LIMULUS LATERAL EYE PREPARATION
This preparation investigates the effect of light on the ommatidia of the Limulus
lateral eye.
 Set up preparation as demonstrated.
 ITENSITY- RESPONSE: Investigate the effect of varying light intensity on
firing rate of the fiber that you are recording from. Use the chart recorder to save
the data. Identify both the transient and sustained components of this activity.
Keep in mind that the eye may adapt after prolong exposure to light, so work to
keep your stimuli brief and discrete. Modulate light intensity either with neutral
density filters or the intensity control of the fiber optic illuminator. Calibrate
using a photometer.
 DARK ADAPTATION: Determine the light intensity needed to reach the
threshold for a response by slowly raising the intensity control of the fiber optic
illuminator until the fiber you are recording from starts to fire action potentials.
Record the intensity setting. Place the eye in darkness and record the time. Every
two to three minutes, raise the intensity of the light until you reach the threshold
for a response. Quickly record the intensity setting and the time then turn the light
off. Remember, you are measuring dark adaptation, so the longer the light is on
during your measurements the less accurate your experiment will be. Continue
measuring thresholds for about twenty minutes. Is the intensity value needed to
elicit a threshold response changing?
 LIGHT ADAPTATION: Start the chart recorder and then raise the intensity of
light to obtain a significant increase in firing rate. Record the firing rate for 40-60
seconds. Keep the light on. Stop data collection. Wait another 5 minutes and
record the firing rate for 10 seconds. Repeat a few times during the next 15
minutes. Be sure to record the duration that the light has been on for each
measurement. Is the firing rate adapting?
 CRITICAL FLICKER FUSSION: Investigate the response to different
frequencies (0.5Hz-60Hz) of light flicker using the Grass Stroboscope. Does the
firing rate show a Critical Flicker Fusion (CFF), i.e. a rate of flicker at which the
firing pattern no longer modulates with the flicker? At what frequency does this
first occur? Keep the stroboscope well outside of the faraday cage, as it can create
noise that will mimic action potentials.

WAVELENGTH SENSITIVITY: Investigate the effects of different colored
filters on the firing rate of the fiber. Using the photometer, adjust the light
intensity of the source so that the effective brightness at the eye is the same for
each filter. Are some wavelengths more effective at eliciting responses than other
wavelengths?