Week 5 - Pattern recognition

Question 1

Agnosia

Answer 1

• inability to recognise objects
• processes such as colour, shape, and motion perception are intact
• recognising a whole object is more than just recognising its parts

Question 2

two cortical pathways for vision

Answer 2

Ventral pathway
- occipital -> temporal
- processes information about object appearance and identity
- important for object perception
Dorsal pathway
- occipital -> parietal
- processes spatial information about objects
- important for guiding action

Question 3

Patient DF

Answer 3

• severe agnosia
• visual acuity and nonvisual object recognition are intact

Question 4

Optic Ataxia

Answer 4

• Intact object recognition
• Inability to use visual information to guide action
• Associated with lesions in the dorsal pathway (typically in parietal cortex)

Question 5

Gestalt principles

Answer 5

our brain naturally organises visual information into cohesive groups or patterns. The four core principles are
- Similarity
- Closure
- Good continuation
- Proximity

Question 6

Template-matching and feature analysis

Answer 6

We tend to recognise different stimuli as the same object irrespective of superficial variations (e.g. letter ‘A’)

Question 7

Feature Analysis

Answer 7

A visual pattern is perceived as a combination of elemental features (Selfridge’s pandemonium model)
- Whole features ten to disappear simultaneously

Question 8

Recognition-by-component theory

Answer 8

• proposed for 3D object recognition
• object is segmented into a set of basic sub-objects (geons) and then recognised as a pattern composed of geons
• When objects are presented as midsegment deletion it is more difficult to identify them in shorter exposure durations.
• Easier with component deletion

Question 9

Neurons in higher-order visual areas…

Answer 9

respond to increasingly complex patterns

Question 10

Grandmother cell hypothesis

Answer 10

Weaknesses:
- final percept of an object is coded by a single neuron
- however, each neuron’s firing is not so reliable
- if that neuron is lost, our perception of the corresponding object would be lost
- perception of novel objects cannot be explained well
- flexibility of object recognition cannot be explained well

Question 11

Object recognition

Answer 11

results from the firing of an ensemble of cells (ensemble coding)

Question 12

recent findings of grandmother cells

Answer 12

these neurons might exist just not necessarily in the visual object recognition system

Question 13

Top-down processing

Answer 13

perception is guided by previous knowledge, the brain applies these influences to interpret sensory information using context

Question 14

bottom-up processing

Answer 14

perception starts with raw sensory input, the brain builds interpretation from this data without using prior knowledge.

Question 15

Word-superiority effect

Answer 15

superior recognition of letters in a word context than alone
- indicates top-down influence on pattern recognition

Question 16

Phenome-restoration effect

Answer 16

using top-down processing the brain fills in missing sounds in speech based on context and prior knowledge
- in a study only 1 in 20 participants reported hearing the tone