-----Oorspronkelijk bericht-----
Van: Veltman, D.J.
Verzonden: maandag 8 februari 1999 15:16
Aan: 'Arturo Hernandez'
Onderwerp: RE: masking vs. conjunctions
-----Oorspronkelijk bericht-----
Van: Arturo Hernandez [SMTP:[log in to unmask]]
<mailto:[SMTP:[log in to unmask]]>
Verzonden: maandag 8 februari 1999 1:58
Aan: [log in to unmask] <mailto:[log in to unmask]>
Onderwerp: masking vs. conjunctions
I am trying to understand exactly what the difference between
masking and
conjunctions is. If I have two contrasts (F1 vs. Rest), (F2 vs.
Rest) what
is the difference between the conjunction of these two contrasts and
F1
masked by F2.
Thanks,
Arturo E. Hernandez, Ph.D.
Department of Psychology
University of California
Santa Barbara, Ca. 93106-9660
Phone (805) 893-7978
Fax (805) 893-4303
e-mail: [log in to unmask] <mailto:[log in to unmask]>
http://www.psych.ucsb.edu/fac/hernande.htm--Arturo
<http://www.psych.ucsb.edu/fac/hernande.htm--Arturo>
Dear Arturo,
The conjunction F1 + F2 will give you the activations common for the
two main effects, with voxels showing a significant interaction (at either p
< .05, .01 or .001, the first being most strict) removed. F1 masked with F2
shows activations which are present in F1 but not (or at least smaller) in
F2, at a user-specified threshold. In a recent discussion (C.Price, Dec.
18th) it was suggested to combine a conjunction analysis with masking,
because the conjunction may yield voxels which show a significant effect for
(say) F1 but not F2.
Regards
Dick Veltman
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