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Lecture notes Sensation & perception - part 1
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Part 1 of the lecture notes from S&P, until class 7
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Lecture notes Sensation and PerceptionCourse info:
- Irene van de Vijver is my workgroup teacher.
- Group presentation (20%)
o Score reduced for skipping presentations by other students.
- Individual assessment (80%)
o Make acceptable reviews of other student’s presentations (10%).
▪ In second half of the term, choose 3 and write a review.
▪ Submit those.
▪ If they are good you just get a 10.
o Two exams:
▪ Part 1 = 35%. March 11th 8:45-10:45.
▪ Part 2 = 35%. April 15th 11:00-13:00.
▪ Revision of only one possible, if the individual part average is a 5.5.
o Exams focus on lectures, but can also be about papers and the book. Only papers
that are discussed in all three workgroups. Check BB.
▪ Study the abstract and the figures of the chosen papers and understand
that!
▪ Absent: toetsvoorziening.fss.uu.nl
Lecture 1: introduction
February 8th 2021
Senses:
- Vision - sight
o Eyes - retina
- Hearing - audition
o Ears - cochlea
- Taste - gustation
o Tongue – taste buds
- Smell - olfaction
o Nose - 0lfactory epithelium
- Touch - somatosensation
o Skin - many
Sixth sense with a sensory organ is balance. Vestibular system. Relies on vestibular labyrinths in the
ear.
Distinct sensations of touch:
- Light touch = texture
- Deep touch = pressure
- Stretch
- Heat-cold-pain
Vision:
- The eye and early visual pathways
- Form (shape)
- Motion
- Colour
- Depth and distance
, - Cognitieve influences: attention and awareness
Audition:
- The ear and early auditory pathways
- Location
- Frequency = pitch
Neural computations:
- There are areas in each neurons and activation of specific cells
and areas gives neural information.
- If multiple neurons are activated together (by a line in a
specific direction) another neuron is activated.
o = neural computation
- important to understand how and why we perceive the world.
Dualism = body and mind are separate.
Monism = mind is part of the body and vice versa.
- Manifestations of the same physical thing.
Sensation = the translation of the external physical environment into a pattern of neural activity (by
a sensory organ).
Perception = analysis of this neural activity to understand the environment and guide behaviour.
→ or: the subjective conscious experience of the outside world.
Sensation and perception reflect interactions between our sensory organs and physical properties of
the world, so they are:
- Dependent on physical properties of the world.
o Light does not travel around corners, we cannot see around corners, but we can
hear around corners.
- Limited by the physical properties of our sensors.
o We have a limited visible spectrum of light.
Sensation and perception have evolved to help us survive and reproduce, so they are:
- Optimised for useful representations of the environment.
- Influenced by interpretation: context and experience.
- Dependent on limited resources of attention and awareness.
o Focus on what we think is most important.
Experimental methods: perception
- To study we need to:
o Change the physical environment of a human or animal
o Measure behaviour or change in neural activity, both due to the change.
- Psychological approach:
- Quantitative measurements of behaviour resulting from perception.
- Psychophysics: the scientific study of the relation between stimulus and sensation.
o Weber and Fechner.
o Test the ‘Just Noticeable Difference’ = JND
▪ Light of a different amount of candles = brighter.
▪ Addition of 1 candle is more noticeable if there are less candles in total.
▪ If you turn brightness up, you see it less accurately, so you need to add more
to notice.
, ▪ The Weber-Fechner Law: logarithmic relationship between stimulus
intensity and perceptual intensity.
▪ Detectable difference increases with average stimulus intensity.
o How to determine a perceptual threshold:
▪ 2-alternative forced choice.
▪ First, present two alternatives.
▪ JND is a range, not just one point.
▪ Method of constant stimuli
▪ Present trials with extent of
differences randomized from one
trial to the next.
▪ Plot the probability that people have
detected it.
= psychometric function.
▪ The function is the most steep
around 75%, also u. This is the point
of interest.
• For that we need to know
the slope.
o Test:
▪ Correct answer → make next trial more difficult.
▪ Wrong answer → make next trial less difficult.
▪ Change stimuli depending on pattern of previous responses.
▪ You take the average twist point of wrong and right and that is your
estimation.
Measuring changes in neural activity:
- biological approach: what are perception’s
neural substrates?
- We correlate a neural activity measure
with a change in the presented stimulus or
behaviour.
- Neural activity is either
o Spiking activity = AP’s
o Synaptic activity = synaptic potentials
o Metabolic activity = changes in oxygen and glucose consumption.
o These are closely related, bc AP’s often lead to synaptic potentials and these
increase metabolic activity. Not always!
Measuring spiking activity:
- Often seen as the golden standard of neural activity
- Very small changes, so need to be measured directly from the neuron.
o Invasive recordings inside the brain.
Measuring synaptic activity:
- Several measures at different scales and resolutions
- Smallest scale: local field potential (LFP)
o Measure complex wave form at different frequencies.
▪ Theta, alpha, gamma etc.
▪ Gamma = increase in activity.
▪ Theta = decrease in activity.
, o Interactions of excitatory pool and inhibitory pool cells.
▪ A loop of excitation → inhibition → base.
▪ That activity makes the spikes.
- EEG = non-invasive.
o Only captures large changes in activity.
o Advantages: cheap, good temporal resolution, moves with the subject (good for
children), silent (good for auditory perception).
o Disadvantages: poor spatial resolution, poor signal-to-noise ratio (you need the
signal a lot of times), only senses activity near the scalp (cortex), slow to set up
(particularly when you use a large amount of electrodes).
- Functional MRI = most commonly used.
o Advantages: high spatial resolution, straightforward analysis/interpretation, safe
and non-invasive, easy access.
o Disadvantages: poor temporal
resolution, indirect measure of
neural activity, low signal to noise
ratio, awkward environment.
- Sometimes you use both at the same time.
- MRI scanner difficulty = extremely strong
magnets.
- Normally: orientation is random, same
orientation when magnetic field is added.
o Realignment after releasing gives
us the image.
(f)MRI recipe:
- find subject
- put subject in magnetic field
- add radio frequency pulse
- turn frequency off after a couple of seconds
- record data
- repeat it a lot
- let subject leave.
Functional MRI:
- Blood with oxygen = no signal.
- Deoxyhemoglobin = oxygen carrier which has no oxygen bound (signal loss)
- Deoxyhaemoglobin affects T2* (MRI signal)
- Blood response follows neural activity.
o This overcompensates.
o This does not compensate accurately for the signal difference.
- So oxyhemoglobin concentration increases due to increased blood flow, this
reduces the signal loss from deoxyhemoglobin, which makes the signal
increase.
- BOLD signal = Blood Oxygenation Level Dependent
o Initial dip when oxygen is consumed.
o Increase in signal due to lots of blood flow = this we measure.
- Less blue cells (with oxygen) after activity.
- Block design is used: go from state 1 to state 2 and keep changing.
- Monkey MRI = vertical design.
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