Carl Iver Hovland (June 12, 1912 – April 16, 1961) was a psychologist working primarily at Yale University and for the US Army during World War II who studied attitude change and persuasion. He first reported the sleeper effect after studying the effects of the Frank Capra's propaganda film Why We Fight on soldiers in the Army. In later studies on this subject, Hovland collaborated with Irving Janis who would later become famous for his theory of groupthink. Hovland also developed social judgment theory of attitude change. Carl Hovland thought that the ability of someone to resist persuasion by a certain group depended on your degree of belonging to the group.
With the advent of government propaganda in support of the United States’ participation in World War II, the artifacts worth investigating helped with increase of persuasive communication with intent to affect behavior, attitude, and values. These artifacts had a remarkable amount of money invested into them, however, were they effective? This concept of effectiveness and affecting change within individuals, interpersonal relations, and persuasion are exactly what Hovland was interested in. Carl Hovland's contributions to the field of communications were three-fold. First, he emphasized micro-level analysis, next he was interested in all facets of interpersonal communication, and finally he revolutionized persuasive research.
Carl Iver Hovland was born in Chicago on June 12, 1912. In Chicago, he attended the Lloyd School and then completed high school at the Luther Institute. He entered Northwestern University at the age of 16, receiving his B.A. in 1932, and an M.A. the following year. He then transferred to Yale, where he obtained the Ph.D. in 1936. Except for a three-year research stint in Washington during World War II, Hovland remained associated with Yale the rest of his life, rising rapidly through the academic ranks to a Sterling Professorship at the age of 36.
As a child, Hovland had a deep interest in music. In fact, up until college when psychology became a major part of his life he was looking into a musical career.  At the age of six years, he read Latin textbooks fluently, beginning the development of the linguistic skills which were to be so important in his later studies of alchemy and religion. In 1938 he married Gertrude Raddatz, a piano student like Hovland, in Chicago. During the late 1930s and early 1940s Hovland made major contributions to several areas of human experimental psychology, such as the efficiency of different methods of rote learning. From his close association with Clark L. Hull and other psychologists working at the Yale Institute of Human Relations, Hovland developed a comprehensive view of the behavioral sciences that led him to extend the analytic experimental approach of research on human learning to underdeveloped areas of research in the human sciences.
Hovland's first opportunity to work intensively in the underdeveloped area of social psychology arose during World War II, when he took a leave of absence from Yale for over 3 years to serve as a senior psychologist in the War Department. He was recruited by Samuel Stouffer, also a sociologist who was on leave from University of Chicago. Carl had the responsibility of leading a research team of fifteen researchers. His main role was to conduct experiments on the effectiveness of training and information programs that were intended to influence the motivation of men in the American armed forces. He assembled a group of six psychology graduate students who worked with him on these studies for several years. One of the most widely cited of the pioneering experiments on opinion change by Hovland and his group involved testing the effects of a one-sided versus a two-sided presentation of a controversial issue. The results contradicted contentions of totalitarian propagandists, who claimed that a communication that presents only one side of the issue will generally be more successful than one that mentions the opposing side of the argument. These wartime studies were reported in Experiments on Mass Communication (1949), written jointly by Hovland, A. A. Lumsdaine, and F. D. Sheffield.
Carl Hovland was a big man, soft in speech, gentle in manner, as incredibly quick and deft in physical movement as in intellection. In his earlier years he was quite shy, but the social rigors of the life to which his extraordinary talents inevitably exposed him helped to develop the quiet ease of manner that characterized his middle age. He was unfailingly cheerful, even in the last tragic year of his life, and continued to work with his students and colleagues until his brief final illness. It was this capacity for being always helpful, always objective, that placed him inconstant demand as a consultant, not only to students, but to all the leading Foundations, to half a dozen major Government agencies, and to the behavioral research arms of several great corporations. He was repeatedly honored by his colleagues in one way or another-as an APA representative to the Social Science Research Council, as a member of that Association's Board of Directors, by election to the American Academy of Arts and Sciences, to the American Philosophical Society, and to the National Academy of Sciences.T he honor he appreciated most deeply, perhaps,was the award of the Warren Medal by the Society of Experimental Psychologists,word of which reached him only a month before his death. 
Psychological research was Hovland's intellectual joy however. Especially in his early career, his investigations covered a wide range of topics. By the time he had secured his doctorate, Hovland had published a dozen research papers and collected data for at least half a dozen. Four of these papers were in the American Journal of Physiology, two in the Yale Journal of Biology and Medicine, and others in psychological journals . His papers in psychological journals included a study of test reliability, a major review of the literature on apparent movement, as well as his four classical papers on conditioned generalization from his doctoral dissertation.
