Dogs in the MRI

On By Beth Morling, University of DelawareIn Chapter 12; Experiments with More Than One Independent Variable
dogs in MRI

Dogs were trained to lie still in this scanner long enough to participate in the factorial design. Credit: REUTERS/Bernadett Szabo

What's not to love about dog research? One recent study, conducted in Hungary and covered here by CNN, trained 13 dogs to lie perfectly still in a functional MRI (Magnetic Resonance Imaging) machine (this story describes how dogs learned to do it). 

After being trained for several weeks, the canine participants donned doggy headphones and heard different words pronounced in different tones of voice. Here's how the CNN journalist described the study: 

The study involved 13 dogs — golden retrievers, border collies, a German shepherd and a Chinese crested — who were trained to lie down and remain still for more than seven minutes while in a brain-scanning MRI machine.
 
The researchers used the machine to record and measure neural activity in the dogs' brains while they listened to a woman trainer, whom they were familiar with, recite various words in various intonations.
 
For instance, positive or meaningful words such as "well done," "good boy" and "clever" were said in both a praising intonation and a neutral intonation. Neutral or meaningless words, such as "even if," "although" and "however," also were said in both intonations.
…
Only when a praise word was spoken to the dogs in a praising tone of voice did the brain's reward center light up like a Christmas tree in the brain scans. The reward center is the part of the brain that responds to pleasurable stimuli, like food treats or being petted.
 

a) This is a factorial design. What are the two independent variables (IVs)? How many levels of each? How would you state the design (in ___ X ___ format?)

b) For each IV, decide whether it was within subjects or independent groups. Then use this information to identify the type of factorial this is (is it an independent groups factorial? A within-groups factorial? Or a mixed factorial design?)

c) What was the dependent variable, or DV, mentioned in the excerpt above? 

d) Sketch a graph of the results that the journalist described. (Hint: Put the DV on the y-axis, as usual. Pick one IV for the x-axis, and another IV for different-colored dots or bars.) 

e) Inspecting the graph you created, is there an interaction in these data? What about each main effect–would you predict they would be significant?