Lecture 2: Neurocognition, Visual perception and Sensory Memory Flashcards
What is neurocognition?
- Cognition does not happen in a vacuum, but is a result of different brain states
- How do the function of neurons and nervous system relate to our understanding of human thought?
What is dissociation?
A disruption in one component of mental functioning but no impairment of another (e.g., HM)
What are Neurons?
- The basic building block of the brain and nervous system
- A neuron is a cell that is specialized for receiving and transmitting a neural impulse
How many neurons are there in the brain?
- 100 billion neurons in the brain
- 100 trillion connections
- Note: milky way has ~100 billion stars
What is the dendrite?
Gather neural impulses into the neuron (input)
What is the soma?
Cell body – bio activity is regulated
What is the axon?
Long extension from soma
What are the axon terminals?
Tree-like. Output to other neurons
What is myelin sheath?
- Insulator for the axon
- Gaps – called nodes of Ranvier
- Note: not all neuron have myelinated sheath
- Mainly on neurons that are long (e.g., periphery of nervous system)
- Myelinated neurons are white matter (myelin is fat)
- Most cortical neurons (cognition) are unmyelinated
- These form what we call “Gray Matter”
What is an action potential?
- The change in electrical charge of a neuron from negative to positive
-This charge propagates from the dendrites and down the
axon.
What is the all or none principle?
- All action potentials are the same.
- Either a neuron fires or it does not.
What are synapses?
- The region in which the axon terminals of one neuron and the dendrites of another come together i.e., where on neuron synapses onto another neuron
- neurons do not actually touch (usually) – small gaps
- May be a few or many synapses (from 100 to 15,000 synapses to other neurons)
- Convergence: many neurons may converge onto a single neuron
What is a neurotransmitter?
- The chemical substance released into the synapse between two neurons
- Responsible for activating or inhibiting the next postsynaptic neuron
- Note: Inhibit occurs because we do not want ALL neurons firing at once
When do connections between neurons change?
Connections between neurons change during
learning.
What is long term potentiation?
- Changes in the ease at which two connected neurons will fire
- Lasts a few hours, days, or weeks
What is consolidation?
- Long-term change over days, weeks, months, or years
- Small Scale: LTP between individual neurons
- Large Scale: LTP changes in assemblies of neurons over long periods of time
What are some important sub-cortical structures?
- the thalamus
- the corpus callosum
- the hippocampus
- the amygdala
What is the thalamus?
Gateway to the cortex: almost all messages pass through the thalamus.
What is the corpus callosum?
Primary bridge for messages to cross to the left and right
hemispheres
What is the hippocampus?
Implicated in storing new information in memory
What is the amygdala?
Important for processing emotional qualities of information
Which layer of the brain is responsible for higher-level
mental processes?
- the top layer of the brain
- neocortex or cerebral cortex
- the lobes of the cortex: frontal lobe ( associated with cognitive control, executive functioning), parietal lobe (involved with spatial processing and to some extent early sensory processing), occipital lobe (where visual processing happens), temporal lobe (involved with auditory processing, linguistic processing and involved in certain types of memory speech area)
What is contralaterality?
- Control of one side of the body is localized in the
opposite-side cerebral hemisphere. - The left hand, for instance, is largely under the control of the right hemisphere.
What is hemispheric specialization?
- Each hemisphere has specialized functions and abilities.
- Left hemisphere: language sounds, letters, words, speech, reading, writing, arithmetic, verbal memory, complex voluntary movement
- Right Hemisphere: non-language sounds, geometric patterns, faces, nonverbal memory, prosody, narrative, inference, spatial processes, movements in spatial patterns.
What is cortical specialization?
- Different brain areas are critically involved in certain
different functions.
– Sensory cortex: processing of sensory information from throughout the body
– Motor cortex: control of voluntary muscle movements
◦ Note: is further localization of function within the sensory and motor cortices e.g., fingers, leg, mouth…
What is an example of further cortical specialization?
- Chains of cells and areas involved in types of processing
goals - Example in vision:
Dorsal pathway: involved in “where” things are in space
Ventral pathway: Involved in “what” things are
What is a CAT scan?
- Computerized axial tomography (CT scans)
- A structural measure that gathers layers of x-ray images (looks at structure), not great for looking at the brain
What is an MRI?
- magnetic resonance imaging
- Gives clearer pictures of the structure of the brain (static- not looking at things happening over time)
- Gives you a good sense of where things are happening
What is single cell recording?
Electrodes record the firing rate of individual cells.
What is an EEG?
- Electrocephalograms (EEG):
- Electrodes are attached to the scalp to record the patterns of brain waves.
- Event-Related Potentials: The momentary changes in electrical impulses when a particular stimulus is presented
- EEG’s don’t tell you where things are happening, but when things are happening.
What is TMS?
- Transcranial Magnetic Stimulation (TMS)
- An electrical field is targeted over brain areas to influence
cortical processing. - This is a disruptive technique (Like a temporary lesion- it immobilizes certain parts of the brain temporarily)
What is a PET scan?
- Positron emission tomography
- Image shows regions of the brain with heightened neural
activity based on levels of blood flow. - Radioactive isotope injected
- Cortical area(s) involved in the cognitive activity “light up”
What is an fMRI?
- Functional magnetic resonance imaging
- Similar to PET, but a more detailed image and does not involve a radioactive isotope
- Measures metabolic rates in specific brain area change
- compare across different cognitive tasks
- Expensive to use
What are some other measures that are used (besides neural imaging)?
- Lesions
- Direct stimulation
- special populations
What are lesions?
- Used by Sperry
- The site and extent of the brain lesion are important
guides to the kind of disruption that is observed.
What is direct stimulation?
- Pioneered by Penfield
- The patient in brain surgery remained conscious and
small electrical charges were administered to the exposed
brain, thus triggering small regions.
