tailieunhanh - Detection Power, Estimation Efficiency, and Predictability in Event-Related fMRI

Once you’ve narrowed down the time of year you’ll need to find out what other events are planned around the same time. As well as walking events you should consider other things that may compete for the same audience. In an ideal world you should pick a date that doesn’t clash with any significant competitor. Look for other organisations’ actual or likely dates on the internet, in forward planning publications and back issues of listings magazines (large public reference libraries are a good source of back issues of publications and of forward planning directories like The Year Ahead). Always check. | NeuroImage 13 759-773 2001 doi available online at http on IDEJkl Detection Power Estimation Efficiency and Predictability in Event-Reiated fMRI Thomas T. Liu Lawrence R. Frank t Eric C. Wong and Richard B. Buxton Department of Radiology and Department of Psychiatry University of California San Diego La Jolla California 92037 and Veterans Administration San Diego Healthcare System La Jolla California 92037 Received September 18 2000 published online February 16 2001 Experimental designs for event-related functional magnetic resonance imaging can be characterized by both their detection power a measure of the ability to detect an activation and their estimation ef ciency a measure of the ability to estimate the shape of the hemodynamic response. Randomized designs offer maximum estimation ef ciency but poor detection power while block designs offer good detection power at the cost of minimum estimation ef ciency. Periodic single-trial designs are poor by both criteria. We present here a theoretical model of the relation between estimation ef ciency and detection power and show that the observed trade-off between ef ciency and power is fundamental. Using the model we explore the properties of semirandom designs that offer intermediate trade-offs between ef ciency and power. These designs can simultaneously achieve the estimation ef ciency of randomized designs and the detection power of block designs at the cost of increasing the length of an experiment by less than a factor of 2. Experimental designs can also be characterized by their predictability a measure of the ability to circumvent confounds such as habituation and anticipation. We examine the relation between detection power estimation ef ciency and predictability and show that small increases in predictability can offer signi cant gains in detection power with only a minor decrease in estimation ef ciency. 2001 Academic Press INTRODUCTION Event-related experimental

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