FAQ: The analog signal from my Host PC is inverted. How do I correct this?

[Sam]

You can invert the analog output signal for the X and Y gaze data. This is done by flipping the minimum and maximum values in the range parameters.

The direction of the analog signal is controlled by the analog_x_range and analog_y_range parameters. By default, the range is set from a lower value to a higher value. To invert the signal, you simply reverse this order.

For example, the default setting for the Y-axis is:

Code:

analog_y_range = GAZE, -0.2, 1.2

To invert this, you would flip the last two values:

Code:

analog_y_range = GAZE, 1.2, -0.2

How to Apply the Changes
You can change these settings using one of two methods:

• Method 1: Edit the FINAL.INI File (Permanent Change)
  This is the recommended method for a permanent change. You will add the inverted commands to the FINAL.INI file on the Host PC*.
  
  Add the following code to the FINAL.INI file, making sure to flip the last two values for the axis you want to invert:
  
  Code:

  ;; DATA -> DAC VALUE DEFINITION:
;; Is set independently for each data type and mode
;; For X and Y, the min and max percentage of total data range
;; that corresponds to the DAC range is specified.
;; For example, (0.0, 1.0) would use the whole range,
;;              (0.1, 0.9) would magnify the center 80% of the data range,
;;              (-0.2, 1.2) would allow 20% over/under range data
;; each time specified, saves values for current setting
;; of pupil_size_diameter and analog_out_data_type
analog_x_range = GAZE, -0.2, 1.2  // allow for +/-20% outside display
analog_y_range = GAZE, -0.2, 1.2
  
  
• Method 2: Send Commands from Your Script (Temporary Change)
  You can also send these same commands directly from your experimental script. This change will only apply for the duration of that experiment. The exact syntax for sending the commands will depend on your programming environment (e.g., Experiment Builder, E-Prime, PsychoPy).
  

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*The FINAL.INI file is in the /ELCL/EXE/ folder in the EyeLink partition on the Host PC. The FINAL.INI file can be edited via the file manager software (EyeLink 1000 Plus and EyeLink Portable Duo) or boot the Host PC to Windows (EyeLink II and EyeLink 1000) and edit the file there (the EyeLink partition shows up as another drive when booted to Windows).