Browsing by Subject "Periodicity"

Now showing 1 - 3 of 3
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    A neurophysiological study into the foundations of tonal harmony.
    (Neuroreport, 2009-02-18) Bergelson, Elika; Idsardi, William J
    Our findings provide magnetoencephalographic evidence that the mismatch-negativity response to two-note chords (dyads) is modulated by a combination of abstract cognitive differences and lower-level differences in the auditory signal. Participants were presented with series of simple-ratio sinusoidal dyads (perfect fourths and perfect fifths) in which the difference between the standard and deviant dyad exhibited an interval change, a shift in pitch space, or both. In addition, the standard-deviant pair of dyads either shared one note or both notes were changed. Only the condition that featured both abstract changes (interval change and pitch-space shift) and two novel notes showed a significantly larger magnetoencephalographic mismatch-negativity response than the other conditions in the right hemisphere. Implications for music and language processing are discussed.
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    Oscillations by minimal bacterial suicide circuits reveal hidden facets of host-circuit physiology.
    (PLoS One, 2010-07-30) Marguet, Philippe; Tanouchi, Yu; Spitz, Eric; Smith, Cameron; You, Lingchong
    Synthetic biology seeks to enable programmed control of cellular behavior though engineered biological systems. These systems typically consist of synthetic circuits that function inside, and interact with, complex host cells possessing pre-existing metabolic and regulatory networks. Nevertheless, while designing systems, a simple well-defined interface between the synthetic gene circuit and the host is frequently assumed. We describe the generation of robust but unexpected oscillations in the densities of bacterium Escherichia coli populations by simple synthetic suicide circuits containing quorum components and a lysis gene. Contrary to design expectations, oscillations required neither the quorum sensing genes (luxR and luxI) nor known regulatory elements in the P(luxI) promoter. Instead, oscillations were likely due to density-dependent plasmid amplification that established a population-level negative feedback. A mathematical model based on this mechanism captures the key characteristics of oscillations, and model predictions regarding perturbations to plasmid amplification were experimentally validated. Our results underscore the importance of plasmid copy number and potential impact of "hidden interactions" on the behavior of engineered gene circuits - a major challenge for standardizing biological parts. As synthetic biology grows as a discipline, increasing value may be derived from tools that enable the assessment of parts in their final context.
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    Stream segregation on a single electrode as a function of pulse rate in cochlear implant listeners.
    (2010) Duran, Sara I
    While cochlear implants usually provide a high level of speech recognition in quiet, speech recognition in noise and music appreciation remain challenging. In response to these issues, several studies have proposed increasing the number of channels of information through multiple pulse rate strategies. For the selection of pulse rates, studies of multi-rate strategies have considered implementation issues such as harmonics, pitch saturation, and tonotopic order but have not considered the fundamental perceptual question of whether two pulse rates can provide independent channels of information on a single electrode. This study measures stream segregation as an indicator of whether different pulse rates on the same electrode can be perceived independently. This approach differs from that of previous stream segregation studies which focused on stimulation of alternating electrodes, with the motivation of determining a relationship between electrode stream segregation and speech perception in challenging noisy environments. Stream segregation in this study was measured using two stimulus sequences following an A-B-A-B structure where A and B were different pulse rates stimulatingthe same electrode. The timing between A and B was controlled to provide either aregular or irregular gap between the two pulse trains. The threshold at which subjects could distinguish a regular rhythm from an irregular rhythm was used as an estimate of stream segregation since detecting an irregular rhythm is an easier task when the streams are fused. Stream segregation in cochlear implant users, as with normal hearing listeners, was hypothesized to be influenced by factors such as frequency and the relative timing between tones. To attempt to assess the relationship between these and stream segregation, subjects’ rate discrimination and gap detection abilities were also measured. The results of this study indicate that stream segregation can occur for two pulse rates on a single electrode; thus, it may be possible to use pulse rates to create additional channels of information. Further, the stream segregation results were not strongly correlated with the gap detection or rate discrimination results. The lack of correlation with the gap detection results suggests that the task was measuring a separate perceptual phenomenon rather than providing another measure of gap detection. The lack of correlation with the rate discrimination results suggests that discriminability may not be a limiting factor in selecting rates for segregation. These results may have implications for the future design of multi-rate speech processing strategies.