After the war Hovland returned to Yale University, where he recruited several members of his wartime research team, with whom he continued to study the factors that influence the effectiveness of social communications. Among Hovland's best-known studies are those elucidating the influence of the communicator's prestige and the ways that prestige effects disappear with the passage of time. For example, Hovland and his collaborators showed that when a persuasive message is presented by an untrustworthy source, it tends to be discounted by the audience, so that immediately after exposure there is little or no attitude change; but then, after several weeks, the source is no longer associated with the issue in the minds of the audience and positive attitude changes appear. This "sleeper effect" was shown to vanish, as predicted, if the unacceptable communicator was "reinstated" several weeks later by reminding the audience about who had presented the earlier persuasive material.
For 15 years Hovland and his group systematically investigated different ways of presenting arguments, personality factors, and judgmental processes that enter into attitude change. While pursuing his own research, Hovland continually encouraged his associates on the Yale project, a study of the conditions under which people are most likely to change their attitudes in response to persuasive messages. The Yale Group's work was first described in Hovland's book Communication and Persuasion, published in 1953.
His major interests in his last few years of life were with concept-formation, which he approached with computer simulation. In 1952 he published a demonstration that the problems of concept-learning can be solved by an hypothetical decoding machine, and also provided both a notational system and an analysis of the problem of concept-learning that were widely adopted by other researchers in this field.
First, Hovland began to emphasize micro-level analysis of propaganda and its effects. Hovland’s army experiments were the beginnings of that micro-level analysis of an individual. Hovland’s “core conceptual variable was attitude.”  With the pre existing research in the discipline being devoted to “measuring attitudes and to investigating factors in involved in attitude change,” it was different for Hovland to come in and look at an individual’s predisposition to action when exposed to persuasive messages.
Hovland believed that if he was able to recognize the attitude an individual has towards a trigger, he would be able to predict the behavior and actions of an individual over time.  However, there were many studies that argued the contrary and showed that “an attitude toward a person or object does not predict or explain an individual’s overt behavior regarding that person or object.”  This interesting revelation of low correlation did not necessarily render findings useless but instead led to further research on how under certain circumstances it was actually possible to change a person’s behavior via their attitudes. While Hovland focused on an individual rather than a group level, he began to take into consideration interpersonal communication in the form of persuasion. Specifically, Hovland was responsible for carrying out a series of studies that contributed to the “cumulative understanding of persuasion behavior that has never since been matched or even rivaled.” 
To test and apply his theorization Hovland worked proposed the SMCR Model. The SMCR model consists of four components – Source Variables, Message Variables, Channel Variables, as well Receiver Variables. By manipulating each of these variables, Hovland was able to advance his “message-learning approach to attitude change.” There were problems with his particular approach, however, in that by focusing on a single dimension of the SMCR model, Hovland was unable to do more than isolate a factor rather than study the synergy between the different variables.  Although there were limitations to these studies, Hovland’s steadfast and fastidious nature allowed for a body of research that was able to continuously investigate this interpersonal communication in the form of persuasion research.
Along with not being able to investigate the interaction of the Source, Message, Channel Receiver elements and their interplay within a study, Hovland’s research arguably had one more flaw. This flaw in Hovland’s research was that communication happened in a singular direction and was furthermore linear in its nature. It is this linear communication that made Hovland and his research seem like an “oversimplification” to some communication scholars. Hovland provided new research in the form of micro-level research, interpersonal research, as well as persuasive research.
Hovland employed experimental research in his studies and was therefore able to trace causality between variables. He showed the effects of various elements in the SMCR model on persuasion: sources (high credibility vs. low credibility, sleeper effect), types of messages (one-sided vs. two-sided, fear appeals) and channels on cognitive and affective changes.
Hovland’s work was great as far as his experimental methods were concerned but critics of his work also found some important problems. In particular, he has been criticized by looking at individuals as unconnected to each other, although he was generalizing them as members of a media audience. He found strong cognitive effects of the war films on his audience but he may have prematurely declared the media as weak in their effects. Also, results from experiments cannot be generalized easily to the population. He wanted to establish laws of persuasion but had to be content with variable effects of his predictor variables on persuasion of individuals.
In the last decade of his life Hovland's research on verbal concepts and judgment led him into an intensive analysis of concept formation. Once again he played a pioneering role in developing a new field of research - computer simulation of human thought processes.
A month before his death, he was honored with the award of the Warren Medal by the Society of Experimental Psychologists.
Carl Iver Hovland died in on April 16, 1961.When Hovland learned that he had cancer,he continued to work with his Yale doctoral students and conduct persuasion experiments. Finally, when he could work no more, he left his office in the Psychology Department, went to his home in New Haven, drew a bathtub full of water, and drowned himself(Schramm,in press b)
A summary of the research developments and theoretical ideas that have grown out of Hovland's pioneering projects is presented in a comprehensive chapter by Irving L. Janis and M. Brewster Smith in Herbert C. Kelman, ed., International Behavior: A Social-Psychological Analysis (1965). Hovland's work is also discussed in Arthur R. Cohen's Attitude Change and Social Influence (Basic Topics in Psychology) (1964).