Psychophysics and Signal Detection Theory

What is sensation?

how sensory organs (eyes, ears etc) convert physical/chemical information into signals that our nervous system can understand

What is perception?

How we acquire information from the environment how we process that information to form internal representations of the environment

What is cognition?

How we use the internal representations to do more complex things

What is difference threshold?

the smallest change in a stimulus that can be detected (JND)

JND

just noticeable difference

What is absolute threshold?

the minimum intensity of a stimulus that can be detected

What is the Weber fraction?

the difference threshold divided by the intensity of the standard stimulus

What is Weber's Law?

the change in a stimulus that will be just noticeable is a constant ratio of the original stimulus

What is Fechner's Law?

human mind is using the weber fraction as a unit for perceiving that stimulus dimension

What is method of constant stimuli?

experimenter varies intensity randomly so it isn't predictabletakes a LONG time

What are advantages of method of constant stimuli?

allows the shape of the psychometric function to be established provides accurate estimate of threshold

What are disadvantages of method of constant stimuli?

requires retesting to roughly estimate threshold wastes a lot of trials difficult to measure changes in threshold

What is method of limits?

measures the threshold without determining the shape of the psychometric functionthreshold is an average of limits from each ascending and descending runs

What are ascending series of the method of limits?

present stimulus at a subthreshold level increase stimuli intensity in small steps until participants can detect the stimulus

What are descending series of the method of stimuli?

present stimulus at a subthreshold level increase stimulus intensity in small steps until participants can detect the stimulus

What are advantages of method of limits?

more efficient, quicker reasonably accurate determining the threshold

What are disadvantages of method of limits?

many trials wasted participant may habituate and thus overshoot the true threshold overall shape of psychometric function cannot be derived