Principal Investigator: Jonathan J. Marotta
How Does Semantic Information About the Function of an Object Affect Grasping?
Category specific visual agnosia (CSVA), resulting from temporal brain damage, is a deficit in which patients may be able to recognize all manners of tools or artifacts but show marked difficulties in recognizing even the most common fruits or vegetables. Patients with CSVA have problems associating the view of an object, in a specific category, with stored knowledge of its identity. Although the mechanisms in the ventral visual cortical stream underlying visual perception do not appear to have access to the semantic knowledge of certain categories of objects in this disorder, an interesting and important question remains. Do the visuomotor mechanisms in the dorsal visual cortical stream have access to semantic information about the function of the object even though the patient cannot identify the object? Although a patient with CSVA may not recognize a hammer, if the patient is asked to pick it up and use it, will he/she do so properly and show good metrically scaled movements.
Patients. Dr. Marlene Behrmann has recently been investigating three young adult males, SM, CR and JPS, who exhibit CSVA. Although object recognition is impaired in these subjects, their discrimination between biological and non-biological items (or living vs. non-living) is particularly interesting. SM is better at recognizing living than non-living objects, whereas the opposite is true for CR and JPS.
Reaching and grasping. My expertise in visuomotor psychophysics can be of benefit to Dr. Behrmann's laboratory, by enabling us to use reaching and grasping paradigms to study the behavior of these patients. We will compare the patients' recognition of an object with their ability to direct a well-formed and appropriate grasp to that same object. By using an electro-magnetic 3D-position sensor from the Robotics and Engineering Department at Carnegie Mellon University, we will be able to accurately record the subjects' reaching and grasping movements to living and non-living objects.
functional MRI. A neuroimaging study will be conducted at the world-renowned University of Pittsburgh Medical Center. Activation patterns along the ventral and dorsal streams, along with the areas in which the two streams interact, in both the patients with CSVA and in intact control subjects will be examined, while subjects view living and non-living objects. In some conditions, these objects will be grasped. Are there differing patterns of activation generated by living versus non-living objects? Which areas in the brain are recruited for the integration of semantic information about an object's function with the metrical scaling necessary for an object-directed action?
Psychophysics. We will use modern psychophysical techniques, such as detailed reaction time and signal detection measures, to determine the stimuli that will be used in the first two experiments. A set of consistently recognizable (and non-recognizable) living and non-living objects will be established. This work will be done in collaboration with Dr. Michael Tarr at Brown University, who has collaborated on the psychophysical investigations of these patients in the past.
Significance. The proposed work that I have outlined here will help to
answer one of the central questions in behavioral neuroscience -- how
sensory inputs are transformed into useful motor acts. This work will
provide us with critical implications for neuro-cognitive theories of
visual object recognition and the control of action and for an interpretation
of the role of the ventral stream, particularly the temporal cortex, and
its interaction with the dorsal stream, in these functions.
