Production, reproduction, and verbal estimation of duration. John Wearden Keele University U.K.

Transcription

1 Production, reproduction, and verbal estimation of duration John Wearden Keele University U.K.

2 In this talk I want to illustrate the use of the techniques of production, reproduction, and verbal estimation I want to discuss different ways of doing all 3 tasks, mention some studies in which they ve been used, and try to draw some conclusions about what s been learned using them

3 All three methods..have been (a) common in time perception studies, (b) used since almost the earliest days of the study of time perception in the 19 th. Century Strangely, none of the methods has received much theoretical treatment, although a number of proto-models of these tasks exist

4 Wearden and McShane (1988) Obviously, this wasn t the first study of interval production, but it s a study which turned out to be quite important in the development of modern time perception People produced intervals of 0.5, 0.7, 0.9, 1.1, and 1.3 s (values chosen to be too short to make counting useful).

5 Methods A start-stop timer was used (!) The person started the interval with one button and stopped it with another They were given immediate accurate feedback as to the time produced The different target intervals were presented in blocks of 12 of the same interval, and data came from trials blocks were given at each target interval The total experimental time was around 30 minutes

6 Mean and sd of times produced

7 Relative frequencies of times produced: note the scalar-type timing

8 Statistics from the times produced

9 Comments The study demonstrated good conformity to scalar timing in humans when counting was not used Very orderly data, orderly even at the level of individuals, were obtained very quickly The experiment was actually done for a completely different purpose from the one discussed in the published article..

10 Feedback Obviously, providing feedback rapidly produces average times produced which are close to the target Another example comes from Wearden, Wearden, and Rabbitt (1997) Here, people from the age of 60-69, and were compared IQ and age were orthogonal in this study, so data could be analyzed in terms of age (with IQ constant) or IQ (with age constant)

11 Production of 1 second: means

12 Production of 1 second: coefficient of variation

13 Comments Feedback reduces between-group differences in mean (to near zero), and the effect of feedback persists Coefficients of variation showed IQ effects even when mean effects disappeared Possible interpretation: clock speed differences?

14 Production by waiting In some cases you might want to control the start of the production, for example, so you can present something before, for a set period of time Penton-Voak et al looked at the effect of click trains on production, as part of their speeding up the clock studies Obviously, you have to control the start time here

15 continued They developed a production by waiting method People were told which interval to produce, and the production was started by a beep They then had to wait for the specified time and press once In different conditions feedback was or wasn t presented

16 From Penton-Voak et al. 1996

17 Reproduction Here, people are given some time interval, usually in the form of a stimulus that lasts for some target time Then they have to reproduce the target duration, by making a response There are various ways of doing this Vierordt (1868) used reproduction extensively, here are some of the data he obtained

18 Data from Vierordt (1868)

19 Method The target interval was presented in the form of 2 taps on a glass plate, then the participant had to make a single tap to make the interval between the second tap and the response the same as between the first two taps This is very similar to the ready set go method used in recent studies

20 Jayazeri and Shadlen: Experimental procedure

21 Other methods A common method these days is to present a target stimulus, then have a short gap, then present the stimulus again. The task is to turn the second stimulus off to make it the same length as the first Some examples like this are available in the workshop Obviously, the length of the target can be varied, as can the gap between the target and the start of the reproduction

22 Sometimes..particularly when durations are longer, as in some retrospective timing studies, people are told to do something like hold down a button for the same length of time as some previous event has lasted Here, the target stimulus isn t re-presented There are other more complex reproduction variants as well, such as a human peakinterval procedure of Rakitin et al.

23 Vierordt s Law When people reproduce a range of intervals, it s very common (albeit not always found) for data to conform to Vierordt s Law The shorter intervals tend to be reproduced as longer than they really are, whereas the longer ones are reproduced a shorter, and somewhere in the middle there s an indifference point where the reproduction is veridical

24 Indifference points from Vierordt 1868 Percentage error of reproduction session 1 session 2 session 3 session Mean target time (seconds)

25 Vierordt s Law, again Why Vierordt s Law is obeyed is an interesting but tricky question, beyond the scope of this talk Most theorizing suggests that it s based on some sort of relative judgement of an interval compared with (a) the previous interval, or (b) the mean of all the intervals Sometimes the indifference point is close to the mean, as in the example at the top of the next slide

26 From Lejeune and Wearden (2009)

27 However. Vierordt s Law can sometimes be found if people make repeated judgements of a single interval, or even judge just a single interval once, as in the next slide

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29 Motor factors A problem with both production and reproduction is that measured responses are contaminated, to an unknown degree, by motor factors, so the response measure taken is some (as yet unknown) combination of timing and motor processes Surprisingly, this hasn t bothered people all that much, perhaps because motor factors may make little difference at long intervals

30 However..in an article in 2003, I produced a crude reproduction model in which motor factors play a role

31 Reproduction model The basic idea is that the participant s representation of the target, t, is on average accurate The participant initiates a response at some time which is close enough to the target (e.g. 70% of it, in general at ct), but the response takes some absolute time, d, to generate So the total reproduction time is ct + d If c =.7 and d = 300 ms, then a t of 500 ms will be reproduced as 650 ms, but a t of 1000 ms will be reproduced accurately, and a t of 2000 ms reproduced as 1700 ms

