Читать книгу The Behavior of Animals - Группа авторов - Страница 30

Each organism is equipped with sets of sensory receptors that open the gates toward the world in which the organism lives. Jacob von Uexküll (1921) pointed out that each animal species lives in, and communicates with, its own sensory world, the “Umwelt.” Different species perceive their Umwelt differently, and quite differently from the way we humans perceive our environment. Knowledge about the capabilities of sense organs indicates the kinds of stimuli perceived by organisms and suggests what their perceptual worlds look like (Prete 2004).

Certain species have evolved perceptual talents. In birds, visual acuity and accommodation speed of the eyes are maximized at 20/4 vision, compared to 20/20 in humans. From high altitudes raptors can magnify and detect small prey on the ground while monitoring a wide field of vision. Many insects—like some birds—are sensitive to ultraviolet light and may use polarized skylight for navigation (Labhart & Meyer 2002). Barn owls, Tyto alba, hunting in darkness, localize sound sources by tiny interaural time differences (Konishi 2003) (Chapter 5). Dogs and mice live mainly in a world of smell, spiders in a world of vibration. Rattlesnakes, Crotalus viridis, have infrared-sensitive pit organs for object detection in the dark (Newman & Hartline 1982). Dolphins and nocturnal bats use biosonar (Suga 1990), and weakly electric fish produce electric fields for object detection and communication (Heiligenberg & Rose 1985). Sharks utilize electroreceptors to detect electric fields of about 0.005 μV/cm, e.g., from breathing-muscle potentials by a flatfish hidden in the sand. Like migratory birds, loggerhead turtles, Caretta, detect geomagnetic cues that vary across the earth’s surface and employ magnetic-compass orientation for long-distance navigation (Wiltschko & Wiltschko 2002).

Male silk moths, Bombyx mori, are “smell champions.” One molecule of the female’s sex attractant pheromone bombykol is sufficient to elicit a nerve impulse in a receptor cell specialized for bombykol (Kaissling 2014). The female’s pheromone glands contain less than 1 µg bombykol, which, theoretically, is sufficient to lure 10¹³ Bombyx males. In males the behavioral olfactory threshold is 10³ bombykol molecules/cm³ in an air stream at a velocity of about 50 cm/s. Actually, 200 simultaneous molecule hits at 200 of the more than 25,000 bombykol receptors tell the Bombyx male: a female is present in the direction from which the wind blows. For comparison, in German shepherd dogs the behavioral threshold for butyric acid, a component of sweat, is 5.9×10³ molecules/cm³.

Whichever type of energy the receptor cells respond to—odor, infrared, sonar, etc.—the corresponding sensory systems have a comparable basic structure: receptor cells and nerve cells connected to them. Perception involves the neurosensory as well as the motivation and attention related processes, by which an organism becomes aware of and localizes and recognizes external stimuli.

A few comments on stimulus recognition are appropriate. Recognition (identification, interpretation, detection) in the present context means that stimuli from the environment are classified into meaningful units, i.e., categories of functional (behavioral) significance. A category can be a class of behaviorally significant objects that approximately share a set of defining features. Approximate, rather than specific, is the suitable term, since it enables “openness” in category formation. How organisms sort objects into different categories according to features is one of the basic questions in the behavioral and cognitive sciences. The problem is general, as an “object” can be any recurring signal (associated with experience or species-specific knowledge) and “sorting” is related to any differential response to it. Categorization—the ways that categorize information—plays a critical role in perception, thinking, and language (see Harnad 1987).