Every time we open our eyes, our visual system is overloaded with information. This is especially true in the peripheral visual field: Although we feel that we are aware of the details of individual objects in our periphery, the number and density of objects in natural scenes means that we are unable to perceive detailed information such as identity or quantity. This inability to scrutinize objects in the periphery when other objects are present is called visual crowding. Counterintuitively, crowding may be beneficial. A number of models have emphasized that crowding can improve processing efficiency or allow us to detect statistical regularities in natural scenes--tasks that are fundamental to all aspects of visual perception. Despite the existence of a unique psychophysical definition for crowding, and its clear importance in visual processing, there are major gaps in our understanding of where in the visual hierarchy crowding occurs, the sorts of objects on which it operates, and the underlying neural mechanism that causes crowding. With funding from the National Science Foundation, Dr. David Whitney and his colleagues at the University of California, Davis, are pursuing two major research goals. First, by measuring behavioral performance, Dr. Whitney will test the hypothesis that crowding operates independently at multiple levels of visual analysis, for low-level visual features such as contours or gratings, and also for high-level objects such as faces. Second, Dr. Whitney's team will isolate and identify the neural mechanisms that mediate both low and high-level crowding using a non-invasive brain imaging method known as fMRI-adaptation.
Understanding visual crowding is fundamental to understanding most other aspects of visual perception. Every natural scene we look at is densely filled with objects, but only a very few of these can be simultaneously scrutinized, largely because visual crowding prevents the visual system from having access to all the details at once. Perception, therefore, is subject to the costs (and benefits) of crowding. Because human vision is perhaps the most thoroughly examined operational visual system, investigating the impact of crowding on human perception will be important in developing a realistic artificial visual system in the future. More broadly, understanding the limits of human spatial vision, including crowding, has the power to improve a range of applications including data visualization (e.g., crowding interferes with visualizing abnormalities on an x-ray), advertising (e.g., too many words or images on a billboard causes car accidents), computer graphics (e.g., too many flashing icons on a website becomes ineffective), visual art and movies (e.g., do not crowd the star actor with too many other nearby faces), and a host of other applications. In addition to the broader impacts noted above, this proposal will support the training of a graduate student. Moreover, Dr. Whitney will establish a unique outreach program in local high schools, with predominantly Hispanic populations, that will use art as a way to introduce visual neuroscience research questions and methods. The educational outreach program is specifically aimed at stimulating interest and increasing the participation of under-represented groups in basic science research.
Visual crowding is what happens when clutter (when many objects are in the visual field) has a deleterious effect on object recognition. It is the most fundamental bottleneck for recognizing objects throughout most of the visual field, most of the time. Here is an example: While staring at any letter in this paragraph, try to identify a letter that is located 4 lines above or below it. It is exceedingly difficult to recognize an object (like a letter) even though we can tell that there is "stuff" there. Visual crowding is so ubiquitous that it has practical consequences for nearly every daily activity, like driving, display design, and visual search in airports (bag screening) and hospitals (radiological scans). Understanding crowding is critical to understanding how we recognize and interact with objects in general and what the limits of human perception are, as well as for designing artificial and assistive visual devices. There were two major goals of the studies conducted under this award. First, we wanted to model how crowding works. We psychophysically tested whether crowding is a unitary process or whether it operates independently at multiple levels of visual analysis, because two classes of models make competing predictions about this (reviewed in Whitney & Levi, Trends in Cognitive Sciences, 2011). Contrary to all existing models, we hypothesized that crowding operates selectively and independently at multiple stages—not simply between low-level visual features (e.g., contours or gratings), but, surprisingly, between high-level objects as well (e.g., upright faces). In a series of papers, we demonstrated that this is indeed the case. This shows that it is crowding that causes much of the difficulty when trying to find a book on a shelf full of books, a friend’s face in a crowd of other faces, or a car in a parking lot full of cars. To make these or similar search tasks easier, it is important to understand the limits that are imposed by crowding and the neural processes that underlie these limits. To this end, the second goal of the proposed projects was to isolate and identify neural mechanisms that mediate crowding. We used a novel combination of fMRI and psychophysical crowding paradigms; the results of the psychophysical experiments and part of the fMRI experiments have been published. One of the key findings was that the pulvinar nucleus in the human may help to filter distracting visual information so that we can focus our attention on objects of interest. These results open the door on future work that can identify the role of the pulvinar in alleviating visual crowding. Together, our behavioral and fMRI results shed light on the prevalence of visual crowding in every natural scene and also show that attention-based mechanisms may help counteract crowding to some degree. In addition to these primary goals, a tertiary goal of the experiments was to develop tools and techniques that could be applied more widely to questions of crowding and clutter perception. These stimuli, psychophysical techniques, and analyses represent a broader impact of the proposed experiments. Finally, an important goal of the project was an outreach program that brings vision science to underrepresented elementary, middle, and high school students in Northern California. Through this outreach program (http://whitneylab.berkeley.edu/outreach/) we have personally interacted with over 1000 middle and high-school children.
