hi anders,
the optimal set of stimulus parameters will depend somewhat on what
cortical area(s) you are trying to map and on the details of your
acquisition. in general, stimulating with both clockwise- and
counterclockwise-rotating wedges for polar angle mapping and with both
expanding and contracting rings for eccentricity mapping improves the
accuracy of the maps, and the proper analysis of this data is implemented
fsfast. the width of the wedge or the ring will depend on the cortical
area you are trying to stimulate, but you may want to consider a thinner
wedge. also, 8 Hz flickering has been shown to activate area V1 more
strongly than other frequencies, and smoothly moving stimuli can also
help. then, depending on your voxel size, field strength, coil array,
etc., you could include more cycles and may need to average together
multiple runs.
marty, roger et al. have a few nice papers that i'd recommend that discuss
some of these details relating to phase-encoded retinotopic stimuli.
Sereno & Tootell. Curr Opin Neurobiol. 2005;15(2):135-44.
Tootell et al. J Neurosci. 1997;17(18):7060-78.
Sereno et al. Science. 1995;268(5212):889-93.
(the '97 paper discusses the ring/wedge thickness, the '95 paper discusses
the advantages of using both expanding + contracting stimuli, and the '05
paper discusses the use of smoothly varying stimuli.)
hope this helps. were you able to get reasonable looking maps with the
stimuli you described below?
-jon
On Thu, 7 Jul 2011, Anders Hougaard wrote:
> Dear freesurfers,
>
>
> Which stimuli do you think provide the best retinotopic maps?
>
> I have done a retinotopy analysis using the following stimuli:
>
> Polar angle:
>
> - 45 deg counter-clockwise rotating wedge
> - 8 unique positions
> - flickering at 2 Hz
> - stimulation period: 36 sec
> - no. of cycles: 6
> - TR = 3
>
> Eccentricity:
>
> - expanding ring
> - 8 unique positions
> - flickering at 2 Hz
> - stimulation period: 36 sec
> - no. of cycles: 6
> - TR = 3
>
> Any suggestions on how to optimize this stimulation?
> E.g. different period length, more runs, bi-directional, different TR
>
> Thank you!
>
> Best regards,
>
> Anders
>
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