Grant Imahara cringes as he prepares to set off the slap machine, while Kari Byron waits.

"Who are the MythBusters? Adam Savage and Jamie Hyneman. Between them more than" 50 years of special effects experience. (Yes, 50 now. The math is easy to check.) Joining them, alas, no more: Grant Imahara, Tory Belleci, and Kari Byron. "They don't just tell the myths. They put them to the test."

On the Discovery Channel series MythBusters' season finale (episode 222, "Plane Boarding") ended with original MythBusters Adam and Jamie announcing that their build team members were leaving the show. Kari Byron had been with the series in one capacity or another since its second pilot episode in 2003; Tory Belleci since 2004; and Grant Imahara since 2005. Kari and Tori grew from being background crew members (whom the cameras sometimes avoided showing) into full cast members, and then robotics expert Grant came along to replace "Mistress of Metal" Scottie Chapman. Now they depart, having fought for truth (justice and American way optional) by testing hundreds of myths that they ultimately deemed "busted," "plausible," or "confirmed." Along the way, they tested only one half of the Yerkes-Dodson curve and left the other half unaddressed. Having "slapped some sense" into understimulated, underaroused build team members, they have not conversely "slapped them silly" or "slapped them stupid" when overstimulated and overaroused.

Once upon a time (2010), Kari, Grant, and Tory put an idiom to the test to see if you really can "slap some sense" into someone. They suffered for their craft, literally, because for this one they each got slapped and then slapped some more. Grant and Tory built a slap machine that would deliver slaps of consistent force to whoever sat in its strike path. Each build team member completed several tests of reflexes, judgment, and coordination at different times under each of three conditioned: normal, impaired, impaired-plus-slap. 

Impairment methods: Grant sat in a truck full of ice blocks before each test; Tory and Kari also went without food or sleep for an entire day, then sat in that ice truck for 30 minutes before each test. They performed worse under "impaired" conditions than they had "normal" baseline conditions. When impaired, a slap helped them focus and do better. Overall, this led them to confirm the "slap some sense" idiom. 

The image below shows an example of how they performed on one of the tests. The data measured compared their performance on a firing range, shooting "bad guy" pictures without shooting any "good guys." 

In their after show video, they discussed why they did not induce panic in anyone before slapping them, citing some similarities in adrenal responses when cold and when panicky. On the face of it, that sounds reasonable enough, but there is a problem there. When underaroused, the body might release adrenaline to try to increase arousal from an understimulated state; metaphorically, the body is trying to "slap some sense" into itself to improve functioning. When panicked, the body releases that adrenaline to elevate one beyond a normally stimulated state into a state of extreme arousal. 

All of the methods used to impair their performance (cold, sleep deprivation, fuel deprivation, and possibly boredom while sitting that ice truck) reduce physiological arousal and cause the body to redirect task-enhancing resources into sheer physical survival. They were, therefore, underaroused and understimulated. When each slap enhanced performance, it moved them closer to optimal arousal levels. None of these methods tested what would happen if they had slapped a person in a state of overarousal or overstimulation. 

For more than a century, researchers have noticed that emotional or physical arousal has something of a curvilinear (upside-down U shaped) relationship with task performance. The so-called Yerkes-Dodson Law refers to Yerkes and Dodson’s 1908 observation that mild or moderate arousal can improve task performance whereas low or high arousal can impede it. When you’re so underaroused that you’re barely awake, you can’t do things well; when you’re so overaroused that you’re jittery, you can’t do well either. There’s a happy medium somewhere in between. Half a century later, Easterbrook’s 1959 cue utilization hypothesis applied this to the range of cues (essentially the amount of information) a person can use while performing a task, at least when the task is simple or well learned. With complicated activities or those at which we’re simply poor performers, a lower level of arousal is optimal.

Source of diagram: Wikimedia Commons.

Despite the many studies that have empirically supported optimal arousal hypotheses, the arousal/performance curve has also generated considerable controversy (e.g., Anderson, 1990, versus Neiss, 1988, 1990) largely due to some researchers' injudicious applications of the curve to explain virtually any experimental findings. Specific predictions about how arousal restricts performance do make this concept testable and can keep the inverted-U from being haphazardly applied to interpret everything. That means it should be falsifiable and, therefore, scientific albeit tricky. Debate over the Yerkes-Dodson arousal/performance curve essentially makes it a myth that can be put to the test.

Even though the MythBusters audience might not fancy having something as convoluted sounding as that put to the test by the same people who tested whether you can "slap some sense" into someone, they might enjoy seeing whether a competing and seemingly contradictory idiom might also be true under the right circumstances? Can you also "slap them silly" or, as I have also heard it put, "slap 'em stupid"? The Yerkes-Dodson Law says you should be able to slap some sense into people and slap them silly as well, each under the right circumstances.

As they discussed in their after show video, experimentally inducing panic can be difficult. There are other methods of boosting arousal, though. Caffeine, anger, or sexual excitement might work well. Personality variables like trait anxiety or introversion (because introverts tend to stay more anxious than extraverts) should make a difference as well. Instead of increasing physiological arousal, someone putting this to test could overstimulate them cognitively. When faced with way too much information to handle, a slap should only make things worse.

I want their slap machine.

Kari, Tory, and Grant, we wish you the best in all things. We will miss you on MythBusters so very much, and we eagerly look forward to finding out what your next adventure will be.


  • Anderson, K. J. (1990). Arousal and the inverted-U hypothesis:  A critique of Neiss's "Reconceptualizing arousal." Psychological Bulletin, 107, 96-100.
  • Easterbrook, J. A. (1959). The effect of emotion on cue utilization and the organization of behavior. Psychology Review, 66, 183-201.
  • Neiss, R. (1988). Reconceptualizing arousal: Psychobiological states in motor performance. Psychological Bulletin, 103, 345-366.
  • Neiss, R. (1990). Ending arousal's reign of error. Psychological Bulletin, 107, 101-105.
  • Yerkes, R. M., & Dodson, J. D. (1908). The relation of strength of stimuli to rapidity of habit-formationJournal of Comparative Neurology and Psychology, 18, 459-482.

Langleys with the MythBusters build team. San Diego Comic-Con International, 2010.

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