Perception (Oct 25/28) Flashcards
Define sensation and perception
Sensation: the detection of internal or external stimulation. Raw information about the environment is made available to the brain through the senses.
Perception: the awareness and interpretation of sensory information by the brain. Perceptual deficits can occur without sensory impairment.
What is the primary visual cortices and what can damage result in.
Primary Visual cortex (V1)
- First part of the cortex to recieve visual information.
- Patients with large lesions to the primary visual cortex occasionally retain some visual abilities: blindsight (better than chance performance on forced-choice discrimination, spatial navigation and coordination surprisingly good.
- don’t know what they saw but can say attributes about it.
What is the secondary visual cortices and what can damage result in.
Secondary Visual Cortices (~24)
- Receive much of their input from V1
- Process form, motion, shape etc.
- akinetopsia - inability to perceive movement.
What are the higher visual cortices and what can damage result in.
Visual association cortices (~7)
- Receive input from the visual cortex and from the cortices of one or more oter sensory systems (e.g., hearing, proprioception) multisensory integration.
Describe two theories of the functions of these two streams and relate this to experimental data
Theory 1: What vs Where
Monkeys trained on one of the tasks. They learned to choose tiems followng a specific rule to get a reward.
1. Choose the item with a certain shape (what)
2. Choose the item with a certain location
(where)
- Monkeys with lesions in the ventral stream couldn’t do #1
- Monkeys with lesions in the dorsal stream couldn’t do #2
Theory 2: Action vs Perception
Patient DF had CM poisoning leading to bilateral ventral-stream lesions.
- DF from far away could not line up the postcard with the slot but up close she could do the action.
- DF could not verbally tell us the difference between 2 different sized boxes but could accurately shape her hands to pick them. up.
Dorsal Stream - action
Ventral stream - perception
According the the Action vs Perception theory the opposite patient from DF would have damage where?
Damage to the dorsal stream
They would have optic atraxia: disorder of visually guided movement.
What happens when someone gets ventral stream damage and what is this called?
Agnosia= absense of knowledge
- Loss of ability to recongize objects and shapes not to eye sight or memory. Purely perceptual.
Explain the difference between apperceptive and associative agnosia’s
Apperceptive Agnosia:
- Failure in object recongition linked to problems in perceptual processing
- Unusual views is where there is impairment matching, not with 2 normal stimulus.
Associative Agnosia: Normal visual perception but unable to use visual information to recognize things. (can’t name a vehicle by seeing it, they ca hear description and copy pictures though.
Name the brain regions that have been implicated in face perception
Face processing invloves a network of occipito-temporal areas including
- fusiform face area (FFA)
- Occipital face area (OFA)
- Anterior Temporal cortex (AT)
Prosopagnosics often have bilateral damage.
Describe the conditions of prosopagnosia and prosopometamorphopsia
Prosopagnosia
- Failure of face recognition with intact object recognition.
- can describe the characteristics of a face without recognition
- retrograde and anetrograde
- can still recognize people by the voice, clothing, hair etc.
- After injury or developmental.
- training programmes are being investigated with mixed results
Prosopometamorphopia
- disorder of which faces are perceived as distorted
- only faces not objects
- can involve one or both sides of the face
