Rationale for the new design¶

Studies of pain and placebo analgesia have historically used a wide variety of stimuli as laborotory analogues including electrical stimuli [2], cold water (i.e. a cold pressor; [3]), heat [4], iontophorensis [5], lasers [6], and pressure [7].

Pain stimuli for laborotory studies can be evaluated on a number of dimensions: the reliability of the stimuli (in the sense the same stimuli can be delivered consistently); validity of the stimuli, in the sense that it corresponds to real world pain experiences; repeatability, in the sense that multiple stimuli can be given in a single experiment; whether deception is possible — that is, whether participants can be convincingly misinformed about the stimuli to be delivered (this would, for exaple, allow placebo-conditioning studies to take place, e.g. [5]; and the expense and practicality of the techniques.

Stimuli	Reliablity	Validity	Repeatable	Deception	Blinding	Expense	Practical
Heat	Good	Good	Yes	Yes	Yes	High	Yes
Cold	Moderate	Good	No	No	No	Low	Yes
Iontophorensis	Yes	Poor	Yes	Yes	Yes	NA	NA
Electrical	Good	Poor	Yes	Yes	Yes	Med	Yes
Laser	Good	Poor	Yes	Yes	Yes	High	No
Focal pressure	Moderate	Good	Yes	No	No	Low	Yes

Focal pressure, applied to the skin over bone, is a method of evoking experimental pain of an ‘aching’ nature. The experienced sensation is relatively closely related to the pressure applied, and many studies of pain and placebo analgesia use pressure stimuli because they are cheap, practical, reliable and have reasonable ecological validity (see Table for a comparison of the different types of pain stimulator available). The FB device is used to apply pressure to the fingers via a lever [8], see figure. However, three important limitations of the original FB device (and related devices such as pressure algometers or myometers, e.g. [9]) are that

1. It is impossible to deceive pariticpants as to the true magnitude of the stimulus to be delivered, ruling out conditioning studies.

It is impossible to blind experimenters to the stimuli to be delivered (e.g. via computer control), and that
The reliability of pain measurements is limited by the resolution of pain self report scales.

The FAB is designed to resolve all three of these limitations.

A Forgione Barber device [8].