W1: General Principles Flashcards
What suggests the complexity of the cerebral cortex?
Only part that controls perception, half of its neurons are related to vision, specificity of deficits from brain damage and computers struggle to mimic even toddlers perceptual processes.
What do you call the instant and effortless experience from a stimulated sensory organ?
Sensation
What are quaila?
Simple sensations e.g. loudness, brightness, heat (named after “qualities of conscious experiences”)
What is the explanatory gap for perceptual theories?
How neural processes turn into subjective sensations/perception (not yet understood)
What is perception?
The mechanism which detects physical energy, processes it to turn it into mental representations and meaningful sensations. These at times require some effort and time.
Sensory modalities
A stimulus aspect, distinguished by different qualias. Modalities are qualitatively different to each other (which means that only sensations within the same modality can be misinterpreted as one)
Three key elements of perception
Stimuli
Neural response
Perceptual response.
Psychophysical Linking Hypothesis
When a perceptual response is explained by its underlying neural response to stimuli within the brain - aka. explanatory gap (but link isn’t understood)
Psychophysics
The study of the relationship between stimuli/physical stimulation and mental events/perceptual experience
Psychophysics perceptual principles
Detectability
Discrimination
Sensory magnitude
Adaptation
Just Noticeable Difference
Psychophysics - perceptual principles - discrimination
Discrimination threshold: minimal amount of change that is discriminable between two stimuli (lower threshold = better)
Weber’s Law
Psychophysics - perceptual principles - discrimination threshold
JND is a constant fraction of the standard weight
Fechner’s Law
Psychophysics - perceptual principles - discrimination threshold
Perceived stimuli size increases with stimulus intensity.
Stimulus growth by JND is equal to perceived size but neither are equal to the increase in sensory magnitude/real intensity (larger increments to large weights are perceived as the same change as smaller increments to smaller weights).
Absolute Threshold
Psychophysics - perceptual principles - detectability
Detection Threshold: intensity required to detect a stimulus - usually 75% of the time. (Lower = better = more sensitive)
Sensitivity
Psychophysics - Perceptual Principles - Detectability
Heightened awareness to lower levels of intensity (higher sensitivity = lower threshold = lower magnitude = better)
Suprathreshold
Psychophysics - Perceptual Principles - Detectability
A stimuli with an intensity that excessively exceeds the absolute/detection threshold.
Sensory Magnitude
Psychophysics - Perceptual Principles - Sensory Magnitude
The perceived size of a stimulus which is positively related to intensity.
Sensory Threshold
Psychophysics - Perceptual Principles - Sensory Magnitude
The weakest stimuli that can be detected 50% -75% of the time (due to probabilistic transition of detection)
Psychometric Function
Psychophysics - Perceptual Principles - Sensory Magnitude
“Any plot relating a quantifiable response to a physical stimulus measure”
A curved plot that represents the positive relationship between sensory magnitude and intensity and the response rate/probabilistic increase of detection (probabilistic as detection occurs at various intensities)
Magnitude Estimation
Psychophysics - Perceptual Principles - Sensory Magnitude
Identifies the non-linear relationship between physical and sensory magnitude by using numerical scale to identify the magnitude of various sized stimuli. Sensory magnitude increases non linearly at different rates in different senses.
Steven’s Power Law
Psychophysics - Perceptual Principles - Sensory Magnitude
A nonlinear relationship between stimulus intensity and perceived magnitude, in which equal ratios of intensity produce equal ratios of magnitude. (e.g. light intensity increases by 8 as brightness increases by 2). Logarithmic axes makes lines linear.
Compressive Non-Linear Function
Psychophysics - Perceptual Principles - Sensory Magnitude
Double intensity is perceived as less than double, creating a non-linear curve.
Adaptation
Psychophysics - Perceptual Principles - Adaptation
Process of altering response range to new conditions/range of stimuli as sensory systems have a small response capacity.
