Object substitution and its relation to other forms of visual masking.

Three experiments compared letter identification accuracy over a wide range of target-mask intervals and mask types, including metacontrast, random dot noise, four surrounding dots, digits and letters. These comparisons were motivated by object substitution theory which makes three general predictions about visual masking: (1) very different looking backward masks will be equivalent in their effects when spatial attention is distributed, such that target identification is delayed, (2) masks will differ most in their effects on target identification when they are temporally integrated with the target, and (3) backward masking will be minimized when attention can be pre-focused on the spatial location of the target and the mask does not interfere with target identification. Results strongly supported the predictions and pointed to a new understanding of masking based on the separate processes of object formation and object substitution.