Lecture 7 & 8 Flashcards
Motion perception
Continuous environmental uptake and allows us to group objects.
What is Illusory motion ?
Apparent motion that is perceived motion in a static stimulus e.g. doodle book, movies
Describe illusory motion
Induced motion that uses a stationary frame to create movement.
What type of motion produces retinal motion?
Real motion
Physiological basis of motion - middle temporal area
(V5) is where almost all neurons are direction selective to process where an object is
Newsome and monkeys
Monkey experiment with moving dot displays and measured neuronal firing rate. With increasing coherence between shape direction the more rapidly neurons fire
What are middle temporal neurons specialised to do?
Detect motion direction
The aperture problem
The direction of moving stimulus through a receptive field is ambiguous.
The superior temporal sulcus
Receives projections from the middle temporal area and inferotemporal cortex
Biological motion
Self produced motion of a biological being- real motion that produces retinal motion
Collary discharge theory
Motion perception depends on retinal motion and eye movements. Eyes have 6 muscles with 3 relevant signals.
What are the 3 relevant signals that create motion
Image displacement signal (IDS): an image moves across the retina and successfully stimulates the receptors Motor signal (MS): a motion command is sent from the muscle to the eye muscles Collary discharge signal: copy of the motor signal
Evidence for collary discharge theory
Behavioural evidence: motion perception matches the model predictions
Neural evidence: real motion neurons respond to moving stimuli but not static stimuli
Sensation
The un-interpreted sensory impressions created by the detection of stimulus
Perception
The physiological process of making sense of a sensation
Recognition
The identification of a stimulus as an object we are familiar with
Object recognition
If visual input matches the representation there is object recognition.
If visual input does not match the representation there is not recognition
Theories of object recognition
Template matching
Feature analysis
Structural analysis
Template matching
Visual input is transformed until it matches a template. Problem- large number of templates required
Feature analysis
Size or orientation used to distinguish. E.g. P and R
Problem- spartial arrangement of features not taken into account
Structural analysis
Objects may differ in their 2D appearance but may become equivalent in 3D space
What does visual object (Structural) analysis proceed through
4 levels of representation
- Raw primal sketch: process brightness
- Full primal sketch: geometric organisation of intensity changes (edges)
- 2 1/2 D sketch: spatial location of visible surfaces
- 3D model: Represents the object independently of the observer’s posision
Ellie & Young
use boxes to show functional processing stages
Arrows show direction of information flow
Blue indicates sensory processing
Red is perceptual processing
Green is recognition
Testing model predictions- Benson and Greenber
Soldier suffered CO poisoning and could: maintain fixations, name colours, describe sensations, detect changes in brightness, detect movement of small objects
He could not: perceive shape or form, or recognise/name objects
Model predicts that there was no viewer centred representation as there was no perception of basic shapes so all following steps were impaired
Testing model predictions- Warrington (Right posterior lesion patients)
Group of patients with right posterior lesions could not: match object size/colour, explain the use of different objects, recognise objects from pictures or recognise objects from unusual views .
Impaired object centred representation so could not recognise objects from unusual views
Testing model predictions - Warrington ( cerebral atrophy)
Ongoing loss of neurons and connections between them.
Patient could not distinguish basic shapes, identify colours, numbers, letters, match pictures, name common objects and could not identify meaningful sounds
Object recognition impaired
Ellis and Young predictions on patients with visual agnosis.
Inability to recognise objects due to impaired perceptual and semantic stages
What does a cognitive model need to do?
Explain the functional components of a mechanism and how they are linked.
Apperceptive agnosia
Cannot copy or match simple shapes
Associative agnosia
Can copy and match objects but intact perception has no meaning
