PSYC2218 Final: PSYC2218
PSYC2218 – CHELSEA GRAY - 21954282
Perception & Sensory Neuropsychology:
Perception shapes the world:
• The big bang and animal evolution → perhaps the most dramatic event in the history of life on Earth. During the blink of an eye in such history, all the
major animal groups found today evolved hard parts and became distinct shapes, simultaneously and for the first time
• This happened precisely 543 mya at the beginning of a period called the Cambrian, and so has become known as the Cambrian Explosion
• But what lit the fuse?
• Within just 5 million years of life on Earth, there developed armaments and defenses, and animals suddenly became both hunters and were hunted
• Vision lit the fuse
The visual system:
• In order to fill different ecological niches, animals have developed specialised visual systems
• Some insects can detect polarised light (lets them navigate using the direction to the sun)
• Eagles have extremely high visual acuity so they can resolve pattern from great heights (2.3x better than human acuity)
• Owls have systems designed to work effectively under very low light levels
Aim of this unit:
• Learn how perceptual systems work
• Vision, audition, touch, olfaction & gustation
• We will study these systems (behavioural assessment, structure and function of neural pathways, theories of perceptual function, information
processing steps in specific tasks, consequences of brain damage)
Why understand it?
• Understanding sensory systems reveals a lot about us and what we can be
• It is also very useful → this information allows us to design our world to prevent serious practical problems
The London Olympic logo:
• The promo video for the logo triggered the largest number of epileptic seizures ever seen in the UK when it was broadcast on TV and the internet (it
even affected lapsed epileptics)
• Epilepsy action said it had received reports of 22 people having fits while watching the video and others vomiting or having migraines
• This should have been avoided
• Tested with Cambridge research systems (arding flash and pattern analyse, found to contravene industry guidelines on at least 126 frames →
showing that automated checking could have prevented this incident
• The Harding Flash & Pattern Analyser → used by many broadcasters to check that programs comply with international guidelines on flashing and
regular patterns
• Professor Graham Harding graduated in psychology from University College in London
Lecture 3 → representation of vision in the cortex:
Phrenology:
• Measuring bumps on the head to measure if you are strong or weak on some characteristic
• Dividing the brain up to sections
• Doesnt really work though
• Function is localized
Representation of the vision in the cortex:
• What techniques can address the question
• Ablation → are the consequences meaningful? → e.g. chopping out certain areas to rid certain
things, but you may disrupt other pathways → doesnt necessarily produce interpretable results
o You can map the input and output stages
o Hope the structure is modular → if you take out one bit it wont affect the other parts
o Need to use multiple techniques to looking at it → a variety of ways to look at the brain and if all deliver similar answers then you
know that it is reliable
o There are a variety of ways that you can segment the brain
Brodmann: Cytoarchitectonic map:
• Cytoarchitecht → segmentation of the brain
• Looks at the organization of cells in the cortex, and found they are organised in
different ways depending on where they were in the cortex
• When he found a place with the same cells, he drew a circle around them and
segmented them from the other cells in the brain
• This resulted in many different parts of the brain being mapped out
find more resources at oneclass.com
find more resources at oneclass.com
PSYC2218 – CHELSEA GRAY - 21954282
Hypercolumn in Primary Visual cortex:
• Lets create zones where the cells do the same thing → have the same
function and similar cells
• Different dividing it up by function that dividing it up by cells →
there would be a difference (rather than individual parts, its more
looped and has masses of similar function and are generally close
together and bigger than dividing by cells)
• Discrete units in the cortex → cant occur by chance
• Deepest layer in the cortex is layer 6
• Layer 4 is the middle layer → input of the eye from the Lnucleus (in
last lec) → you get inputs in this layer
• Layer 4 is heavily Myelinated → striated cortex
• Alternating left and right eye inputs
• Pattern of organisation in V1 →
• Blobs → colour circulating regions
• Orientation columns if you go across
• Hypercolumn → combination of left & right eye inputs and orientation columns
• When you go down a Hypercolumn → receptive fields of neurons in the same
place
• When you go across a hyper column → fixation point moves laterally
Retinotopic map:
• Shows where the visual field disappears when parts of the visual cortex are taken
away or damaged
• The foeval section of the image occupies a larger area of the primary visual cortex
• Fibers going forward → information gets straight into layer 4 without going into
deep and superficial layers
• If fibers go backward → sends signals from superficial and deep layers to superficial
and deep layers of the receiving end
• High levels of information can be passed back and forth
Corpus callosum connections represent vertical midline of the visual field:
• Holds the two hemispheres together
• If you cut the corpus callosum, it cuts the midline of the visual field
• Corpus callosum pulls the distortion of what the left and right eye see together
Hierarchy of visually responsive areas – 1192 (macaque):
• Monkey brain
• Visual areas
• Streams with different visual functions
• Motion and position coding stream → lower part of the cortex
• Form processing stream
• Hierarchical levels also differ in response latency
• Structures defined faily clearly
• In 2016 → map with 180 areas mapped in the brain
Techniques vary in spatial and temporal resolution:
• Lesions → can look at things for a matter of days or months/years
• Fmri → gives us images of the brain
• Often use a preliminary computerized axial tomography scan (CAT scan)
• CAT scan detects density differences
• Some people should not enter an fMRI scanner → e.g. metal parts in body will magnetize out of the patients body
• PET and fMRI use a differencing procedure
• Consumption of radioactive substance → through oxygen or veins → shows changes of blood flow
• PET → measures ____
• FMRI→ measure levels of oxygen in the blood
• You have a baseline of activities people are interested in and what they arent and you can see whether the task activation causes baseline activation
• Choosing a correct baseline is critical
• Baseline tasks → fixation points, etc.
