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Introduction to Perception and Cognition


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What is perception?
Conscious sensory experience.
Sequence of events between the environment and behaviour.
Perception -> Recognition -> Action
Define cognition
'Higher' faculties such as reasoning, knowledge, memories and expectations that influence our perceptual experiences.
Thomas Willis
Pioneered research into anatomy of the brain Coined term 'neurology' Numbered and studied function of cranial nerves. Mapped spinal vascular anatomy of CNS. Wrote book, "Cerebri Anatiomic" in 1664.
Franz - Joseph Gall
Phrenology - Brain is seat of character, emotions, perception, intellect etc. Bumps and indentations on skull represent specific brain areas. Mental faculties are located in 27 different brain organs on skull surface. Brain organs used more frequently grow larger than those that aren't. First comprehensive, pre-modern theory of cerebral localisation of brain function.
Johannes Purkinje
First to make wafer thin slices of tissue for microscope analysis. 1837: Discovered Purkinje cells, which are large neurons in the cerebellum with many branching dendrites.
Ramon y Cajal
Elaborated Purkinje's work and examined detail and structure of neurons Propose that neurons are the basic units of the nervous system.
Paul Broca
Studied language and limbic system. Studied patient who could only say the word 'tan'. Could understand speech and written word. Carried out post-mortem to find a lesion caused by syphilis in patient's left frontal lobe. Broca's aphasia.
Karl Wernicke
Abnormalities can be localised to specific cortical regions, revealing the function of these regions. Brain contains neural pathways that connect different parts of the brain. 1873: Found patient who could speak but not understand spoken or written words. Post-mortem: Lesion in rear parietal / occipital lobe in left hemisphere. Wernicke's area.
John Hughlings Jackson
Observed behaviour of patients with brain damage. Epileptic patients - noted that at the start of seiziures, patients moved in a characteristic way - seziure appeared to be stimulating a set map of the body in the brain. Map of the body represented in a particular cortical area Certain regions of the brain contribute to certain behaviours - topography.
David Ferrier
1873: precisely mapped motor functions in dogs and monkeys. High intensity stimulation of motor areas caused movements in face and neck. 1876 and 1886: The function of the brain 1888: The localisation of brain disease 1878: Co-founded journal Brain. Dog work replicated by Fritsch and Hitzing.
Robert Batholow
1874: Presented with a 30 year old patient, Mary Rafferty, who had a 2 inch hole in her skull. Applied electrical current to the exposed 'dura' during surgery. Applying the current to different parts of brain surfaces caused different body parts to move.
Korbinian Brodmann
Used tissue staining techniques to analyse different cell types in different brain regions - Cytoachitectonics Found S2 distinct brain region. To a large extent, cytoarchitectural differences correspond to function distinctions.
Ida Hyde
Invented first microelectrode for intracellular work with lower organisms. Constructed an electrode filled with salt solution Connected it to a small column of mercury. Level could be altered by the introduction of varying electrical current. Mercury forced salt solution towards or away from tip of electrode, and could also transmit electrical stimulation to the cell through the salt solution.
Cognitive neuroscience
Represents a multi-disciplinary way to study the brain and the nature of thought. Bridge between neuroscience and psychology. Purpose: to investigate the psychological, computational and neuroscientific bases of cognition. Study of perception and cognition is a part of cognitive neuroscience.
Structure of a neuron
3 main components: Cell body - Contains the nucleus, aka Soma Dendrites - branches that carry information FROM other neurons Axon - branch that carries information TO other neurons
Definition of an action potential
a change in the electrical properties of a neuron membrane. Neural impulse that travels down axon to axon terminal buttons. Means by which one neuron can communicate with another.
What is the only part of a neuron that can produce action potentials and why?
The axon - because it is the only part with voltage-gated ion channels.
Definition of a cell membrane
Cell membrane - a barrier that determines what goes into or out of a neuron.
Resting potential of a neuron
-70mV (inside:outside)
Process of an action potential
1. Resting potential 2. Na+ enters the cell, cell depolarises Cell depolarisation - negative potential is reduced (at -50mV cell membrane becomes completely permeable and the charge momentarily reverses) 3. Cell repolarises -> Action potential K+ flows out through the voltage gated K+ channels -> closes the voltage gated Na+ channels -> Negative potential restored. 4. Hyper polarisation - K+ channels continue to operate -> Causes an overshoot -> Makes it more difficult for the axon to depolarise again straight away. 1. Resting potential...
How does an action potential travel down an axon?
