10 Chapter 3. Animal behaviorperiod of time. Related to temporal summation is sensitization, where a reflexive responsemay by more easily evoked (<strong>in</strong> practice hav<strong>in</strong>g a lower threshold) follow<strong>in</strong>grepeated stimulus presentation.Spatial summation: Two or more stimuli applied with<strong>in</strong> a short distance from each othermay evoke a response where one stimulus would fail to do so. Thus, a reflexiveresponse has a receptive field.Momentum (after-discharge): The response of some reflexes will outlast the stimulusevok<strong>in</strong>g the response. The duration as well as the magnitude of the after-dischargegenerally <strong>in</strong>crease with stimulus <strong>in</strong>tensity.Habituation: Repeated reflex responses may eventually lead to a decrease <strong>in</strong> response<strong>in</strong>tensity, and f<strong>in</strong>ally to no response at all. Habituation to a weak stimulus generallyoccurs sooner than to a strong one. Related to habituation is spontaneous recovery,the fact that the effect of habituation ceases with time.Fatigue: Sense organs tire out, so that the animal is unable to detect stimulus, or musclesbecome exhausted, which make them unable to perform any movement.Reflexes may <strong>in</strong>teract <strong>in</strong> various ways, e.g. by competition, thus <strong>in</strong>hibit<strong>in</strong>g each other,or by cooperation. The adaptive behavior emerg<strong>in</strong>g from sensitization and habituationis regarded as the simplest form of learn<strong>in</strong>g <strong>in</strong> biological organisms. Both processes,however, are reversible and thus the organism will eventually return to its orig<strong>in</strong>al state ifleft alone for a sufficient long period of time. In general, this is not true for other types oflearn<strong>in</strong>g mechanisms.3.2.2 Fixed action patternsFixed action patterns (FAPs) is def<strong>in</strong>ed by a stereotyped series of actions follow<strong>in</strong>g areleas<strong>in</strong>g stimulus. Thus, the response of an FAP typically outlasts the trigger<strong>in</strong>g stimulus,but <strong>in</strong> contrast to reflexive behavior, the duration of the response is not dependent onstimulus characteristics such as duration and <strong>in</strong>tensity. See e.g. [40, 60] for a discussionon, and examples of, FAPs.3.2.3 Orientation of movementThe orientation of animal movement may be roughly divided <strong>in</strong>to three categories, i.e. k<strong>in</strong>esis,taxes, and navigation.K<strong>in</strong>esis: Indirect follow<strong>in</strong>g of a gradient for orientation of movement. As an example,bacteria are, <strong>in</strong> general not capable of detect<strong>in</strong>g a gradient of the concentration of a
3.2. Patterns of movement 11chemical substance [62]. However, by mak<strong>in</strong>g use of time dimension, they are ableto sample a gradient which can be used to reorient movement.Taxes: Direct gradient follow<strong>in</strong>g. Gradient ascent (or descent) <strong>in</strong> response to a perceiveddirected stimulus.Navigation: More complex orientation of movement is found e.g. <strong>in</strong> hom<strong>in</strong>g pigeons,which use the sun as a compass to f<strong>in</strong>d the direction of their home location. Beesand ants, for example, use landmarks to guide them on their routes. These morecomplex navigation strategies will not be considered <strong>in</strong> this project, but the <strong>in</strong>terestedreader is referred to e.g. [36, 39, 40, 60].
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