实验心理学6psychophysics单击此处编辑母版标题

1、Experimental Psychology School of Psychology Zhao FanA Psychology Course in Central China Normal UniversityQQ: 1024-2410-81 PsychophysicsGeneral View about this Course:Part 1： Fundamentals of ResearchOne: Explanation in Scientific PsychologyTwo: Research Techniques: Observation and CorrelationThree:

2、 Research Techniques: ExperimentsFour: Ethics in Psychological ResearchFive: How to Read and Write Research ReportsGeneral View about this Course:Part 2： Principles and Practices of Experimental PsychologySix: PsychophysicsSeven: PerceptionEight: Attention and Reaction TimeNine: Conditioning and Lea

3、rningTen: Remembering and ForgettingGeneral View about this Course:Part 2： Principles and Practices of Experimental PsychologyEleven: Thinking and Problem SolvingTwelve: Individual Differences and DevelopmentThirteen: Social PsychologyFourteen: Environmental PsychologyFifteen: Human FactorsPsychophy

4、sics: Psychological reaction to events that lie along a physical dimension. Edwin Boring (1950) claims that this marked the onset of scientific psychology. The first mathematical laws of psychological phenomena. Classical Psychophysics: Aimed at evaluating thresholds.Modern theory in Psychophysics:

5、SDT (Decision processes)The Core Issue in Psychophysics:How Physical value/magnitude（stimulus intensity）is mathematically related with Psychological value/magnitude（sensation intensity）. Everyday experience tells us: the relationship between the increase of sensation intensity and the increase of st

6、imulus intensity does not follow 1:1 ratio.Classical Psychophysics deals with two major topics:Measurement of sensory thresholds;Measurement of supra-threshold sensations, i.e. Production of Psychological scales.The development of Signal Detection Theory (SDT) inputs new blood into classical Psychop

7、hysics.Psychophysics: Physical Visual Intensity - Psychological Brightness Physical Auditory Intensity - Psychological Loudness Physical Measure of Weight - Psychological Heaviness Physical Electrical Intensity - Psychological Pain You may think it simple to decide the loudness or painfulness of sti

8、muli. However, it turns out that there is rarely a direct one-to-one relation between physical values and psychological values. For example, 10 times of energy increase is needed for a listener to judge the sound to be twice as loud. What practical usage for this finding? Modality effect: For one sh

9、ock to be judge twice as painful, the intensity of the shock needs an increase of only about one-third. Operational definitions: Describe the procedures used to produce a concept and allow us to communicate successfully about the concepts we are studying. Operational definition aims to transform abs

10、tract definition into observable and measurable properties.Why it is necessary in science?A common language in the scientific community; Increase precision of terminology. In such a way that other scientists can duplicate it, by specifying the operations used to produce and measure it. For example,

11、Recipe.Example Threshold: the operational definition of a theoretical construct. Basic Methods in Psychophysics:The method of Limits:Staircase method:Constant Stimuli Method:Method of Adjustment- subject controls levelsBasic Concepts in Psychophysics:Classical Psychophysics: Aimed at evaluating thre

12、sholds.Absolute Threshold:Difference threshold:JND:Psychophysical function/curve:Modern theory in Psychophysics: SDTBasic Laws in Psychophysics:Webers lawFechners Law:(Probably yields an ordinal scaling of psychological judgments.)Stevens Power Law:(Yields a ratio scale.)The method of paired compari

13、son/对偶比较法对偶比较法和和The rank-order method/等级排列法等级排列法 (Yields a ordinal scale)Threshold: Method of Limits (极限法极限法 又叫最小变化法、序列探又叫最小变化法、序列探索法、最小可觉差法索法、最小可觉差法)Threshold as a theoretical construct: In theory, classical psychophysicists believed that stimuli had to cross a (hypothetical) barrier (physical valu

14、e) to enter the brain or the mind of an observer. Since each physical stimulus will produce a normal distribution of mental events (varies from trial to trial). This threshold (as a stimulus value) should be a statistical concept (mean of the normal distribution of mental events produced by the phys

15、ical stimulus) in that the threshold can be detected 50 percent of the time. Threshold: Method of Limits (极限法极限法 又叫最小变化法、序列探又叫最小变化法、序列探索法、最小可觉差法索法、最小可觉差法)How we use Method of Limits to produce the operational definition of Threshold? Method of Limits: Devised by Fechner, provides an operational defi

