Migraine and the Visual System
Migraine headache affects approximately 3 million Canadians. Many migraine sufferers are very light-sensitive, and experience visual auras at the onset of their migraine episodes. Migraine research in my laboratory addresses two fundamental issues:
Intermediate Level Form Vision
- Migraine Aura: What is the mechanism underlying migraine auras, what is their locus within the visual system, and what is it about the structural and functional organization of the visual system that makes it prone to this sort of hallucinatory activity. Auras have been attributed to cortical spreading depression within V1 - we are currently testing predictions of that hypothesis. Our studies involve having subjects make structured observations of their auras as they are in progress.
- Visual Hypersensitivity in Migraine: Are the visual systems of migraineurs abnormal in ways that are measurable using psychophysical techniques during the period between episodes? How can this hypersensitivity be characterized? Are particular aspects of vision affected more than others? We are currently examining a wide range of psychophysical measures of contrast and motion perception. We are also interested in whether light acts as a stressor in autonomic terms in migraineurs.
Over the past several years, studies in my laboratory have focused on understanding the intermediate levels of visual form analysis. We use psychophysical and computational approaches to ask how visual information, initially extracted from the image by the early filtering operations of the retina and V1 are combined to reveal basic information about object shape. Much of this work has been carried out using novel stimulus sets of radial frequency patterns and Glass patterns. We are currently pursuing related studies using fMRI imaging to observe the function of the ventral visual pathway in vivo in human subjects.
Of all the objects humans recognize by sight, faces are the most complex and yet in many ways the most important. Social interaction depends on recognition of conspecifics and on decoding the ongoing stream of information conveyed by facial expression that accompanies speech. Our research builds on our ongoing work on intermediate level form perception to address questions about how information about facial properties is combined configurally by the visual system, and how it is used for different purposes (individual recognition, detecting direction of gaze, gender identification etc).
Textural change is a very important cue to both surface segmentation and surface shape. Studies in my laboratory have investigated the spatial conditions under which an array of visual elements act as a 'texture'. We have found that human subjects make sharp and repeatable categorizations of arrays which are 'textures' versus arrays the elements of which appear as 'separate objects'.
Under the spatial conditions supporting the percept of texture we have found that thresholds for detecting change in a single element are elevated (lateral masking), and that the percepts of certain element properties (contrast, spatial frequency) are altered in a textural context. Recent work has also investigated the spatial tuning of mechanisms supporting detection of spatial frequency gradients in textures.