The introduction reads as follows: During his experiments with dogs, Ivan Pavlov noticed them salivating before food was even presented. Somehow the dogs had learned to associate the lab assistant’s approaching footsteps with eating. This observation led to Pavlov’s discovery of classical conditioning, in which we learn to associate a neutral stimulus with an unconditioned stimulus that produces an automatic, natural response. The crucial stage of this process involves repeated pairings of the two stimuli. At the left is a series of three graphics with the heading, “Pavlov’s Experiments.” The first frame is labeled, “Before conditioning.” In the left graphic, a bowl of dog food labeled “Unconditioned stimulus” has an arrow pointing to a dog looking at the bowl with drops of saliva drawn on the graphic, and a label reading, “Unconditioned response (salivates.) The caption reads, “Dog salivates automatically when food is presented.” In the right graphic, an image of a buzzer is labeled “Neutral stimulus (buzzer sound),” and an image of a dog with a thought balloon showing a “Nil” character is labeled “No response.” The caption reads, “Buzzer means nothing to dog, so there is no response.” The second frame of the graphic is labeled “During conditioning.” The upper graphic shows an equation written as Neutral stimulus (buzzer sound) below an image of a metal buzzer + Unconditioned stimulus below a bowl of dog food = Unconditioned response (salivates) below an image of the dog looking at the bowl with drops of saliva drawn on the graphic. Below the graphic equation is a timeline showing the equation four times, with a label reading “repeated over time.” The caption reads, “In the process of conditioning, buzzer is repeatedly sounded right before dog receives food. Over time, dog learns that buzzer signals arrival of food.” The third frame of the graphic is labeled “After conditioning.” An image of the buzzer labeled “Conditioned stimulus (buzzer sound)” is followed by an arrow pointing to a picture of the dog with drops of saliva drawn on the graphic, labeled “Conditioned response (salivates).” The caption reads, “Dog has now learned to associate buzzer with food and will begin salivating when buzzer sounds.” At the right is a series of three panels titled, “Have you been conditioned?” The top panel is labeled “Before conditioning.” A drawing of the McDonald’s arches is labeled “Neutral stimulus,” and a stick figure with a Nil sign beside it is labeled “No response.” A drawing of a carton of French Fries labeled “Unconditioned stimulus” has an arrow pointing to a stick figure with jagged lines on either side labeled “Unconditioned response (stomach growls).” The center panel is labeled “During conditioning” and shows a pictorial equation. A drawing of the McDonald’s arches is labeled “Neutral stimulus” + a carton of French Fries labeled “Unconditioned stimulus” à a stick figure with jagged lines on either side labeled “Unconditioned response (stomach growls).” A graphic of a clock is labeled “Repeated over time.” The lower panel is labeled “After conditioning” and shows a drawing of the McDonald’s arches labeled “Conditioned stimulus” with an arrow pointing to a stick figure with jagged lines on either side labeled “Conditioned response (stomach growls).” The lower text reads as follows: Classical conditioning is an involuntary form of learning that happens every day. Does your stomach rumble when you see the McDonald's “golden arches”? Just like Pavlov's dogs, we learn through repeated pairings to associate neutral stimuli (the golden arches) with food (French fries). Once this association is formed, the sight of the golden arches can be enough to get our stomachs rumbling.