Table 2 below shows the extent to which the referents of lexical NP subjects persist in the discourse.  The first column indicates the morphosyntactic form of the lexical NPs.  The 'No Persist' column indicates the number of lexical NPs that refer to a referent that is not referred to again in the next ten lines of discourse.  The 'Full Lex' column indicates the number of lexical NPs that refer to a referent that is subsequently referred to with another lexical expression.  The  'Subset' column indicates the number of lexical NPs that refer to a set of referents of which a subset is referred to in the subsequent ten lines of discourse.  The 'Pronominal' column indicates the number of lexical NPs that refer to a referent that is subsequently referred to with a pronoun.
 

1.  When they first said the subject, my mind went kind of blank.(sw_0305)
2.  lightning or something knocked it out.(sw_ADD)
3.  the food here is outrageous.(sw_0223)
4.  The thing I don't like about dogs sometimes is that the house will just reek, of the dogs, and constantly.(sw_0338)

The referent in 1 is anchored to the speaker through the use of the possessive determiner.  Furthermore, the referent may be considered inferrable based on general assumptions regarding speech participants and the statement borders on the idiomatic.
In 2, generic reference does not create a new the topic.  Example 3 appears to be a case of subject or perhaps adverb focus.  The conversation is about outrageous prices.  Speaker A has just mentioned the outrageous price of hot dogs and  speaker B responds with 3 and continues with a discussion of the prices for tickets. Example 4 demonstrates the 'the thing' + relative clause construction that was common in the definite determiner data.

Full Lexical Persistence
    The numbers for a second full lexical referring expression following the use of a lexical subject NP are relatively low.  Here are some examples:

5.  my wife did some teaching at like, uh, like a private tutoring place.(sw_0067)
6.  well, of course to them a dollar was a dollar at four and five years old.(sw_0055)
7.  and, and supposedly this money is going into some kind of fund so that when it comes our turn to retire, the money will be there for us.(sw_0032)

In 5, the referent is referred to again as 'mom' after a shift of perspective.  Example 6 is perhaps the most typical of the data despite the fact that it is a tautology.  Many of the instances of full lexical persistence were predicate nominal constructions. In 7 an almost identical lexical referring expression is used for a subsequent mention. Instances of this type are rare in the data.

Subset Persistence
    Lexical NP subjects were coded 'Subset' if they referred to a set of referents of which reference to a member or subset was continued.  Here are some examples:

8.  the band saw is really nice.(sw_0315)
9.  Well certain schools do it.(sw_0346)

In 8, the singular definite referring expression is used with generic meaning. After 8 the speaker continues "I have an Inca," referring to a brand of band saw. Example 9 is part of a chain of lexical referring expressions: 'certain schools' leads to 'this school' as a lexical subject, which in turn leads to 'your school' in a shift in perspective similar to 5 above.

Pronominal Persistence
    The high number for pronominal persistence suggests that one of the functions of lexical subjects may be to introduce or maintain topics.  Here are some examples:

10.  Um, the death penalty surely fits in well with, uh, in a penal situation where you 're trying to punishment (sw_0061)
11.   But, um, I mean, ev-,  evidently a normal cow produces that much too,(sw_0280)

In 10, the referent of the lexical subject is maintained by two pronominal references to the end of the discourse segment.  The generic use of the indefinite singular expression in 11 coerces plural pronominal reference in the following clause: "but they're just so spread out on ranches and stuff..."(sw_0280).