An analysis of visual masking, with a defense of ‘Stopped Processing’

The use of a backward mask (a patterned mask which follows the target in time) to ‘stop the processing’ of the target illustrates an important application of masking – the study of the ‘microgenesis’ of visual perception, that is, visual processing over about the first one-fifth of a second. This paper provides evidence for stopped processing and some applications of this to object recognition and letter detection. The paper also discusses the notion of an ‘active filter’ which may help to account for Type-A masking but at best can only account for Type-B masking in part. I conclude that masking, while illuminating various areas of vision science, is under-utilized, perhaps because the theoretical justification for such masking is still uncertain, and perhaps because of the care needed to establish that the mask does indeed ‘stop’ processing.