Under most circumstances, our visual systems are bombarded with much more information than they can handle. Because of this information overload, the majority of visual information is not subjectively experienced and seemingly goes unnoticed as well as unprocessed within the brain. Despite this impression, however, an increasing body of evidence suggests that unconscious visual information is indeed processed within our visual systems even though we remain unaware of it. With support from the National Science Foundation, Dr. Ro and his colleagues will examine the cognitive and neural mechanisms for conscious and unconscious vision. One set of experiments will use procedures that will render some visual events unconscious to participants in order to determine whether the representations of unconscious visual stimuli are encoded at processing levels that are distinct from consciously perceived ones. Another set of experiments will use transcranial magnetic stimulation of the human primary visual cortex to manipulate neural processing and hence awareness of visual events. These transcranial magnetic stimulation experiments will investigate differences in information coding, neutral structures, and cortical pathways for conscious and unconscious vision.
This research will provide a better understanding of visual information processing in the human brain and will lend some clues for developing useful compensatory strategies in patients with visual deficits. This work could also contribute towards the development of better visual assistive devices or prostheses for patients with congenital or acquired visual deficits. In addition, this project will provide training opportunities for undergraduate and graduate students and postdoctoral fellows at The City College of the City University of New York. The results of this funded research will be broadly disseminated to both scientific and lay audiences and should contribute towards enhancing scientific understanding by the public.
The major goals of this project were to better understand the cognitive and neural mechanisms for conscious and unconscious vision in the human brain. We used converging methods in cognitive neuroscience to study the neural mechanisms involved with visual awareness, including psychophysical studies that employed transcranial magnetic stimulation (TMS), electroencephalography (EEG), fast signal optical imaging, and functional magnetic resonance imaging (fMRI). Our findings are showing how it is that our brains, and in particular, our visual systems, process visual information so that we become consciously aware of our visual surroundings. The results from these studies have further demonstrated that we represent a substantial amount of information unconsciously, but in different ways from consciously represented information. In particular, we found using fMRI that visual areas as early as primary visual cortex (V1) show evidence for unconscious visual processing, even for features that are not relevant to the task at hand. We also unexpectedly found, using TMS over V1, that certain types of visual stimuli are less susceptible to visual suppression from TMS, suggesting that some salient visual representations are robustly represented in the brain. Two other studies from this project, one using psychophysical procedures and the other using TMS, have shown that more complex visual information, namely the shape of objects, can also be processed unconsciously. Finally, we have been using electroencephalographic (EEG) recordings to assess differences in neural responses when subjects are aware vs. unaware of visual events. We previously showed that the phase of the alpha (10 Hz) oscillation predicts visual awareness. We now find that applying TMS at 10 Hz over a particular region of the brain can induce an alpha rhythm that modulates visual perception in a phase-specific manner. Taken together, these studies provided fundamental insights into the normal operations of our visual sensory and perceptual systems and may provide important clues for generating successful rehabilitative tools for patients with congenital or acquired visual deficits.