16、nition for the concepts of AT and DT. Table 6.1 (different starting points). In Table 6.1. what result will be for an ideal observer?Threshold: Method of Limits absolute thresholdThreshold: Method of Limits：Influencing factors: Expectation (two types, eager（期望误差）（期望误差） / reluctant (习惯误差习惯误差) to chan

17、ge);So the threshold is operationally defined as the mean (average) of the points. A threshold based on an observers ability to detect a signal is called an absolute threshold.Another type of threshold Difference threshold, Table 6.2; Based on relative judgments, in which a constant unchanging stimu

18、lus (Standard-S) is judged relative to a series of changing stimuli/Comparison-S (with order).Threshold: Method of LimitsThe difference between the lower and upper thresholds is called the interval of uncertainty. The difference threshold is operationally defined as half of the interval of uncertain

19、ty. The mean of the upper and lower thresholds is called the point of subjective equality (for example Actual bulls-eye：Perceived-Standard-S usually deviates from physical bulls-eye：Standard-S)! Threshold: Method of Limits difference thresholdThreshold: Method of Adjustment (MOA)The method of adjust

20、ment asks the subject to control the (continuous) level of the stimulus, instructs them to alter it until it is just barely detectable against the background noise, or is the same as the level of another stimulus. This is repeated many times. The method is also called the method of average error (平均

21、差误法平均差误法 ), the method of reproduction, or the method of equivalent stimuli.In this method the observer himself/herself controls the (continuous) magnitude of the variable stimulus beginning with a variable that is distinctly greater or lesser than a standard one and he/she varies it until he/she is

22、 satisfied by the subjectivity of two.Threshold: Method of Adjustment (MOA)The difference between the variable stimuli and the standard one is recorded after each adjustment and the error is tabulated for a considerable series. At the end mean is calculated giving the average error (direct proportio

23、n to DT) which can be taken as the measure of sensitivity.Need to counterbalance S0 and S1 in spatial, temporal or beginning order of greater or lesser.Threshold: Webers Law Webers law: For a particular sensory modality, the size of the difference threshold relative to the standard stimulus is const

24、ant. I / I=K Webers law works for more than 90% of the range of standard stimuli tested in a particular sensory modality. It fails for very weak stimuli, such that K for very light standard stimuli is much larger than 1/30. Since the method of Limits is very inefficient, so a new version of the meth

25、od of limited, called the staircase method (Adaptive psychophysical methods) was developed. See Table 6.3. Keep the stimuli much closer to the threshold (operationally defined as the mean value of all stimuli presented, starting with the second round).Threshold: Staircase Method - Adaptive psychophy

26、sical methodsThreshold: Constant stimuli method (CSM, 恒定刺激法：二类恒定刺激法：二类反应反应 ) On the basis of the method of limits, we further fix the number of changed stimuli, but randomize the order of presentation. The lower (25% Yes) and upper (75% Yes reporting) thresholds; the interval of uncertainty. The dif

27、ference threshold is operationally defined as half of the interval of uncertainty. Threshold: Constant stimuli method (CSM, 恒定刺激法：二类恒定刺激法：二类反应反应 ) The DT here is called DT of 75% since both the lower and upper limits have 75% chance to report the difference. This is due to Ss are not required to rep

28、ort equal, e. g. we dont know the physical ranges covering from larger to equal and from equal to smaller. So, a bit different from the definition of DT in the method of limit. Threshold: Constant stimuli method (CSM, 恒定刺激法：二类反恒定刺激法：二类反应应 ) Classical DT defined as 50% report difference(Standard S la

29、rger / OR smaller)and 50% no differentiation(by = report); while the 50% point in two-option reporting has no 50% no differentiation(by = report ), also has no 50% report difference(Standard S larger /OR smaller ), only has 50% report larger AND report smaller simultaneously (i.e. another type of no

30、 differentiation); thus this 50% point has no differentiation; since the 0% and 100% points have full differentiation ability, the middle value of differentiation should be either 75% point (by larger report to differentiate difference),i.e. mean value of no differentiation and 100% larger Standard

