The first experimental evidence that attention and awareness are fundamentally different processes has been provided in a new study.
Researchers from the Max Planck Institute for Biological Cybernetics have argued that the primary visual cortex, the entrance stage to cortical visual processing, is modulated only by attention and not by awareness.
They took a closer look at the BOLD signal from the primary visual cortex by experiments with participants in a two-by-two factorial design - the visual target "visible" versus "invisible" and attention "to" versus "away" from the target.
Cleverly designed composite images shown at high frequency intervals to one eye allowed a target presented in the same or the other eye to be either visible or invisible, whether or not the subject directed their attention to it.
"It was important not to depend on the participant to report the visibility of the target," explains Masataka Watanabe, a visiting student from the University of Tokyo, said.
"The results of the experiments astonished even the scientists. "I, myself, was surprised by the finding, it shifted my mind a little," Watanabe said.
They found that paying attention to the target almost doubled the bold activity in the visual cortex, while sheer visibility of the target had almost no effect.
"Here the BOLD signal is not modulated by awareness," Watanabe added.
The study has been published in the journal Science.