The highest downvote to upvote ratios and highest downvote to comment tree depth increase (i.e. discussion happening) occur in the time periods of 12-1 and 3-4 US East coast time by a factor of about 2. Those are actually the only hours of the day when my account personally (the only one I was tracking) has an upvote/downvote ratio less than 1 (ratio was 1.5-2 for the rest of the day). Based on the fact that I would say that there certainly exists a group of users who "reflexively" downvote. An alternate explanation is that people who hate what I have to say are most likely to use HN during those hours. Both those options seems highly plausible to me.
This analysis is about a year old and based on about 6mo of data. I have since lost the script and the records so don't expect any further analysis.
For comments I went to https://news.ycombinator.com/threads?id=dsfyu404ed and whatever URL the "more" link was, found every comment of mine that was < 1 day old and then every comment not by me that was a reply to one of those and then listing the ids of additional comments by me and additional replies to my comments for that minute. Comments were tracked by ID to avoid duplicates.
Pages were grabbed with wget and all the parsing was done with the standards linux/bash utilities