31、report, or 25% point (by smaller report to differentiate), i.e. mean value of no differentiation and 100% smaller Standard report.Threshold: Constant stimuli method：二类反应：二类反应 PSE = Point of subjective equality (Orange, for example Perceived Target：Perceived-Standard-S very often bias from Physical T

32、arget：Standard-S): Point at which the difference is reported as larger (and smaller) 50% of the time.Interval of uncertainty: Difference between 25% point and 75% point (light blue).(75% - 25 %) / 2 = The difference thresholdThreshold: Constant stimuli method：Two-option Response What is DT of 75%，an

33、y advantage？ Participants reporting has only two options; 50% reporting means Ss can not differentiate Comparison stimulus from Standard stimulus. The upper limit of equal zone is defined as a Comparison intensity that is reported heavier than Standard S in 75% times. This is because it is the middl

34、e point (of 50% times and 100% times) to report a Comparison S heavier than the Standard S; Similarly, the lower limit is defined as a C intensity reported heavier than SS in 25% times. This DT calculation is not consistent with the classical operational definition of threshold (50% differentiation)

35、, thus we call it DT of 75%. Since heavier than SS in 25% times is equal to lighter than SS in 75% times, both upper and lower limits can be differentiated from SS in 75% times.Threshold: Constant stimuli methodSubjects are required to perform discriminations to presented stimuli. In the case of thr

36、ee-option comparison, Sss reports include higher, equal or lighter . Denoted as “+”、“=”、“”. 。In the case of two-option comparison, Sss reports include higher or lighter. Repetition for each condition To calculate DT by CSM, we need first set a SS and several CSs. Decide an intensity range for them,

37、and pick up 5-7 intensities as CSs, one of them can be used an SS (an intermediate intensity).Threshold: Constant stimuli methodCalculation of DT：either use Interpolation or Plotting method，need get participants upper DT and lower DT first. See below：(1) DT for three-option comparison： DTu=X(+)X (=)

38、 DTl=X (=) X (-) DT=（ DTu+DTl）/2 X (+) 、X (=) 、X (-) : mean C intensity for “+”、“=” 、“-” (x value at y=50%).(2) DT for two-option comparison： DT=（Lu - Ll）/2 Lu 、 Ll: mean C intensity for “+” 、“” (x value at y=75%) .Linear Interpolation between two known points：If two points (x0,y0) (x1,y1) are alrea

39、dy known，Then(y-y0)/(x-x0)=(y1-y0)/(x1-x0)transformed as：y=y0+(x-x0)*(y1-y0)/(x1-x0)LI for Absolute Threshold（two point threshold）constant stimuli method：DT Calculation based on LI ：CSM: 3-option comparisonPlot “+”、“=”、“-” 3 curves，use LI method to get the point of 50 heaver reporting than SS, which

40、 is 2045g and 50 lighter reporting which is 1966g. These two values are upper and lower limits（i.e., Lu=2045g，Ll1966g）, then：DTu= 204.5g - 200g = 4.5gDTl= 200g - 196.6g=3.4gDT Calculation based on LI ：CSM: 3-option comparison vs. 2-option comparisonIn the case of 2-option comparison , the two curves

41、 (heavier & lighter) will intersect at 50% point，e.g. upper limit = lower limit. Now, we need use the principle of 75%, or say use LI to get the middle point between completely differentiable (100%)and no differentiable (50%)with the SS, to get upper/lower limits. This is called DT of 75%. DT Ca

42、lculation based on LI ：CSM: 3-option comparison vs. 2-option comparisonIf you introduce equal report into CSM, upper/lower limit is defined as 50% report larger/smaller, thus DT (0.5*UL-LL) is related with peoples confidence level. For that reason, most researchers prefer two-option rather than thre

43、e-option reporting! Notes: We can not use 50% point of 2-option comparison minus SS to define DT, this is because the 50% points are qualitatively different between 2-option and 3-option comparisons. In 3-option case，the 50% point in the left side has50%percentage to report heavier SS, and large per

44、centage35% to report equal (The 50%-heavier+35%-equal percentage is equal to that in method of limits, e.g. 50% heavier-50% equal), and also small percentage15% to report lighter SS; While in 2-option case, the 50% point has50%percentage to report heavier SS and 50% lighter SS，i.e. 50% heavier-0% eq