An action potential in one part of the axon opens voltage gated Na+ channels in adjacent parts.
What is mylein?
Mylein - fatty substance that surrounds some cells (speeds up conduction). Blocks normal Na+/K+ transfer -> makes action potential jump down the length of the axon at the NODES OF RANVIER.
How are action potentials communicated across the synaptic cleft between two neurons?
Via neurotransmitters
What are neurotransmitters?
Chemical signals released by one neuron that affect the properties
What is a synapse?
The gap between neurons in which neurotransmitters are released.
Define the pre and postsynaptic neurons.
Presynaptic neuron - Neuron before synapse (sends information). Postsynaptic neuron - Neuron after synapse (recieves information).
How do neurotransmitters affect the post-synaptic membrane?
They bind to receptors on the dendrites or cell body of the post-synaptic neuron and create a synaptic potential.
How does a synaptic potential produce an action potential?
If passively-conducted currents are sufficiently strong when they reach the beginning of the axon -> active conduction -> action potential.
Difference between Active nad Passive conduction.
Passive conduction - short range Active conduction - long range
Navigating the brain (Front, back, top and bottom)
Front - Dorsal / Rostral Back - Posterior / Caudal Top - Dorsal / Superior Bottom - Ventral / Inferior
Slices and sections (Coronal slice, Saggital section, Medial section, Axial section)
Coronal slice - Vertical slice going across both hemispheres Saggital section - Vertical slice going through 1 hemisphere Medial section - Saggical section down the midline Axial section - Slice in the horizontal plane
What is the main structure supplying blood to the brain?
The circle of Willis
Composition of grey and white matter.
Grey matter - consists primarily of neuronal cell bodies White matter - Tissue of the nervous system - consists primairly of axons and support cells.
What are ventricles?
Hollow chambers in the brain that contain cerebrospinal fluid.
Location of grey and white matter within the brain.
Grey matter: Cerebral cortex, subcortex, basal ganglia, limbic system White matter: Association tracts, Projection tracts, Commisures.
The Cerebral cortex
2 folded sheets of grey matter. Around 3mm thick. Organised into layers. Different layers - different cell types. 2 hemispheres, 4 lobes.
Define Gyri
Raised folds in the cerebral cortex.
Define Sulci.
Buried grooves in the cerebral cortex.
The Basal Ganglia
Part of the SUBCORTEX Involved in regulating motor activity and skill learning. Disorders: Hypokinesia and Hyperkinsia. Consists of the caudate nucleus, putamen and globulus pallidus. Caudate and putamen recieve cortical input and send it to the globus pallidus - sent to the thalamus.
The Limbic System
Part of the SUBCORTEX. Involved in relating an organism to its past and present and in the detection and expresssion of emotional responses. Includes: Amygdala - Fear response Cingulate gyrus - Emotion and cognition Hippocampus - Learning and memory Mamilary bodies - memory Olfactory bulb - Connected to limbic system.
Part of the SUBCORTEX. Thalamus - Major subcortical relay centre. Important for transporting sensory information to the cortex. Hypothalamus - regulates the body. Lies beneath the thalamus. Contains a variety of nuclei that are primarily concerned with regulating the body. Thalamus - 2 interconnected structures in the centre of the brain. Main relay station for the senses. Also contains projects to almost all parts of the cortex and the basal ganglia.
The cerebellum
Attatched to the posterior of the hindbrain via the cerebellar penducles. Lots of grey matter folds. 2 interconnecting lobes. Involved in dexterity and smooth execution of movement. Pons connects to cerebellum and cerebral cortex. Medulla oblongata: Connects pons to the spinal cord.
Define single cell neurophysiology.
Single cell neurophysiology - Measuring the response of a single neuron/cell. Invasive process.
Difference between Intra and Extracellular recording.
Intracellular recording: Recording from inside the axon. Extracellular recording: Recording from outside the cell membrane.
Unit of measurement of electrophysiology.
Spikes per second.
Electrophysiology procedure (for anaethetised behaviour).
Surgery and experiments are carried out while the animal is heavily anaethetised. Presented with a stimuli while recordings are taken from cells e.g. vision. After recording, animal is euthanised.
Electrophysiology procedure (for awake behaviour).
Animals are anaethetised and undergo surgery to fix recording apparatus. After recovery from surgery. They are trained to before psychophysical tasks. Recordings are taken while awake and behaving.
Recording awake behaviour
Humans: No Monkeys: Yes - they have similar brains to humans and can be trained to perform behavioural tasks.
Rules for animal experimentation (3 R's).
