JiscMail Logo
Email discussion lists for the UK Education and Research communities

Help for SPM Archives


SPM Archives

SPM Archives


SPM@JISCMAIL.AC.UK


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Proportional Font

LISTSERV Archives

LISTSERV Archives

SPM Home

SPM Home

SPM  2000

SPM 2000

Options

Subscribe or Unsubscribe

Subscribe or Unsubscribe

Log In

Log In

Get Password

Get Password

Subject:

Re: setting hrf parameters

From:

Jesper Andersson <[log in to unmask]>

Reply-To:

[log in to unmask]

Date:

Tue, 5 Dec 2000 11:23:22 +0100

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (103 lines)

Dear Tanaka,


> Dear SPMers,
>
> I would like to know if my modification of hrf is suitable for our event
> fMRI study analysis.
> We did an event related study about sentence comprehension. Our concern is
> the relation between the word order in a sentence and cerebral activation.
>
> Event length was 30 seconds and TR=1.
> There were two conditions (two types sentences), A and B, in a random order,
> 12 events for each (then 24 x 30s). The total scan time was 720 second and
> the total scan was 720 (actually the total number of the scans was 725  and
> the first 5 scan was not used).
> The stimuli sentences were consist of 3 words (e.g., John kissed Mary)
> presented word by word. Each event was 30s and the first 10s was rest. At
> 11s, 12s and 13s, the first, the second and the third word was presented.
> Then, to test the subjects surely read the stimuli, a question sentence was
> presented at 15s and the subjects responded by button press (the response
> occured around17-18s). The rest of the event (from 18-19s to 30s) was also
> rest (a small fixation was presented).
>
> We would like to see the activation againt the first word. (type A sentence
> is more difficult than type B to understand because of its word order)
>
> All our concern is the cerebral activation occured 11, 12, 13s.
> Then I changed spf_hrf
> delay of undershoot   16 -> 7
> length of kernel         32 -> 12

I do not quite understand the rationale for changing the shape of the synthetic
HRF. These parameters would give you a slightly squashed (shortish) HRF without
appreciable undershoot. Do you have any data from these specific subjects to
support this particular HRF?

>
>
> At fMRI models and estimation, I selected all 720 scans.
> condition =2
> SOA = variable
> I set the vector onset for the two conditions as
> for condition 1:     11, 101, 131..., 701
> for condition 2:     41, 71, 161, ..., 671
> Those are the onset time of the first words presentation (at 11s).
>
> For 12s, vector onset was set as, 12, 102, 132, ..., 702,
> and For 13s, it was set as, 13, 103, 133, ..., 703 for condition1 and did
> the same way for condition 2.
>
> The result seems reasonable. But I am not sure if this process is correct or
> not.
> Is this way of analyzing is wrong? Or are there any better ways?
>

If I understand you correct your primary concern is the difference between
responses to words from sentence category 1 and sentence category 2. So for
example you are interested in w1c2 - w1c1 (w1 for word 1, and c2 and c1 for
categories 1 and 2).
I can see a slight problem with you design/analysis. For each of your "events"
you have effectively bursts of three events with a 1sec spacing, followed by
another (variable length) burst and finally a last event of a different kind.
Since the spacing within the bursts are shortish compared to the HRF you will
have a rather poor determination of the response to each type. So in you first
analysis above where you model only the variance from the first word there will
be a strong contribution from the subsequent two words (and your attempt to
"squash" the HRF doesn't really address this).
Strictly speaking, in order to look at the difference w1c2-w1c1 you would need
to include also the other words in your model, i.e. you would need to use at
least 8 conditions in your model, six for each of the words in each category
and two to try to capture the variance from the question. Ideally you would
need to model the question sentence word-by-word as well. Having done that you
could look at w1c2-w1c1 after all variance explicable by the other words had
been regressed out.
The problem with that is that there will be very little of it left and you will
be very insensitive.

I think your best bet would be to (possibly) model the three words as separate
conditions, but assessing the category difference with an F-contrast. I think
the easiest way to do that is to use three conditions to model all three words
in BOTH categories, and another three conditions to model them in one of the
categories (arbitray). Your F-contrast should then compare the model with and
without the second set.

However, that still leaves you with the problem of removing the variance caused
by the question. I don't really see a good solution for that (perhaps someone
else does). If you haven't performed the entire study yet I would suggest
redesigning it such that you put the question well away (>10sec) from the
presentation of the target sentence.

The above has assumed that your main interest is category differences. If your
main concern is word order within a sentence, I think that is a very tricky
question. You could try modelling event-by-time interaction within each little
three word burst, only it would look very much like a temporal derivative and
would therefor be very difficult to interpret. Also, for any sentence presented
at anywhere near a natural pace there will surely be non-linear interactions
between successive "events" (words), and these would be hard to disentangle
from "true" position differences.
I don't really have a suggestion. I would love to hear if anyone has any ideas
about how to model something like this.

Good luck Jesper

Top of Message | Previous Page | Permalink

JiscMail Tools


RSS Feeds and Sharing


Advanced Options


Archives

November 2019
October 2019
September 2019
August 2019
July 2019
June 2019
May 2019
April 2019
March 2019
February 2019
January 2019
December 2018
November 2018
October 2018
September 2018
August 2018
July 2018
June 2018
May 2018
April 2018
March 2018
February 2018
January 2018
December 2017
November 2017
October 2017
September 2017
August 2017
July 2017
June 2017
May 2017
April 2017
March 2017
February 2017
January 2017
December 2016
November 2016
October 2016
September 2016
August 2016
July 2016
June 2016
May 2016
April 2016
March 2016
February 2016
January 2016
December 2015
November 2015
October 2015
September 2015
August 2015
July 2015
June 2015
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
October 2014
September 2014
August 2014
July 2014
June 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
October 2013
September 2013
August 2013
July 2013
June 2013
May 2013
April 2013
March 2013
February 2013
January 2013
December 2012
November 2012
October 2012
September 2012
August 2012
July 2012
June 2012
May 2012
April 2012
March 2012
February 2012
January 2012
December 2011
November 2011
October 2011
September 2011
August 2011
July 2011
June 2011
May 2011
April 2011
March 2011
February 2011
January 2011
December 2010
November 2010
October 2010
September 2010
August 2010
July 2010
June 2010
May 2010
April 2010
March 2010
February 2010
January 2010
December 2009
November 2009
October 2009
September 2009
August 2009
July 2009
June 2009
May 2009
April 2009
March 2009
February 2009
January 2009
December 2008
November 2008
October 2008
September 2008
August 2008
July 2008
June 2008
May 2008
April 2008
March 2008
February 2008
January 2008
December 2007
November 2007
October 2007
September 2007
August 2007
July 2007
June 2007
May 2007
April 2007
March 2007
February 2007
January 2007
2006
2005
2004
2003
2002
2001
2000
1999
1998


JiscMail is a Jisc service.

View our service policies at https://www.jiscmail.ac.uk/policyandsecurity/ and Jisc's privacy policy at https://www.jisc.ac.uk/website/privacy-notice

Secured by F-Secure Anti-Virus CataList Email List Search Powered by the LISTSERV Email List Manager