45、ual.Besides, in the 2-option case the 75% DT describe subjects sensibility is totally different from PSE describe subjects response bias. They are two independent changing parameters in Psychophysics.When the Confidence Level of subjects = reporting is reduced, the apex of the normal distribution of

46、 = becomes lower, +/- intersecting point becomes higher(extreme value is the 50% point of 2-option comparison), leads to reduction of DT(extreme value is 0); In contrast, when the CL of = reporting is increased, = curve becomes higher, x-values of reaching 50% + and - reporting shift to the two side

47、s, i.e. increase of DT. Thus, in 3-option case, CL affects DT.Discussion: Are those Research Claims OK?22. One researcher planed to test a hypothesis that males are more creative than females. She further hypothesized that males advantage will increase when self is involved. A 2X2 factor design was

48、used, with gender as one factor and the degree of self-involvement (SI) as another. SI was manipulated by telling half participants that the task is an intelligence test and their scored will be posted in public (high SI), while telling another half that the test is about reliability and their perfo

49、rmance will be kept secret (low SI). The task used to measure creativity is unusual use test, in which each participant must list unusual use of an object (such as a hammer) as much as he/she can in 5 minutes. Each level of SI had 25 males from military training course and another 25 females from ho

50、usewifery training course. The objects used included a military compass and a spanner. The results demonstrated that the males average scores were 4.1 for low SI, 7.6 for high SI; the females average scores were 3.2 for low SI, 2.4 for high SI. Both main effect and interactions were statistically si

51、gnificant, thus provided support to her theory. Discussion: Are those Research Claims OK?23. A psychologist notices that residents living around the Chernobyl Nuclear Power Plant had more out-marriage sex after diagnosed with unknown disease. He interviewed some patients and detected excessive- and

52、other abnormal- sex behaviours among them. He then proposed a kind of mysterious love potion inside the nuclear precipitate and plan to use rats to test this hypothesis.Discussion: Are those Research Claims OK?24. A researcher proposed that Hippocampus is related with complex learning but not simple

53、 one. He randomly picked up 20 rats, dissected their Hippocampus, and allocated 10 rats to learn a simple maze and other 10 a complex maze. The first group used 10 trials to learn the maze while the second group 30 trials. Thus, the researcher concluded that rats without Hippocampus are more unable

54、to learn a complex task relative to a simple one.Modern theory in Psychophysics: Signal Detection Theory Modern theory in Psychophysics, such as SDT (Signal Detection Theory) has no concept of threshold, e.g. replacing the threshold concept with two other operationally defined concepts: d and . The

55、issue of signal detection in radar system.SDT:Perception is controlled by decision processes, which is influenced by both the evidence and response biases. For example, blind date “yes” marriage; same information but different costs and benefits combinations.Theoretic model of What happens in Signal

56、 Detection, Figure 6.3Modern theory in Psychophysics: Signal Detection Theory: Theoretic model Figure 6.3Modern theory in Psychophysics: Signal Detection Theory: Theoretic model Sensory analysis based Evidence values (are on the abscissa of Figure 6.4 and 6.5; are mental events rather than physical

57、energy!) are a function of signal strength and the acuity of the observer.Response bias comes from the payoffs, motivations, and attention processes. Together the sensory and bias components determine the response of the observer.Modern theory in Psychophysics: Signal Detection Theory: Theoretic mod

58、elSDT has two assumptions： Repeatedly presents same stimulus doesnt produce same sensation. Observers use subjective criteria to judge whether a sensation is due to signal or noise. This criteria fluctuates by factors such as pre-defined probability of SN and Response Rewards-Punishments.Different f

59、rom classical psychophysics, SDT can differentiate observers sensibility and judgment criteria.With the pre-defined probability of SN kept constant, Response Rewards-Punishments lead to different motivation levels and . If Rewards-Punishments encourage to say more signals, is slow; If to say less si

60、gnals is encouraged, is high.Signal Detection Theory: Basic principles SDT assumes background noise is always present when a human attempts to detect signals, due to environmental changes, equipment changes, spontaneous neural activity, and direct experimental manipulations. It is just either you have a pure n