Transcranial magnetic stimulation (TMS):
• Delivers a magnetic pulse which electrically stimulates the underlying neurons to disrupt processing
• A pulse over the cortical area, MT removes the percept of motion in moving stimuli
find more resources at oneclass.com
find more resources at oneclass.com
PSYC2218 – CHELSEA GRAY - 21954282
The danger of neuro-phrenology:
•
Lecture 4 →Adaptations:
• Lecture different from others in the course
• Not covered in text book or in chapters
• What can we learn about perceptual and neural coding from studying
adaptation (adaptation as a tool)?
• What causes adaptation?
• What is the function of adaptation?
• Are we all equally adaptable?
What do these phenomenon’s have in common?
• Illusions → you experience stuff that isnt there e.g. motion when there is
none)
• Exposure to something consistent → e.g. downward motion of waterfall
• The stuff you see tends to be biased away/opposite to what was consistent in the exposure → e.g. perception of upward motion
• You get less sensitive to the consistent thing → e.g. smelly loo
What is adaptation and why would you care?
• What does adaptation mean?
• Dictionary definitions:
1. To make suitable to requirements or conditions; adjust or modify fittingly
2. To adjust oneself to different conditions, environment, etc.
• Evolutionary adaptation
• Literary adaptation
So what is perceptual adaptation?
• No simple definition but:
• Adaptation adjusts sensitivity according to the set of stimuli the observer is exposed to
• Key features:
o Experience/exposure drives this adjustment
o It is dynamic
• An example of the plasticity of the perceptual system, especially the brain → how the brain changes to adapt to certain environments
Timescales:
• Adaptation may operate over a wide variety of timescales:
o Milliseconds/seconds
o Minutes
o Hours
o Days, months, weeks
o Years
o Millennia (evolutionary adaptations)
• We will focus on the milliseconds to hours timeframes
Why would you care about adaptation?
1. Some of you have to write a lab report on it
2. Secondary reasons to care:
o Adaptation ubiquitous property of perception → occurs in all sensory domains
o May be a fundamental attribute of neural processing in the brain generally
o Adaptation is a powerful tool we can use to investigate perceptual/neural processing
o Demonstrates the way experience shapes even our most basic perceptual abilities
Part 1 → adaptation starts in the sense organs:
Dark adaptation:
• Light to dark → it takes time to adjust → around 5 minutes
or so
• Why does it take so long to adjust?
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The big bang and animal evolution perhaps the most dramatic event in the history of life on earth. During the blink of an eye in such history, all the major animal groups found today evolved hard parts and became distinct shapes, simultaneously and for the first time. This happened precisely 543 mya at the beginning of a period called the cambrian, and so has become known as the cambrian explosion. But what lit the fuse: within just 5 million years of life on earth, there developed armaments and defenses, and animals suddenly became both hunters and were hunted. In order to fill different ecological niches, animals have developed specialised visual systems. Some insects can detect polarised light (lets them navigate using the direction to the sun) Eagles have extremely high visual acuity so they can resolve pattern from great heights (2. 3x better than human acuity) Owls have systems designed to work effectively under very low light levels.
