[R] psychometric functions

[Doran, Harold]

I am pretty certain a function for this model does not exist. Jan
Deleeuw or Dimitris Rizopolous may suggest otherwise. There is a package
for a model that would allow for the lower asymptote of the function to
be > 0; it does not however, allow the upper asymptote to vary from 1
(well, it tends to 1) and this is in the ltm package. 


> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Mario Maiworm
> Sent: Thursday, August 21, 2008 7:05 AM
> To: r-help at r-project.org
> Subject: [R] psychometric functions
> 
> Hi,
> I want to fit some psychophysical data with cumulative 
> gaussians. There is quite a convenient toolbox for matlab 
> called 'psignifit' (formerly known as 'psychofit'). It allows 
> the lower bound of the sigmoid to vary slightly from zero, 
> aswell as the upper bound to vary from one. with these two 
> free parameters, the fitted function is less sensitive to 
> noisy data and outliers.
> Apart from advertising this toolbox I want to ask for 
> possibilities in R to fit psychometric functions, as I would 
> rather use R than matlab. Is there a comparable package 
> specific for psychophysics in R? otherwise: which function 
> would be a good choice? Can I have functionality equal to 
> 'psignifit' with glm() from MASS. I would be grateful for 
> some suggestions of people who have experience in 
> sigmoid-fitting in R.
> Best,
> Mario.
> 
> 
> __________________________________________________________________
> 
> Mario Maiworm
> Biological Psychology and Neuropsychology University of 
> Hamburg Von-Melle-Park 11
> D-20146 Hamburg
> 
> Phone: +49 40 42838 8265
> Fax: +49 40 42838 6591
> 
> http://bpn.uni-hamburg.de/Maiworm_e.html
> http://cinacs.org
> 
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