fixation durations only, not also fixation end times should be extended by duration of the fixation end sample

Author: dcnieho

functions/I2MC/getFixations.m

@@ -73,8 +73,8 @@
 end
 
 %% beginning and end of fixation must be real data, not interpolated.
-% If interpolated, those bit(s) at the edge(s) is excluded from the
-% fixation first throw out fixations that are all missing/interpolated
+% If interpolated, those bit(s) at the edge(s) are excluded from the
+% fixation. First throw out fixations that are all missing/interpolated
 for p=length(starttime):-1:1
     if all(missing(fixstart(p):fixend(p)))
         fixstart(p) = [];
@@ -95,22 +95,26 @@
     end
 end
 
-%% caluclate fixation duration
+%% calculate fixation duration
 % if you calculate fixation duration by means of time of last sample during
 % fixation minus time of first sample during fixation (our fixation markers
 % are inclusive), then you always underestimate fixation duration by one
 % sample because you're in practice counting to the beginning of the
 % sample, not the end of it. To solve this, as end time we need to take the
 % timestamp of the sample that is one past the last sample of the fixation.
-% so, first get new end time
-endtime     = timestamp(min(fixend+1,length(timestamp))); % make sure we don't run off the end of the data
-% if last fixation ends at end of data, we need to make up how long that
-% sample is and add that to the end time
+% so, first calculate fixation duration by simple timestamp subtraction.
+fixdur      = endtime-starttime;
+% then determine what duration of this last sample was
+extratime   = timestamp(min(fixend+1,length(timestamp)))-timestamp(fixend); % make sure we don't run off the end of the data
+% if last fixation ends at end of data, we need to determine how long that
+% sample is and add that to the end time. Here we simply guess it as the
+% duration of previous sample
 if ~isempty(fixend) && fixend(end)==length(timestamp)   % first check if there are fixations in the first place, or we'll index into non-existing data
-    endtime(end) = endtime(end) + diff(timestamp(end-1:end));
+    extratime(end) = diff(timestamp(end-1:end));
 end
-% now calculate fixation duration correctly.
-fixdur      = endtime-starttime;
+% now add the duration of the end sample to fixation durations, so we have
+% correct fixation durations
+fixdur      = fixdur+extratime;
 
 
 %% check if any fixations are too short