32 continued With reasonable values for c and d, the model predicts indifference points at the lower part of the range found by Vierordt, but has difficulty with much longer values The indifference point, of course, has no special significance here, but the later typical value of 0.75 s is compatible with reasonable c and d values, so perhaps it comes from a combination of decision threshold (c) and response time (d) which haven t changed much since the 19 th. Century

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34 However. this model deals with the effect of motor factors on the mean time reproduced, but doesn t take account of the potential contribution of motor factors to variance Droit-Volet (2010) explicitly looked at relations between reaction time means and reproduction performance mean and variability in children and adults

35 Some details She used children of 5 and 8, and adults The target reproduction times were 2.5 and 4.5 s There was also a simple RT task (as well as some other tests) The next slides show what relative mean and the coefficient of variation of the reproductions

36 Reproduction means

37 Reproduction cvs

38 Both of these were correlated with RT

39 In addition..she used my 2003 model to fit data

40 Parameter values from modelling

41 Comments Timing variance was higher in the younger children Response times were longer, and more variable

42 Verbal estimation Here, people are asked to estimate durations using conventional time units, milliseconds, seconds, minutes and so on Advantages: a wide range of intervals can be judged, with a large ratio available even in the non-counting-based range (up to around 1.2 seconds); no contamination by motor factors Disadvantages: wild estimates, quantization [you ll hear more about this later]

43 Avoiding wild estimates People can sometimes give extremely strange estimates of duration, and this contaminates group means One way of avoiding this is to give the allowed range before the experiment starts Suppose the scale was 1000 = 1 second, then you might say All values are between 50 and 1500 on this scale. Then you filter out any values outside the range

44 Auditory and visual stimuli The next slide shows estimates of the duration of short auditory and visual stimuli, with data from Wearden et al., 1998 The same people judged both auditory and visual stimuli randomly mixed up

45 Wearden et al. 1998

46 Auditory and visual again Wearden et al also found the auditory/visual difference with verbal estimation even in a between-group study, where people received either visual or auditory stimuli, but not both The effect seemed the same size as when they received both Possibly some extra-experimental standard is being used

47 Wearden et al., 2006

48 Older people Older people and PD patients can also do verbal estimation without much problem, although young children obviously can t

49 Wearden et al. 2008

50 Sensitivity Verbal estimation is sensitive to small duration differences, at least on average The next slide shows data from the click trains manipulation of Penton-Voak et al and the one after a replication of this effect from Wearden et al. 1998

51 Penton-Voak et al., 1996

52 Wearden et al., 1998

53 Filled and unfilled intervals People can also estimate the duration of unfilled intervals, e.g. those started and ended with brief clicks The next slides shows an example of the filled-interval illusion from Wearden et al. 2007

54 Data from Wearden et al. 2007

55 Long intervals Very long durations can be verbally estimated: in fact it s about the only method when intervals are long The next slide shows data from Vierordt himself, taken from his 1868 book

56 Data from Vierordt (1868)

57 Feedback and calibration In many studies with verbal estimation methods, no feedback or calibration is given Obviously, you can t present a stimulus lasting t seconds, give feedback, then present it again! People often say that they d be helped with some sort of feedback or examples Wearden and Farrara (2007) tested this

58 Experiment 1 People received a series of durations to estimate, and received accurate feedback after half of them The other half were the targets that were repeated One group got feedback after half the stimuli, the other got the same stimuli with no feedback

59 Wearden and Farrar (2007)

60 Comment Rather surprisingly, the mean estimates from the two groups weren t different In a second study, Wearden and Farrar presented 2 stimuli on each trial. People had to estimate the second one, but they were told what the value of the first one was, so this could be used for calibration. Another group got the same stimuli without knowing what the value of the first one was

61 Wearden and Farrar (2007)

62 Comment Once again, the calibration operation didn t have dramatic effects However, it did have some subtle effects: you ll have to read the paper for details Why doesn t feedback and calibration have much of an effect?

63 Possible answer I may be that people are using some sort of extra-experimental standard (e.g. a second feels like this ), so are resistant to attempts to change estimates This may also explain the auditory/visual effect obtained in Wearden et al. 2006

64 Verbal estimation. seems like a nice method, so what s the problem? The problem is quantization People don t use any value from a range, but instead tend to use round numbers So no-one says that a stimulus lasts 473 ms, even if it does, they say 500, 400, etc.

65 So what? The existence of quantization means that although mean estimates might reliably reflect underlying processes, measures of variability are highly contaminated by quantization, so can t really be used [.even though I ve used them myself in published papers.]

66 Can quantization be avoided? There are a number of possibilities, not yet tested One is to give people potential values and get them to choose one. This doesn t avoid quantization, but at least it s partially controlled Another is to use an analogue scale between two anchor values and get people to use this

67 Conclusions The three classic methods of obtaining data in time perception studies can all produce orderly data quickly Production and reproduction involve motor factors, verbal estimation has the problem of quantization In the workshop you ll see some more practical questions relating to how experiments using these methods are carried out