Week 39 - Signal Detection Theory Flashcards
psychophysics
the study of interaction between physical stimulation and perceptual experience. It investigates how we detect, interpret and respond to stimuli.
sensations
simple, immediate, and automatic experiences triggered by the stimulation of a sense organ (e.g. eye). They involve direct awareness of experiences e.g. the sweetness of honey.
perceptions
complex, meaningful interpretations of objects and events. Can require time and effort to reach a stable state and allow us to recognize and make sense of what we sense e.g. perceiving a drawing through interpreting its colors and shapes.
Fechner’s Law
bases on Weber’s Law by explaining how our perception of a stimulus’s intensity grows with the physical intensity of the stimulus itself. Our perception of sensation increases at a slower rate compared to the actual increase in stimulus intensity. The psychological experience (Ψ) is proportional to the logarithm of the stimulus intensity (X).
Ψ = (k)log(Χ)
Weber’s Law
states that the sensitivity to changes in stimulus magnitude decreases as the stimulus magnitude increases. The Just Noticeable Difference (JND) is the minimum change in stimulus magnitude needed for a change to be perceived. The ratio of the smallest noticeable change in a stimulus (∆ stim) to the original intensity of the stimulus (stim) is a constant (K).
∆stim/stim= KW
Q: What is meant by the ‘explanatory gap’ (Levine, 1983, 1999) with regards to modern theories of perception?
(Mather, 2016)
A: Perception theories assume a link between sensations and corresponding brain states, but it has yet to be explained how sensations (mental) are explained by neural activity (physical).
Q: Where do psychophysics and neuroscience overlap, and where do they differ? (based on this scheme: stimuli → neural responses → perceptual experiences)
(Mather, 2016)
A: They are both concerned with how stimuli affect the brain, but psychophysics focuses on the relations between stimuli and perceptual experiences, while neuroscience primarily studies the links between stimuli and neural responses.
Q: What is the main issue with classical psychophysical methods, and what is an alternative solution?
(Mather, 2016)
A: They mix up a person’s true ability to detect a stimulus with their personal biases, making the results less accurate.
Signal Detection Theory was created to fix this by separating actual sensitivity from bias.
Q: What is the phenomenological approach in psychophysics and what are its limitations?
(Mather, 2016)
A: A method that uses people’s verbal reports to study the relation between stimuli and perceptual experiences.
Limitations:
1) there is a language requirement (excluding pre-/non-verbals and animals)
2) different people use language differently
3) it is open to bias due to its subjectiveness
What is the Signal detection theory (SDT)?
It is the theory of performance in psychophysical experiments in which subjects’ decisions are determined jointly by their sensory response and by a tendency to respond in a certain way. It acknowledges the importance of bias effects by assuming that stimulus detection is a two-stage process.
What happens in the first stage of the SDT?
The first stage is a purely sensory process in which a specific stimulus level produces an internal sensory response that depends on the intensity of the stimulus and the sensitivity of the sensory system. This internal response is subject to random internal “noise”.
What happens in the second stage of the SDT?
The second stage is a decision process in which the sensory response magnitude is compared to an internally set criterion.
If sensory response > criterion: Stimulus present.
If sensory response < criterion: No stimulus present.
What are the two different presentations in SDT methods?
noise representations (not containing a stimulus)
noise + signal representations (containing a stimulus)
What two kinds of tasks are commonly used where the subject must discriminate between the two presentations?
Yes/no task
Forced-choice task
What happens in the Yes/no task?
In this task, the subject is presented with a single stimulus event in each experimental trial, which may or may not contain a signal. The subject must respond “yes” if he or she decides that a stimulus was presented in that trial, and “no” otherwise.
