Pixels versus Degrees of Visual Angle

Pixels describe display coordinates. Degrees of visual angle describe angular size at the eye. Converting between them requires physical display geometry and viewing distance.

Required information

For degree-based margins provide screen width/height in pixels, physical screen width/height in the same physical unit, and viewing distance in that unit.

deg = ep.convert_aoi_margin_to_degrees(
    (20, 20),
    screen_width_px=1920,
    screen_height_px=1080,
    viewing_distance=60,
    physical_screen_size=(53.1, 29.9),
)

Horizontal and vertical degrees-per-pixel are retained separately because screen pixel density need not be identical on both axes.

Safeguard

A degree-based perturbation fails if neither explicit degrees-per-pixel values nor complete screen/viewing geometry is available. Units are never changed silently.

Reporting

Report resolution, physical screen dimensions, viewing distance, and perturbation unit. If viewing distance was not controlled, state that limitation explicitly.

Continue to Interpreting AOI Assignment Stability.