The stimuli for the experiment were generated from the set of 48 sentences described in the previous section. A complete list of all sentences used in the study is given in Appendix A. These sentences were used in all the experiments of this study (Experiments 1 – 5).
The stimuli were digitized (44.1 KHz) and edited for the presentation in the experiment. In the first experiment a pause with the duration of 1 s was inserted into the sentences (cf., Hirsh-Pasek et al., 1987). Two conditions were generated depending on the position of the pause. In the natural condition, the pause was inserted at the clause boundary before the coordinating conjunction und (‘and’). To create an unnatural version
45 This exclusion criterion was pre-defined on the basis of the duration of the first clause in the original
material. The durations of the first clause ranged from 2284 ms to 2963 ms (mean: 2585 ms). Thus, infants with a mean orientation time of less than 3 seconds in one condition were considered not to have heard enough of the sentences to recognise the critical difference between the natural and unnatural samples at all.
of each sentence, a pause was inserted between the infinitive particle zu (‘to’) and the verb of the first clause, a position which did not coincide with a phrase boundary.
In the natural condition, the naturally occurring pause at the clause boundary, that is, before the coordinating conjunction und (‘and’) was deleted and replaced by an artificially generated silent pause of 1 s duration. In the original sentence material, the naturally occurring pauses at the clause boundary had a mean duration of 523 ms, with a range from 368 ms to 750 ms.
In the unnatural condition a pause was inserted between the infinitive particle zu (‘to’) and the verb in the first clause. In the original sentences there was not always a measurable pause between the two words. In only 19 of the 48 sentences a pause occurred. The duration of these pauses was between 0.02 and 0.09 s. This indicates that usually no pause is inserted between the two words in naturally spoken sentences. In addition, the naturally occurring pause before und (‘and’) was shortened to 100 ms in the sentences in this condition. This additional manipulation was made to avoid too much variability in the duration of the sentences between the natural and the unnatural condition (cf., Hirsh-Pasek et al., 1987, second experiment; and Gerken et al., 1994, footnote 5). All other naturally occurring pause locations were the same in both conditions and therefore remained intact.
To test the possible range of a shortened pause duration that would not interfere with the overall sentence intonation, a pre-test with adults was conducted. Two sets of test sentences were prepared. The first test-set had the original pause duration at the clause boundary shortened to 200 ms before und (‘and’). The second test-set had a shortened pause of 100 ms duration at the boundary. To verify whether the shorter duration did not impair the perception of the prosody of the whole sentence, a rating was conducted. Five adult listeners, all native speakers of German and naïve with regard to the purpose of the experiment, listened to the two sentence sets. The sentences were presented pairwise in randomised order. The listeners indicated on a sheet of paper whether the first or the second presentation of each sentence sounded more natural (two-alternative forced-choice decision task). The analysis of these ratings showed that the five adult listeners performed at chance level. They had a 50.3% preference for the test sentences with a 100 ms pause duration compared to a 49.7% preference for sentences with a 200 ms pause duration at the clause boundary. Based on the result of this pre-test, the naturally occurring
pauses at the clause boundary were shortened to 100 ms in the sentences of the unnatural condition in the infant experiment. Other features, like final lengthening or pitch in the surroundings of the artificially inserted pauses were not manipulated.
As the original material consisted of isolated sentences as opposed to natural conversation, pauses also had to be inserted between the six subsequent sentences constituting a test passage in the experiment. Research on pause structures in natural speech indicated that pauses between sentences are longer than pauses within sentences (e.g., Butcher, 1981, for German). To preserve this natural pause hierarchy, a pause of 1.5 s duration was inserted between the sentences. The resulting auditory stimuli for the infant experiment consisted of 16 blocks of six sentences each. Half of the blocks (natural condition) had an artificial pause of 1 s duration inserted at the clause boundary and the other half (unnatural condition) had the pause inserted at a non-phrase boundary location within the first clause of the sentence, resulting in stimulus blocks like the following example, which is the first block of the training trials in the experiment (for the organisation of the 48 sentences into text blocks see Appendix B):
Natural condition:
Der Bäcker verspricht Anja zu lächeln ___1 s und die Sache zu vergessen. ___1.5 s Der Cousin droht Markus zu verschwinden ___1 s und das Fahrrad zu stehlen. ___1.5 s Die Mutter schwört Holger zu überlegen ___1 s und das Gedicht zu schreiben. ___1.5 s Der Onkel droht Sonja zu lärmen ___1 s und das Bild zu zerreißen. ___1.5 s
Die Köchin verspricht Peter zu gehen ___1 s und den Einkauf zu erledigen. ___1.5 s Der Bruder schwört Ellen zu schleichen ___1 s und die Angst zu überwinden.
‘The baker promises Anja to smile ___1 s and to forget about it.’ ___1.5 s
‘The cousin threatens Marcus to disappear ___1 s and to steal the bicycle.’ ___1.5 s
‘The mother vows (to) Holger to think ___1 s and to write the poem.’ ___1.5 s
‘The uncle threatens Sonja to be noisy ____1 s and to tear apart the picture.’ ___1.5 s
‘The cook promises Peter to go ___1 s and to do the shopping.’ ___1.5 s
Unnatural condition:
Der Bäcker verspricht Anja zu ___1 s lächeln und die Sache zu vergessen. ___1.5 s Der Cousin droht Markus zu ___1 s verschwinden und das Fahrrad zu stehlen. ___1.5 s Die Mutter schwört Holger zu ___1 s überlegen und das Gedicht zu schreiben. ___1.5 s Der Onkel droht Sonja zu ___1 s lärmen und das Bild zu zerreißen. ___1.5 s
Die Köchin verspricht Peter zu ___1 s gehen und den Einkauf zu erledigen. ___1.5 s Der Bruder schwört Ellen zu ___1 s schleichen und die Angst zu überwinden.
‘The baker promises Anja to ___1 s smile and to forget about it.’ ___1.5 s
‘The cousin threatens Marcus to ___1 s disappear and to steal the bicycle.’ ___1.5 s
‘The mother vows (to) Holger to ___1 s think and to write the poem.’ ___1.5 s
‘The uncle threatens Sonja to be ___1 s noisy and to tear apart the picture.’ ___1.5 s
‘The cook promises Peter to ___1 s go and to do the shopping.’ ___1.5 s
‘The brother vows (to) Ellen to ___1 s tiptoe and to overcome the fear.’
The mean duration of the sentences in the natural condition was 5.28 s (range: 4.90 s to 5.70 s) and the mean duration of a sentence in the unnatural condition was 5.35 s (range: 4.93 s to 5.80 s; see Appendix C).
The mean duration of the blocks for the natural condition was 39.17 s (ranging from 38.60 s to 40.43 s) and the mean duration of the blocks for the unnatural condition was 39.60 s (with a range from 39.05 s to 40.75 s; see Appendix D).