The code you posted does not compile because it is missing semicolons at the end of a few lines. Here is code that compiles (and is perltidy):

open RAN, "f03_20859_04aug08RANmri_block2.log"
  or die "Unable to open file!";
open NEW, ">>Out.txt"
  or die "Unable to open file for output!";
open AVG, "Avg.txt"
  or die "Unable to open file for averaging!";
while ( my $text = <RAN> ) {
    if ( $text =~ /\bResponse\b/ ) {
        @response = split( /\s/, $text );
        print NEW $text, "\n";
    }
    print AVG $response[4];
}
close NEW;
close RAN;
close AVG;
[download]

If you still have problems, you need to be specific: show us a few lines of the input file, your actual output and your expected output.