Newt Gingrich, campaigning in Iowa with his wife Callista, has been the target of negative advertising.  Editor's note: Ruthann Weaver Lariscy, is a professor in the department of advertising and public relations in the Grady College at the University of Georgia. Her research in political and health advertising is published in academic and professional publications.  (CNN) -- Negative ads in the Iowa caucuses are just the tip of the iceberg. While as recently as three election cycles ago there were still some reservations about slinging mud, in 2012 negative ads are a virtual must-have component of every political campaign.  Many people say they dislike how ugly American campaigns have become. In fact, some research explores whether political apathy and disengagement are associated with increasing negativity. But the evidence is inconclusive -- about as many of us seem to be entertained by attack ads as are turned off by them.  Most of us maintain that we dislike negative ads, especially certain types of them. Among those that are strongly disliked are ads that are considered too personal or that shed a negative light on a family member. Running an ad that criticizes Newt Gingrich's three marriages, for example, borders on dangerous.  The danger is that if people judge the attacking candidate as being "too dirty" there is a good possibility the ad will boomerang -- that is, turn more voters against the attacker than the candidate being attacked. One way candidates slip around this possibility is to reserve the most harmful attacks for outside PACs and interest groups to sponsor.  We seem to dislike least those attack ads that stick to topics directly relevant to the campaign -- most notably voting record and positions on issues. These ads are unlikely to boomerang and likely to have some impact. Other elements that are important for an attack to be successful include new information, being entertaining and being plausible.  So if we don't like negative ads and even perhaps suspect they contribute to political malaise, why are they increasingly dominating candidates' strategies?  Gingrich's drop in polls in Iowa last month was no accident -- it was choreographed by negative advertising. Ruthann Lariscy  The answer is simple: They work. And they work very well. Gingrich's drop in polls in Iowa last month was no accident -- it was choreographed by negative advertising.  Our brains process information both consciously and non-consciously. When we pay attention to a message we are engaged in active message processing. When we are distracted or not paying attention we may nonetheless passively receive information. There is some evidence that negative messages may be more likely than positive ones to passively register. They "stick" for several reasons.  First, one of the most important contributors to their success may be the negativity bias. Negative information is more memorable than positive -- just think how clearly you remember an insult.  Second, negative ads are more complex than positive ones. A positive message that talks about the sponsoring candidate's voting record, for example, is simple and straightforward. Every negative ad has at least an implied comparison. If Mitt Romney is "not a true conservative," then by implication the candidate sponsoring the ad is saying he or she is a true conservative. This complexity can cause us to process the information more slowly and with somewhat more attentiveness.  I often use an analogy of running water from my garden hose. If I stand at the top of a smooth concrete driveway and turn on the water, it flows quickly, directly, and fairly seamlessly to the bottom. This is much how a positive message goes through the brain. If I take my same hose and stand at the top of a grassy hill and turn it on, the water travels more slowly than on the concrete hill, it picks up some loose dirt, and inevitably some of it gets "stuck" in grass along the way.  Negative information, too, travels more slowly because of its enhanced complexity. It benefits from the negativity bias, and inevitably some of that negative information gets "stuck" in our minds, even if we don't like the ad or agree with its contents.  There is another benefit negative messages achieve that positive messages largely do not. In psychology the principle is called the sleeper effect.  Over time, a message is likely to become disassociated from its sponsor. There is some evidence that negative ads benefit from this effect: Immediately upon hearing and seeing an attack, you might dismiss it as being "just politics." Then, typically several weeks later when you are making your voting decision, something in your mind recollects the negative information. You have likely forgotten when or where or from whom you heard it -- but the negative content "stuck."  I wish I could say that mud-slinging in politics will end -- that since we are largely disgusted by its usage, negative political advertising will fade away. But I can't. Though negative political messages have always been around, they are increasing in quantity and are reaching different kinds of campaigns. While at one time attacks were reserved largely for campaigns for national office, today they are evident in local and statewide campaigns as well.  Unfortunately, negative political ads work. And unless you live in a cave, you are likely not immune to their effects.  The opinions expressed in this commentary are solely those of Ruthann Lariscy.
Though most people claim to dislike them, negative ads are now a must-have for every presidential campaign. Ruthann Lariscy explains why.