Detection of Signals Presented at Random Times
James P. Egan, Gordon Z. Greenberg, Arthur I. Schulman · The Journal of the Acoustical Society of America · 1959
Three types of experiments measured the decrement in (de)12 that results from uncertainty in the time of onset of a sinusoid (1000 cps, 0.25 sec) presented against a continuous background of noise. (1) A light defined an observation interval during which the signal either was or was not presented [p(SN) = 0.5]. The signal, when presented, started at an instant randomly selected within the observation interval. The interval of time uncertainty during which the tone might start was systematically varied from 0 to 8 sec. After each observation interval, the listener indicated his confidence that a tone was presented by using a rating scale. (2) The sinusoid was or was not presented [p(SN) = 0.5] at a randomly selected instant. A fixed time after this instant, the listener was informed (by a flash of light) of the real time at which the signal might have occurred, and he responded with a rating. (3) The sinusoid was presented a number of times in a 2-min observation interval. The temporal intervals between the presentations of the tones were randomly selected. No further indication was given to the listener as to the times at which the tones were presented. Over a series of sessions, the listener adopted various criteria, and he pressed a single “yes-key” whenever he “heard a tone.” This situation is the most difficult one to analyze, because a trial is not defined. Nevertheless, this method of free response results in a family of curves of temporal coincidence [n(y)/sec as a function of time after onset of the signal]. These curves allow an estimate of the coordinates of the point of intersection, (de)12, of an assumed operating characteristic. Results for the three types of experiments are based on a total of around 105.3 responses. [This research was supported by the Operational Applications Laboratory, Air Force Cambridge Research Center, under Contract AF 19(604)-1962.]