Humans have an amazing ability to visually identify a virtually limitless number of objects and to categorize them into classes such as faces, cars, or houses. We are capable of this feat despite the enormous variability in an object's appearance due to environmental factors such as distance, viewing angle, lighting, etc. With funding from the National Science Foundation, Sabine Kastner, Ph.D., of Princeton University is studying one of the major areas in the field of cognitive neuroscience, the neural mechanisms underlying efficient visual recognition. Object vision has long been associated with a specific part of the visual system, known as the 'ventral system.' Patients who suffer from damage to the ventral system often have deficits in recognizing objects. However, recently, a second system for the representation of object information has been found in a different part of the visual system, known as the 'dorsal system.' This finding suggests that object information might be represented in at least two parallel neural systems that likely serve different behavioral goals. In this project, several issues with regard to the dorsal object information system are being addressed by using brain imaging (functional magnetic resonance imaging; fMRI) on 3 types of participants: (1) healthy humans, (2) monkeys, and (3) patients with lesions of the ventral system. For the first part of the project, the researchers are studying the nature of the dorsal object information, and how it differs from the information represented in the ventral stream. For the second part of the project, they are studying whether the representation of object information in the dorsal system differs between humans and monkeys, perhaps, reflecting an evolutionary process to support complex human-specific behaviors (e.g., tool use). For the third part of the project, through the examination of patients, they are addressing the important question of whether the dorsal system depends on the ventral system, or whether it functions as an independent parallel object pathway. These objectives are being pursued by using virtually identical methods across different species and across different participant populations. The researchers hypothesize that the dorsal stream object processing system is unique to humans and has evolved to support sophisticated tool use.
While much research has been directed at object representations in the ventral system, this project focuses on object processing within the dorsal system, a vastly understudied aspect of object vision. Importantly, the approach using virtually identical methods across different species and participant populations can lead to rare insights into the evolution of cognition. The developments of sophisticated tool use and language functions are considered unique to humans. While much is known about the neural basis of language, the neural basis of tool use is not well understood. The results of this project are designed to fill this gap. The knowledge gained from this project is expected to be important for other disciplines, such as anthropology. Comparative studies in humans and monkeys using identical techniques and experimental designs are predicted to become increasingly important for the next generation of neuroscientists. Dr. Kastner's laboratory is one of very few in the world where the methods for such studies are used regularly. Therefore, the project provides a unique training opportunity for postdoctoral fellows, graduate and undergraduate students. The results are being used in Dr. Kastner's continued outreach program to public audiences and in local public schools. Such programs raise awareness and excitement about the importance of brain research, and demonstrate the interdisciplinary nature of modern neuroscience research to motivate young students to pursue scientific careers and help increase public support of basic science research.
This project sought to shed light on one of the critical questions in visual neuroscience. That is, how is information about objects we see and hear in the world around us represented and processed in the brain? Classical theories of "object processing" have hypothesized the existence of a single "stream" of brain areas that process object form information in a hierarchical fashion from simple to complex properties. This stream consists of brain areas along the underside of the cerebral cortex, and is known as the "ventral visual pathway". Our project explored whether a second stream of brain areas that weren’t originally thought to process object form, but instead process spatial information, is also involved in representing object form. This "dorsal visual pathway" runs toward the top side of the brain, but starts in the same region as the ventral stream. In a series of experiments using functional brain imaging of healthy adults and several patients with brain damage, we found that this dorsal stream also plays an important role in object form processing. This stream may have evolved in its complexity in the human brain since we are so adept at manipulating objects such as tools compared to other species.
