Week 1 Phsyics+ intro Flashcards
Epistemological scepticism:
the view that we cannot know anything certain - there is a chance that what we hear and see and taste is not actually what it is. - chuang tzu
Plato’s cave
prisoners chained in a cave face a blank wall, watching shadows and hearing sounds created by people passing in front of a fire behind them. They think the sounds are coming from the shadows. The shadows are the prisoners’ reality, but are not accurate representations of the real world - just the fragment of reality that we can normally perceive through our senses.
Aristotle
believe perception is taking on form without matter - the sense of organ or the sense itself takes on the perceptible quality.
Galileo
“Hence i think that taste odours, colours and so on are no more than mere names as far as the object in which place them is concerned and that they reside only in the consciousness. Jence if the living creature were removed all these qualities would be wiped away and annihilated” he challenged Aristotle in 19660.
Dualism
mind-body distinction. Attempts to overcome the question of how matter (brain) can give rise to inner mental life. Originally focused on the role of the soul/mind
Extended substance: material entities (physical) Mental substance: - mind/soul/consciousness (non-physical)
Monism
distinguished from dualism (there is no duality).only brain gives rise to perception (from internal and external stimuli).
Whilst part of what we perceive comes through our senses from the object before us, another part always comes from our head.
Notes: most people today would hopefully agree that sensation by definition requires a physical force and that a nervous system is required for perception.
Most would also agree that the brain(without external triggers) can generate some elements for perception. The midbrain problem is still debated mainly in terms of “how” not “if”. Many would agree that physical/biological phenomena give rise to psychological phenomena.
Sensation
physical process - receiving stimuli from the environment via the sensory system.
Perception
cognitive process - interpreting sensory signals into a conscious experience - interpreting sensory signals is where things get complicated. Transforming them into conscious experience.
Recognition
cognitive process -process of identifying and/or categorising our perceptions. - identifying is where things get complicated.
Sensation recognition
bottom up processing - taking the elementary building blocks of sensation from the sensation world and using them to building a pattern of electrical signals that are fed into the brain -will only travel in that direction which is why its called bottom up process
Perception recognition
taking the electrical signals from the sensory system and building on them integrating them, converting them into higher order signals - bottom up process
There is also a top down process - the higher order levels of the perceptual process can influence what is happening at the lower order levels which is not necessarily directional (one way only). For example, two or three jabs in the arm from the doctor. People normally look away but that doesn’t change the sensory signals coming in, you will still feel the pain sensation (bottom up process).people look away Sensitivity: get measures from proportion
Because they don’t want to attend to that painful stimulus. If you look away it’s not anticipated as much and don’t expect it to happen. Most people find there is a significantly less degree of pain when looking away - this is top down processing higher order elements influencing the lower order levels of perception.
Weber’s two concepts:
Weber is Psychophysics
- The absolute threshold (detection)
The minimal limit of detection. The minimum stimulus that produces sensation 50% of the time. Keep adding weight and the patient won’t feel it and once they feel it that’s the absolute threshold. - The relative threshold (discrimination) The minimal change in stimulus required to elicit a change in sensation 50% of the time. Now called the ‘just noticeable difference’ (JND).
Examples of absolute thresholds
- Vision - a candle burning 20 miles away on a dark night
- Hearing - a watch ticking 20 feet away
- Touch - a bees wing dropped on your
check from 1cm - Taste - 1stp of sugar in 2 gallons of
water - Smell - 1 drop of perfume in a 6 room
building
Weber fechner law
The relationship between the stimulation level and the perceived sensation is proportional %based, not consistent
- To detect change in stimulus intensity must increase relative to the current level
- In other words, the larger the stimulus magnitude the greater amount of difference needed to produce a JND
- Webber constant (k): a constant proportion of the initial stimulus value the represents the JND
How much needs to be change to notice a difference:
K values
Vision - 1/60 (2%) Hearing - 1/10 (10%) Smell - 1⁄4 (25%) Taste - 1⁄3 (33%) Touch 1/50 to 1/7 (2-14%) - the reason its a range is because touch covers many things such as pain, pressure, itch, heat
Adaption
ekman et al. adaptation to odour presentation
- Perceived magnitude (intensity) decreases over time if stimulus is constantly present.
