Consciousness is an umbrella term utilised to refer to a variety of mental phenomena. Cognitive psychologists have focused their efforts in understanding access consciousness, or how information carried in conscious mental states is available to different cognitive processes. This is linked to attention and working memory. However, consciousness is difficult to quantify and hence most pieces of research study consciousness by contrasting the characteristics between conscious and unconscious processes. Although with some limitations, research has provided enough information for the formulation of several models of consciousness. Besides, the combination of behavioural and neuropsychological data is slowly advancing the understanding about what consciousness is and what it is for although much is yet to know.
Consciousness is a fascinating but challenging topic in cognitive psychology. The concept of consciousness is difficult to define not only because it refers to heterogeneous phenomena but because it is difficult to measure objectively (Atkinson et al, 2000). It is an inclusive term for a number of central aspects of our existence; the state of being awake and aware of ourselves in our environment as opposed to being asleep; being aware of particular sensations or mental events or being aware of the quality of our experiences; and also, self-consciousness, our awareness and monitoring of what we are doing and thinking (Andrade, 2010). Pinker (1997) summarises these aspects in three: sentience or Block’s (1995, as cited in Andrade, 2010) phenomenal awareness; access to information or Block’s (ibid.) access consciousness; and self-knowledge. Chalmers (1996, as cited in Andrade, 2010) refer to sentience as the ‘hard problem’ whilst access consciousness is the ‘easy problem’. Thus, access consciousness, including how information is shared between neural and cognitive modules and the neural correlates of consciousness, has been the most widely researched. Nevertheless, Dennett (1991) asserts that the so-called hard problem will be solved in the process of answering the easy ones, as consciousness cannot be separated from function.
Consciousness cannot be measured directly but indirectly through the relationship between objective data such as behaviour or brain phenomena during cognitive functions and subjective information such as conscious experience. Hence a wide range of methods have been used in its study, including experiments and neuropsychological studies in normal participants or participants with altered states of consciousness due to drugs, brain injury, coma or hypnosis. In many of these studies, the functions of consciousness are inferred by using ‘contrastive analysis’ (Baars, 1988, as cited in Andrade, 2010), that is, establishing the differences between conscious and unconscious cognition by comparing similar events that differ only in that one event is conscious while the other is not. Of particular interest are those paradigms that reveal dissociations between conscious awareness and stimulation and/or behaviour.
Among these dissociations, the study of perceptual processes has the longest history. Inherently, the study of conscious experiences relies on the assumption that they are selective and limited in nature as we are not aware of everything that we perceive (Lamme, 2003). Perception without awareness can be demonstrated in normal subjects with multistable percepts, e.g. ambiguous figures or visual illusions such as the Rubin vase; or using binocular rivalry. This consists in presenting different images to each eye; instead of the images appearing superimposed, they alternate in their visual awareness (Logothetis, 1998). Perception without awareness can also be demonstrated in brain damaged patients. For...