Neuroscience 2005 Abstract
| Presentation Number: | 850.20 |
|---|---|
| Abstract Title: | The predicted level-dependence of click intensity-difference limens and click loudness can hypothetically be computed from the N1 component of the compound action potential but are inaccurate unless the presumed spike count includes the spikes underlying |
| Authors: |
Nizami, I. R.*1
1Boys Town National Research Hospital, Omaha, NE |
| Primary Theme and Topics |
Sensory and Motor Systems - Auditory -- Cochlea and neuropathy |
| Session: |
850. Auditory: Cochlea and Neuropathy Poster |
| Presentation Time: | Wednesday, November 16, 2005 11:00 AM-12:00 PM |
| Location: | Washington Convention Center - Hall A-C, Board # N4 |
| Keywords: | AUDITORY, SIGNAL DETECTION THEORY, COCHLEA, ENCODING |
The acoustic click evokes no peristimulus firing in individual primary afferents. Hypothetically, then, click level must be encoded in the synchronous burst of voltage spikes evoked across the entire eighth nerve (E.A. Radionova, Sov. Phys.-Acoust. 8, 1963, 350-355). It is impossible to count those spikes, but they do produce a measurable epiphenomenon, the N1 component of the peripheral compound action potential (CAP). Each spike contributes equally, so that N1 can be assumed proportional to spike count. If spike count is assumed to have a Gaussian distribution whose variance does not change over a just-detectable-change in level, the intensity-difference limen is given by Signal Detection Theory as follows: d-prime times the standard deviation of N1, divided by the rate-of-change of N1 with level. The term “N1” can be replaced by “loudness” if loudness is assumed proportional to spike count, and if a just-detectable-change in loudness is the change in percept corresponding to a just-detectable-change in level. Hypothetical intensity-difference limens were obtained by applying the equation above to the empirical N1s of Frishkopf (M.I.T. Res. Lab. Electron. Tech. Rep. 307, 1956, 1-74). The predictions are larger at moderate levels and smaller at low and high levels than the observed intensity-difference limens, which show a “mid-level hump” (e.g. Raab & Taub, JASA 46, 1969, 965-968). Further, the assumption that N1 is proportional to spike count forces the predicted loudness relation to mimic the mid-range “knee” seen in the plot of N1 versus click level; but the empirical loudness relation has no “knee”. The departure of models from data implies that the click-evoked spike count cannot be inferred from N1. But convergent evidence in the literature suggests that a portion of the evoked spike count is hidden as the N2 potential. Accounting for the latter can qualitatively explain the discrepancies between models and data.
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2005 Neuroscience Meeting Planner. Washington, DC: Society for Neuroscience, 2005. Online.
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