Awareness of Absence and Absence of Awareness: Failures of Sensation and Attention

Abstract

Failure of conscious visual perception occurs under a range of circumstances. The causes and processes leading to incidences of stimulus-blindness are poorly understood. Failure of conscious report could be, for example, a consequence of reduction of the sensory signal or lack of attentional access to sensory signals. When examining these phenomena one has the intuition that in some types of invisibility, a target is phenomenally invisible (awareness of absence), whereas in other types of manipulations, we do have a sense that we missed a target (absence of awareness). To distinguish different causes leading to a failure of visual awareness, we employed a new measure, termed subjective discriminability of invisibility (SDI) that measures whether confidences of reporting the absence of a target are different for trials in which visual awareness was impaired (miss trials) from those where no target was present (correct rejections). Targets misses were subjectively indistinguishable from physical absence when contrast reduction, backward masking and flash suppression were used. Confidence could be appropriately adjusted when dual task, attentional blink and spatial uncertainty methods were employed. These results show that failure of visual perception can be either a result of perceptual or attentional blindness depending on the circumstances under which visual awareness was impaired.