Reduction - ensuring appropriate number of animals used. Replacement - Using the best sentient species. Refinement - Improving experimental design.
Define electroencephalography.
Measuring dendritic currents in neuronal populations. Records electrical signals generated by the brain through electrodes placed at different points on the scalp. Non-invasive.
Requirements for detecting an EEG signal.
A whole population of neurons must be active in synchony to generate a large enough electrical signal to be detectable on the scalp. Neurons must be aligned in parallel orientation so that their activity summates (rather than cancels out).
What does structural imaging do?
Measures the spacial configuration of different types of tissue in the brain.
Equipment used for structural imaging.
Computerised tomography (CT) scanner or Magnetic resonance imaging (MRI) scanner
Is structural imaging active or static?
How does Computerised Tomography work?
It is based on the amount of X-ray absorbtion in different tissue types (densities).
How do parts of the brain appear on a CT scan?
Skull - White Brain matter - Grey Ventricles - Black
Uses of CT scans.
Diagnosis of brain tumours, hemmorages, and gross brain abnormalities.
How does Magnetic Resonance Imaging work? (brief)
It is based on the behaviour of hydrogen atoms in a magnetic field.
How does Magnetic Resonance Imaging work? (complex)
Most of human tissue is water based. Protons haave a weak, random magnetic field. MRI introduces an external magnetic field. Some protons alighn themselves with it. A radio frequency pulse is then turned on briefly, causing the protons to absorb some of its energy. When it is turned off, the protons release this energy which causing them to spin. Variations in the rate at which protons return to their aligned state are used to distinguish between different tissue types.
Comparison between MRI and CT scans.
MRI has a much better spatial resolution than CT. There is no limit to the number of times a person can safely have an MRI scan (no radiation issues). Better discrimination between grey and white brain matter in the MRI.
Definition of functional imaging.
Measures temporary changes in brain physiology associated with cognitive processing.
Function imaging techniques.
Positron Emission Tomography (PET) or Functiontal Magnetic Resonance Imaging (fMRI).
Is functional imaging dynamic or static?
How Positron Emission Tomography works. (brief)
Measures blood flow in the brain using a radioactive isotope.
What is the commonly used isotope, and how is it administered?
Oxygen-15 Commonly administered as water (H2O15)
How Positron Emission Tomography works. (complex)
Radioactive isotope is injected into the bloodstream. Waiting period while active molecule becomes concentrated in tissue of interest. Patient placed into an image scanner. As the radioisotope undergoes decay, it emits gamma rays. More gamma rays -> higher level of function.
What is the typical time course for a PET scan?
30 seconds for tracer to enter the brain. 30 seconds for radiation to peak. H2O15 half life of around 2 minutes. Temporal resolution: ~30 seconds Spatial resolution: ~10mm
Uses of PET scanning.
Evaluate metabolic characteristics of tissues. May detect onset of disease before anatomical changes are evident.
How fMRI works. (brief)
MRI signal can also provide information about the concentration of deoxyhaemoglobin in the blood.
How fMRI works. (complex)
BOLD response - Blood oxygen-level-dependent contrast. Oxygenated blood (oxyhaemoglobin) -> Used by neurons in the brain. Oxygen consumed by neurons. Oxyhaemoglobin -> deoxyhaemoglobin. Deoxyhaemoglobin has strong paramagnetic properties (distorts magnetic field). Introduces distortions in local magnetic field. Amount of distortion = amount of deoxyhaemoglobin in the blood.
What is the Haemodynamic response function? (HRF)
This is the change in the BOLD signal over time.
What are the tree phases of the Haemodynamic Response function (HRF)?
* Initial dip (may not occur) Neurons consume oxygen -> Small rise in amount of deoxyhaemoglobin -> Reduction in BOLD signal. 1. Overcompensation Increased oxygen consumption -> Increased blood flow -> Increased oxygen consumption -> Increase in BOLD signal. 2. Undershoot 3. Blood flow and oxygen consumption dip and return to original levels.
What affects the size of haemodynamic changes?
The size of the magnet used in the scanner. 1T magnet - changes of 1-3%. New generation of magnets (3T and 7T) produce bigger changes.
What is auditory space?
The area around your head where sound is located.
What is auditory localisation?
The ability to localise sounds within auditory space.
How can we quantify our ability to localise sounds in space?
By using auditory co-ordinates.
What are azimuth co-ordinates?
Sound locations that are to the left or right of the listener.
What are elevation co-ordinates?
Sound locations that are above or below the listener.
What are distance co-ordinates?
