Philosophy, Psychology and Neuroscience

How Does the Human Brain Represent Size?

One of the most puzzling abilities of the human brain is size constancy: an object is perceived as having the same size even though its image on the retina varies continuously with viewing distance. An accurate representation of size is critical not only for perceptual recognition, but also for goal-directed actions, such as grasping. In fact, to successfully grasp an object, our grip aperture needs to be scaled to the true size of the object regardless of changes in retinal image size due to variations in viewing distance. In this talk, I will present a number of studies using functional magnetic resonance imaging (fMRI) and behavioural (i.e. perceptual judgments, kinematics) approaches to demonstrate that the human brain supports multiple representations of size, some of which do not require conscious processing and are more automatically driven than others. I will discuss the findings, which provide evidence for separate mechanisms responsible for size- and grip-constancy, in light of the ongoing debate on the neural basis of size perception.