Twenty operators were given a task which required answering one of two simultaneous voice messages. The task was performed under a variety of conditions produced by combinations of four experimental “aid” variables: horizontal spatial separation of the sound sources, aural shaping filters which made the tone quality different in each channel, visual cues which indicated the channel about to call the operator, and facilities to “pull down” a desired message from the initial source into a headphone or a loudspeaker near the operator's ear. It was found that the use of horizontal separation and/or the filtered messages greatly improved the operator's performance. Visual cues had no apparent effect on ability to answer the message except when used with pull down facilities. The pull down facilities aided the operator to some extent. Some speculations are advanced about the nature of recognizing and attending to a message in the presence of another message.

The pressure-flow equations used in computer simulation studies of phonation lack experimental validation. Two polyester resin models of the laryngeal airway with rectangular glottal ducts were constructed in order to obtain the relationships between translaryngeal pressure drop and volume flow through the airway. The results are in disagreement with the early estimates of Wegel [Bell Syst. Tech. J. 9, 207-227 (1930)], but match the predictions given by Ishizaka and Matsudaira [SCRL Monograph No. 8 (1972)] to within approximately +/- 10% for typical translaryngeal pressures for speech, with larger discrepancies being found for the model with the larger glottal diameter. The equation given by van den Berg et al. [J. Acoust. Soc. Am. 29, 626-631 (1957)] may not be properly compared because their supraglottal pressure hole location may have been different from that used in the present study. The data from the two models also are compared to recent empirical studies using an enlarged model of the larynx [J. Gauffin et al., Conference on Vocal Fold Physiology, Madison (1981)].

Cinéfluorographic films of velar movement were made simultaneously with surface electromyographic recordings of velar muscle contraction during the production of selected syllables and sustained vowel and nasal phonemes. The data were analyzed to determine (1) the extent of variation in velar position during the production of various phonemes in relation to alterations in duration and phonetic context; (2) the extent of variation in velar electromyographic activity during the same speech utterances; and (3) the extent to which velar elevation and electromyographic activity covary during the production of sustained vowel and nasal phonemes and during alterations in duration and phonetic context. These data are discussed in relation to the hypothesis, advanced by certain investigators, that the velum acts in an all-or-none (ON-OFF) fashion.

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