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Not Too Slow: The Goldilocks Effect

How words per minute affect engagement in commercials.


It is no secret that television advertisers try to convey a lot of information in a short amount of time; the most common length of a commercial is 30 seconds. To accomplish this, they might have their actors or voice-over speak quickly. However, recent research suggests that speaking too fast (over 200 words per minute) causes an increase in the effort necessary for viewers to comprehend the message. This increase in effort disengages viewers, and the message is lost.

These results might lead ad creators to slow down the speech rate, but this study also found that commercials with 160 words per minute caused the worst performance (memory recall, recognition of information, and physiological responses). There is a sweet spot. The author concluded that a speech rate of 180 words per minute was optimal for conveying a message. The title of this study (Do Your Ads Talk Too Fast To Your Audio Audience? How Speech Rates of Audio Commercials Influence Cognitive and Physiological Outcomes) may have been misleading as some other blogs used this study to state that speech rate should slow down, ignoring the author’s actual results.

The previous study primarily examined memory but did not measure engagement. Barnett and Cerf used EEG to measure neural engagement (as measured by CBC) in movie trailers. They found that engagement increased in trailers with fewer total words — the more words, the less engagement. But again, is the best answer simply slowing the speech rate down in commercials?

To address this question, we collected EEG data while participants viewed 11 publicly available commercials from fast-food restaurants, automobile companies, household products, and financial institutions (two were 15 seconds, and nine were 30 seconds spots.) The commercials had a wide range in speech rate, from zero words to 184 words per minute, with an average of 112. Engagement in the commercials was measured using CBC. The results suggested a positive correlation between words per minute and CBC (Figure 1). That is, as the rate of speech increases, so does engagement, at least up to 184 words per minute.

The previously mentioned research suggested that high speech rates in commercials and movie trailers reduce viewer engagement and later recall. However, these results indicate that the speech rate should not be too slow either. One of the commercials used no words and was also the least engaging. When making commercials, the creators should use caution when deciding the speech rate. If you want your ad to engage the audience and be memorable, use a speech rate that is not too fast but not too slow. Our results suggest the optimal speed is between 120 and 190 words per minute.


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