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Adaptive tracking is much quicker than the method of con- stant stimuli, although thresholds have been found to be un- stable using the former method in some species of animals such as mice (Klink et al., 2006).
Human psychoacousticians also widely use the method of adjustment, where listeners turn a dial until two sounds match along a certain dimension. Although it is fairly easy to instruct a human to move a dial to equate the levels of two sounds, such instructions are probably impossible to give to nonhuman subjects.
Another common human technique that does not trans- late well to animal psychophysics is magnitude estimation, where stimuli are labeled along some dimension, such as loudness. Thus, the method of constant stimuli and adaptive tracking procedures are more common in animal psycho- physics than the method of adjustment or magnitude esti- mation (although response latencies are often used to infer magnitude across stimulus types).
In operant experiments, animals are typically shaped (trained) to respond, with successive stages of the shaping process requiring more and more of the subject. Classical conditioning experiments can be just as useful for determin- ing stimulus properties that differ along certain dimensions for different animal species. Finding the appropriate task type for each animal species can be a major challenge. Small birds such as budgerigars (Melopsittacus undulatus) can be trained to peck light-touch microswitch keys (Dooling and Okanoya, 1995; Figure 2) even when wearing headphones (Welch and Dent, 2011; Figure 3), whereas larger birds such as barn owls (Tyto alba) are better suited to a looking (e.g., Johnen et al., 2001) or a flying (Dyson et al., 1998; Figure 4) task. Cats (Felis catus) also respond well to a visual fixa- tion paradigm (Populin and Yin, 1998) or to releasing a le- ver with their paw (May and Huang, 1996). Bottlenose dol- phins (Tursiops truncatus) and killer whales (Orcinus orca) can push paddles or levers (Hall and Johnson, 1971) or pro- duce a whistle (Houser and Finneran, 2006). Fishes such as goldfish (Carassius auratus) suppress their respiration in a classical conditioning task (Fay, 1995). Rodents such as mice (Mus musculus) are good at nose (snout) poking (Radziwon et al., 2009), continuously drinking from a spout (Heffner and Heffner, 2001), or running around an arena (Klink and Klump, 2004). Next, other considerations need to be made, such as deciding what time of day to test animal subjects (owls and mice work best at night, whereas songbirds prefer the daylight hours) and what reinforcement type (food, wa- ter, shock, timeout) should be used.
Figure 2. Budgerigar (Melopsittacus undulatus) facing two keys in an operant chamber in the Dent laboratory. The bird is required to peck a left key to start a variable waiting interval and to peck the right key when it detects a signal presented from an overhead speaker for a millet reinforcer.
Figure 3. Budgerigar wearing headphones. This bird from the Dent laboratory ran the same task as described in Figure 2 but had stimuli presented through the headphones instead of from the overhead loudspeaker.
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