Burkhart
Many thanks for your reply. Can I ask the following additional questions
1) How have you identified a fixation period? Do you think it would be
satisfactory to say that a fixation period is defined as a period of time
when the eye velocity is less than X deg/s where x is defined
2) We too are looking at intrusive saccades. Other workers have broken these
into square wave jerks and oscillation etc. At this moment we are not sub
classifying. In your work, what is the range of saccadic intrusions found
during fixation?
Many thanks again
Canice
-----Original Message-----
From: Eye-movement mailing list [mailto:[log in to unmask]]On
Behalf Of Burkhart Fischer
Sent: 15 October 2002 09:09
To: [log in to unmask]
Subject: Re: [EM_LIST] Ocular Fixation
Dear Canice
we have been looking at fixation stability both in terms of intrusive
saccades duing fixation of a stationary fixation point (simple fixation
instability)and in terms of slow drifts of the two eyes defined by the
non-zero relative velocity between the rigth and the left eye (binocular
fixation instability)
We have been using velocity and amplitude criteria for detecting saccades
that are within the range of the main sequence thereby eliminating most
artifacts. We have been using also velocity criteria to find
significant deviations of the relative velocity from zero.
We have been applied this analysis to the data of 72 control and 68
dyslexic children. We found that there exits a long lasting development of
both types of stability. The data of the two domains do not correlate.
Dyslexic children have poorer stability in both domains. Because of the
scatter in the data the estimate of the proportion of dyslexics involved is
about 25%.
Best regards
BFischer
--
Burkhart Fischer, Universitaet Freiburg, AG Hirnforschung
Hansastr. 9, 79104 Freiburg, Germany, Tel ++49 761 203 9535, Fax 9540
[log in to unmask] www.brain.uni-freiburg.de/fischer/
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