The relationship between the semantics of words and the acoustics of the way they are spoken is explored. Actors spoke warning signal words in an urgent, nonurgent and monotone style, and participants rated the urgency of the words. Results showed effects for signal word and style of presentation. Acoustic analysis showed that the urgent words were spoken at higher frequency with a broader pitch range and were louder than the nonurgent or monotone words. These acoustic differences were used to synthesize artificial versions of signal words in urgent and nonurgent formats. The urgent words were rated as more urgent than the nonurgent words, a finding attributable to their differing acoustics. Within each speaking style the words were acoustically the same, yet effects for signal word were found, suggesting that semantics is also important in urgency perception. This research has implications for the design and implementation of speech warning systems, particularly those in which urgency mapping is required.

Three experiments are reported which explore the relationship between semantic, acoustic and phonetic variables in the judgement of eight warning signal words. Experiment 1 shows that listeners can distinguish very clearly between urgent and non-urgent versions of the words when spoken by real speakers, and that some signal words such as 'deadly' and 'danger' score more highly than words such as 'attention' and 'don't'. It also shows that the three dimensions of perceived urgency, appropriateness and believability of these words are highly correlated. Experiment 2 replicates Experiment 1 using synthesized voices where acoustic variables are controlled. The semantic effects are replicated, and to some extent appropriateness and believability are found to function differently from that of perceived urgency. Experiment 3 compares the same set of eight signal words with a set of phonetically similar neutral words, showing that warning signal words are rated significantly higher, and largely maintain their previous rank ordering.

Two experiments arc described in which participants were required to respond to auditory warnings known to vary in their perceived urgency. In the first, they simply responded to a warning of high, medium or low urgency whilst performing a simultaneous tracking task. Responses to the high urgency warning were faster than to the others. In the second experiment participants carried out an addition task on hearing the warning, and tbe warnings were either matched or mismatched to the difficulty of the task. Results show that responses to the most urgent warnings were again faster, and also that the degree of mismatching between warning and task degraded performance in some conditions.

Two experiments are reported that investigate the effects of acoustics and semantics in verbal warnings. In the first experiment subjects rated the urgency of warning signal words spoken in different presentation styles (URGENT, NON-URGENT, MONOTONE). Significant differences in urgency ratings were found between presentation styles. Acoustic analysis revealed how acoustic parameters differed within these different presentation styles. These acoustic measurements were used to construct synthesised speech warnings that differed in urgency. They were rated in experiment 2 and the predicted differences between the urgency of the words were found. These studies indicate that urgency in natural speech is produced by alterations in a few acoustic parameters and that these alterations can easily be incorporated into synthetic speech to reproduce variations in urgency.

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