies
What is Biederman recognition by components?
Turning 2D information into 3D information
What is the first stage in Biederman recognition by components?
Early edge extraction stage responsive to differences in surface characteristics
What is the next step in Biederman recognition by components?
Deciding how a visual object should be segmented to establish its components
What are of particular value in Biederman recognition by components?
The concave parts of an object’s contour
What are the 5 properties of edges in Biederman recognition by components?
Curvature, parallel, cotermination, symmetry and collinearity
What is Milner and Goodale’s two system model?
Object recognition and perception depend on the ventral visual stream
Is hierarchically organised
What happens to the stimuli causing the greatest neuronal activation in Milner and Goodale’s two system model?
Becomes progressively more complex as processing moves along the ventral stream
What are the certain conjunction of contours?
T-vertex, Y-vertex and arrow-vertex
What is view independent representation?
The ability to visual an object and see it from a different perspective such as rotation of the object
How do we recognise an object?
We have to have an idea of its 3D shape
What is the role of expectation?
Each person brings different experience and expectations and stimuli show that what we expect has influence on what we perceive
Why do we consider face perception separately?
Important as part of our communication with each other in an evolutionary process and is very constrained
What is the first step of face detection?
The first step of the process has to be the detection of the face which requires extracting feature that all faces have in common through template matching
What occurs when a face is detected?
It can be further analysed to categorise
What do we ascribe in face recognition?
Various attributes
What are the challenges for face recognition?
Discrimination
Generalisation (transformation, lighting conditions, varying contexts
How are faces special?
Faces are such important stimuli with a special class of complexity we might need to process them in a different way than other objects
Who looked at evidence for innate ability?
Goren et al, 1975
What did Goren et al do?
Preferential looking task
Newborn infants
Show a paddle to baby one with nothing, one with a face and one with face scramble
The baby looked at the face for the longest
Hardwired to look at faces
What is face inversion effect?
How faces are harder to identify when presented inverted than upright
Who looked at face inversion effect?
Yin, 1969
Who looked at negative contrast faces?
Kemp et al, 1990
What did Kemp et al do?
Inverted contrast difficult to recognise
What local image information is preserved?
Shape, distance between features
What is the upside down and negative faces?
The key is that inversion has a greater effect for faces than other objects
What did Gaultier et al, 1999, find?
Activation of the middle fusiform face area. Increases with expertise in recognising novel objects but less activation than for faces. Experts in cars, writing, dogs and fingerprints do not get the same size of inversion effect
What information is ambiguous?
Shading
What information is stereoscopic?
Disambiguate
What did Hill and Bruce look at?
Hollow faces and hollow potato illusions
What did Hill and Bruce find?
Hollow face seem to move when you move the picture up, down, left
Seems like the face is looking at you
What does the existence of the hollow potato illusion show?
Shows that the visual system expects objects in general not just faces to be convex but the illusion is stronger for faces
When is the hollow face illusion stronger?
When one eye is closed
What happens when you get closer to the hollow face illusion?
It disappears
What is the expectations for faces?
Convex seems to override our knowledge
What are the key facts about faces?
They have many things in common making them a constraint set of stimuli
They are highly variable due to the demands on the memory
What happened to Patient CK?
Has trouble recognise objects but no trouble recognising faces
What is prosopagnosia?
Inability to recognise familiar faces but object recognition is not impaired
Who looked at prosopagnosia?
Simon et al
What did Simon et al find?
Presented with familiar and unfamiliar faces showed an absence of conscious recognition of familiar face
What did Perrett et al, 1979, find?
Primary electrophysiology and cells in the superior temporal sulcus are selective for faces
What did Hasselmo et al, 1989, look at?
Object centred vs viewer centred
What did Hasselmo et al, 1989, find?
Some neurones responded in view independent way. Neurones in STS respond to facial motion, posture and eye gaze. Neurones in inferior temporal cortex more likely to respond on the basis of identity
What do the neurones form the steps in Hasselmo et al?
Form steps in cognition (mental rotation, emotion, speech recognition, social attention and memory recall
Where is the fusiform face area?
In the ventral temporal cortex
What did Kanwisher et al,1997, find?
fMRI revealed fusiform face area as 80% of participants show greater activation within FFA to faces than other objects
How is the face composed?
Into features
How are faces recognised?
Feature decomposition and description
What is feature decomposition?
The process of breaking down faces into features to understand them
What does feature decomposition involve?
The detection and localisation of where the features are for reference points
Extracting the local feature descriptions to characterise certain features
What is a technique for feature decomposition?
Principle Component Analysis
Why do faces appear special in human perception?
The face inversion effect
Single cell tuning in response to faces
Infant preferential looking at faces
Who found the photofit theory?
Penny and Ryan, 1971
What is photofit theory?
Photographed features allow subject to build a face
Who looked at holistic processing?
Tanaka and Farah, 1993
What did Tanaka and Farah, 1993, find?
Some evidence shows that we do not store faces as parts but holistically
Who looked at composite face effect?
Young et al
What did Young et al find?
Composite faces interfered with recognition of a half face, the effect disappeared upside down. The holistic processing obliges us to combine information automatically
What is composite face effect?
When the top half of one face is aligned with the bottom half of another
It is presented upright
What is the result from composite face effect?
Results composite arrangement induces a compelling perception of a novel facial configuration
What does composite face effect suggest?
People are unable to ignore the bottom halves so processing of composite faces is holistic
What is Thatcher illusion?
In upside down faces we process features separately and don’t see the relationship between them and in holistic processing the upright faces makes the unusual arrangement salient
What is the Thatcher illusion evidence for?
Holistic processing of faces
Who looked at the individual differences with object and face recognition
Russell et al
What did Russell et al find?
Face recognition depends more on surface reflectance information
What are the other individual differences?
Genetic factors explaining the existence of super-recognisers
