The Beckman Institute Graduate Student Seminar Series presents the work of outstanding graduate students working in Beckman research groups. The seminar starts at Noon in Beckman Institute Room 1005 and is open to the public. Lunch will be served.

What happens when we fail to find what we’re looking for?
Brian Levinthal

Traditional research in visual search (the ability to find, select, and process a target among distractor items) has focused on either very high level factors such as goals and instructions, or very low level factors such as the physical properties of the search environment. An intermediate category of factors, known as inter-trial effects, are neither high nor low level. Inter-trial effects refer to the influence of very recent experience on current searching behavior, and appear in a wide variety of search contexts. Our research focuses on one particular inter-trial effect, which characterizes the visual system’s response to the failure to find a target item. As it turns out, the visual system responds quite strongly, and inhibits “features” that defined a failed search. Our research demonstrates that this response is broad, occurs for simple features (e.g. colors) as well as complex categories (e.g. faces or houses), and is generalizable beyond a single simple search task.

Single Molecule Absorption Spectra of Carbon Nanotubes Detected by Scanning Tunneling Microscopy
Greg Scott

The scanning tunneling microscope (STM) is a powerful tool for the study of surfaces and adsorbates due to its high spatial resolution.  The addition of optical excitation to the STM introduces a means for examining single-molecules with high spatial and spectral resolution simultaneously.  We utilize rear-illumination and frequency-modulation of a laser excitation source to overcome the thermal problems association with optically-assisted STM.  We directly detect absorption in molecules by monitoring changes in their electronic structure.  Carbon nanotubes have generated significant interest due to their unique physical properties and may find use in a number of nanotechnologies.  We use our single-molecule absorption monitoring technique to probe the optical absorption spectrum of the first electronic transition of semi-conducting single-walled carbon nanotubes on silicon surfaces.  Discrepancies exist between the calculated optical spectra and experimental spectra measured with other techniques.  We aim to use our spatially-resolved direct-detection method to resolve these inconsistencies.

Diffuse Optical Imaging of Songbirds
James Lee

Diffuse Optical Imaging (DOI) uses light to study brain activity. The noninvasive nature of this method opens new avenues of exploration for the study of song recognition and possibly song production in songbirds.

DOI is potentially compatible with many other neuroscience or molecular methods.  Used alone, DOI may permit long-term studies with the same subject.  This would allow us to explore the effects of accumulated experience on learning.

DOI runs silently so it is well suited for studying auditory responses. It is also inexpensive, portable, and free from scheduling constraints associated with shared instruments.

In experiments with the anesthetized animal, reliable signals have been recorded.  These responses to auditory stimuli appear to localize to auditory areas in the brain.  Future steps involve recording from awake animals and attempting to image brain activity in the behaving animal.