I've been working through some data from a student who is using PAL_AMUD() to run a simple 1-up 3-down staircase. We've noticed an unexpected behaviour in that the function appears to act like a '1-up 1-down' until after the first reversal.
In principle, this behaviour makes sense, since it means we move towards threshold more quickly early on in the experiment. However, we were just a little concerned as we didn't explicitly request this behaviour. There doesn't appear to be an option in PAL_AMUD_setupUD() to control this behaviour. This can be reproduced by initialising a staircase and recording a response as follows:
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StaircaseObject = PAL_AMUD_setupUD('up',1,'down',3);
StaircaseObject = PAL_AMUD_updateUD(StaircaseObject,1)
From the above, I would expect that you would have to respond '1' three times in a row in order for the procedure to suggest a different 'x' level. However, 'x' is changed after just one trial. I notice that if we have a single trial in which the response value is '0', i.e.:
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StaircaseObject = PAL_AMUD_updateUD(StaircaseObject,0)
...Then after this, we do start to get the expected behaviour, i.e. it takes three '1's in a row for x to change. My question is
have I interpreted this correctly, i.e. am I right in thinking that it's the first reversal that triggers the '3-down' aspect coming into play and
is there any way to control / turn off this behaviour in Palamedes?
As I said, it's not a problem and actually makes a lot of sense; I just wasn't expecting this behaviour without requesting it and can't see any way to change it.