Consequences of a sustained stimulus
- Detection thresholds increase
- Perceived stimulus intensity lowers
- Perceived properties of other similar stimuli can appear biased (e.g. the motion aftereffect)
Cognitive Neuroscience
“study the parts of nervous system involved in cognition”
Non-Invasive/neuroimaging cogneuro recording techniques
General principles:
Visually Evoked Potential: sensors on scalp that records electrical activity of neurons
Magnetoencephalography: sensors on scalp recording magnetic fields
Computerised Tomography: many x ray beams from one side of the machine are sent through the brain and absorbed by detectors on the opposite side. Shows brain structure and damage.
Functional Magnetic Resonance Imaging: sends radio waves through the head to detect oxygenated active neurons - localization of function by recording during different tasks
Positron Emission Tomography: “inject radioactive glucose & track it around the brain”
Neuroscience: Invasive recording techniques
General principles: cognitive neuroscience: techniques
Lesion experiments
Microelectrode single-unit recording
Microstimulation: stimulating small population of neurons while participant is awake and see what sensation they experience - to discover their function
Optical Imaging: taking pics of brain to examine changes in blood flow (pinker/redder parts = active neurons)
Cognitive Neuroscience: other noninvasive experimental techniques
Direct brain stimulation: use of TMS to interfere with neural activity, temporarily “knocking out” cells which can be considered a temporary lesion
Clinical cases
Cognitive neuroscience: anatomical techniques
Staining: cells allows us to see the cell itself (incl. Size and density), its axons/connections to other cells, and or highlight the region that these cells reside in
Observing visible differences: of grey and white matter in dead brains
White matter: where axons are, white due to fat called myelin (insulates axons)
Grey matter: location of cell bodies
Transduction definition
General Principles: Cog Neuroscience: Physiological Principles: Transduction
first stage of the sensory process where receptors within our sense organs convert energy from physical stimuli into nerve impulses to be organised and interpreted by the brain.
What is a neural impulse?
General Principles: Cog Neuroscience: Physiological Principles: Transduction
electrical activity that carries information from cell to cell throughout the nervous system.
How do Neural impulses send information across cells?
General Principles: Cog Neuroscience: Physiological Principles: Transduction
Axons to travel from dendrites to terminal button - TB synapses to next cell (excitatory or inhibitory neurotransmitters are released when impulse hits synapse).
Axons
General Principles: Cog Neuroscience: Physiological Principles: Transduction
‘wire’ that carries neural impulses throughout a cell.
Dentrites
General Principles: Cog Neuroscience: Physiological Principles: Transduction
‘branches’ that connect to other cells terminal buttons for axons to travel along
Terminal Buttons
General Principles: Cog Neuroscience: Physiological Principles: Transduction
“a bud at the branched end of an axon, which makes contact with the dendrites of another neuron.” Through the synapse
Synapse
General Principles: Cog Neuroscience: Physiological Principles: Transduction
links two neurons by the terminal button of one and the dendrite of another. This allows communication between cells through the release of excitatory and inhibitory neurotransmitters.
Excitatory vs Inhibitory Neurotransmitters
General Principles: Cog Neuroscience: Physiological Principles: Transduction
Increases vs decreases the chance of the receiving neutron firing an impulse.
Hierarchal Processing
Gen P’s: Cog Neuroscience: Physio P’s: Hierarchal Processing
after transduction: neural impulses are sent up through a number of synapses (they further processes info) -> cortex -> associated areas. (e.g. 5 synapses for audition)
Thalamus is a synapse for every sense but smell (due to olfactory bulb)
Bottom-up Processing
Gen P’s: Cog Neuroscience: Physio P’s: Hierarchal Processing
neural signals are sent up to higher processing areas - way we receive information
Top-down Processing
Gen P’s: Cog Neuroscience: Physio P’s: Hierarchal Processing
connections to higher cortical areas allow information to feedback down to thalamus or sent laterally to associated areas - when reanalysing info to alter format it was initially processed in.
Feedback vs Lateral Connections
Gen P’s: Cog Neuroscience: Physio P’s: Hierarchal Processing
Feedback and lateral connections: to higher cortical areas allow information to feedback down to thalamus or sent laterally to associated areas
Specific Nerve Energy
Gen P’s: Cog Neuroscience: Physio P’s
distinguishes sources of electrical signals by their destination in the cortex - different cortical areas interpret different senses
Selectivity
Gen P’s: Cog Neuroscience: Physio P’s: Selectivity
Neurons selectivity means that they are tuned to particular dimensions of stimuli (e.g. location in sensory field, colour, size, orientation) and will respond less to the stimuli as the stimulus changes, which will increase the response of other neurons.
