Patrick Cavanagh, PhD - US grants

Vision allows us to live a little bit in the future, to see things and react to them before they actually bump into us. The advantages of vision to an organism are overwhelming and, of all of the predictive functions of vision, the perception of motion is arguably the most valuable: it explicitly and rapidly deals with not just where things are but where things are going. In fact, the advantages of motion perception are so great that two very different motion systems appear to have emerged independently in the human visual system. The goal of this grant is to define and characterize the least understood of these two systems, the "high-level" motion system. Our work has shown that the high-level system appears to be based on selection and pursuit of targets by attention, a system analogous in many ways to the smooth pursuit system of eye movements. Attentive tracking is a critical part of many everyday activities - driving, playing sports, and responding to dynamic computer displays. Understanding its limitations and mechanisms in isolation from the properties of low-level motion detectors is crucial to understanding human performance in demanding environments. I propose to study the role of attention in high-level vision in normals and in individuals with damage to the parietal region, an area involved in attention. To isolate the high-level motion system, we must also understand the low-level system which is based on directionally selective neurons in the visual cortex. Several experiments are planned to identify low-level processes and catalog their number and properties. We also will continue to examine the smooth pursuit system used when tracking targets with eye movements. Our early results show that high-level motion signals may play a significant role in initiating and correcting smooth pursuit. Finally, we look at how the visual system identifies the position of stimuli despite constant large and small motions of the eye. We have discovered a stabilization system, a "Steadycam" process, based on low-level motion signals that keeps the world stable despite movement and vibration of the eye. We will continue our work on these projects and begin a new project on the perception of stimuli from outside the visual field. In this last study we will stimulate the retina through the sclera and address the question of how the perceived location of object is corrected for the direction of gaze. We will examine whether the early responses to the stimulation are gated out of awareness for directions of gaze where the stimulated retinal location corresponds to a location outside the normal visual field. In these final studies I will test normal and neurological subjects and record brain activation using fMRI.

Many researchers study how nonhuman animals visually perceive the world; to date, however, only certain types of experiments have been possible, given the limitations of animal learning and response capabilities. With funding from the National Science Foundation, Drs. Cavanagh and Pepperberg are investigating visual processing in a Grey parrot named Alex, who can vocally answer many questions at the level of a 4- or 5-year-old human child. The investigators are examining visual attention beginning with basic studies of visual illusions, i.e., stimuli that appear to humans to vary in size but in reality do not. These experiments leverage Alex's ability to vocally report the color of the larger or smaller of two items or reply 'none' if no difference is seen. Such experiments are accompanied by attention tasks in which two targets must be detected in a rapid stream of items. The targets will be the digits 1 through 8 that Alex can recognize. For humans, the second target in such a stream is often lost if it follows the first too closely. This interference from the first target is called the 'attentional blink' and it is a measure of the speed with which attention can switch from one target to the next. Do parrots, which are prey species that must monitor for sequential predator movement and attack, have the same speed of attentional switching as humans? Or will this task reveal differences in cognition between birds and humans? Drs. Cavanagh and Pepperberg are investigating a broad range of visual tasks to determine which attention abilities share the same underlying mechanisms in birds (grey parrots) and humans and which do not. Similarities between these two species, with very different brain sizes, will allow us to understand which components of cognition can be implemented with smaller scale neural architecture. Differences will indicate the components that require greater brain size and/or complexity. The data will guide future comparisons with other species and providing insights into the structure and function of the human brain and for the design of artificial visual processors.