Usual settings for the transformed up-down procedure

[Massimo Grassi <massimo.grassi@xxxxxxxx>]

Dear list members (and transformed up-down user in particular),

we are extending our MLP software 
(http://www.psy.unipd.it/~grassi/mlp.html) to the transformed up-down 
adaptive procedure so the user of our software can decide to run a given 
threshold-experiment with either the maximum likelihood procedure or the 
transformed up-down (wow! what a fun!).

We are now working on the software and facing the first problem: what 
are the "traditional" settings for the transformed up-down?
In brief:
- how many "downs"?
- how many reversals before stopping the procedure?
- how many reversal with a small step-size and how many with a large one?
- how many step-sizes?
- what's the (is there any) "usual" ratio between small and large step-size?
- how to calculate the subject's threshold?

Here the traditional rules base on my own reading:
- Number of "downs". I found only studies using the 2(or 3)-down 1-up. 
No study using the 4-down (or higher) 1-up rule. Furthermore, no study 
using the 1-down, 2/3/4...-up.

- Reversals and step-size. So far I found that people tend to use two 
step sizes only (e.g., factor 2 and factor 2^(1/2), i.e., sqrt(2)) and 
to run 4 reversals with the large step size and 8 (or 12) reversals with 
the small step size.

- For the threshold calculation I found that it is usually calculated on 
the last 8 (or 12) reversals points of a given block. Moreover, I found 
that people calculate indifferently arithmetic, geometric mean or median.

I'm particularly interested in exceptions to the "traditional rules" I 
found: we want to include these exceptions to our software.

Thank you in advance for the help you can provide,
m