12:00 pm

From paws to hands:  The evolution of the forelimb and cortical areas involved in complex hand use

Leah Krubitzer

560 Evans

Forelimb morphology and use in mammals is extraordinarily diverse.  Evolution has produced wings, flippers, hooves, paws and hands which are specialized for a variety of behaviors such as flying, swimming and grasping to name a few. While there is a wealth of data in human and non-human primates on the role of motor cortex and posterior parietal cortical areas in reaching and grasping with the hand, these cortical networks did not arise de novoin primates, but likely arose early in mammalian evolution since most mammals use the forelimbs for reaching and grasping as well as other behaviors. Yet, we know relatively little about how frontoparietal networks that control the forelimb have evolved in mammals. Our laboratory has previously described the organization of somatosensory cortical areas in a variety of mammals and find that both morphology of the limb and how the limb is used are reflected in the organization of cortical fields that represent both mechanosensory receptors and proprioreceptors.  In recent studies we examine the organization of movement maps using intracortical microstimulation techniques in a range of mammals to determine the extent of cortex from which movements can be evoked, and how behavioral specializations of the limb are represented in movement maps in the cortex. While there are some features of organization that are similar across species, such as gross topography, most of the details of map organization are species specific.  Thus, movement maps are much more variable across species than are somatosensory maps, and are variable across individuals within a species, suggesting that these maps are, in large part, a product of experience.  We propose that motor cortex co-evolved with modifications to the hand and forelimb, and is built during development based on commonly used muscle synergies.


12:00 pm

Visual coding strategies implied by individual differences or adaptation

Kara Emery

Evans 560

An important goal of vision science is to understand the coding strategies underlying the representation of visual information. I will describe experiments and analyses where we have explored these coding strategies using two different approaches. In the first approach, we factor-analyzed individual differences in observers’ color judgments to reveal the representational structure of color appearance. In contrast to conventional opponent-color models, these results point to a population code in which different color categories vary independently and for which there are no opponent axes. We also show that the factors underlying two-dimensional color space are fundamentally different from those of other two-dimensional visual attributes, such as planar motion. In a second study, we developed criteria for using patterns of adaptation aftereffects to discriminate between alternative coding models. We focus on two contrasting models of face aftereffects that have been proposed based on exemplar vs. norm-based encoding strategies. We show that the critical difference between these models, in terms of the aftereffect patterns they predict, depends more on how the channel activations are combined (decoding) rather than the properties of the channels themselves (encoding). Together, these results challenge assumptions of traditional coding theories and add to the value of individual differences and adaptation as tools for probing the coding strategies of visual perception.