Varieties of attention and of consciousness: evidence from neuropsychology

Do we need to attend to an object in order to be conscious of it, and are the objects of our attention necessarily part of our conscious experience? A tight link between attention and consciousness has often been assumed, but it has recently been questioned, on the basis of psychophysical evidence suggesting a double dissociation between top-down attention and consciousness. The present review proposes to consider these issues in the light of time-honored distinctions between exogenous and endogenous forms of attention and between primary and reflective forms of consciousness. These distinctions shed light on results from several sources of evidence, including patterns of performance of brain-damaged patients with visual neglect. These findings strongly suggest that exogenous attention is a necessary condition for primary visual consciousness to emerge. Visual neglect, which typically results from damage to frontoparietal networks in the right hemisphere, entails an inability to orient to and to detect contralesional objects. Importantly, neglect patients are not only unable to verbally report contralesional objects, but may also act as if these objects did not exist, for example by bumping into them, thus suggesting an impairment of primary perceptual consciousness. Less frequently, neglect patients may instead show forms of “implicit” knowledge of neglected items, perhaps indicating a deficit of more reflective forms of consciousness, such as those subserving verbal reportability. The integration of several sources of evidence, such as phenomenology, experimental psychology and neuroscience, is needed to further explore the taxonomy of these processes and to identify their neural correlates. Bartolomeo – Attention and consciousness 3