Abstract :
In a two-dimensional intensity-modulated display such as theplan position indicator used in radar systems, the observer is looking forand recognizing the signal as an area, or pattern, of brightness differingfrom that of the surround. By using a closed circuit television system it waspossible to reproduce the essential features of this type of display whilsthaving complete control over the important parameters¿signal area,background noise, target presentation time, etc. In particular, the backgroundcan be changed from being uniformly illuminated, i.e. the situationstudied by many psycho-physiologists, to the more realistic situationappertaining to radar displays, i.e. when the background is completely perturbed by noise. Threshold signal/noise ratios have been measured for a number of such conditions and compared with those of an equivalent theoretical model. The results suggest that the visual detection system is a sub-optimum one and its efficiency is dependent, among other things, on the area of the signal. This point goes some way to explain some previously observed discrepancies between experimental and theoretical rates of improvement with increase of area.
