Week 4: Sensation and Perception and Object recognition

Two viewpoints of the brain

View-dependent and view-invarient

Object constancy

Ability to recognize an object despite variation in low-level visual features

What was wrong with patient GS?

He had visual agnosia and could not put object recognition, visual perception, and memory together

What areas of the brain are associated with object recognition?

Occipital lobe, fusiform gyrus, parahippocampal area

What are the two pathways of visual perception?

Dorsal and ventral

What is the ventral occipitotemporal pathway?

The what pathway of the brain that terminates at the temporal lobe

What is the dorsal occipitoparietal pathway?

The where pathway of the brain that terminates at the parietal lobe

How was the difference between the dorsal and ventral pathway discovered?

Brain lesion studies on monkeys found that lesions in the temporal and parietal lobes caused different object recognition problems

What are the two pathways of auditory perception?

Anterior and posterior

What does the anterior pathway of auditory processing do?

Determines what the sound is

What does the posterior pathway of auditory processing do?

Determine where the sound is

What was wrong with patient DF?

She was exposed to carbon monoxide resulting in lesions on the lateral occipital complex of her brain, causing apperceptive agnosia

What are the three components of object recognition?

Feature extraction, shape description, and memory matching

Hierarchical coding hypothesis

We recognize things in stages, features→ connections between features→ component shapes→ object

Grandmother cell theory

One single cell is specialized for a certain object, like Jennifer Aniston

What are the drawbacks of grandmother cell theory?

Cells die, sensations are multi-system, objects are similar, and people/objects change

Ensemble coding hypothesis

Recognition is due to a unit of cells, rather than a single cell

Problems with the ensemble coding hypothesis

Similar objects may look the same

Apperceptive Agnosia

Problems in recognizing objects from different viewpoints caused by lesions in the ventral region

How is apperceptive agnosia diagnosed?

Unusual view task and shadow test

People with what lesions do worse on the unusual view task and shadow test?

Right hemisphere posterior lesions

Integrative agnosia

A subset of apperceptive agnosia, unable to integrate features into a coherent whole

What patients had integrative agnosia?

Patients CK and GS

What test can people with integrative agnosia pass?

unusual view task

Associative agnosia

Trouble acquiring the use of objects

What test is used to diagnose associative agnosia?

Matching by function test

Are animate or inanimate harder for patients with visual agnosia?

Animate objects

Why are inanimate objects easier to recognize?

Inanimate objects provide visual cues that tell us what motor function goes along with the object

How are faces perceived?

By recognizing the parts and then recognizing themselves as a whole.

Prosopagnosia

Deficits in the perception of faces

What type of lesions are associated with prosopagnosia?

Bilateral temporal lobe lesions