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I'm performing a study where subjects rate their perceived, subjective intensity of a stimulus presented to them at different magnitudes. To submit a rating, they click on on a logarithmic scale presented to them on a monitor, and that selected pixel value is used as the rating. They must rate several different stimuli, for roughly an hour. During pilot runs, subjects have told me that sometimes they change how they go about rating in the middle of a session. They arbitrarily find it easier to change the reference rating in their memory to something different from before, perhaps a more recent intense stimulus is used as the new reference.

Are there any traditional ways to compensate for this? My initial thought is to have the subject rate something in the training session, and then show them on every subsequent stimulus the location at which they rated that training stimulus.

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I don't understand where you're coming from. You are measuring the rating behaviour of your subjects. Their behaviour is not "flawed" and in need of compensation. For example, suppose you presented the very same temperature warm water bath for people to immerse their hand in every 2 min for an hour, and each time they give a temperature rating. You would find that the rating declines regularly as a function of elapsed time, and this is known as sensory adaptation. It is a real sensory phenomenon, it exists, and if you fail to find it, your expt is poor. Or are you trying to use humans as a thermometer? If so, I'd say fit a curve to the rating vs time data (power law maybe). Then you have an "isotherm", ie this curve defines how ratings behave for a fixed temperature stimulus.

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  • $\begingroup$ Yes it is like I am treating subjects as thermometers. The actual experiment involves presentation of different odors. which they smell and rate the strength at varying concentrations. They actually wait 30 seconds between trials to avoid sensory adaptation, and the stimulus is regulated in such a way that it is briefly experienced. The problem with a power law is that multiple odors are presented at varying concentrations in a randomized manner, so rating vs time is a little trickier. but i will look at the time trends for each odor yes $\endgroup$
    – user100100
    Feb 8, 2016 at 20:52
  • $\begingroup$ OK as I understand it, they rate how intense the odor is, and there is an objective characteristic that is varying, namely the chemical concentration. Is the following correct? To simplify, each odor has five concentrations, odorants are presented in random order, and on each trial subjects identify which odorant concentration was presented with a rating 1-5. $\endgroup$
    – stan
    Feb 9, 2016 at 11:33
  • $\begingroup$ They do not identify the odorant. They only rate their perceived intensity during the trial. Each trial exposes them to 1 odorant at a particular concentration. The way you wrote your simplification made it seem to me like the subject would identify the odorant, and THEN the concentration, whereas they only measure the perceived intensity they felt but without regard to the actual odorant in the trial. Sorry if I misinterpreted what you said. $\endgroup$
    – user100100
    Feb 9, 2016 at 14:11
  • $\begingroup$ Also their rating is pixel valued, so there is more room for variation than a discrete 1-5 scale $\endgroup$
    – user100100
    Feb 9, 2016 at 15:14

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