September 16

"What does V1 have to do with perception?"
Cheryl Olman, Assistant Professor,
Departments of Psychology and Radiology

Primary visual cortex (V1) has the distinction of being the cortical area for which we have the most complete characterization of neural response properties – we know a great deal about both individual neuron tuning functions and the relative spatial organization and interconnectivities of neurons tuned to different visual features. Six decades of electrophysiological investigations have taught us that each V1 neuron is sensitive to only a limited region of the visual field; a useful model of V1 is of an over-complete wavelet-based filter set that decomposes images into local features that can be passed efficiently to higher visual areas for scene segmentation and object recognition. However, in the last 10 years, many fMRI studies have shown that the blood flow response in V1 can be modulated by changes in perceptual state or global scene organization – image properties and cognitive states generally considered to be beyond the purview of V1. Complicating these discoveries is the fact that single-unit studies in primates performing similar perceptual tasks often find very limited, if any, modulation of V1 by perceptual state changes or global scene structure. While there are many theoretical reasons that feedback from higher visual areas should modulate V1 responses in order to improve visual performance for a given task, testing these theories and delineating the neural mechanisms by which V1 neural responses are modulated requires high-resolution measurement of neural responses throughout multiple cortical areas; unfortunately, high-resolution and large field-of-view are generally incompatible imaging goals. However, high-field fMRI offers us this opportunity. I will present results of a recent study using sub-millimeter resolution to characterize perceptual modulation of V1 responses at different cortical depths, one technique that adds a new dimension to our study of the role of V1 in perception.

Suggested reading: Maier, A., Wilke, M., Aura, C., Zhu, C., Ye, F. Q., & Leopold, D. A. (2008). Divergence of fMRI and neural signals in V1 during perceptual suppression in the awake monkey. Nature Neuroscience, 11(10), 1193.

September 23

“Neural coding and perception of pitch: Implications for speech and music”

Andrew L. Oxenham, Professor,
Department of Psychology

Pitch - the perceptual correlate of acoustic periodicity - plays an important role in music, speech, and acoustic communication in general. Despite over a century of empirical and theoretical study, much about how pitch is coded in the auditory system remains in dispute. This talk will provide an overview of what we know and don't know about pitch perception, and will describe some recent studies designed to shed further light on the basic mechanisms as well as their implications for speech and music perception in normal and impaired hearing.

Reference for background reading: Oxenham, A. J. (2008). Pitch perception and auditory stream segregation: Implications for hearing loss and cochlear implants Trends in Amplification 12, 316-331.

September 30

Apostolos P. Georgopoulos
Director, Center for Cognitive Sciences
"Neuroprosthetics, Neuromarkers and Cognition: Common Threads in Brain Information Processing"

October 7

Paul Schrater Assistant Professor, Psychology & Computer Science
"Rational control of aspiration in learning"

How much to explore in an unknown environment is controlled by the agent’s beliefs about the value of unexperienced states, which we refer to as the agent’s “aspiration.” To examine the effect of aspiration on exploratory behavior in humans, we conducted a series of experiments that explore whether prior beliefs and inferences about the reward potential of the environment controls investment in exploratory behavior. We show that prior beliefs about the generative model for the environment can account for individual differences in exploration, that statistical information about reward magnitudes modifies exploration, and that knowledge that other's reward experience exceeds their own creates a complete reinitialization of exploration. Theoretically, we have developed a hierarchical model-based Bayesian reinforcement-learning framework that can mimic all of these behaviors by manipulating the agent’s initial prior belief about the size of the state space and/or the magnitude of potential rewards.

October 14

Jacqueline M. Fulvio

"Human observers maximize their individual potential when selecting extrapolation strategies"

It is not uncommon in nature for distinctive strategies to emerge from differences in ability (e.g. distinctive mating strategies for lizards based on physical size), however, this idea has never been expressed or tested in human visual perception. I will present work on visual extrapolation through occlusion, which requires observers to predict the path of a moving object once it has disappeared behind another object. I will first discuss the role of perceptual ability on predictive performance. I will demonstrate that individuals with different perceptual abilities can be statistically better off using distinctive strategies that trade off bias and variance when these abilities are taken into account, and I will provide compelling evidence that this trade-off does occur in human data. I will then discuss the role of experience on extrapolation performance and provide statistical evidence that the nature of task training and exposure changes how well an individual can be expected to perform. I will present data from human participants who were trained under different conditions that show the predicted performance discrepancies. I will conclude with a general discussion about the implications of these findings for current theory and future work.

