Computation of gaze duration and amplitude in pro and antisaccade data


Jyoti Nath


February 18, 2023

In this post, I will present the computation of gaze duration and gaze amplitude in pro and antisaccade data.

Figure: Prosaccade eye movement recordings highlighting different fixation events between S1 end and S2 begin

Gaze duration depicts the movement of the eye away from Target A (Centre) and fixation on Target B (Peripheral). In doing so, eyes make a number of adjustments or fixations.

Figure shows the number of fixations between S1 end to S2 begin. For example, the top trial shows two fixations while the bottom trial shows three fixations between S1 end to S2 begin.

We first compare \(gavx\) i.e. \((average ~ gaze \times position)\) of consecutive fixations.

For our dataset, we set the defualt \(gavx\) threshold as \(10\).

We then check the following two conditions:

\[\large abs(gavx ~ Fix1 - gavx ~ Fix2) <10\] If this condition is true, then we add durations of consecutive fixations (i.e. \(Fix1\) and \(Fix2\)).

Similarly, we check for other consecutive fixations and select the longest fixation as the \(gaze ~ duration\).

Gaze duration is adjusted for peripheral target B duration.

\[Gaze ~ Duration ~ = ~ \frac {Duration ~ of ~ the ~ longest ~ fixation ~ between ~ S1 ~ end ~ to ~ S2 ~ begin} {Peripheral ~ target ~ B ~ duration}\]

We also record the \(mean(gavx)\) of the longest fixation and calculate \(gaze ~ amplitude\) as:

\[\large \frac{abs(mean(gavx) ~–~ centre ~ target ~ A ~ position)} {abs(peripheral ~ target ~ B ~ position ~–~ centre ~ target ~ A ~ position)}\]