09-03-2020, 08:21 AM
When generating reports with Data Viewer, the time-base of variables that represent the timing of gaze events (e.g. CURRENT_FIX_START, CURRENT_FIX_END, CURRENT_SAC_START_CURRENT_SAC_END) are specified with respect to the number of milliseconds since the trial recording began. Conversely, the TRIAL_START_TIME variable itself and other time-boundary variables (e.g. IP_START_TIME, IP_END_TIME) are specified with respect to EDF time. This is the number of milliseconds since the Host PC software was launched.
It is sometimes useful to derive the timing of these gaze events relative to the onset of a particular target screen / stimulus onset. Since the timing of target screens (stimulus presentations) are typically represented in Data Viewer by means of Interest Periods, to derive relative timing between gaze events with respect to an Interest Period we must establish a common-time base for two variables. The easiest way to do this is to use a spreadsheet editor, like Excel, and to export your gaze data variables, as well as the IP_START_TIME and TRIAL_START_TIME.
For example, to generate a fixation report that specifies the onset time of fixations as the time after the start of an Interest Period, create a new column in the spreadsheet editor, and enter a formula that combines the available variables, as follow:
The explanation is that (IP_START_TIME – TRIAL_START_TIME) will derive the start of the Interest Period relative to the start of the trial. Then, it is easy to subtract this value from the start time of the gaze event, CURRENT_FIX_START, to find the relative onset of the fixation from the start of the Interest Period.
It is sometimes useful to derive the timing of these gaze events relative to the onset of a particular target screen / stimulus onset. Since the timing of target screens (stimulus presentations) are typically represented in Data Viewer by means of Interest Periods, to derive relative timing between gaze events with respect to an Interest Period we must establish a common-time base for two variables. The easiest way to do this is to use a spreadsheet editor, like Excel, and to export your gaze data variables, as well as the IP_START_TIME and TRIAL_START_TIME.
For example, to generate a fixation report that specifies the onset time of fixations as the time after the start of an Interest Period, create a new column in the spreadsheet editor, and enter a formula that combines the available variables, as follow:
Code:
CURRENT_FIX_START – (IP_START_TIME – TRIAL_START_TIME)The explanation is that (IP_START_TIME – TRIAL_START_TIME) will derive the start of the Interest Period relative to the start of the trial. Then, it is easy to subtract this value from the start time of the gaze event, CURRENT_FIX_START, to find the relative onset of the fixation from the start of the Interest Period.