Figures 4 and 5 present the results obtained in the binary identification tasks, i.e., the forced choice between ‘command’ ~ ‘no command’ (Figure 4) and between ‘question’ ~ ‘no question’ (Figure 5).
igure 4. Percent ‘command’ responses as a function of stimulus step (terminal F0 increments in 0.25 ERB steps) in a binary identification task (‘command’ ~ ’no command’).
he psychometric function for the ‘command’ responses is very steep. The category boundary between ‘command’ and ‘no command’ is located at a step size of 2.7, and the margin of uncertainty runs between 2.2 and 3.7, i.e., a cross-over from 75% to 25% ‘command’ responses is effected by an increase in the terminal pitch of the stimulus of 1.5 step (i.e., 0.37 ERB).
Figure 5. Percent ‘question’ responses as a function of stimulus step (terminal F0 increments in 0.25 ERB steps) in a binary identification task (‘question’ ~ ’no question’
A complete cross-over is also found for the ‘question’ ~ ‘no question’ task. The category boundary finds itself at a stimulus value of 3.6, whilst the margin of uncertainty runs between 2.3 and 4.9, i.e., an interval of 2.6 increments of 0.25 ERB. We may note that the category boundaries in the ‘command’ and the ‘question’ tasks do not coincide, but are separated along the stimulus axis by almost a complete step: 2.7 versus 3.6 or 0.9 step. Note, once more, that none of the subjects had been alerted to the possible existence of an intermediate category between ‘command’ and ‘question’. Therefore, the emergence of the interval between the ‘command’ and the ‘question’ boundaries might be taken in justification of such an intermediate category.
et us now turn to the results of the ternary identification task in which all the listeners who had already responded to the stimuli were now required to classify the nine stimulus types as either ‘command’, ‘conditional subclause’ or ‘question’. These results are shown in Figure 6.
Figure 6. Ternary identification of stimuli as ‘command’, ‘conditional clause’ or ‘question’. Category boundaries are indicated.
The boundary between ‘command’ and the ‘continuation’ categories is at 2.8; this is hardly different than the ‘command’ ~ ’no command’ boundary that was found in the binary response task. This, then, would seem to be a very robust boundary, showing that at least ‘command’ intonation has well-defined linguistic status. The boundary between ‘continuation’ and ‘question’ is less clearly defined. Also, the maximum scores in these two categories are around 80% rather than 90% or more. Although there is no ambiguity in the listeners’ minds whether a stimulus is a command or something else, the choice between ‘continuation’ and ‘question’ seems more ambiguous leaving room for a minority response in the order of 20%. This would indicate to us that we are dealing here with a continuum rather than with a dichotomy. Finally, we may note that the (soft) category boundary between ‘continuation’ and ‘question’ is located at a stimulus value of 7.2. The boundary, then, that sets off ‘question’ from ‘no question’ responses proves very unstable: there is a shift from the binary response task (3.6) to the ternary task (7.2) of no less than 3.6 points along the stimulus continuum.
It would seem, then, that the ‘command’ category is highly stable and well-established in the minds of the listeners. The ‘question’ boundary, however, is rather poorly defined, as a result of several circumstances. The cross-over points for the ‘question’ category of individual listeners vary over a wide range of stimulus values, i.e., between 2.2 and 8.5 step number, with a fairly even spread of values in between these extremes. Moreover, for two listeners no cross-over to the ‘question’ category could be found at all; here the listeners never gave the ‘question’ response in more than 75%. Also, some listeners have extremely sharp cross-overs to the ‘question’ category, but others show large margins of uncertainty.
Figure 7 presents the mean percentage of successfully discriminated stimuli that were actually different (hereafter ‘hits’), and the percentage of false alarms, i.e. ‘different’ responses to (identical) AA stimuli. The false-alarm rate is roughly 20% across the entire stimulus continuum. This value can be seen as a bias for responding ‘different’. Generally, an increment of 0.25 ERB is discriminated above the 20% bias level, with the exception of the difference between stimulus steps 5 and 6. The discrimination function shows two local peaks. The first one is very large, and is located between stimulus steps 2 and 3. This peak obviously coincides with the stable category boundary found between ‘command’ and the non-command responses (whether binary or ternary). A much smaller second discrimination peak may be observed between stimulus steps 6 and 7, which location may well reflect the rather poorly defined category boundary between ‘continuation’ and ‘question’.
igure 7. Percent ‘different’ judgments to nine identical stimulus pairs (false alarms) and eight pairs differing by one step (hits).