How far a sound is from the listener.
How do we localise sounds?
Location cues - the way sound interacts with a listeners' head and ears provide information about the location of its source.
What are monoaural cues?
They are location cues that only involve one ear.
What are binaural cues?
They are location cues that involve both ears.
What is spectral information?
This is a MONOAURAL cue! Interaction of sound with head and pinna. Provides information about sound in the VERTICAL plane.
Whaat are Interaural time differences (ITDs)?
This is a BINAURAL cue! Differences between the times at which sound reaches the left and right ears.
Interaural Level Differences (ILDs)?
Difference in thepressure level of sound reaching each ear.
What is the Head-related transfer function?
This is a MONAURAL cue! Frequency-dependent filtering that modifies the phase and amplitude spectra of an external sound.
Which co-ordinates do monaural cues give information about?
Elevation co-ordinates.
Which co-ordinates do binaural cues give information about?
Azimuth co-ordinates.
What are interaural time difference detectors?
These are neurons in the AUDITORY CORTEX that respond to specific interaural time differences. Each interaural time difference detector responds best to a different delay.
How does the brain maps where a stimulus is in 3D space?
Using cortical topography. The auditory cortex contains a topographic map of localised sounds. A specific sound location has a specific representation in the primary auditory cortex.
What is a receptive field?
This is an area of auditory space from which sound makes a neuron in a particular part of the auditory cortex fire.
The 5 principles of Auditory Grouping.
Location Proximity in time Similarity of timbre and pitch. Good continuation Experience
Location in sound identification
The characteristics of sound change as it moves towards or away from us. Because sound usually follows a predictable course, we can use this information to identify it.
Proximity in time in sound identification.
Sounds that have an identifiable temporal relationship are grouped together. e.g. sounds that occur in rapid succession tend to be from the same source.
Timbre and pitch in sound identification.
Timbre - Perceptual quality that distinguishes between 2 tones despite having the same volume, pitch and duration. Pitch - tone height or frequency
Good continuation in sound identification.
Sound stimuli with the same frequency of smoothly changing frequencies are percived as continuous. Maintained even if they are interrupted by another stimulus (sound).
Experience in sound identification.
Past experience can be of a sound can be used to identify it's source.
Dowling and Harwood (1986) work on Experience in sound identification.
Played subjects interleaved melody of "Three blind mice" and "Mary had a little lamb". Subjects could not determine the melody. When informed of the melody they were listening to, subjects were able to identify each song.
Wavelength of visible light.
400nm to 700nm.
What is the cornea?
The transparent outer coating at the front of the eye. It is the principle means of focus.
What is the Sclera?
The white, opaque outer coating.
What is the pupil?
Circular hole in the centre of the iris through which light enters.
What is the lens?
Transparent focusing element of the eye.
What is the retina?
The array of photoreceptors and neural circuitry that covers the back of the eye.
What is the fovea?
The part of the eye on which the centre of an image falls.
What is the optic nerve?
A bundle of nerve fibres that carry nerve impulses from the retina to the brain.
What is the anterior chamber?
Between the cornea and the iris.
What is the posterior chamber?
The chamber between the iris and the lens.
What is in the anterior and posterior chambers?
Aqueous humour.
What is the vitreous chamber?
The chamber behind the lens.
What is in the vitreous chamber?
Vitreous humour.
What is the near point, and how does it change as you age?
Near point - the point at which they eyes can no longer focus. As you age, your near point gets further away because your lenses harden and your cilliary muscles weaken.
What is the process by which the retina converts light energy to electrochemical energy?
Information about a rod cell
Rod-shaped photoreceptor Responsible for vision at low light levels. Very sensitive to darkness. Coarse spatial structure.
Information about cone cells.
Cone-shaped photoreceptor. Responsible for vision in bright light. Responsible for colour vision. Fine details.
Number of cone cells on the retina.
6 million.
Number of rods in the retina.
120 million.
What type of photoreptors does the fovea entirely consist of?
What photopigment do rods contain?
What different varieties of photopigments are there for cones?
Blue / Green / Red Short / Medium / Long
Process of bleaching a photopigment.
Photopigments contain opsin and retinal. When a retinal molecule absorbs light it changes shape. Activates opsin and alters photoreceptor membrane state. Light is changed into an electrical impulse.
Route of electrical impulses from retina to the brain.
Photoreceptors -> Bipolar cells -> Ganglion cells -> Optic nerve -> Brain
Pathway to the optic nerve
Light -> Cornea -> Pupil -> Lens -> Retina -> Optic nerve

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