Channel-Capacity, Intelligibility and Immediate Memory

When subjects try to remember lists of digits played to them through pulse-modulated white noise the number of errors they make is greater than would be expected if digitrecognition errors and immediate memory errors were independent (Exp. 1). A second experiment compared recall of digits in early list positions, when digits in subsequent list positions were presented through noise, and in clear. Digits in early positions were less well remembered when digits in later list positions had to be discriminated through noise. In a third experiment prose passages were played to subjects who subsequently answered questions about their factual content. Judged by this technique recall of the first half of a prose passage is less accurate if the second half must be heard through noise than if the entire passage is heard through a good fidelity system. These results together are interpreted as demonstrations that increased difficulty of recognition of speech through noise may interfere with other activities, (conveniently termed “rehearsal”) which may be necessary to efficiently retain data in memory.