hmmm...i think it depends on whether the two ends of the bow-tie are ever in the same hemifield simultaneously, which would lead to ambiguity in the mapping of stimulus phase. scott slotnick had a paper on this a few years back...
in principle the bow-tie stimulus for mapping polar angle is more efficient and works well if the subjects fixate well and if you are interested in visual areas with relatively small receptive fields and purely contralateral responses.
i believe that you can use a phase encoded analysis since the stimulus is still periodic---as long as it was designed without this phase ambiguity. you just need to specify the correct number of cycles, which is a count of the number of times either end of the bow-tie crosses a point in the visual field in each run.
do you also have a stimulus for mapping eccentricity? if not doug recently posted a way to analyze only one of the two maps with the retinotopy analysis routines by making a copy of the acquired data to substitute in for the expected data, so you can calculate the polar angle maps alone.
-jon
On Mon, 2 Apr 2012, Douglas N Greve wrote:
I'm not sure. So the stimulus uses a bow tie instead of a wedge? Maybe Jon has an idea.
On 04/01/2012 02:22 PM, Kiley Seymour wrote:
Dear freesurfers,
I am wondering whether there is a simple way of analysing retinotopy data that was collected using a rotating bow-tie stimulus? Or should I somehow artificially segment the cycle into different visual field poition conditions and run a glm analysis? I just realised I have made a mistake by using this kind of stimulus. :(
Thanks in advance.
Kiley
p.s. Thanks for all the previous help. It has been great.
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