Electronic averaging of potentials recorded from the human scalp reveals the presence of small average responses following the presentation of click stimuli. These responses are first detectable near the subject's psychophysical threshold and vary in amplitude with click intensity. It is suggested that the short-latency components of these responses are cortical in origin.

No abstract

Difference limens for three frequencies (250, 1000, and 4000 cps) were determined for two trained observers by two psychophysical methods: the ABX procedure and the method of constant stimulus differences or AX procedure. Though the two observers differ considerably insensitivity, their DL's for the AX procedure are less than one-half of their DL's for the ABX procedure. Comparison of these data with data in the literature on DL's for frequency indicates a wide range of values for different psychophysical procedures and for different subjects. Some observations are reported that illustrate the effect of such factors as practice and ensemble of stimulus conditions upon the size of the DL. The influence of the stimulus ensemble upon judgement time is discussed briefly. In view of all the experimental data, it would be rather imprudent to postulate a “true” DL, or to infer the behavior of the peripheral organ from the size of a DL measured under a given set of conditions. While there is undoubtedly some relation between the size of the DL and the so-called channel capacity, there is little reason to assume that the relation is a particularly simple one, given the different operations by means of which these two quantities are determined.

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The hypothesis is advanced that a time-invariant pattern of frequency response can be discriminated in the presence of a variable pattern of frequency-response irregularity only when the listening interval is of sufficient duration to allow the variable part of the total response pattern to be averaged out. Qualitative evidence seems to support the hypothesis, but quantitative evaluation of the needed integration times is still wanting. If the effect is real, however, it may have an important bearing on the interpretation of the conventional A--B tests used for the assessment of sound reproducing systems.T can easily be demonstrated that a fixed pattern of black on white, such as block printing, can be recognized visually through a moving overlay which consists of a random pattern of opacity and transparency, even when the moving pattern of black and white is dense enough to mask the signal pattern completely when the overlay is not in motion. In effect, the fixed contrasts of the signal pattern appear to be integrated at some stage of the visual process so that the signal pattern is "detected" even in the presence of time-variable black and white "noise" that fluctuates about a mean gray. The purpose of this note is to suggest that a similar effect may occur in audition: that a time-invariant pattern of frequency response can be discriminated in the presence of a variable pattern of frequency-response irregularity when, and only when, the listening exposure is of sufficient duration to allow the variable part of the total response pattern to be averaged out.Several lines of indirect evidence tend to support this hypothesis. Unfortunately, we do not yet have the data needed to determine the quantitative relation between the fixed and variable components of the frequency-response irregularity and the integration time or averaging interval required to detect one in the presence of the other. We ought perhaps to be chagrined about this lack of data since the acoustical situation in question is one to which we are exposed almost constantly. It is represented most typically by the judgments we form of the quality of sound reproducing systems heard under ordinary listening conditions in normally reverberant rooms. It is well known that the pure-tone steady-state frequency response of such rooms, as measured between a fixed simple source and a fixed "point" receiver, is always highly irregular. Neither the fact that speech and music signals seldom do excite such rooms to the steady state nor the ability of the ear to respond selectively to first arrivals can gainsay the fact that the point-to-point transfer function of the room is characterized by such an irregular frequency response. In view of this the listener would appear to be entitled to ask the impertinent question, why do we care whether a loudspeaker has a "flat" response or not when the listening room is sure to introduce a link in the chain of reproduction that is much more highly irregular in frequency response ?Of course, the fact is well established that w...