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Perception

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Title: Perception


1
Perception
  • Animal Cognition
  • Keith Clements

2
Aims
  • To illustrate how perceptual systems filter
    information from the outside world.
  • To describe research on prey catching in frogs
    toads, as an extreme example of the use of
    visual rules of thumb.
  • To discuss the senses which are thought to allow
    homing pigeons to find their way home.

3
The perceptual world
  • Von Uexkull argued that the inner world
    (innenwelt) differs from the external environment
    (umwelt). The umwelt is filtered by each species
    sensory systems.

4
Sign Stimuli
  • Ethologists often studied stereotyped behaviours
  • Fixed Action Patterns
  • triggered by Sign Stimuli
  • E.g. Tinbergen (1951)
  • threat mating displays elicited by red markings
    on male sticklebacks belly.
  • Turkeys respond differently to bird silhouette
    depending on direction of motion

Hawk
Goose
5
Prey catching in frogs toads
  • Lettvin et al. (1959) identified distinct types
    of retinal ganglion cells in Leopard frogs.
    Ganglion cells filter input by size and movement.
  • Ewert, (1974, 1980) Cells in the thalamus
    tectum respond to complex stimuli, small moving
    objects trigger a sequence of responses,
    including leaning towards the object and
    attempting to catch it with the tongue.

6
Visual rules of thumb
Turn towards
Avoided
  • Barnard (2004) called these visual rules of
    thumb,
  • These innate responses can be modified by
    learning.

7
How pigeons see the world
  • Narrower binocular vision than humans (35), but
    wider total field of view (340).
  • Typical of preyed-upon species.
  • Sensitive to ultraviolet light and have 6
    different colour receptors (humans have 3).
  • They rely on vision to guide flight and identify
    edible grains, etc.

8
Navigation in homing pigeons
  • Pigeons do use visual landmarks.
  • However when vision is obscured by frosted lenses
    they can still find their way home
    (Schmidt-Koenig Keeton, 1977)
  • What other cues do they use?

9
Odours as navigational aids
  • Anosmic birds often show poorer homing, but the
    extent seems to vary with location.
  • Strain differences?
  • Housing conditions?
  • Local stimuli?
  • Deflecting odours with baffles (Baldacini et al.,
    1975) alters the initial heading when released.
    However baffles may influence other cues (e.g.
    sunlight)
  • Birds exposed to artificial odours (Ioale et al.,
    1978) do make use of the information.

10
The sun compass
  • The direction of the sun, adjusted for time of
    day, can provide a bearing. The next lecture will
    consider other species ability to track the
    passage of time.
  • Schmidt-Koenig (1960) shifted pigeons internal
    clocks with artificial light. This altered
    vanishing bearings on sunny, but not overcast
    days.
  • Sensitivity to polarization of light allows
    pigeons to detect the sun even if only part of
    the sky is free of cloud.
  • Some migratory species (e.g. sylviid warblers
    indigo bunting) use a star compass Emlen (1970)
    used a planetarium to show that buntings would
    learn to use artificial constellations. Initially
    the axis of celestial rotation is used, but birds
    learn to recognise constellations close to the
    pole.

11
Magnetic senses
  • The intensity and inclination of the Earths
    magnetic field varies with position.
  • Wiltschko (1968) raised robins in enclosed rooms
    with an imposed magnetic field variations in the
    inclination altered their bearing during
    migration
  • Studies (e.g. Keeton, 1974) show fitting magnets
    to pigeons impairs their navigation on overcast,
    but not on sunny days.
  • Here too there are conflicting findings, possibly
    related to geographical or strain differences.

12
Further Reading
  • Chapter 4 in Wynne covers this weeks topic.
  • Theres a good summary of work on prey detection
    in toads on pages133-138 of Barnard (2004) Animal
    Behaviour Mechanism Development, Function
    Evolution. Pearson Education
  • For more on navigation, and the senses which
    guide it see either
  • Wiltschko, R. Wiltschko, W. (2003). Avian
    navigation from historical to modern concepts.
    Animal Behaviour, 65, 257272
  • a chapter by Bingman, Jechura Kahn, in a
    cyberbook on animal spatial cognition
    http//pigeon.psy.tufts.edu/asc/Bingman/Default.ht
    m
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