Decision making in the absence of conscious awareness

Our sensory systems continuously process streams of information from our environment, most of which will never reach conscious awareness. The extent to which unconsciously processed information influences our decisions has been a particularly controversial question over the past decade. This thesis investigates whether information processed in the absence of a stimulus—or of conscious awareness of a stimulus—can influence decision accuracy. Using a motion decision task, in Chapter 2 we show that simply delaying responses after stimulus offset can almost double decision accuracy, even In the absence of new visual information. We further show that performance gains are eradicated by the presentation of a sensory mask during the delay, or when concurrent working memory load is high. We propose that these results are best explained by the continued accumulation of information from a decaying sensory memory trace. In Chapter 3, we investigate the controversial idea that unconsciously processed information can modulate decision accuracy. Using a novel dichoptic suppression paradigm to titrate conscious and unconscious evidence, we show that unconscious information can be accumulated over time and integrated with conscious elements presented either before or after to modulate decision accuracy. Our data are explained well by a simple model of conscious decision making in which the rate and variability of evidence accumulation is reduced but not eliminated by the removal of conscious awareness. We further show that the increased accuracy due to unconscious processing is not accompanied by corresponding increases in confidence, suggesting that we have poor metacognition for unconscious decisional evidence. InChapter 4, we show that unconscious learning can increase decision accuracy by improving unconscious decisional processing. We demonstrate that a short period of training on either a partially or fully suppressed motion stimulus results in improved accuracy when tested on a partially suppressed motion stimulus travelling in the orthogonal direction, even when performance during training was at chance. Computational modelling revealed that these results are best explained by an improvement in the rate of unconscious information accumulation. Together, these results present compelling new evidence that unconsciously processed information can affect our decisions, without us being aware of it