Not sure what your question is but what you say sounds correct. The
accumulation happens. So if you use accuracy coding and the correct
response in one condition is not constant (e.g. sometimes left, sometimes
> On Monday, September 10, 2012 11:21:20 AM UTC-4, Guido Biele wrote:
>> hi thomas,
>> glad that we are agree!
>> I never exclude that I am missing something ;-)
>> I'll think about something for the how to, but I first want to test a
>> few things, because I think that this issues is really not so trivial
>> cheers - guido
>> On Mon Sep 10 17:17:04 2012, Thomas Wiecki wrote:
>> > Hi Guido,
>> > On Mon, Sep 10, 2012 at 11:04 AM, Guido Biele
>> > <g.p....@psykologi.uio.no <mailto:g.p....@psykologi.**uio.no>> wrote:
>> > In your response you mention using a hybrid. I agree with the
>> > approach, even if I don't understand why you call it
>> > stimulus-coding, because 1 is always associated with the correct
>> > response, and not always with "left response" or always with
>> > "right response".*
>> > You are right, in fact it's accuracy (upper is correct) and stimulus
>> > (upper is left/right, depending on condition) coding simultaneously.
>> > More generally, when the data are from a task where correct and
>> > incorrect responses can be determined, I think one should always
>> > use accuracy coding, so that one can estimate the difficulty of a
>> > condition (or capability of a participant/group). I am not sure
>> > what the meaning of the drift rate would be if the data were
>> > stimulus/direction-coded.
>> > Agreed. I suppose I haven't thought too much about these issues
>> > because in our tasks there is no reason to assume a bias so I always
>> > use accuracy coding.
>> > It does seems as if the hybrid should always be preferred over pure
>> > stimulus coding so maybe a convenience function to recode the
>> > responses to be in accordance this would be handy. This might also be
>> > better described in the howto. Let me know if you want to give either
>> > of those a crack.
>> > Thomas
>> > Cheers - Guido
>> > *c.f. your documentation: "There are two ways you can code subject
>> > responses (these are the values you put in the ‘response’ column
>> > in your data file). You can either use accuracy-coding where 1
>> > means correct and 0 means error, or you can use direction-coding
>> > [GB: which i understand meaning the same as stimulus-coded] where
>> > 1 means left and 0 means right ..."
>> > On Mon Sep 10 15:23:34 2012, Thomas Wiecki wrote:
>> >> Hi,
>> >> I couldn't find those passages:
>> >> From White: "position of starting point relative to the
>> >> boundaries (values
>> >> above .5 indicate bias to respond ‘‘word’’ and values below .5
>> >> indicate bias to respond ‘‘nonword""
>> >> From McKoon where they introduce response bias in exp 3: "Because
>> >> the
>> >> proportions of the two stimuli tested for the high- versus
>> >> low-probability stimuli produced an asymmetry between re- sponses
>> >> accuracy of the two responses and also RTs for correct responses
>> >> error responses, they were not combined as they were for
>> >> experiments 1
>> >> and 2."
>> >> You could use a hybrid (I think they do this in the last
>> >> where they have 2 conditions: left correct, right correct (i.e.
>> >> stimulus coding)).
>> >> In left correct you could code left to represent the upper
>> >> (i.e. 1) and in right correct you could code right to represent
>> >> upper boundary. This way upper boundary would always be correct
>> >> you are still using stimulus coding. That way positive drift would
>> >> always mean >50% accuracy.
>> >> I think it is helpful to think about this in terms of which
>> >> you want to mean what and that bias is relative to those
>> >> HDDM just estimates whatever you present it with.
>> >> Thomas
>> >> On Mon, Sep 10, 2012 at 8:49 AM, Guido Biele
>> >> <g.p....@psykologi.uio.no <mailto:g.p....@psykologi.**uio.no>
>> >> <mailto:g.p....@psykologi.**uio.no>
>> >> <mailto:g.p....@psykologi.**uio.no>> wrote:
>> >> Hi,
>> >> first thanks for publishing a new, improved version oh hddm!
>> >> the hddm manual suggests that one should not accuracy-code ata
>> >> when estimating a response bias.
>> >> diverging from this recommendation, I just stumbled about 2 papers
>> >> by ratcliff and colleagues, who do exactly this.*
>> >> is the recommendation (to not accuracy code for experiments with a
>> >> response bias) due to a reason that has to do specifically with
>> >> Ratcliff and McKoon (2008) examine if prior probability influences
>> >> the starting point or the drift rate. to test the effect on drift
>> >> rate, they seem to decompose the total drift rate into 2
>> >> components, one due to stimulus quality and one due to prior
>> >> probability.
>> >> Is this kind of analysis possible in the new version of hddm?
>> >> (I am happy to do some additional coding myself if this is
>> >> required to get this working)
>> >> Cheers - guido
>> >> * see
>> >> (a) White, C. N., Ratcliff, R., Vasey, M. W., & McKoon, G.
>> >> (2010). Using diffusion models to understand clinical disorders.
>> >> /Journal of Mathematical Psychology/, /54/(1), 39–52.
>> >> page 42, section 4.1
>> >> (b) Ratcliff, R., & McKoon, G. (2008). The diffusion decision
>> >> model: theory and data for two-choice decision tasks. /Neural
>> >> Computation/, /20/(4), 873–922. doi:10.1162/neco.2008.12-06-**420
>> >> page 897, section 4.3
>> > --
>> > ------------------------------**------------------------------**----------- -
>> > Guido Biele
>> > Email:g...@psykologi.uio.**no <mailto:g.p....@psykologi.**uio.no>
>> > Phone:+47 228 45172 <tel:%2B47%20228%2045172>
>> > Website <https://sites.google.com/a/**
>> > Visiting Address
>> > Psykologisk Institutt
>> > Forskningsveien 3 A
>> > 0373 OSLO
>> > Mailing Address
>> > Psykologisk Institutt
>> > Postboks 1094
>> > Blindern 0317 OSLO
>> ------------------------------**------------------------------**----------- -
>> Guido Biele
>> Email: g.p....@psykologi.uio.no
>> Phone: +47 228 45172
>> Website <https://sites.google.com/a/**neuro-cognition.org/guido/home<https://sites.google.com/a/neuro-cognition.org/guido/home>
>> Visiting Address
>> Psykologisk Institutt
>> Forskningsveien 3 A
>> 0373 OSLO
>> Mailing Address
>> Psykologisk Institutt
>> Postboks 1094
>> Blindern 0317 OSLO