As we interact with our surroundings, the gap between looking and knowing is usually quick and effortless. But by what processes is this accomplished? How do we make sense of what we see?
Current projects in the lab are exploring the dynamic nature of visual processing. In the real world, visual observers constantly update their view of their environment by changing their direction of gaze. At the same time, objects in the environment are often themselves animate, and the characteristic dynamic behaviors of these objects provide rich information about the identities and actions of objects in the world. We are particularly interested in how the brain acquires a dynamic stream of visual information and efficiently parses this information to reach conclusions about the presence or absence of noteworthy objects to which actions should be directed.
We are also investigating how representations in the brain are dynamic, changing over time to reflect the learned structure of individual objects and the context in which these objects appear. Perceptual learning and visual expertise are perhaps the most obvious forms of plasticity that continue to manifest in adult animals, and we believe changes in receptive field properties of individual cells and networks of cells underlie changes in perceptual capacities. Our aim is to simultaneously explore changes in behavioral performance associated with expertise along with changes in neural response properties that can be recorded from individual neurons while these same tasks are being carried out. Changes in larger-scale neural response are also hotly debated, and we are investigating how EEG signals track increasing familiarity of learned images.
As we gain expertise with a new class of visual objects, our facility with instances of that class changes - we become better able to discriminate between individual exemplars, and we are less able to focus exclusively on isolated parts. We are studying how the parts that make up an object are used to identify the object, and how the neural representations of those parts come together to form a representation of the whole. Do these processes depend on our familiarity with the objects in question, or with the object classes? Are there particular kinds of objects, such as faces, that have specific dedicated modes of processing?
By simultaneously recording from multiple neurons in actively behaving subjects, we hope to understand which neural features show a quantitative variation that parallels ability. Subjects perform classification tasks relying on conjunctions of visual stimuli; behavioral measures indicate learning of these conjunctions and when they are treated as configurations versus new whole objects. We record from inferotemporal neurons and use these data to develop and evaluate statistical methods for understanding how it is that we "know" when two objects "go together" - the binding problem. Are the joint firing statistics of two inferotemporal neurons respectively selective for two stimuli more informative for predicting grouping status than each neuron considered independently?
To directly test possible causal effects of neural activity in parts of the ventral visual pathway on perceptual decisions and looking behavior, we are testing effects of stimulation of small populations of these cells. By carefully controlling the timing and duration of stimulation, we seek to demonstrate the role that cells in inferotemporal cortex play in forming perceptual decisions about the structure of visual objects or the presence of known objects in complex environments.