Dear Folks,
May I ask your advice about designing a new fMR experiment.
I envisage 4 trial types (a1, a2, b1, b2), each spaced by an ISI of 3 seconds.
Two of the trial types (a1, a2) would be performed in one response domain
(say auditory) and would be pseudorandomised in order in a block (A), and
similiarly b1 and b2 would be in the another domain (say visual) and
pseudorandomised in a block (B). Blocks A and B would be ordered with an
appropriate control block C in a pseudorandom or palindromic order.
My principal interest would be comparing blocks A and B against themselves
and against block C, and this I feel would constitute a valid 'cognitive
subtraction' for an epoch-based analysis.
However, since I hope to be able to guarantee timing exactly (ie. known
event SOAs) I would also be interested in trying to apply an event-related
analysis to the within-block trials. For this I suspect I am at risk of
low-statistical power, having fallen between the simplicity of an block
design and the more 'stochastic' ordering of events. Obviously by
pseudorandomising the trial order within blocks I hope to have derived some
statistical power. My questions are then -
1. The relative poor power notwithstanding, is this sort of within-block
event-related analysis feasible ?
2. Should I be weaving 'null' events pseudorandomly into my trial sequence
over and above the control blocks C as a baseline ?
Thanks you for your time and thoughts on these questions.
Best Wishes
Dominic
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Dominic J. Mort
Clinical Research Fellow to Professor C. Kennard
The Neuro-Ophthalmology Group
Department of Sensorimotor Systems
Division of Neuroscience and Psychological Medicine
Imperial College School of Medicine
10th floor East Wing
Charing Cross Campus
LONDON
W6 8RP
UK
Mobile : 0797 49 48 48 6
Direct Line : +44 20 8846 7505
Fax : +44 20 8846 7715
Email : [log in to unmask]
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