2.2.2. Lang Two Pencil Test
The Lang Two Pencil Test (LTPT; Lang, 1983) was used as a measure of participants’ ability to act in depth using monocular and binocular depth cues. The task used two eraser-tipped pencils; one of which was held by the experimenter as a target at the participant's eye level and arm's length away and the other pencil used by the participant to touch just the tip of the eraser of their pencil to the target as quickly as possible. The task was demonstrated to the participants by the experimenter, who held both pencils to demonstrate how to correctly touch just the tip of the target. A participant passed a trial only when the end of their pencil clearly touched just the tip of the target pencil; touching of the side of the target eraser or readjustment to touch the end of the eraser was classed as a failed trial. Target locations were random points along the plane of the participant's arm-length, with the target in vertical and horizontal orientations. The horizontal LTPT is a variant of the original vertical LTPT and has a high sensitivity and negative predictive value when screening binocularity (Nongpiur & Sharma, 2010). The order of orientation of the pencil (horizontal or vertical) and the viewing condition (binocular or monocular) was randomised for each participant. Participants completed five trials per viewing condition in each orientation (20 trials in total). The experimenter recorded the accuracy of each trial (correct or incorrect).