The neurochemistry of memory remains to be determined. Acetylcholine may be one of the neuotransmitters which mediates memory function, since the anticholinergic drug scopolamine produces amnesia in man. This study of scopolamine-induced memory deficits further defines those cognitive processes which are disrupted. The drug does not diminish attention, as assessed with an auditory vigilance task, or initial signal detection. More complex auditory decoding is affected, however. Scopolamine impairs aspects of initial memory acquisition (e. g., encoding and consolidation) and spontaneous memory retrieval. Retention is unaffected. Precise delineation of the neurochemistry of human memory will require comparative studies of amnesia-producing compounds, systematically examining the neuropsychological processes impaired by each.

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The effects of an interference tone on frequency discrimination of a brief tonal signal were investigated. The interference tone was 500 msec in duration and the same intensity as the signal. Changes in frequency discrimination were measured as a function of signal duration, the frequency separation between the interference tone and signal, and the temporal delay between the two. Both ipsilateral-and contralateral-interference conditions were investigated. The addition of an interference tone significanfiy degraded preformance in only one condition: 10-msec signal, trailing interference tone delivered to signal ear. For all other stimulus configurations, frequency discrimination was unaffected by the presence of the interference tone. These data are generally consistent with analogous sensory masking effects characterizing backward and forward masking and do not support cognitive-perceptual models of pitch and recognition.

The time course of the impedance changes caused by the contralateral acoustic reflex was investigated in five normal hearing, young adult subjects The acoustic reflex function was measured with equipment having a time constant of 15 milliseconds which permitted precise temporal measures. Temporal intervals from signal onset and termination to various portions of the acoustic reflex function were derived using an analysis procedure based on the slope function underlying the acoustic reflex response. These temporal intervals are related to physiological events underlying the acoustic reflex.There are three important applications for temporal measures of the acoustic reflex. First, precise temporal measurements may lead to a better understanding of the relationship between the physiology of the stapedius muscle and peripheral auditory input into the reflex mechanism, since impedance measurements of the acoustic reflex reflect stapedius muscle activity."'. ''7 13s4' Second, the acoustic reflex may provide a unique, nonbehavioral measure of initial temporal processing in the auditory system, because the acoustic reflex depends upon peripheral input for its function and involves brain stem central auditory mechanisms.2-Third, a potential diagnostic procedure may be developed for use in clinical audiology if valid and reliable differences in the time course of the acoustic reflex can be demonstrated between normal and hearing-impaired subjects. Previous research has indicated that such temporal measurements of the acoustic reflex may be affected by both cochlear and retrocochlear hear-Unfortunately, there are two major problems to overcome in order to make valid measures of the time course of the acoustic reflex. First, temporal measures must be made with instrumentation that has a short time constant. Second, the analysis of temporal intervals must be based upon a stable aspect of the acoustic reflex waveform.The time constant of many of the reflex measurement systems used in previous research is quite long. For example, an unmodified Madsen 20-70 impedance instrument, commonly used for temporal measures, has been shown to have a time constant on the order of 90 msec.29*30*35 The use of a measurement system with a time constant longer than the phenomenon to be measured casts doubt upon the validity of the temporal measures obtained. The present research used an acoustic impedance instrument with a time constant of 15 msec in order to circumvent this potential problem.A second difficulty is the determination of a stable aspect of the waveform of the acoustic reflex response upon which to base temporal measurements. The waveform of the reflex response is influenced by many factors and is not stable enough to be desirable for use as a foundation upon which to base temporal measures. The present research addressed this problem by using an analysis technique which concentrated upon the first derivative or slope function of the acoustic reflex response. By basing temporal measures upon the points of maximum and minimum slope...