Capacity Demands in Short-Term Memory for Synthetic and .Natural Speech

Abstract

Three experiments were performed that compared recall for synthetic and natural lists of monosyllabic words. In the first experiment, presentation intervals of 1, 2, and 5 s per word were used. Although free recall was consistently poorer overall for the synthetic lists at all presentation rates, the decrement for synthetic stimuli did not increase differentially with faster rates. In a second experiment, zero, three, and six digits were presented visually for retention prior to free recall of each spoken word list in a preload paradigm. Fewer subjects were able to correctly recall all of the digits for the six-digit list than the three-digit list when the following word lists were synthetic. The third experiment required ordered recall of lists of natural and synthetic words. Differences in ordered recall between the synthetic and natural word lists were substantially larger for the primacy portion of the serial position curve than the recency portion. These results indicate that difficulties observed in the perception and comprehension of synthetic speech are due, in part, to increased processing demands in short-term memory. Allen (1976) and Nickerson (1975) have suggested that prosodic differences between synthetic and natural speech present the major difficulty to the comprehension of synthetic speech, particularly fluent synthetic speech. In natural speech, intensity, relative durations of segments and words, and changes in pitch are modulated by a complex set of physiological, phonetic, and linguistic factors that are as yet poorly understood (see Klatt, 1976). To attain

Constraints on the perception of synthetic speech generated by rule

“…In another experiment, Luce et al (1983) presented subjects with lists of 10 natural words or 10 synthetic words to be memorized and recalled in serial order. Overall, natural words were recalled better than synthetic words.…”

Comprehension of natural and synthetic speech: effects of predictability on the verification of sentences controlled for intelligibility

“…It is not immediately obvious to us how one would account for these findings, given the results of an earlier study by Luce, Feustel & Pisoni (1983), which showed increased error rates in serial recall when capacity demands of the task were increased. We do not know of any current theory of human information processing or language comprehension that would predict the results observed by Moody & Joost.…”

“…When subjects listened to more difficult information in some passages, differences in performance between the natural speech group and the synthetic speech group were not observed. However, when the comprehension materials were easy, significant differences between the natural and synthetic speech groups emerged.It is not immediately obvious to us how one would account for these findings, given the results of an earlier study by Luce, Feustel & Pisoni (1983), which showed increased error rates in serial recall when capacity demands of the task were increased. We do not know of any current theory of human information processing or language comprehension that would predict the results observed by Moody & Joost.…”

“…It is not immediately obvious to us how one would account for these findings, given the results of an earlier study by Luce, Feustel & Pisoni (1983), which showed increased error rates in serial recall when capacity demands of the task were increased. We do not know of any current theory of human information processing or language comprehension that would predict the results observed by Moody & Joost. If there is some relationship between comprehension difficulty and signal quality, then differences in performance among natural speech, synthetic speech, and digitally vocoded speech should emerge more robustly under experimental conditions in which there are greater capacity demands on the processes used in perception or comprehension.…”

Perception of Synthetic Speech

“…We also carried out a series of exper iments to determine the effects of encoding synthetic speech on working memory and rehearsal processes [LFP83]. Subjects were given two different lists of items to remember: The first list consisted of a set of digits visually presented on a CRT, screen; the second list consisted of a set of ten natural words or ten synthetic wordi.…”