Adaption is critical for survival
Threshold methods
Fechner’s 3 methods
Signal detection theory
Magnitude estimation
Fechner’s 3 methods
- Constant stimuli
- To determine absolute threshold
- Stimuli 1,2,3,4 … present multiple
times, random order
- To determine JND
- Is the other weaker/stronger/same
Detections are set to 50% detection by convention. - limits
Determining absolute threshold
- Stimuli 1,2,3,4… present ascending/descending order Determining JND
- Standard vs comparator stimuli a,b,c,d… in ascending value
- Tell me when comparator goes from weaker/stronger - Now - adjustments
Determining absolute threshold
- Adjust the stimulus until you can detect it
Determining JND
- Standard stimulus provided
- Adjust the comparator stimulus until it
matches the standard
- Magnitude of variance = JND
Dial it up or down until it matches the standard
Q: how certain are we that we are just measuring sensitivity to the stimulus? You are depending on the participants’ self report - waiting for a yes i can detect it or no i can not detect it or yes/no there is/isn’t a difference. This is subjective
Inherently prone to bias - these measures are biassed and need to get around the biasism.
Neurons
electrically active, multiple subtypes classified by anatomy, location or function – unique ability to conduct bioelectric signals
Glia
electrically passive, involved in support roles, immune response, aiding neuronal transmission, growing awareness of other roles
Synapses
Junctions between cells – when the presynaptic cell is excited past threshold, it releases neurotransmitter onto the postsynaptic cell
Sensory receptor neurons 3 key features:
- Sense organs always
- Must respond to stimuli from environment
- Convert to electrically stimuli
Traditionally 5 senses (“modalities”):
- Sight (vision)
- Hearing (audition)
- Touch (somatosensation)
- Smell (olfaction)
- Taste (gustation)
- Balance (the vestibular sense)?
Sensory systems
• Four criteria
- Specialized to receive particular stimulus – i.e. has specific receptors for specific physical energy/chemical molecules
- Performs signal transduction (stimulus → neuronal potential)
- Relays the neural signal to the brain via certain pathway (synapse 1 → synapse 2 → synapse 3 …)
- Has its own cortical region for processing (sensory cortices + association cortices)
Example of sensory system 4 criteria– the olfactory system
- Specialized to receive particular stimulus
– olfactory neurons have special receptors that respond to odorants - Performs signal transduction (stimulus → neuronal potential)
- odorants trigger action potentials in olfactory receptor neurons - Relays the neural signal to the brain via certain pathway
- olfactory receptor neurons → olfactory bulb neurons → brain - Has its own cortical region for processing (sensory cortices + association cortices)
- olfactory cortex
Muller’s Doctrine of Specific Nerve Energies (1842):
brain distinguishes between different senses by monitoring activity in different sensory nerves
• e.g. anything that activates optic nerve will elicit ‘light’, anything that activates auditory nerve will elicit ‘sound’
Specificity Coding
– qualities are represented by activation of specific neurons
Quality X is perceived when only ‘X specific’ neurons fire Quality Y is perceived when only ‘Y specific’ neurons fire
Requires neurons that respond only to a specific environmental stimulus e.g. “Grandmother cells” (Lettvin & Konorski, 1960s)
“Luke Skywalker cells” (De Falco et al., 2016)
These neurons represent associated concepts, not individual items/qualities per se!
Population Coding
qualities are represented by the pattern of activity across a group of neurons
Allows the representation of many different stimuli by the firing of a group of neurons
Rate coding
qualities are represented by the firing rate of the neuron
Useful for coding stimulus intensity
Useful for coding stimulus duration
rate coding can occur in single neurons or at the population level
Computational neuroscience
David Marr - proposed 3 critical levels of analysis:
- Computational theory – what is the goal of the computation?
- Representation & algorithm – what represents the input and output? What is the algorithm (formal set of rules) used to convert input to output?
- Hardware implementation – how can the representation be realised physically?
Representation
a key component in computational models of perception
• Perception must involve the formation of representations in the brain – how does the brain construct and use these representations?
• Analog representations: magnitudes in one system map to analogous magnitudes in another system (such as brain)
• Symbolic representations: arbitrary symbols in one system map to states/entities in another system
Representation in sensory systems
Each processing stage receives a representation of the sensory stimulus as its input.
• Each representation is transformed to a new representation that is passed on to the next processing stage (and so on).
• The modification that takes place at each processing stage can be considered as a computational operation that transforms one representation into another.
