Recently, there has been a growing interest in the relationship between spatial attention and consciousness. Since William James (1980 Principle of Psychology New York: Holt) emphasized the interconnection between attention and consciousness, they have been considered inseparable (Posner, 1994 PNAS). However, Koch and Tsuchiya (2007 Trends in Cognitive Sciences 11 16–22) suggested attention can be dissociated from consciousness, producing a state such as attention without consciousness. Previous studies supported this claim by showing attention can modulate the amount of adaptation from invisible stimuli (Bahrami et al., 2008 Perception 37 1520–1528; Shin et al., 2009 Attention, Perception & Psychophysics 71 1507–1513). However, these studies did not examine the interaction between attention and visibility. To investigate this, we measured the effect of attention on both visible and invisible stimuli that were attended simultaneously. Participants were adapted on two motion gratings which were presented to the dominant eye and thereby always visible, and on two tilted gratings presented invisibly to the corresponding locations of the opposite eye. Participants paid attention to one of the two locations by performing a contrast decrement detection task on one of the motion adapters during adaptation. We separately measured motion aftereffects (MAE) and tilt aftereffects (TAE) for both attended and unattended locations. Spatial attention increased the amount of MAE, but not that of TAE. These results suggest the effect of spatial attention can vary depending on the visibility of stimuli, indicating the interaction between the two.
