ABSTRACT
For a more systematic study of these detection distances, some device is needed that permits specifying the row that is being scanned at the moment the target is detected. If the control areas were asymmetrical, the upper target would then have the same chance of being detected as a lower target at the same distance. If the control areas were perfectly asymmetrical, upper targets could not be detected at all. With respect to the assumed differences between central versus eccentric vision, the model is loosely related to Trevarthen’s distinction between ambient and focal vision. With respect to the functional nature of the operations involved it draws back to the distinction between automatic detection and controlled search suggested by Shiffrin and Schneider. Structural asymmetry arises from an asymmetrical distribution of sensitivity that cannot be changed in itself because it is related to anatomical and physiological differences between the upper and the lower half of the visual field.
