Sensation and perception
College 1: foundations and psychophysics
Why should we study perception? Perception is fundamental to our life. Physical reality vs
perceptual reality can be different to everyone (and all animals).
Is our perceptual system the perfect measuring device?
Kant (1742-1804): ‘the senses do not error - not because they always judge rightly, but
because they do not judge at all’.
The perceptual process:
1. Distal stimuli (we can perceive)
2. Proximal stimuli (things that are generated by the distal stimuli, like light, sound or
pressure of something on the skin of your hands)
3. Proximal stimuli converted to neural signals, which are sent to the brain
4. Signal processing in the brain (perception)
5. Conscious awareness
Bottum-up → from 1 to 5
Top-down → from 5 to 1 (van eerdere ervaringen van de wereld, waardoor verwachtingen
bestaan)
Three main types of questions:
- How does the proximal stimulus carry information about the thing that is perceived
(de distal stimulus)?
- How is the proximal stimulus transformed into neural signs?
- What is the relationship between perceptual experience and the distal stimulus, the
thing that is perceived?
The senses:
,Measuring perception
Behavior: psychophysics
First vs. third person data: to assess objectively the relationship between stimuli and
experience.
Topics of psychophysics: thresholds (what is the minimum intensity and minimum difference
we can perceive), and scaling (op welke verhoudingen/schalen/maten neem je dingen
anders waar).
Psychophysics. Finding the absolute threshold (detection; minimale waarneming van iets;
niet welke mate van verschil of zoiets, maar echt detection of er überhaupt iets is.).
1. Method of constant stimuli: alle waarnemingen testen
2. Method of limits / method of adjustment: stoppen met testen waarbij er een
verandering van waarneming is; de rest zal dan hetzelfde zijn (wel/geen licht zien)
The psychometric function:
a) Op een punt ga je een bepaalde treshold overheen, en vanaf daar neem je iets opeens
wel waar (tot een bepaalde intensiteit is het 0% en vanaf bepaalde intensiteit is de
waarneming 100%).
b) de s-vorm; er is altijd een kans dat iemand bij een lage intensiteit wel iets waarneemt, of
iemand met een hoge intensiteit iets niet waarneemt.
3. Staircase method: ook efficiënter dan optie 1. Test begint aan een kant, en bij de
volgende test begin je vanaf één stapje lager vanaf de
andere kant.
Signal Detection Theory (SDT)
People can surprise you: how do yes/no responses come to
be? And decision strategies (bias) next to just random noise
(sensitivity).
Neural noise.
Difference between Target-present vs. Target absent signals
(like spikes).
But… what if the criterion value varies?
Catch trials allow separation of actual sensitivity (d; the line) and decision-making bias
(criterion; b; where you put the criterion).
Respond ‘yes’ Respons ‘no’
signal present Hit; true positive Miss; false negative
signal absent False alarm; false positive Correct rejection: true
negative
, The criterion visualized on a Receiver Operating Characteristic (ROC) plot:
Psychophysics. Back to finding thresholds: the difference threshold (discrimination): also
known as the just noticeable difference (JND).
The JND changes with the intensity of the standard stimulus.
Weber’s Law:
- Δ I (the JND) = k I, where I = stimulus intensity, and k = Δ I / I
- Example: With k = 0.1, for a standard weight of 100 g, Δ / is 0.1 x 100 = 10g.
So a comparison weight of <90 or >110 g.
- For a standard weight of 1000 g, Δ / is 0.1 x 1000 g = 100 g; so a comparison
weight of <900 or >1100 g.
Scaling
Fechner’s Law (using JND):
Steven’s power law: S = c l ^n, where S = sensation, I = intensity, c = constant, and n
= exponent. :
College 1: foundations and psychophysics
Why should we study perception? Perception is fundamental to our life. Physical reality vs
perceptual reality can be different to everyone (and all animals).
Is our perceptual system the perfect measuring device?
Kant (1742-1804): ‘the senses do not error - not because they always judge rightly, but
because they do not judge at all’.
The perceptual process:
1. Distal stimuli (we can perceive)
2. Proximal stimuli (things that are generated by the distal stimuli, like light, sound or
pressure of something on the skin of your hands)
3. Proximal stimuli converted to neural signals, which are sent to the brain
4. Signal processing in the brain (perception)
5. Conscious awareness
Bottum-up → from 1 to 5
Top-down → from 5 to 1 (van eerdere ervaringen van de wereld, waardoor verwachtingen
bestaan)
Three main types of questions:
- How does the proximal stimulus carry information about the thing that is perceived
(de distal stimulus)?
- How is the proximal stimulus transformed into neural signs?
- What is the relationship between perceptual experience and the distal stimulus, the
thing that is perceived?
The senses:
,Measuring perception
Behavior: psychophysics
First vs. third person data: to assess objectively the relationship between stimuli and
experience.
Topics of psychophysics: thresholds (what is the minimum intensity and minimum difference
we can perceive), and scaling (op welke verhoudingen/schalen/maten neem je dingen
anders waar).
Psychophysics. Finding the absolute threshold (detection; minimale waarneming van iets;
niet welke mate van verschil of zoiets, maar echt detection of er überhaupt iets is.).
1. Method of constant stimuli: alle waarnemingen testen
2. Method of limits / method of adjustment: stoppen met testen waarbij er een
verandering van waarneming is; de rest zal dan hetzelfde zijn (wel/geen licht zien)
The psychometric function:
a) Op een punt ga je een bepaalde treshold overheen, en vanaf daar neem je iets opeens
wel waar (tot een bepaalde intensiteit is het 0% en vanaf bepaalde intensiteit is de
waarneming 100%).
b) de s-vorm; er is altijd een kans dat iemand bij een lage intensiteit wel iets waarneemt, of
iemand met een hoge intensiteit iets niet waarneemt.
3. Staircase method: ook efficiënter dan optie 1. Test begint aan een kant, en bij de
volgende test begin je vanaf één stapje lager vanaf de
andere kant.
Signal Detection Theory (SDT)
People can surprise you: how do yes/no responses come to
be? And decision strategies (bias) next to just random noise
(sensitivity).
Neural noise.
Difference between Target-present vs. Target absent signals
(like spikes).
But… what if the criterion value varies?
Catch trials allow separation of actual sensitivity (d; the line) and decision-making bias
(criterion; b; where you put the criterion).
Respond ‘yes’ Respons ‘no’
signal present Hit; true positive Miss; false negative
signal absent False alarm; false positive Correct rejection: true
negative
, The criterion visualized on a Receiver Operating Characteristic (ROC) plot:
Psychophysics. Back to finding thresholds: the difference threshold (discrimination): also
known as the just noticeable difference (JND).
The JND changes with the intensity of the standard stimulus.
Weber’s Law:
- Δ I (the JND) = k I, where I = stimulus intensity, and k = Δ I / I
- Example: With k = 0.1, for a standard weight of 100 g, Δ / is 0.1 x 100 = 10g.
So a comparison weight of <90 or >110 g.
- For a standard weight of 1000 g, Δ / is 0.1 x 1000 g = 100 g; so a comparison
weight of <900 or >1100 g.
Scaling
Fechner’s Law (using JND):
Steven’s power law: S = c l ^n, where S = sensation, I = intensity, c = constant, and n
= exponent. :
