Heather Hill. Imagine. . . . . .yourself in a grocery store, trying to reach the milk on the rack in front of you, or the last milk at the very top that is stuck in the back . . . Your brain begins to calculate the options . . .
How far do you need to reach to get the object in front of your face or above your head? Can you do it? Are you short and need to stand on the bottom of the refrigerator to jump and knock the milk you want forward? Or are you tall and can simply stand and reach to the top shelf with a little stretch of your arm?
What can a Body Embody?
The various mind-body options constitute embodied cognition while the perceptual calculations involve affordances – a concept summarized by J. J. Gibson in his original book on visual perception. Affordances are the possibilities of performing a particular behavior, such as reaching for the milk carton or plucking an apple from a tree. Affordances are action scaled, which means the perceptual possibilities are dependent upon the task itself and one’s perception of being able to perform the task.
People are very good at making these judgments and know when to transition between the different modes of performing a particular behavior to achieve a goal, or in other words, perform a “task-specific fit.”
For example, in the images below, a person may be able to reach an apple simply by stretching the arm (left image), or a person may need to stretch with their arm and the body to reach that apple that is just out of reach (right image).
Interestingly, people with long arms and people with short arms ultimately use the same ratio of object-distance-to-arm length. That is, while the absolute distance needed to reach an object with an arm-only reach vs. an arm-plus-torso reach is different for the long-armed people vs the people saddled with shorter limbs, the ratio between the two distances is the same between the two arm lengths. This constant ratio suggests that the same perceptual mechanism is operating for both types of people. This mechanism may be innate as it occurs across modalities and contexts. For example, this ratio occurs when using vision to perceive distances as well as when using sound to perceive distances; e.g., Rosenblum (2011).
Who Let the Dogs In?
In a recent article published in the Psychonomic Bulletin & Review, researchers Jeffrey Wagman, Matthew Langley, and Valeri Farmer-Dougan explored if dogs also perceive affordances and if so, would they perform like humans and display action scaling?
Nineteen dogs of different ages, breeds, sex, stature, and status were tested on a reaching task involving food that was placed above their head at some distance. Each height was adjusted specifically to each dog as the dogs included Beagles and Terriers all the way up to Rottweilers and Pyrenees. Although dogs can use their paws to “reach” for objects, the researchers chose to measure reaching using the dogs’ heads (i.e., an arm length) or rearing up on their hind legs (i.e., arm plus torso length) to test the boundaries for each mode of reaching.
The dogs were initially trained to eat a hot dog from a cup placed at eye level. Sometimes the experimenter had to prompt the dog to eat the treat, but most dogs started eating the treat spontaneously after 3-5 trials. Once the dog was eating the hot dogs reliably, the researchers began to manipulate the height of the treat to elicit a head only reach (left panel below) and a rearing reach (right panel below). This procedure was used to establish a height for each position. It took 5-7 attempts at each height to get the heights that elicited the most consistent head reach and rearing reach for each dog.
Different but Equal!
Whether it was the tasty hot dog or the challenge, all the dogs completed the task and demonstrated that they could perceive affordances and the affordances were action scaled. That is, tall dogs reached higher distances than short dogs, but both sizes of dogs had the same ratio of treat-height-to-shoulder-height. These data suggest that affordances are a perceptual skill that are shared across phylogenetic histories and may not depend on a type of brain or nervous system that is more advanced or complex.
The authors suggest that similar work should be conducted with other animals to test this speculation, arguing that a comparative approach is necessary to unravel the evolution of affordances in an attempt to establish universal principles among different species. (That is, do dogs and cats act the same?)
Another line of inquiry that could be pursued is whether older and younger dogs experience affordances differently like humans of different ages do. Young humans are less accurate in their reaching actions than adults but are consistent in their decisions and make adjustments based on changing environments like adults (Ishak, Fanchak, & Adolph, 2014).
Going to the Fish . . .
Being a researcher who studies animals that are limited in movable body parts or that have a limited reach with their movable body parts (e.g., dolphins or fish), it would be interesting to see how the study of affordances based on reaching could be adapted to them. The morphology of a dolphin/whale or a fish generally requires them to move their body only as a whole unit (as illustrated below by the young beluga that is attempting to remove the yellow disk from the ledge with her head) rather than with a movable appendage like an elephant’s trunk. Perhaps we should ask the fish!
Article focused on in this post:
Wagman, J. B., Langley, M. D., & Farmer-Dougan, V. (2016). Doggone affordances: Canine perception of affordances for reaching. Psychonomic Bulletin & Review. DOI: 10.3758/s13423-016-1183-6.