This is as close to your desired output as I can achieve.

#! perl -slw
use strict;

( my $data = do{ local $/; <DATA> } )=~ s[\n\+][]g;

print "'$1'" while $data =~ m[
    ( .+?                        ## Capture everything (minimally)
       (?: [.!?] \s+             ## A terminator followed by whitespac
+e
         | [a-z]                 ## or a lowercase letter
       )    
    ) 
    (?= [A-Z] | \z )             ## followed by a an uppercase letter 
+or EOS
]xg;

__DATA__
The Tell-Tale HeartEdgar Allen PoeTRUE! nervous, very, very dreadfully
+ nervous I
+ had been and am; but why WILL you say that I am mad? The disease had
+ sharpened
+ my senses, not destroyed, not dulled them. Above all was the sense o
+f hearing
+ acute. I heard all things in the heaven and in the earth. I heard ma
+ny things i
+n hell. How then am I mad? Hearken! and observe how healthily, how ca
+lmly, I ca
+n tell you the whole story.
[download]

c:\test>junk5
'The Tell-Tale Heart'
'Edgar Allen Poe'
'TRUE! nervous, very, very dreadfully nervous I had been and am; but w
+hy WILL you say that I am mad? '
'The disease had sharpened my senses, not destroyed, not dulled them. 
+'
'Above all was the sense of hearing acute. '
'I heard all things in the heaven and in the earth. '
'I heard many things in hell. '
'How then am I mad? '
'Hearken! and observe how healthily, how calmly, I can tell you the wh
+ole story.
'
[download]

Which doesn't quite match, but then I do not see how (or more importantly why?) you differenciate between splitting after the question mark here I am mad? The disease but decide not to here How then am I mad? Hearken!?