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3.Results

3.1.Identification

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).

F
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’).
T
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.

L
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.