Earspeaker coupling effects on auditory action potential and brainstem responses.

Human auditory nerve action potential and brainstem evoked response input-output functions were obtained with standard audiometric earspeakers coupled in three different ways, commonly used in auditory evoked potential laboratories (ie, free field, circumaural cushions, standard audiometric cushions). All other stimulus values were matched as closely as possible. Under the different coupling conditoins, substantially different amplitude-intensity and latency-intensity functions were generated for both auditory nerve N1 and brainstem V peaks. Differences among the input-output functions were predictable from differences in click frequency spectra.

Normal short-latency electrophysiological filtered click responses recorded from vertex and external auditory meatus.

We recorded normal electrophysiological responses to third-octave filtered clicks from external auditory meatus (EAM) and vertex electrodes referred to coupled earlobe electrodes (forehead ground). From both vertex and EAM, polarity-sensitive responses predominated at low frequencies and exhibited characteristics of both phase-locked neural responses (frequency-following response or FFR) and cochlear microphonics (CM). The FFR-like response predominated at the vertex site and the CM-like response predominated at EAM. At high frequencies, polarity-insensitive responses closely resembled rectangular-pulse click action potentials and brainstem evoked potentials, with clearly defined N1 and V peaks recorded from EAM and vertex, respectively. As frequency was lowered, the N1 and V peak latencies increased, the peaks broadened, and the latency-intensity curves steepened with greater prolongation occurring at lower click intensities. Lowering click frequency also shortened the N1-V interval and caused the plot of N1-V interval versus click intensity to become steeper. Plots of polarity-insensitive response amplitudes and thresholds against frequency revealed a high frequency bias for both N1 and V, but the V "frequency response" was flatter. A possible explanation of the shortened N1-V interval at low click frequencies based on this flatter V "Frequency response" is presented.

Pion radiotherapy: studies with nuclear emulsions.

Nuclear emulsions were used to provide information on (1) the pion star distribution for a therapy beam; (2) star production as a function of pion energy and residual range in nuclear emulsion; (3) the distribution of nuclear framgent ranges in emulsion; and (4) the neutron energy spectrum and fluence produced by negative pion capture in tissue, during treatment of a patient. This last item is important for determining the whole-body dose delivered to a patient undergoing pion radiotherapy.