October 21

Zeb Kurth-Nelson
"Effects of contingency representation on decision making"

We perform computational simulations of decision making under varying contingency beliefs. The contingency beliefs of the agent are represented as state spaces, where discrete situations are classified as states, and the states are linked by transitions describing how one situation leads to another. We characterize how different state spaces result in different patterns of decision making. In particular, a simple change of representation, without changing the actual contingencies of the world, can cause a switch from addictive to non-addictive behavior. These results raise the possibility that addiction (and other disorders of choice) may be treatable by training general cognitive skills or by influencing the construction of contingency representations. Conversely, drugs may exert addictiveness partly by pharmacologically disrupting the construction of healthy state spaces.

Nov 4

Megan R. Gunnar Professor, College of Education + Human Development
"Early Experience and Neurobehavioral Development: Studies of Children Adopted Internationally from Orphanages"

Studies of orphanage-reared infants and toddlers have long figured prominently in the arguments about the importance (or not) of early experiences. Studies in the mid-20th Century on the impacts of early institutional rearing led to the closing of institutions in most western industrialized nations in favor of foster care for young children without permanent parents. The easing of the cold war and opening of the former Soviet Republics and China to international adoption has led to a new wave of research on early institutional care and neurobehavioral developing. This lecture will overview key findings from this new wave of research with a specific focus on the neurobiological correlates of the types of cognitive and socioemotional problems observed in children who spend their first months and years in institutional care.

Nov. 11 

Susan Gelman University of Michigan

"Sharks attack humans, but most sharks don't attack humans: Learning to express generalizations in language"

My talk will examine the challenges that learners face when learning to express general categories (e.g., "sharks" in "Sharks attack humans"). These expressions, known as "generics", are both conceptually and linguistically challenging. Although we experience the world in terms of individual objects and events, we must form abstractions that extend beyond these individual entities. Moreover, the same forms of language that are used to express generics are also used to refer to particular individuals (compare "The dog is a 4-legged animal" to "The dog is sleeping"). I discuss different kinds of learning models, and suggest that generics are a default mode of generalization for human learners.

Nov. 18  

Michael Wilson, Anthropology  and Ecology, Evolution  and Behavior 

Dec. 9    

Ida Toivonen Carleton University, Ottawa, Canada

"The role of duration in sound systems"

The sound systems of natural languages employ a variety of techniques to signal linguistically relevant distinctions. For example, the voicing of the first sound of "bat" distinguishes the word from "pat". This talk focuses on the use of duration in sounds and syllables. Many languages (perhaps most languages) make use of duration in some way in their sound systems. For example, in English, vowels before voiced consonants are longer than vowels before voiceless consonants. This is said to provide an additional cue to a distinction that is otherwise not very salient. In other languages, duration alone marks the difference between words. In Italian, for example duration is distinctive: fatto (fact) and fato (fate) differ in segment duration. The present paper discusses duration in two typologically distinct languages: Inari Saami and Swedish. The two languages both make use of duration, but their quantity systems are reported as radically different. The paper will present results from new data collected from the two languages.

References

• Bye, Patrik, Elin Sagulin, Ida Toivonen. 2009. Phonetic duration, phonological quantity and prosodic structure in Inari Saami. Phonetica 66 (4): 199--121.
• Collinder, Björn. 1952. Three degrees of quantity. Studia Linguistica 5: 28-43.
• Sapir, Edward. 1933.The psychological reality of phonemes. Published originally in French under the title "La Realité psychologique des phonemes, Journal de Psychologie Normale et Pathologique, 30: 247-265. Reprinted in: Sapir Edward. 1949b [1985].Selected Writings in Language, Culture, and Personality ed. and with new foreword by David G. Mandelbaum, epilogue by Dell Hymes. Berkeley and Los Angeles: University of California Press. First paperback edition 1985.