CHAPTER 19 Reflections, Images, and the Precedence Effect Figure 19.15 shows detection thresholds for sounds chosen to exemplify different degrees of "continuity," starting with continu- ous pink noise and moving through Mozart, speech, castanets with reverberation, and "anechoic" clicks (brief electronically generated pulses sent to the loudspeakers). The result is that increasing "continuity" produces the kind of progressive flatten- ing seen in Figures 19.8 and 19.9. The perceptual effect is similar if the "continuity" or "prolongation" is due to variations in the structure of the signal itself or due to reflective repetitions added in the listening environment. In any event, pink noise generated an almost horizontal flat line, Mozart was only slightly different over the 80 ms delay range examined, speech produced a moder- ate tilt, castanets (clicks) with some recorded reverberation were even more tilted, and isolated clicks generated a very compact, steeply tilted threshold curve. Assuming that the patterns seen in previous data for speech and Mozart apply to other sounds as well, Figure 19.16 shows a com- pilation and extension of data portraying detection thresholds and second-image thresholds for Mozart, speech, and clicks. To achieve this, the second-image curve for clicks had to be "cre- ated" by elevating the click threshold curve by an amount similar to the separation of the speech and music curves. Absolute proof of this must await more experiments, but it is interesting to go 20 10 Second image--Moza rt 0 Relative level (dB) Se con d im -10 age --s peec h -20 Detection--Mozar t De tec tio n -30 --speech -40 -50 0 10 20 30 40 Delay (ms) 50 60 70 80 FIGURE 19.14 Data from Figure 19.6a showing thresholds obtained using speech and