Using Color as a Model System for studying Perception, Thoughts, and Action

National Eye Institute

Investigators

Linked publications, trials & patents

Abstract

1.Testing the extent to which the macaque is a model of the human case Vision is possible because of how the brain interprets information from the eyes. This study has two sub aims: 1A. The development of a new way of analyzing cortical function that discovers the kinds of patterns in sensory data that are exploited by the brain in generating vision. The study uses the tool in a specific example, to identify the functional signatures of the areas in the cortex that encode the image that is projected by the eye’s optics onto the retina. The results provide hypotheses for the different roles that different parts of visual cortex play in vision and help resolve apparent differences between human and macaque visual cortex organization that make the macaque a very useful tool in understanding the human case. The tool itself promises to be useful beyond the specific application in this study, for visualizing and understanding complex neuroimaging datasets. 1B. The quantitative comparison of human and macaque functional organization using fMRI. We have developed a new data-driven approach for comparing neural responses in macaques and humans using fMRI. Humans and monkeys engaged in the same experiments, under the same behavioral conditions: we collected a large data set of neural responses to natural images (movies) and controlled visual stimuli. We then developed a new version of “hyperalignment” (optimized for group comparison) to identify representations shared between species, and representations unique to each species. The method provides a useful tool that can be used by other investigators to make predictions about the patterns of brain activity in either species to any arbitrary stimulus and allows tests of the evolutionary homology of brain structures. 2. Visual concepts and their neural substrate Object concepts are important tools of cognition that often reflect the interaction of a color and a shape. So, “banana” is a yellow crescent that promises nutrition. The brain areas that store color-shape interactions are poorly understood. Testing various hypotheses has been challenging because concepts differ between people, and the corresponding likelihood functions and priors about object shapes and colors are not precisely known. Moreover, functional brain patterns differ among individuals. To overcome these challenges, we raised macaque monkeys to learn about the colors and shapes of a set of objects and then engaged the animals in non-invasive brain imaging experiments (using the same techniques used with human subjects) to determine the neural loci that support concept acquisition and deployment. 3. The origin of concepts A characteristic and essential feature of the human mind is the use of concepts. For example, if you are looking for a lost item in a cluttered environment, you can hold in mind the color of the item (which is linked to its shape by the concept in your mind) to recover the shape information you cannot see because the shapes are occluded. How are concepts constructed and stored by the brain? Addressing this question is important for the development of treatments for brain disorders that impact cognition and could be leveraged for brain-machine-interfaces for the treatment of blindness in cases where the eyes are broken but the brain is healthy. This study addressed a question that has been very challenging in the field: Are people innately equipped with concepts? Prior research has addressed the question using color, because color is experienced categorically: color categories reflect concepts of color. This study tested for color categories in macaque monkeys, a species with the same visual-encoding systems as humans. The study found that the conception of the ordering of colors (red, orange, yellow, green, blue, purple) is probably innate but the ability to form categories out of the continuous ordering of color requires learning. The results imply that cognitive mechanisms such as language are required for the expression of consensus color categories, which provides an opportunity to exploit large language models as interfaces in prosthetic devices for visual restoration in blindness. 4. Neurophysiological mechanisms of vision at the center of gaze Almost nothing is known about the spatial structure of V1 receptive fields at the center-of-gaze, yet these neurons are the building blocks for high acuity vision. Knowledge of these mechanisms is essential for teh development of machine-brain interfaces for the treatment of blindness caused by loss of eye function. The present knowledge gap is due to the technical challenges in measuring receptive fields (RFs) at the resolution of single-cone inputs present in the retina (~1 arcminute resolution). Given the distinct anatomical and physiological characteristics of foveal retina, it is possible that RFs in foveal V1 are not simply finer versions of parafoveal cells and may have distinctive aspects of visual processing. Here, we developed a new neurophysiological eye tracking approach that recovers eye positions with photoreceptor resolution. The results provide the first spatiotemporal chromatic receptive fields at the center of gaze in macaque V1.