Week 5 - Pattern recognition Flashcards
Agnosia
- 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
two cortical pathways for vision
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
Patient DF
- severe agnosia
- visual acuity and nonvisual object recognition are intact
Optic Ataxia
- Intact object recognition
- Inability to use visual information to guide action
- Associated with lesions in the dorsal pathway (typically in parietal cortex)
Gestalt principles
our brain naturally organises visual information into cohesive groups or patterns. The four core principles are
- Similarity
- Closure
- Good continuation
- Proximity
Template-matching and feature analysis
We tend to recognise different stimuli as the same object irrespective of superficial variations (e.g. letter ‘A’)
Feature Analysis
A visual pattern is perceived as a combination of elemental features (Selfridge’s pandemonium model)
- Whole features ten to disappear simultaneously
Recognition-by-component theory
- 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
Neurons in higher-order visual areas…
respond to increasingly complex patterns
Grandmother cell hypothesis
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
Object recognition
results from the firing of an ensemble of cells (ensemble coding)
recent findings of grandmother cells
these neurons might exist just not necessarily in the visual object recognition system
Top-down processing
perception is guided by previous knowledge, the brain applies these influences to interpret sensory information using context
bottom-up processing
perception starts with raw sensory input, the brain builds interpretation from this data without using prior knowledge.
Word-superiority effect
superior recognition of letters in a word context than alone
- indicates top-down influence on pattern recognition