Tuning
Gen P’s: Cog Neuroscience: Physio P’s: Selectivity
is the rate at which neurons respond to stimuli based on their selectivity
Organisation
Gen P’s: Cog Neuroscience: Physio P’s: Organisation
Neurons are organised by stimuli preference within the brain - preference slowly alters as you move finger along brain
Receptive Field
Gen P’s: Cog Neuroscience: Physio P’s: Organisation/Selectivity
“The area of a stimulus field in which presentation of a stimulus causes a change in the firing rate of a given sensory neuron.” receptive fields are very small
Gen P’s: Cog Neuroscience: Physio P’s: Organisation
the pattern reflected onto the retina is also the same pattern that the active neurons create on the cortex (“about the organisation of neural activity reflected in a map of projection from the retina”)
Topographical Organization
Gen P’s: Cog Neuroscience: Physio P’s: Organisation
Cortical surface size devoted to body part reflect the the importance of the body part rather than the size.
Cortical Magnification
Gen P’s: Cog Neuroscience: Physio P’s
neural coding principal: a neurons rate of firing
“can be produced by different combos of stimulus values (e.g. position, size, orientation, motion direction).” ‘This means one neuron can respond to many stimuli, and one stimuli can excite many different neurons.’
Univariance
Plasticity
Gen P’s: Cog Neuroscience: Physio P’s
sensory systems adapt themselves as one grows (so we still know body position as our limbs grow with us) and to different sensory environments (e.g. colour castle adaptation trick)
Noise
Gen P’s: Cog Neuroscience: Physio P’s
Variability of neural signals response to same stimuli after repeated presentation
influenced by stimuli factors and other factors.
Two sources of variability: fluctuations in neurons excitability or synaptic transmission Spontaneous Activity: when neurons fire at a baseline rate w/o stimuli
‘measure a neuron’s activity level by the freq. Of electrical impulses’ 0-800 impulses/second, averaging from 100-200/second. ‘Change of response reflects the outer world’
Computational Neuroscience
Gen P’s:
the study of computations performed by the nervous system
Gen P’s: Comp Neuroscience: Main Theories
every powerful computing device is basically the same and can therefore perform the same functions. Consider the brain a computing device - can use a computer to imitate functions of the brain
Universal Computation Theory (Turning)
Information Theory (Shannon)
Gen P’s: Comp Neuroscience: Main Theories
how info processing systems send info from the signal source through the transmission line to the receiver, which can be applied to neural systems. The following components influence the behaviour of neural activity:
“Channel capacity— the number of signals it can transmit simultaneously
Transmission rate— signals travel speed along channel
Signal redundancy— the amnt of info carried in signal w/o info loss - relates to selectivity and adaptation (only respond to useful info to preserve energy)
Noise— intrusion of information unrelated to signal.”
Three levels of Perceptual Analysis (Marrs)
Gen P’s: Comp Neuroscience: Main Theories
“Computational theory: What is computations goal, why is it appropriate, and what is the logic of the strategy for carrying it out?
Representation and algorithm: implementation of theory. representation of input and output + transformation algorithm
Hardware implementation: How can the representation and algorithm be realized physically?””
Representation
Gen P’s: Comp Neuroscience: Core Ideas
Perception is a representation of the outer world.
neural activity gets processed by internal representations at synapses on it’s way to the brain.
The physical brain system represents the state of outer world’s system - can be applied to other systems (e.g. thermometer reflects the worlds temperature). This perceptual system is considered a representational system of the world
Analog Representation
Gen P’s: Comp Neuroscience: Core Ideas: Representation
“magnitudes in one system, such as spatial position or response rate, map onto analogous magnitudes in another system (e.g. height in thermometer = temp, progress bar when downloading something)”
Symbolic Representation
Gen P’s: Comp Neuroscience: Core Ideas: Representation
“A representation in which discrete symbols in one system, such as characters or words, act as tokens to denote states or entities in another system.”
