Perception and Action

- Whole greater than sum of its parts
- How we group parts of stimulus and separate figure from ground - segregation and grouping
- Against structuralism - perception is combination of individual sensations that can be reduced to simple individual elements

- Underplay parallel processing and unconscious processing
- Laws provide description rather than explanation

- Bottom-up - perception is direct, complex cognitive processes unnecessary
- Intrigued by way world flowed and expanded towards and contracted and flowed away - optic flow

- Combination of parallax and retinal size
- Horizontal lines painted on road become closer to create illusion of speed

- Provide unambiguous information about environment, directly perceived
- e.g., Horizon ratio relation or texture gradients

Things further away move slower than things nearby

- Opportunity for action determined by what object affords
- E.g., can it be sat on? Grasped?

- Grey level description - intensity of light at each point in image
- Primal sketch - representation of conteast change
- 2 1/2D sketch - representation of orientation, depth and colour
- 3D object-centred description - representation of objects independent of observer

- Retinal image does not provide sufficient information
- Perception depends upon stored knowledge

- Involuntary, pre-rational and reflex-like mechanism
- Fixed unconscious neural processing - illusions etc.

Variations of the same item can still be recongised as the item itself

Mini copy in LTM of all known patterns e.g., letters, barcodes, fingerprints

Possess average of each individual characteristic of an object

Patterns consist of set of features or attributes (e.g., A consists of 2 diagonal lines and connecting bar)

Describe nature of components of a configuration and structural arrangement of parts

Marr and Nishihara
- All objects are comprised of cylinders, must specify relationship
- Structural relations expressed by hierarchical organisation of cylinders

Biederman
- Geometrical ions(36 variants)
- Viewpoint invariant
- Specified in terms of non-accidental properites (curvature, parallel etc.)

Tarr and Bulthoff
- Changes in viewpoint reduce speed and/or accuracy of object recognition

Humphreys
- Structural description --> semantic representation --> name representation
- 3 stages all interact

Problems with early processing (shape extraction), affects visual representation directly

Problems with later processing (recognition), visual representation intact but can't be accessed in recognition

- Biederman's geons specified by edges obtained from primal sketch
- Surface characteristics play no role in defining geons but could play role in disambiguating similar looking objects

- Orientation-tuned neurons respond best to preferred orientation, but respond to similar
- Perceived orientation determined by distribution across cells

- Perceptions of line thickness changes after viewing a wider stimulus
- Size tuned cells in V1

- Number of bars per unit distance
- High spatial frequency = fine details

- Caused by ambiguity in shading and perspective
- Make assumptions - can sometimes lead to perceptual error

- Compromise
- Dominance
- Interaction - where one cue is incomplete/ambiguous, need another source to differentiate

Young et al.
- Computer-gen stimulus defined by texture and motion
- Where they conflicted, perception was a compromise unless one cue was more reliable

- Planning and timing
- Sequencig
- Imagery
- Expertise

- P&T - execution - primary motor cortex
- Sequencing - preparation of action - premotor cortex
- Imagery - higher level of planning - prefrontal cortex
- Expertise - sensory motor links - parietal cortex

- Somatotopic organisation - point-for-point correspondence between body area and CNS
- Coding of movements - M1 cells have preferred direction of movement, code direction of movement

- Body part specific for fine motor control
- Somato-cognitive action network for integrating goals and whole body movement

- Lateral premotor cortex - externally generated actions
- Medial PC - internally generated actions

- Perseveration (repeating action)
- Utilisation behaviour
- Disinhibition
- Frontal apraxia - not able to follow steps to complete an action

Required for novel/less automatic actions
- Contention scheduling selects correct schema - deficit in those with perseveration and utilisation behaviour

- Caused by damage to parietal cortex
- Idea and execution disconnected
- Can recognise action but cannot replicate
- Can perform sequence but not individual components

- Cerebella patients show actions temors, dysmetria (over and undershotting), deficits in timing and coordination

- Input from putamen, output by medial globus pallidus
- Direct and indirect pathways allow/prevent desiredndesired movements

- Desired movement disinhibited, competing inhibited
- Parkinsons - lack of dopamine impacts both pathways

- Reduces effect of indirect pathway
- Greater excitation of motor cortex

- Chorea - uncontrolled movement
- Degeneration of putamen
- Underactivity of indirect pathway - too much movement
- Difficulties in processing speed, emotion recognition, attention etc.

- Increased dopamine from substantia nigra
- Overactivity of direct pathway
- Aberrant focus of activity in striatum

- Mapping visual representation of actions onto motor system to copy it
- Meltzoff and Moore

- Associative sequence learning - learning thorugh experience

- Semantic (meaningful, stored in repertoire)
- Direct (meaningless, mirror neurones)

- F5 of premotor cortex and inferior parietal lobe
- 3 types of neurons: action-observation related visuomotor, motor, canoical visuomotor neurons (objects)

- Faster responses when compatbility between observed and executed movements

- Overlap in brain imaging between imagined, observed and executed movement

Motor evoked potentials show that observing an action produces increased motor excitability

- Mirror neurons found in medial frontal lobe and medial temporal lobe (hippocampus)