Competition and Attention in the Human Brain Eye-Tracking and Single-Neuron Recordings in Healthy Controls and Individuals with Neurological and Psychiatric Disorders

• Main Author: Cerf, Moran
• Format: Others
• Published: 2009
• Online Access: https://thesis.library.caltech.edu/6020/5/Moran_Cerf_-_PhD_Thesis.pdf; Cerf, Moran (2009) Competition and Attention in the Human Brain Eye-Tracking and Single-Neuron Recordings in Healthy Controls and Individuals with Neurological and Psychiatric Disorders. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/BFNE-C518. https://resolver.caltech.edu/CaltechTHESIS:09022010-004952870 <https://resolver.caltech.edu/CaltechTHESIS:09022010-004952870>

<p>At any given moment, our brains are bombarded with enormous amounts of information from the environment. External stimuli from the senses travel through our eyes, nose, or skin, and internal reflections and imagery travel from within. All these stimuli are processed in parallel and compete with each other toward one ultimate goal: becoming the single percept which we are aware of at this unique present moment.</p> <p>This work studies the way by which this competition occurs in our brains. The mechanisms and the methods which allow the brain to overcome this load of information by selecting one of many thoughts to reach the upper level of our consciousness.</p> <p>We studied healthy controls in eye-tracking experiments where they viewed sets of images in different tasks. In the first task, subjects freely viewed images with semantic high-level cues such as faces and social scenes. Subjects showed a significant tendency to rapidly attend to the faces in their first fixation. In a second task, subjects viewed similar images in a search task where they were instructed to find objects or faces in the scene. Subjects showed the same tendency to look at faces independent of the task. In a following study, subjects were looking at images with text and phones as control and were shown to look at text rapidly and early, but not as much as faces. Phones, as control, showed no increased rapid attentional attraction. In order to test the magnitude of the effect, we had subjects participate in a third experiment where they were instructed to refrain from looking at these objects, but were not able to do so as easily for faces as they were for text and phones. This suggests an innate mechanism that draws our attention to faces and social scenes early — even in situations where other stimuli compete for our attention. Faces win the competition for our attention regardless of the task. We used this striking result to modify an existing computer model for bottom-up attentional allocation to better predict human’s fixation in images.</p> <p>The results were tested additionally in two groups of individuals with disorders that manifest themselves primarily in decreased social attention: autism and agenesis of the corpus callosum (AgCC; subjects who are missing the bridge between the left and right hemispheres in the brain). Individuals with these disorders were tested in the same paradigms and indeed showed decreased attention allocation to faces or social cues in the images. AgCC subjects showed an even lower level of interest in social cues. While the results suggested a competition for attention that has social cues win over alternative cues in healthy controls, the psychiatric disorder groups show no such effect. In order to test the competition in the brain even further we tested individuals with epilepsy undergoing brain surgery, who were implanted with electrodes to record from single neurons in their medial temporal lobe (MTL). These patients participated in a task where they were projecting their thoughts of one of various concepts onto a computer screen, in real-time, using a decoder that interpreted their thoughts and imagery. Patients performed a task in which they were instructed to think of one of four concepts, and by accurately doing so were fading into an image representation of that concept on the computer screen. Multiple images that were shown on the screen simultaneously while the patient tried to suppress one and maintain an imagery of the other allowed us to directly create a situation where competition between various external stimuli, and in turn multiple brain regions, is tested. Subjects were able to reach high level of control of their single MTL neurons after very little training. In this direct measure of the competition between brain regions and neurons in the brain, we show that attention can be modulated to direct the flow of information to one or the other area, even though the external stimuli from the environment is identical. We used the results from the fading experiment to construct a model of the mechanism by which competition between external stimuli and internal imagery modulates attention in the brain.</p> <p>Subjects who were able to reach an even higher threshold of control of a single neuron played a computer game in which they were controlling an airplane on the screen using their thoughts alone. These subjects reached a high level of control suggesting an ability to use single neurons in the MTL for brain-machine interfaces with very high accuracy.</p> <p>Finally, we report various case studies from experiments involving direct measures of attentional allocation by individuals with face blindness (Prosopagnosia) who performed poorly in tasks involving competition between facial and social attention attractors; a subject with no amygdalae who was unable to direct her attention to fearful entities including images of herself posing while displaying fearful emotions; identical twins who showed an extremely high correlation in their attentional allocation metrics — both eye-tracking and individual rating of interest in images; and a similar high correlation between a mother and her autistic son.</p> <p>Altogether, these results shed light on the processes and the mechanisms undergoing in our brain, in the milliseconds between the moment information starts flowing in our brain from the environment, through the spotlight of attention that selects which of various inputs will be selected to reach our consciousness.</p>