Definitions:
Sensory Adaptation occurs when
sensory receptors change their sensitivity to the stimulus. This phenomenon
occurs in all senses, with the possible exception of the sense of pain.
Dark Adaptation
adaptation to reduced light intensity and involves enlargement of the
pupil, increased sensitivity of the cones and rods
Light Adaptation adaptation
to increased light intensity and involves an immediate change in pupil size (it
becomes smaller, admitting less light), decreased sensitivity of cones and rods
Concept:
This activity clearly demonstrates the process of
light-dark adaptation and provide you with an excellent opportunity to learn
about this phenomenon through your own individual experience.
Materials Needed:
1. Some sort of eye
patch to wear over one eye for 20 minutes
2. Timepiece that
can measure seconds such as a stopwatch
Instructions:
This experiment is best conducted in an environment in
which the light can be reduced quickly to a lower level where vision can still
occur after dark adaptation. At home at
night should suffice.
Place the patch over one eye, then go about your regular
activities (e.g. studying—yeah, right, reading, talking on the phone, watching
t.v.) for 20 minutes. At the end of this
time, turn off the lights. Now remove
the eye patch. Look at various objects
in the room. Note the marked differences
in visual ability between the light-adapted and dark-adapted eyes.
While this difference is still apparent, turn the lights
on and observe at what speed the eyes become equal in their light
adaptation.
Record your observations and times. Repeat this procedure at another time with
the other eye.
Write-up:
Was there any difference between light adaptation and
dark adaptation?
What are some possible explanations for the time
difference between light adaptation and dark adaptation?
Where does light-dark adaptation take place? In the retina or in the brain?
What observations support your answer?
Report your thoughts on the experience.
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