The idiom "can't see the forest for the trees" is used metaphorically to mean that one is too focused on details to see the big picture. However, this idiom also captures an important literal aspect of visual perception: objects can be perceived globally as integrated wholes (the forest) or locally as independent components (the trees).
There is evidence that humans tend to prioritize global information, whereas other animals, like pigeons, tend to focus on local information. However, it may be adaptive to vary processing style based on the task at hand or the information available. For instance, a farmer may need to distinguish between cows in a herd based on unique individual markings, and birds may need to identify prey in fog that obscures feature information.
In recent work published in the Journal of Comparative Psychology, Aust and Braunöder (2015) (PDF, 186KB)opens in new window investigated the extent to which humans and pigeons can flexibly use global and local information to learn visual categories. Humans and pigeons were trained to categorize images in a similar protocol until a mastery criterion was met.
Pigeons required more training to reach mastery when training images were blurred (a manipulation that preserves global information about object configuration but disrupts local feature information), compared to when training images were scrambled (a manipulation that preserves local information but disrupts global information), or when training images were unaltered. In contrast, humans reached mastery equally quickly regardless of the format of the training images.
In a subsequent transfer phase, subjects were tested with images in untrained formats. For example, subjects trained with blurred images were tested with scrambled and unaltered images. Whereas humans showed good transfer to all image formats regardless of training condition, pigeons only showed transfer between unaltered and scrambled formats. That is, pigeons trained with unaltered images were able to categorize scrambled images, and vice versa. However, pigeons trained with unaltered and scrambled images were impaired at categorizing blurred images, and pigeons trained with blurred images were impaired at categorizing unaltered or scrambled images.
There was no evidence that the use of global versus local information in humans or pigeons depended on task constraints, as the results were the same regardless of whether category membership was arbitrary and individual items had to be learned, or was defined by a single perceptual rule.
Together, these results suggest that pigeons always rely on local information, even when it is suboptimal, whereas humans are able to flexibly use local or global information depending on available visual cues.
The authors acknowledge that the ease with which humans learned across training conditions may be due to the use of verbal labels. However, this highlights the value of comparative experiments like this one: the fact that nonlinguistic animals (pigeons) could master some of the same categorization tasks as humans suggests that visual category learning does not entirely depend on language.
Citation:
Aust, U., & Braunöder, E. (2015). Transfer between local and global processing levels by pigeons (Columba livia) and humans (Homo sapiens) in exemplar- and rule-based categorization tasks. Journal of Comparative Psychology, 129(1), 1–16. https://dx.doi.org/10.1037/a0037691
Note: This article is in the Basic/Experimental Psychology topic area. View more articles in the Basic/Experimental Psychology topic area.