In this post, I will discuss the computation of saccade proportion and selection of latency saccades in pro and antisaccade data.
Figure shows selection of S1 and S2 latency saccades. The top prosaccade recording highlights microsaccades, S1, S2 latency saccades. The bottom antisaccade recording shows two S1A, S1B and S2 latency saccades.
Saccade proportion
For our data, we set the \(average ~ velocity ~ threshold\) of \(50^{\circ}/s\) to reject microsaccades i.e. \(avel < 50^{\circ}/s\).
Saccade proportion gives the proportion of longer saccades after rejecting the microsaccades in the trial (from the centre target A beginning to the centre target C end).
Hence, \(saccade ~ proportion\) is given by:
\[\frac {Saccade ~ count ~ with ~ avel > 50} {Total ~ number ~ of ~ saccades ~ in ~ a ~ trial}\]
S1, S2 latency saccade selection
Default threshold is set as \(avel > 50^{\circ}/s\)
Prosaccade
S1 latency saccade selection is based on the first saccade which has \(avel > 50^{\circ}/s\) after the start of the peripheral target B.
S2 latency saccade selection is based on the first saccade which has \(avel > 50^{\circ}/s\) after (centre target C begin - 100ms).
Antisaccade
S1A and S1B are first two consecutive saccades selected based on \(avel > 50^{\circ}/s\) after the start of the peripheral target B.
S2 latency saccade is selected based on the amplitudes of first two saccades that appears after centre target C beginning; the longest saccade is taken as S2 latency saccade.
Prosaccade: S2 Latency Error
In prosaccade, S2 latency saccade is selected after \((centre ~ target ~ C ~ begin ~ - ~ 100ms)\)
Default 100ms interval is set to pick up S2 latency error.
\[If ~ (S2 ~ saccade ~ start ~ time ~ – ~ peripheral ~ target ~ B ~ end) > 0: ~ S2 ~ latency ~ error ~ = ~ 0\]
\[Else: ~ S2 ~ latency ~ error ~ = ~ 1\]