for my $index (0..$#params) {
  next if $index % 2 == 0;
  my $parameter = $params[$index];
  my $spec = $params[$index + 1];
  # do something from here...
}

##</code><code>##

for (grep { not $_ % 2 } 0 .. $#params) {
    my ($parameter, $spec) = @params[$_, $_+1];
    ...
}