sensation & perception, psychophysics Flashcards
L1-3, reading 1
sensation
Physical process - receiving stimuli from the environment via the sensory systems
perception
Cognitive process - interpreting sensory signals into a conscious experience
internalist
assumes that perceptions of objects (in the environment), and knowledge or beliefs about those objects, are aspects of a person’s mind
externalist
Objects/observations etc constitute real aspects of the world, i.e. a true representation of the world.
naive realism
our perception = how the objects actually are
arguments against naive realism
- humans have cognitive biases which can distort their perception of reality.
- theory of relativity, which states that our perception of space and time are not objective realities but creations of our minds.
john locke on perception
2 stages for perception
- direct perception of the object
- internal representation of the object
In sum: perceptual experience of an object is a copy of the object’s primary qualities, mixed with subjective elements caused by the observer.
dualism
- mind = non-physical, conscious
- body = material substance, physical
monism
brain gives rise to perception from internal plus external stimuli
functions of CC
- perceptual-motor functions (i.e. coordinating the hands in space)
- sensory-perceptual functions (i.e. unifying the two visual fields of space)
absolute threshold
The minimal limit of detection. i.e. the minimum stimulus that produces sensation 50% of the time
relative threshold
The minimal change in stimulus required to elicit a change in sensation 50% of the time (= Just Noticeable Difference or JND)
Weber-Fechner law (in words)
The just noticeable difference (JND) between 2 stimuli is a function of the magnitude of the original stimulus
The larger the stimulus magnitude, the greater the amount of difference needed to produce a JND
Weber constant (k)
a constant proportion of the initial stimulus value that represents the JND
Weber’s Law
Δ I / I = k
low k means…
…good at detecting difference
adaptation
Perceived magnitude (intensity) decreases over time if stimulus constantly present
Only when stimulus changes or is removed does our perceived intensity change
Fechner’s 3 Methods - list
- constant stimuli
- limits
- adjustment
Constant Stimuli to determine absolute threshold:
set of stimuli presented multiple times, random order - do you detect?
Constant Stimuli to determine JND:
standard stimulus vs comparison stimuli (multiple times, random order) - weaker/stronger/same?
Limits to determine absolute threshold
stimuli in ascending order - when do you detect?
Limits to determine absolute threshold
stimuli in ascending order vs constant stimuli - when does it change from weaker to stronger?
Adjustment to determine absolute threshold
adjust the stimulus until you can just detect it (like using a dial)
Adjustment to determine absolute threshold
adjust until it matches the comparison stimuli
D prime in signal detection theory
measures perceptual sensitivity
- Difference between the mean amount of sensory activity generated by the noise alone trials and the signal+noise trials will equal sensitivity (d’)
= hits - false alarms
bigger d’ means
stronger signal or less noise (easier to detect)
Criterion (β) in signal detection theory
Y/N bias
Yes bias =
- shifted criteria left
- increases proportions of hits and false alarms
- -ve C
3 laws of qualia - list
- irrevocability
- flexibility
- endures ST memory
irrevocability
once the qualia is perceived, it cannot be denied or changed [the input side]
flexibility
you can interpret the perception of something in the world in a multitude of ways [the output side]
Endures in short term memory
need to be able to hold the representation of the qualia in short term memory to perceive it
Stevens’ Power Law
- Based on magnitude estimation (0-100)
- perceived magnitude increases nonlinearly at different rates in different sensory modalities
- log = linear increase ⇒ power-law relationship between stimulus intensity and perceived magnitude
Müller contribution to the field of sensation and perception.
- 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
Penfield contribution to the field of sensation and perception
- neurosurgeon, mapped the homunculus
- decussation and contralateral mapping (pathways cross midline)
three neural encoding schemes
- rate coding
- specificity coding
- population coding
rate coding
qualities of a stimulus are represented by changes in firing rate
specificity coding
qualities of a stimulus are represented by activation of specific neurons
population coding
qualities are represented by the pattern of activity across a group/population of neurons
criteria for a sensory system (4)
- Specialised 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)
problem of univariance (explanation and solution)
Q: all info enters brain as APs, so how do we get different modalities and sub-modalities?
A: different ways of coding - rate, specificity, population
qualia
a quality or property as perceived or experienced by a person
the raw feel of sensations such as the subjective quality of “pain” or “red” or “gnocchi with truffles”