*perceptual representations tend to be analog, object perception is symbolic
Rate Coding
Gen P’s: Comp Neuroscience: Core Ideas: Representation
“Neural coding principle in which the firing rate of a neuron carries information about the stimulus; it is associated with neural coding of magnitude (light intensity, loudness, mechanical pressure, or stretch).”
*perceptual representations tend to be analog, object perception is symbolic
Computation
Gen P’s: Comp Neuroscience: Core Ideas
- manipulating quantities or symbols in line with rules/algorithms.
- The brain is considered a computing device - neural processes (e.g. analog: brightness; symbol: object property) can be described as a computational process.
Algorithm
Gen P’s: Comp Neuroscience: Core Ideas: Computation
“A specific computational procedure used to transform one representation into another.”
Representation and Computation
Gen P’s: Comp Neuroscience: Core Ideas: Rep & Comp
as a representation goes through each processing stage within the brain, computations cause the representation to be further refined, transforming new representations at each stage. The type of computation performed depends on the form of representation.
Computations for analog representation/signal processing: creating and manipulating quantities of values from og representation according to rules Computations for symbolic representation: “comparisons between symbols to test for equality, and the combination of symbols to create new symbol structures. (IF Size = Small AND Flight = Undulating AND . . . THEN Bird = Goldfinch)”
Bottom-up Processing
Gen P’s: Comp Neuroscience: Core Ideas
from receptors to cortex
Top-Down Processing
Gen P’s: Comp Neuroscience: Core Ideas
between thalamus and higher cortex
Psychometric Functions
Gen P’s: Comp Neuroscience: Measurement
“Any plot relating a quantifiable response to a physical stimulus measure”
Classical methods in computational neuroscience
Gen P’s: Comp Neuroscience: Measurement
measure participants threshold and psychometric function. Two following methods are the only ones still used today
Method of Adjustment (MoA)
Gen P’s: Comp Neuroscience: Measurement: Classical Methods
participant adjusts stimulus (e.g. dial that controls intensity) until they can detect stimulus.
+ Quick and easy
- Unreliable: participants control of stimulus can bias their sensitivity towards higher or lower intensity levels
Method of Constant Stimuli (MoCS)
Gen P’s: Comp Neuroscience: Measurement: Classical Methods
“preselected stimuli are presented to the subject in random order over a series of trials; the subject makes a binary response after each trial.”
+ More reliable: participants unaware of stimulus intensity level
+ More reliable: “constructs full psychometric function”
+ Increased efficiency: computers can select stimulus
- More labor intensive
Yes-No response: yes = detected; no = not detected
Bias in Comp neuroscience classical methods
Gen P’s: Comp Neuroscience: Measurement: Classical Methods
arise in both MoA and MoCS - SDT takes this into account
Signal Detection Theory
Gen P’s: Comp Neuroscience: Measurement
“takes bias into account by assuming stimulus detection is a two step process… A theory of performance in psychophysical experiments in which subjects’ decisions are determined jointly by their sensory response and by a tendency to respond in a certain way.”
Signal detection theory stages
Gen P’s: Comp Neuroscience: Measurement: Signal Detection Theory
Stage 1: ‘sensory response occurs, depends on stimulus intensity and sensory system sensitivity - subject to noise’
Stage 2: ‘decides state of detection, based on if response magnitude exceeds criteria or not’ - subject to bias
Yes-No Paradigm
Gen P’s: Comp Neuroscience: Measurement: Signal Detection Theory
“A psychophysical procedure in which only 50% of presentations contain a stimulus, and the subject must respond “yes” or “no” after each.”
estimate sensitivity d-prime (d ′ )
Two-Alternative Forced Choice
Gen P’s: Comp Neuroscience: Measurement: Signal Detection Theory
“A psychophysical procedure in which each presentation contains two intervals, only one of which (randomly selected) contains the stimulus; the subject must select the correct interval.”
estimates bias
What are the experimental and control conditions referred to as in computational neuroscience?
Gen P’s: Comp Neuroscience: Measurement: Signal Detection Theory
Experimental conditions where stimuli is presented is called noise + signal presentation; control condition is noise presentation
Gen P’s: Cog Neuroscience: Physio P’s: Selectivity
the range of stimuli that our senses can detect. Single unit recordings can determine this.
Sensory Space
