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Broad Summary Sensation & Perception Part 1 - Chapter 1-7
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Summary of S&P - midterm (lecture 1-7)
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Lecture 1 – IntroductionIntroduction: The Senses
Sense (sensory organ): Vision (eyes), Hearing (ears), Taste (tongue), Smell (nose), Touch (skin etc.),
Balance (vestibular labyrinths)
• Vision: The eye and early visual pathways
o Form, motion, color, depth and distance, cognitive influences
o Vision is the primary sense in humans, almost every action we make is guided by
vision. Very large part in the brain.
• Audition: The ear and early auditory pathways
o Location, frequency
Properties of S&P
- Dualism: mind and body are separate things
- Monism: mind and body are integrated, mind is part of the body
- Panpsychism: mind exists as a property of all matter
- Sensation: a translation of the external physical environment into a pattern of neural activity
(by a sensory organ)
- Perception: an analysis of this neural activity to understand the environment and guide
behavior (or the subjective conscious experience of the outside world; subjective)
S&P reflect interactions between our sensory organs and physical properties of the world, so they
are: dependent on physical properties of the world (visible properties) and limited by the physical
properties of our sensors. Limitations of the physical properties of our sensors: color, UV, infrared
etc. It differs per organism.
S&P have evolved to help us survive and produce, so they are: optimized for representations of the
environment, influenced by interpretation (context and experience) and dependent on limited
recourses of attention and awareness (some things you don’t see because it is not important).
Experimental Methods
How do we investigate perception and sensory processing in the brain?
A translation of the physical environment into a pattern of neural activity that can be used by
our brain to guide behavior. So, to study perception experimentally:
• Change the physical environment of a human or animal (sensory stimulus)
• Measure the resulting behavior
• Measure the resulting change in neural activity
6 methods used in the study of the senses):
1. Thresholds (faintest sound, loudest sound)
a. Psychophysics
b. Scaling – measuring private experience (experience when hearing or tasting)
c. Signal detection theory – measuring difficult decisions (diagnosing a disease)
2. Sensory neuroscience
a. Sensory neuroscience (e.g., hot peppers, burning lips and tongue)
b. Neuroimaging – an image of mind (suppose you arrange to view completely
different images with different eyes; 2 images would compete to dominate
perception -> you see only 1)
3. Development: Biology of Perception
,Thresholds (first approach)
Psychological approach: quantitative measurements of behavior resulting from perception,
psychophysics: the scientific study of the relation between stimulus and sensation
Weber-Fechner Law: the relationship between a
physical intensity and its perceived intensity,
logarithmic relationship; detectable difference
increases with average stimulus intensity
- Challenge: how to determine a perceptual
threshold
- 2-alternative force choice: first, present 2
alternatives: correct/incorrect, yes/no,
more/less, etc.
- Method of constant stimuli: present trials
with extent of differences randomized from
one trial to the next, plot detection
probability against extent of difference -> the
psychometric function
à Weber’s Law: the Just Noticeable Difference (JND, smallest change in stimulus needed to detect
difference) is a constant fraction of the comparison stimulus (for 40g weight you need 1g difference
to detect, for 400g weight you need 10g)
à Fechner’s Law (extended from Weber): the relationship between mind and matter (S = k*logR)
à Steven’s Power Law: sensation is related to the stimulus intensity by an exponent. For exponents
larger than 1 (e.g., electric shock), Fechner’s law does not hold, and Steven’s Power Law should be
used
(further explanation on these 3 laws: p. 12)
Psychophysical methods:
1. Method of constant stimuli: creating stimuli with different intensities to find the tiniest
intensity that can be detected. Tones must be presented multiple times: subtle perceptual
judgments are variable. Consequently, always more than 1 measures needed. The intensity
at which a stimulus would be detected 50% if the time would be chosen as the threshold
(absolute threshold) -> there exists no hard boundary: some stimuli near the threshold will
sometimes be detected and sometimes not -> gradual detection graph.
2. Method of limits (more efficient): tones presented in increasing or decreasing intensity. Task
of listener: report when they first hear the tone/when the tone is not audible anymore ->
average of outcomes is the threshold
3. Method of adjustment: same as 2, but the person itself increases/decreases intensity
Scaling methods (for measuring how strong experiences are):
1. Magnitude estimation: participant assigns values according to perceived magnitudes of
stimuli
2. Cross-modality matching: ability to match the intensities of sensations that come from
different sensory modalities; allows insight into sensory differences between people (e.g.,
ask participant to adjust brightness of a light until it matches the loudness of a particular
tone). Hard with taste because genetically different.
, Signal detection theory:
• The stimulus that you’re trying to detect is always being detected in the presence of noise.
Down near a threshold, it will be hard to tell a real stimulus from a surge of internal noise.
External noise can also be present, creating uncertainty.
• 4 possible outcomes: correct/false & yes/no. By knowing the relationship of hits to false
alarms, you can calculate sensitivity. When you wait for a call, you move the criterion level
of response (left), so you will have more false alarms. If you move it to the right, you will
miss calls.
• Receiver operating characteristic (ROC) plots false alarms (x) against hits (y) for different
criterion values.
• Criterion depends on different subjective factors (‘How important?’)
Fourier analysis:
• Better describe how complex sounds such as music and speech, complex head motions and
complex images can be decomposed into a set of simpler components
• Example: sounds à sine wave: pure tone which is almost non-existent in real-life situations.
But all sounds are a combination of sine waves à Fourier analysis, which is also applicable
to other fields: visual stimulus can be broken down into component spatial frequencies
Sensory neuroscience (second approach)
It is more important which nerves are stimulated, not how they are stimulated. 12 pairs of cranial
nerves, leading in and out of the skull, conduct information for sensation, motor behavior or both (p.
21). Recap over hoe neuronen werken: p. 22-25
Neural activity is either:
1. spiking activity (action potentials), the gold standard of neural activity, very small changes,
so they must be measured directly from the neuron, invasive recordings inside the brain of
an animal/human
2. synaptic activity (synaptic potentials), several measures at different scales and resolutions,
smallest: local field potential (electrode between 2 neurons), EEG: cheap, high temporal
resolution, moves with the subject, silent, but: poor spatial resolution, poor signal-to-noise
ratio, only senses activity near the scalp (cortex), also slow to set up, MRI: mostly used: safe,
non-invasive, easy access, straightforward, high spatial resolution, but: indirect measure of
neural activity, low signal to noise ratios, poor temporal resolution
3. metabolic activity (oxygen and glucose consumption), fMRI and PET
à The three are closely related, but different measurements
Neural activity:
- MUA (multi-unit activity): action potentials (spikes) -> neural output
- LFP (local field potentials): slow electrical signals and sub-threshold activity, including
synaptic activity and voltage-dependent membrane oscillations -> neural processing
Neuroimaging methods:
1. EEG
o Measures electrical activity through electrodes on scalp à roughly localize whole
populations of neurons, excellent temporal accuracy, many repetitions needed
o Results in ERP: averaged waveform of many EEG recordings
2. MEG
o Measures magnetic field changes across many populations of many neurons in the
brain. Better than EEG, but way more complex and expensive.
3. CT
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