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<Paper uid="W05-0501">
  <Title>The Input for Syntactic Acquisition: Solutions from Language Change Modeling</Title>
  <Section position="7" start_page="7" end_page="7" type="evalu">
    <SectionTitle>
5 Results
</SectionTitle>
    <Paragraph position="0"/>
    <Section position="1" start_page="7" end_page="7" type="sub_section">
      <SectionTitle>
5.1 Sufficient Restrictions
</SectionTitle>
      <Paragraph position="0"> Figure 1 shows the average VO access value over time of an Old English population restricted to learn only from degree-0 unambiguous trigers.</Paragraph>
      <Paragraph position="1"> These restrictions on acquisition seem sufficient to get the shift from a strongly OV distribution to a strongly VO distribution to occur at the right time.</Paragraph>
      <Paragraph position="2"> We also note that the sharper population-level change emerges after a build-up of individual-level changes in a growing population.</Paragraph>
      <Paragraph position="3">  to learn only from degree-0 unambiguous trigers. Thus, we have empirical suport for the acquisition proposal since it can satisfy the language change constraints for Old English word order.</Paragraph>
    </Section>
    <Section position="2" start_page="7" end_page="7" type="sub_section">
      <SectionTitle>
5.2 Necessary Restrictions
</SectionTitle>
      <Paragraph position="0"> We have shown these restrictions - to learn only from degree-0 unambiguous trigers - are sufficient to get the job done. But are they necessary? We examine the &amp;quot;unambiguous&amp;quot; aspect first - can we stil satisfy the language change constraints if we don't restrict ourselves to unambiguous trigers? This is especially attractive since it may be resource-intensive to determine if  an uterance is unambiguous. Instead, we might try simply using surface word order as a triger. This would create many more trigers in the input - for instance, a Subject Verb Object uterance would now be parsed as a VO triger. Using this definition of triger, we get the folowing data from the historical corpus:  degree-0 (D0) clauses at various times, based on data from the historical corpus.</Paragraph>
      <Paragraph position="1"> The most salient problem with this is that even at the earliest point in time when the population is suposed to have a strongly OV distribution, it is the VO grammar - and not the OV grammar - that has a significant advantage in the degree-0 data. A population learning from this data would be hardpressed to remain OV at 100 A.D., let alone between 100 and 150 A.D. Thus, this definition of triger wil not suport the historical facts - we must keep the proposal which requires unambiguous trigers.</Paragraph>
      <Paragraph position="2">  We turn now to the degree-0 data restriction. Recall that the degree-1 data has a much higher OV advantage before 150 A.D. (see Table 1). It's posible that if children heard enough degree-1 data, the population as a whole would remain OV to long and be unable to shift to a VO &amp;quot;enough&amp;quot; distribution by 120 A.D. However, the average amount of degree-1 data available to children is about 16% of the input, based on estimates from modern English children's input. Is this small amount enough to keep the Old English population OV to long? With our quantified model, we can determine if 16% degree-1 data causes our population to not be VO &amp;quot;enough&amp;quot; by 120 A.D. Moreover, we can estimate what the threshold of permisible degree-1 data is so that the modeled Old English population can match the historical facts. Figure 2 displays the average VO access value in 5 Old English populations exposed to different amounts of degree-1 data during acquisition. As we can see, the population with 16% of the input comprised of degree-1 data is not able to match the historical facts and be VO &amp;quot;enough&amp;quot; by 120 A.D. Only populations with 1% or less degree-1 data in the input can.</Paragraph>
      <Paragraph position="3">  for populations with differing amount of degree-1 data available during acquisition.</Paragraph>
      <Paragraph position="4"> This data suports the necessity of the degree-0 restriction since the amount of degree-1 data children hear on average during acquisition (~16%) is to much to allow the Old English population to shift at the right time.</Paragraph>
    </Section>
  </Section>
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