4.Conclusions and discussion
Let us now try to formulate answers to the research questions that we asked in section 2. The first two questions, which I will attempt to answer together, asked whether the domain-final boundary tones are contiguous categories along a single tonal dimension, and map onto the command, continuation and question meaning in a one-to-one fashion. The results of our experiments clearly indicate that this is indeed the case. Our listeners had no difficulty in using the three response alternatives provided to them. When the terminal pitch was lower than the preceding pivot point in the contour the responses were almost unanimously for ‘command’. When the IP-final pitch was higher than the preceding pivot point, the incidence of ‘continuation’ responses increased up to and including step 4, and decreased for higher terminal pitches which were more readily identified as questions as the terminal pitch was higher. Although there was always some ambiguity between the ‘continuation’ and ‘question’ alternatives, the results clearly indicate that ‘continuation’ is signaled by moderate final pitch, and question by (extra) high pitch.
The latter finding corresponds with our suggestion that asking a question involves a higher degree of appeal by the speaker to hearer than asking the listener’s continued attention. We may also note that our result clashes with Caspers (1998). She found that the intermediate final pitch (or high level pitch in her experiment) was unambiguously identified as continuation; extra high final pitch ambiguously coded either continuation or question. Comparison of Caspers’ and our own results is hazardous since the utterance-final tone configurations differ, not so much at the underlying tone level, but at the surface. It seems to me that the discrepancy between Caspers’ and our own findings can be resolved if we accept the possibility that Caspers’ extra high terminal pitch was simply not high enough to elicit the 80% ‘question’ responses that we got in our experiment.
The results so far concur with van Heuven & Kirsner (2002). However, we may now go on to consider the third, fourth and fifth question, which asked where the category boundaries are located along the final pitch continuum between ‘L%, ‘%’ and ‘H’, in the binary and ternary response tasks, and to what extent the boundaries coincide with a peak in the discrimination function.
The results obtained in the binary (‘command’ ~ ‘no command’) and ternary (‘command’ ~ ‘continuation’ ~ ‘question’) identification tasks are virtually the same, yielding the same location of the boundary (at step 2.7) separating the ‘command’ category from the rest of the stimulus continuum. However, a very unstable boundary is found in the binary ‘question’ ~ ‘no question’ task (at step 3.6), which is reflected in the poorly defined boundary separating the ‘continuation’ and ‘question’ categories in the ternary response task (at step 7.2). Moreover, we have seen that the category boundary between ‘command’ and ‘no command’ coincides with a huge peak in the discrimination function. Although there is a modest local maximum in the discrimination function that may be associated with a boundary between ‘continuation’ and ‘question’, this peak is not very convincing.
I take these findings as evidence that there is a linguistic, or phonological, categorization of the IP-final boundary tone continuum in just two types, which is best characterized as low and non-low. The low boundary tone signals dominance or superiority on the part of the speaker. This is the boundary tone that is suited for issuing statements and commands. The non-low boundary tone signals subservience of the speaker to the hearer; the speaker appeals to the hearer for his continued attention or for an answer to a question.
The non-low part of the boundary opposition, however, represents a gradient, paralinguistic continuum between a moderate appeal (asking for the hearer’s continued attention) and a stronger appeal (asking the hearer for a verbal reply to a question). Here the lower terminal pitches are associated with weaker degrees of appeal (or subservience), and the higher levels with strong appeal, but in a continuous, gradient, non-phonological manner.
Our results indicate that earlier findings reported by Remijsen & van Heuven (1999, 2003) are to be viewed with caution. We now know that the proper task to be imposed on listeners should not be to decide whether the stimulus is a statement (or a command) versus a question. If binary response alternatives are required, then the categories should be ‘statement’ versus ‘no statement’ but a better procedure would be to ask the listener to respond by choosing from three categories: ‘statement’ (equivalent to ‘command’ in our experiments ~ ‘continuation’ ~ ‘question’. Had such precautions been taken by Remijsen & van Heuven, their category boundary would have been much better defined with less listener-individual variation.
Methodologically, we argue that the classical identification-cum-discrimination paradigm is a useful diagnostic tool in intonation research which allows linguists to decide experimentally whether a melodic contrast is categorical and therefore part of the phonology, or continuously gradient and therefore phonetic or even paralinguistic.