Published and Forthcoming Papers

Sales Taxes and Internet Commerce
L. Einav, D. Knoepfle, J. D. Levin, and N. Sundaresan
American Economic Review, forthcoming
[was NBER Working Paper  No. 18018  (2012)]
We estimate the sensitivity of internet retail purchasing to sales taxes using eBay data. Our first approach exploits the fact that a seller's location—and therefore the applicable tax rate—is revealed only after a buyer has expressed interest in an item. We document how adverse tax "surprises" reduce the likelihood of purchase and shift subsequent purchases toward out-of-state sellers. We then use more aggregated data to estimate that every one percentage point increase in a state's sales tax increases online purchases by state residents by almost 2 percent, while decreasing their online purchases from state retailers by 3-4 percent. [forthcoming, American Economic Review; accepted May, 2013]
Value Computations in Ventral Medial Prefrontal Cortex During Charitable Decision Making Incorporate Input from Regions Involved in Social Cognition
T. A. Hare, C. F. Camerer, D. T. Knoepfle, J. P. O'Doherty, and A. Rangel
Journal of Neuroscience  30  583-590  (2010)
Little is known about the neural networks supporting value computation during complex social decisions. We investigated this question using functional magnetic resonance imaging while subjects made donations to different charities. We found that the blood oxygenation level-dependent signal in ventral medial prefrontal cortex (VMPFC) correlated with the subjective value of voluntary donations. Furthermore, the region of the VMPFC identified showed considerable overlap with regions that have been shown to encode for the value of basic rewards at the time of choice, suggesting that it might serve as a common valuation system during decision making. In addition, functional connectivity analyses indicated that the value signal in VMPFC might integrate inputs from networks, including the anterior insula and posterior superior temporal cortex, that are thought to be involved in social cognition.
Studying Learning in Games Using Eye-Tracking
D. T. Knoepfle, J. T. Wang, and C. F. Camerer
Journal of the European Economic Association  7  388-398  (2009)
We report results from an exploratory study using eye-tracking recording of information acquisition by players in a game theoretic learning paradigm. Eye-tracking is used to observe what information subjects look at in 4x4 normal-form games; the eye-tracking results favor sophisticated learning over adaptive learning and lend support to anticipatory or sophisticated models of learning in which subjects look at payoffs of other players to anticipate what those players might do. The decision data, however, are poorly fit by the simple anticipatory models we examine. We discuss how eye-tracking studies of information acquisition can fit into research agenda seeking to understand complex strategic behavior and consider methodological issues that must be addressed in order to maximize their potential.
Hypersensitivity to oxygen and shortened lifespan in a Drosophila mitochondrial complex II mutant
D. W. Walker, P. Hajek, J. Muffat, D. Knoepfle, S. Cornelison, G. Attardi, and S. Benzer
Proceedings of the National Academy of Sciences  103  16382-16387  (2006)
Oxidative stress is implicated as a major cause of aging and age-related diseases, such as Parkinson's and Alzheimer's, as well as ischemia-reperfusion injury in stroke. The mitochondrial electron transport chain is the principal source of reactive oxygen species within cells. Despite considerable medical interest, the molecular mechanisms that regulate reactive oxygen species formation within the mitochondrion remain poorly understood. Here, we report the isolation and characterization of a Drosophila mutant with a defect in subunit b of succinate dehydrogenase (SDH; mitochondrial complex II). The sdhB mutant is hypersensitive to oxygen and displays hallmarks of a progeroid syndrome, including early-onset mortality and age-related behavioral decay. Pathological analysis of the flight muscle, which is amongst the most highly energetic tissues in the animal kingdom, reveals structural abnormalities in the mitochondria. Biochemical analysis shows that, in the mutant, there is a complex II-specific respiratory defect and impaired complex II-mediated electron transport, although the other respiratory complexes remain functionally intact. The complex II defect is associated with an increased level of mitochondrial hydrogen peroxide production, suggesting a possible mechanism for the observed sensitivity to elevated oxygen concentration and the decreased lifespan of the mutant fly.