[Homer-users] GLM Beta

[Yucel, Meryem A.]

Hi Ajivit,

When you use Gaussian, GLM models the HRF with a consecutive sequence of Gaussian functions with a typical width of 0.5 s, on the other hand, when you choose gamma, GLM will model the HRF with a fixed shape (a gamma function). For the former, the number of beta will depend on the number of Gaussian functions fitted within the time range of HRF. Which one to choose is up to you. The former is a flexible model and will allow you to see the temporal characteristics of HRF at every channel/condition whereas the second would fit a similar shape to each but vary the magnitude.

Hope this helps.

Meryem

From: homer-users-bounces at nmr.mgh.harvard.edu [mailto:homer-users-bounces at nmr.mgh.harvard.edu] On Behalf Of Avijit chowdhury
Sent: Thursday, April 26, 2018 2:51 AM
To: homer-users at nmr.mgh.harvard.edu
Subject: Re: [Homer-users] GLM Beta


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OK, So I looked into it and it seems the reason I am getting 4 rows of betas is because I am using a Gaussian temporal basis function and not a Gamma (which gives only one row of beta). Any idea why this is so? And which one should I use?
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