Spatial contrast sensitivity does not explain random figure discrimination latency

Both humans and other mammals can more easily discriminate eight-sided figures from one another than they can figures having more or fewer sides. The hypothesis that this effect is based upon spatial contrast sensitivity was tested by varying viewing distance and hence spatial frequency content. Because viewing distance had tittle effect upon relative discrimination latency, it was concluded that the superior discriminability of eight-sided figures is not based upon spatial contrast sensitivity. The possibility that orientation tuning of visual cortex neurons may account for the effect is discussed.