How are special populations used as a measure?
- Groups of people who have known differences in brain function
- Examples: HM, Korsakoff patients, aging
What is a sensation vs. perception?
- Sensation: Reception of stimulation from the environment. Initial encoding into the nervous system
- Perception: Process of interpreting sensory information
What is the retina?
- The layer of the eye with rods and cones
- Initiates visual sensation and perception
- lightwaves are projected onto the retina
What are the parts of the retina?
- Rods and cones (The back layer of neurons – these are stimulated by light. 120 M rods, 7 M cones)
- Bipolar cells (Receive patterns of neural firing from the rods and cones. Many rods and cone cells converge onto the bipolar cells)
- Ganglion cells ( Receive messages from the bipolar cells. Bundled to form the optic nerve.)
- optic nerve (Projects neural messages to visual cortex in occipital lobe)
What is the fovea?
- The highly sensitive area of the retina responsible for
precise, focused vision - Covers about 1 to 2 degrees of visual field
- Most cones are in the fovea
What is compression?
- Only fraction of light waves reach retina
- Some cones have own bipolar
- But many rods converge onto 1 bipolar
- In the periphery (20+ degrees): mainly rods (so no colour vision in periphery). 120M rods reduced down to about only 1M ganglion cells… Thus – compressed / reduced messages from the retina to the brain
How do the eyes transmit visual information to the
brain?
- Each eye transmits visual information to the occipital
lobes of both hemispheres. However, We can send things to a certain hemisphere based on the visual field we process it in. Things in the left visual field are projected in the right hemisphere and vice versa (because light info in the left visual field is projected/ received on to the right side of the eye in both eyes). - This region is known as the visual cortex.
How do we gather visual information?
Series of fixations and saccades
What are saccades?
- Movement of the eyes from one fixation point to another
- Jerky & variable: 25ms – 175 ms
- Nothing “seen” during a saccade
What are fixations?
- Eyes pause to foveate and gather visual information
- Fovea is highest resolution in eye
What is sensory memory?
- Also know as Sensory Registers
- Neural activation is brief and stops when external
stimulation is terminated - But perception of an event persists even after the
stimulus is terminated.
-This implies a “memory system” - Vision: iconic sensory memory, Audition: echoic sensory memory Etc. – one per sense
What is the three store model (Atkinson & Shiffrin, 1986)
- Sensory memory (sensory registers)
- Short term store
- Long term store
How does information accumulate in sensory memory?
- Information accumulates over time (it takes 50 ms to get info. into visual sensory memory)
- Not “all-or-none”
- Audition: echoic sensory memory
- Etc. – one per sense
What is visual persistence?
- The apparent persistence of a visual stimuli beyond its physical duration (duration of visual sensory memory)
Describe the study by Eriksen & Collins (1967) on visual persistence
- Superimposed dot patterns (showed people a pattern of dots, and then there was either a short pause or a long pause and they showed a second pattern of dots)
- Delay varied: 0 to 500 ms
– @ 0 ms delay: 1 pattern, see letters (VOH)
– @ ~75 ms: 2 patterns, but perceive letters (meaning the dots are still in someone’s sensory memory)
– @ > 250 ms: 2 patterns, no letters (the image of the first display had faded away, it was no longer available in their sensory memory) - Conclude: Visual SM lasts for a short period of time!
About between 250 ms- 500 ms
Describes the studies that examined the capacity of visual SM by Sperling (1960)
Whole report technique:
- instructed to Report all items in the display
- Only able to report ~3 of 9 items
- Why? By the time they report the first 3 letters, the rest of the letters had faded out of sensory memory. SO not a good way to estimate the size of sensory memory
Partial report technique:
- Report cued items only ( hear a certain tone, told to report only the line associated with the tone
- If interval short, then close to 100% accurate
- Conclude: capacity of SM is very large (everything was able to get in there but leaves quickly)
What do we know about coding in visual SM?
Using Sperling Partial Report Technique
Can select items from display based on:
- Location
- Colour
- Even angles/line versus circles
- However, cannot select based on higher-level features:
e.g., not able to select based on letters vs. digits
What can we conclude about coding in visual SM?
- Information in SM is pre-categorical
- Not semantic
What did people originally think happened with information in sensory memory?
- Originally thought that information in SM simply decayed
over time. The mere passage of time degraded the icon, making it illegible after a short interval. - But, turns out that information can be erased from SM
How did the study done by Averbach & Corriel (1961) show evidence of erasure/interference in SM
- Initial purpose of their study was to examine duration of icon
- Partial report technique using a bar or circle cues
- Varied interval between display of letters and the bar/circle cues
- Using the bar or the circle cue had a big impact
- Around 100 ms, if you received the circle cue no one could report the letter but if the delay was a little longer they could report it. The circle seemed to be erasing the number.
- Implications: Information in SM can be erased through Masking!
What are the two possible directions of visual masks?
- Backward Masking: when Target followed by Mask
- Forward Masking: when Mask before the Target
What are the two types of visual masking?
Energy: such as a flash of light (e.g., the flash of a camera)
Pattern: has features (information)
What is monocular masking?
target & mask to one eye
What is binocular masking?
target & mask to both eyes
What is dichoptic masking?
target to one eye, mask to other eye
What type of masking does energy masking occur with?
Occurs with mono & binocular, not with dichoptic
What type of masking does pattern masking occur with?
Is effective with all, even dichoptic
What does this information suggest about masking?
- energy masks affect peripheral (early)
- pattern is central & interrupts processing of features
What are the implications of masking?
- Shows that features coded in SM (not just energy)
- Processing in SM is NOT passive, but dynamic
Why is there masking in SM?
Erases information to allow for next event to be cleanly
encoded into SM
