The document discusses several classical psychophysical methods for measuring thresholds: 1. The method of constant stimuli measures thresholds using fixed sets of stimulus intensities presented in random order to determine the psychometric function. 2. The method of limits uses ascending and descending series to find the transition points between detectable and undetectable, avoiding habituation errors. 3. The method of adjustment allows observers to vary the stimulus until it is just detectable to prevent boredom but can be difficult to apply. These methods are used to determine absolute and difference thresholds as well as effects like loudness enhancement between stimuli. Sensation is defined based on stimulus-response relationships.

1. The Classical Psychophysical Methods CHAPTER 3, Detection Theory: A User’s Guide

2. Outline Method of constant stimuli Absolute Thresholds Difference Thresholds Method of limits Absolute Thresholds Difference Thresholds Variation of the Method of Limits Method of adjustment Absolute Thresholds Difference Thresholds Application of classical psychophysical methods to problems of stimulus matching

3. Introduction The threshold has been defined as the stimulus value which is perceptible in 50% of the trails. Three methods of threshold measurement: 1.Method of constant stimuli 2.Method of limits 3.Method of adjustment

4. Method of constant stimuli - Absolute Thresholds Procedure: using the same set of stimuli(5~9 different values in the set) , each stimulus is present repeatedly, usually 100 times or more, but in a random order. The percentage of detections as a function of stimulus intensity, φ is determined. Yes or No response: the proportion( p ) of yes response is computed, and a graph called a psychometric function is constructed.

6. Method of constant stimuli - Absolute Thresholds Absolute threshold: the stimulus intensity for which the proportion of trials resulting in yes response is 0.5 Ogive function : S-shaped, is a cumulative form of normal distribution. Fitting ogive function to threshold data range: z-score method of least squares

9. Method of constant stimuli - Difference Thresholds Standard stimulus(St): fixed value Comparison stimulus(Co): the value is changed from trial to trial Space error Time error

11. Method of constant stimuli - Difference Thresholds Point of subjective equality(PSE): The 0.5 point on the psychometric function , is perceived subjectively as equal to standard stimulus Constant error(CE) CE = PSE - St

12. Method of constant stimuli - Difference Thresholds Upper difference threshold(DL u ) the stimulus range from PSE to the .75 point Lower difference threshold(DL l ) the stimulus range from PSE to the .25 point  DL = (Dl u + DL l) / 2 The method of least squares

13. Method of limits - Absolute Thresholds Ascending series : begin with very weak subthreshold stimulus, then increased by a small amount until the observer report the presence of the sensation Descending series : the value of stimulus is decreased until the observer report the absence of the sensation Threshold : the average of the transition points

15. Method of limits - Absolute Thresholds Error of habituation: the tendency for an observer to develop a habit of repeating the same response Error of expectation: an observer may falsely anticipate the arrival of the stimulus at his threshold and prematurely report that the change has occurred before it really has Minimize the errors:avoid using long trial series, vary the starting point

16. Method of limits - Difference Thresholds Upper limen(L u ): the point on the physical dimension where “greater” response change to “equal” response Lower limen(L u ): the point where “less” response change to “equal” response Interval of uncertainty(IU): the range on the stimulus dimension over which an observer cannot perceive a difference between the Co and St

17. Method of limits - Difference Thresholds IU = L u – L l DL =1/2 IU = ½(L u – L l ) PSE = ½(L u + L l ) Error of habituation Error of expectation Space error Time error

18. Variation of the Method of Limits Up-and-down/ staircase method (Cornsweet, 1962) - efficient - step size : must chosen with care Threshold tracking method (Bekesy, 1947) Forced choice method(Blackwell, 1953) - temporal-forced choice - spatial-forced choice - threshold: two correct responses in succession - response bias: the tendency to report the presence of subthreshold or absent stimuli

19. Method of adjustment - Absolute Thresholds Procedure: set the stimulus intensity level either far below or far above threshold and ask the observer either to increase the intensity level until it is just perceptible or vice versa. Can prevent boredom Error of habituation Error of expectation

20. Method of adjustment - Difference Thresholds Method of average error: the observer is instructed to adjust a Co until it seems equal to some St Mean of X = PSE CE = PSE – St Standard deviation: high degree of central tendency when discrimination is good

21. Method of adjustment - Absolute Thresholds Shortcomings: - difficult to apply when stimulus are not continuously variable - difficult to apply when pairs of stimulus cannot be presented simultaneously - difficult to maintain constant conditions

22. Application of classical psychophysical methods to problems of stimulus matching Equal sensation contour: a stimulus critical value function, in which absolute threshold is plotted against some property of stimulus

23. Application of classical psychophysical methods to problems of stimulus matching Loudness enhancing effect : the increment in loudness of a sound caused by the presentation of another sound

25. Conclusion Sensation is treated as a concept which must be defined in terms of stimulus-response relationships.