Just how fast is ultra-rapid scene processing
Ten years ago we reported that humans can decide whether previously unseen complex natural scenes contain an animal on the basis of roughly 150 ms of processing (Thorpe et al, Nature, 1996). But recent experiments using a saccadic choice task impose even greater constraints on the underlying processing. When subjects are presented with two images, one on the left and one on the right, they can make saccades to the side where the image contains a human face with a mean reaction time of just 140 ms, and reliable saccades can already be seen at only 100-110 ms. If we allow roughly 20 ms for saccade initiation, this implies that face detection in natural scenes can be achieved in under 100 ms. I will discuss the implications of such results for models of visual processing.