2. SIGNAL DETECTION THEORY
Definition
“Signal detection theory deals with the delectability of signals and criterion that are used for the
detection of signals”
Explanation
This theory can be an application of psychologysics because the observer’s response is according
to their sensitivity to stimulus and the judgment is accordingly.
Signal detection theory is basically a sensory experiment to us and it helps us to analyze much
kind of decision making problems.
Information and criterion
For example a radiologist is looking for evidence of tumor.
Interpreting images on CT scan is hard and need a lot of experience to interpret a tumor.
There is always uncertainty about the presence of tumor or not.
4 possibilities of detection the stimulus
Doctor sees the tumor and says “yes”
Hit (tumor present and doctor says “yes”)
Miss (tumor present and doctor says “no”)
False alarm (tumor absent and doctor says “yes”)
3.
Correct rejection (tumor absent and doctor says “no”)
Present
Hit
False
alarm
Yes
Miss
No
absent
Correct
rejection
Decision making process
Decision making process involves
Information acquisition and
Criterion
Information acquisition
Healthy lungs are of different shape and lungs a tumor may have a different image .
Characteristics
1. Brighter or darker
2. Different texture
When doctor get complete training he or she learn what kind of tumor they looking for.
4. With more training they will be able to acquire more information increased information increase
the possibility of errors.
Criterion
1. In addition to use technology to gain information a doctor also uses his own judgment.
2. Different types of errors are not equal for example missing the opportunity of earns
diagnosis means that difference between life and death. A falls alarm is further tested
through routine biopsy operation. They may choose the “yes” decision.
3. Other doctors may be more conservative and give the repute of “no” (no tumor) to
reduce the unnecessary surgery.
4. The doctor may pick up the tumor at net check up.
Internal response and internal noise
There are two kinds of noise factors that produce uncertainty.
1. Internal noise
2. External noise
External noise
Many sources of external noise are there which can be the part of photographical process.
Like a smudge or something in the person’s lung that is looks like a tumor. They are the
example of external noise.
Doctor can reduce the external noise but there is nothing to reduce the internal noise.
5. Internal noise
Suppose that doctored has a set of tumor detector neurons and he determines the tumor as his
neurons responds to the image (actually the doctor detect a thing which is looks like tumor)
PURPOSE AND APPLICATIONS
1. It is applied to humans and as well as other animals.
2. Application in a recognition paradigm.
3. Sensitivity index: used in statistics for computing.
4. Non parametric measures: it means the area which comes under the ROC curve.
Bias: bias is independent of the sensitivity (a person may be more likely to respond at the
stimulus or more likely to respond at the stimulus which is not present.
PURPOSE OF SIGNAL DECETION THEPRY
1. The purpose of signal detection theory is to increase the sensitivity of stimulus.
2. Various disciplines:
I.
Psychology
II.
Audiology
III.
Speech perception
IV.
Engineering
V.
VI.
Animal psychology
Medical forensic science weather forecasting.
3. Audition: the application which is applied in clinical measurement of threshold or
stimulus.
6. 4. Speech perception: used in the recognition speech messages and to carried out
psychophysics researches.
5. Psychology: in the field of memory and attention.
6. Engineering: it is also used in x-rays, in CAT scan for the interpretation of cancer or
tumor.
7. Short increment sensitivity index: to test hyper sensitivity to small change in intancity
and developed the SISI test.
