Lecture 4

Perception

Perception

How we recognise, organise and make sense of what we see, hear, smell etc

Involves manipulation of sensory information but it also involves linking these sensations to representations

Gibson’s theory of direct perception

Argues we don’t need higher processing systems to navigate between our senses and the brain

We just need sufficient contextual information to make these judgements

Perceptual illusions

Suggests that what we see is not necessarily what we perceive

Gestalt’s theory of visual perception

Argued we tend to perceive things as a whole - we assemble elements into one stable image

Gestalt’s principles

There are 4 different principles:

1. Figure ground

2. Grouping

3. Continuity

4. Closure

Figure ground

Some aspects of a scene stand our while others recede

Grouping

Grouping of objects according to proximity and similarity

Continuity

Prefer continuous representation over discontinuous

Closure

Tendency to close up objects that are not actually closed

Emergence

Process of complex pattern formation from simple rules

Multistability

The ability to see an image in two different ways but not at the same time

Reification

Constructive or generative part of perception

What your brain sees is more than the sensory input

Invariance

The shape will continue behind itself even if you can’t see it

Closure

Filling gaps to make a whole shape

Similarity

If we group things that look alike them we will see something extra in there

Proximity

Things that are close together are grouped as they are together

Continuity

Wanting things to be made up of smooth continuous lines

There are different views on how we perceive the world

Top-down processing

Bottom-up processing

Gibson’s theory of direct perception (ecological perception)

Argued there is no higher level of cognitive processing - the world gives us enough info

Three component of Gibson’s theory of direct perception

Optic flow patterns

Invariant features

Affordances

Optic flow patterns

flow of light into your eye provides information to your brain

Invariant features

Gives important cues about the environment

expanding and contracting of textures

Affordances

An object has to mean something to us based on its physicality

There re cues in the environment that aid perception

Environment cues

Perceptual constancy

Depth cues

Perceptual constancy

Perception of an object remains the same even if sensory information changes

Depth cues

Distance from a surface

Two kinds:

1. Monocular depth cues

2. Binocular depth cues

Monocular depth cues

Can be represented in 2D

• Texture gradient

• Interposition/occlusion

• Linear perspectives

• Relative size of objects

• Motion parallax

Binocular depth cues

Use the relative positioning of your eyes

• Binocular disparity

• Binocular convergence

Binocular disparity

when both eyes send different messages to the brain

Binocular convergence

When your eyes cross to look at something close to your face

Duality of perception

Top-down processing

Bottom-up processing

Bottom-up processing

Known as ecological or direct perception

Based on proximal stimulus only

Top-down processing

Known as constructive processing

Driven by higher cognitive processes

Top-down processing based on 3 things

1. What we sense (sensory)

2. What we know (knowledge)

3. What we infer (high-level)

Context effects

The surrounding environment affects the speed and accuracy of our perceptual processes

Theories of top down processing

Prototype theory

Feature matching theory

Prototype theory

Detailed representations stored in memory

Grouped by similarity features

Feature matching theories

Pandemonium model

Feature integration theory

Facial recognition

Two systems for recognising faces:

1. Feature analysing system

2. Configurational systems

Prosopagnosia

Inability to recognise faces

Facial blindness

Connectionist neural net

Parallel distributed processing (PDP)

processing takes place simultaneously