John T. Hogan

Evaluation of vowel duration as a cue for the voicing distinction in the following word‐final consonant

Previous measurements have indicated that vowels before voiced and voiceless consonants exhibit a systematic duration difference, the former being longer approximately by a 3:2 ratio than the latter. Experiments with synthetic speech have shown that vowel duration is an important cue for the voicing distinction of the following consonant in word-final position. In the present paper the role of this cue is evaluated for natural speech, which may also contain secondary cues for maintaining this distinction. The stimuli, spoken by a female speaker, were 24 English monosyllabic words ending with voiced stops, fricatives, and consonant clusters after intrinsically long and intrinsically short vowels. Duration of the vowel nucleus was systematically reduced using a digital gating technique. Recognition rates as a function of vowel duration were obtained. Category change takes place mainly for intrinsically long vowels and for high vowels in combination with final fricatives alone or in consonant clusters. In other cases, category change cannot be established even after the vowel duration is reduced to only 30% of its original duration. In particular, the presence of a long voice bar for a final voiced stop will make shortening of the vowel perceptually less effective. A multiple regression analysis of the experimental data indicates that in natural speech not only vowel duration, but also voice bar duration, duration of silent closure preceding the final release transient, and duration of the release burst or frication noise, depending on the consonant type, vary in weight as cues for voicing under different vowel- and consonant-type conditions.

Dispersion in models of categorical perception

Abstract A signal detection theory model of auditory discrimination with a nonlinear mapping from stimulus continuum to perceptual continuum can account for the enhanced discrimination at the category boundary found in categorical perception. Properties of this transformation are specified by a unimodal “dispersion function”. Furthermore, it is shown that a system consisting of two acoustic feature detectors with an associated decision function is also a dispersive system, which models categorical perception of a stimulus continuum as well as boundary shifts under adaptation. The effect of detector adaptation on discrimination is discussed in view of three different types of decision variable and different types of detector noise.

The effect of context on dative position

Abstract The putative freedom of dative position in English sentences is questioned. In terms of the distribution of Given and New information in discourse, it is hypothesized that in certain (‘motivating’) contexts, dative position is highly constrained, while in other (‘non motivating’) contexts, it is not. An experiment is reported which tests such a hypothesis by means of a recognition memory task for sentences in different types of contexts. It was found that subjects are indeed sensitive to changes in dative position in motivating contexts but not in nonmotivating contexts. The results provide experimental support for the Given-New strategy of information distribution. Furthermore it is argued that such a strategy can be extended to numerous other syntactic phenomena, and it is concluded that a sentence-bound grammatical description is inadequate to represent such facts, while an alternative formal system sensitive to discourse phenomena can handle the facts in a natural and revealing way.

Publications Received for Review

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Markedness as a discourse management device: the role of alternative adverbial clause orders

The hypothesis is explored that a major function of marked structures, specifically marked clause orders in complex sentences containing adverbial clauses, is to signal the beginning of a new discourse unit. A method is presented for defining discourse units and their boundaries which avoids the circularity of definition of discourse units and markedness. The resuts from the narrative data reveal that marked structures are found significantly more often than unmarked ones at discourse unit boundaries, while unmarked structures are significantly more frequent within discourse units. It is conclued that an important function of marked structures is to manage discourse flow

Audible alarm signals for anaesthesia monitoring equipment

To address the problem of auditory alarms on anaesthesia monitoring and delivery devices whose signal is masked by the noises of other operating room equipment, a set of signals having the characteristics of spectral richness, frequency modulation, and temporal patterning were electronically generated, and were tested for detectability against operating room equipment noises in a laboratory setting. A set of signals was identified which can, under these circumstances, be detected with at least 93% accuracy at −24 dB signal-to-noise ratio.

Affective responses to commercial and experimental auditory alarm signals for anaesthesia delivery and physiological monitoring equipment.

The affective response of subjects to the sounds of commercial and experimental auditory alarm signals was tested using a standard experimental protocol for measuring mood states and changes. Both types of signal evoked affective response. The commercial signals, however evoked more response than the experimental signals, and that response was more negative in affect. A subset of the experimental signals, distinguished by specific acoustic characteristics, evoked particularly low levels of affect. The implications of low-affect alarms for the operating room are discussed.

An Analysis of the Temporal Features of Ejective Consonants

This paper reports some temporal measurements of glottalic ejective consonants. Measurements of pre-release silence before stops, the time from consonant release to vowel onset, and the post-release silent interval are obtained and submitted to analyses of variance. Also several interesting properties emerge from the study. First, the silent interval between release of consonant and vowel onset is an important factor relating to the characterization of voice onset time. Second, F2 and F3 transitions do not regularly appear in the beginning of the vowel nucleus as a cue for place of articulation.

A Study of Kono Tone Spacing

Measurements were made of the fundamental frequency of a register two-tone language, Kono, a Northern Mande language from the Niger-Congo group. This language has the tonal feature of downstep which conveys linguistic information in specific contexts and introduces a terracing effect on successive high tones. The physical values were converted into their musical scale equivalents and comparisons were made with a three-tone system. They were found to be different. Observations of local and global tone ranges were made and were discussed in terms of tone spacing.

Generation of speech continua through monaural fusion

A procedure based on monaural fusion has been developed to construct acoustic continua between natural speech sounds, to be used in studies of speech perception. Two speech stimuli of similar temporal structure and different spectral composition are precisely aligned in time and presented simultaneously to the listener. By mixing both stimulus components in varying intensity ratios, a transition from one component to the other can be achieved. Such stimulus continua have several advantages over the synthetic continua commonly used in studies of categorical perception and related phenomena: They are based on real speech stimuli; the endpoint stimuli are unambiguous; and the stimuli are characterized by a well-defined physical variable, the relative intensity of the two components.