Sensory Biology of Sea Turtles
83
An ERG is a recording of rapid action potentials between the cornea and retina
when the eye is stimulated, and is a robust measurement of early retinal stages in
the visual pathway (preganglion cell responses) (Davson, 1972; Riggs and Wooten,
1972; Ali and Klyne, 1985). Granda and O’Shea (1972) found the spectral sensitivity
for C. mydas to peak at 520 nm, with secondary peaks at 450–460 and 600 nm. The
spectral sensitivities recorded using these methods were longer (except for the
shortest wavelength) than those found through light microspectrophotometric measurements (440, 502, and 562 nm; Leibman and Granda, 1971), and the discrepancy
of wavelength measurements is attributed to the interaction of the visual pigments
and the cone oil droplets (Granda and O’Shea, 1972). For cone photoreceptors, light
must first pass through oil droplets before it reaches and excites the photopigments.
In C. mydas , the cone oil droplets are saturated oil globules that can be clear, yellow,
or orange. The orange and yellow droplets are optically dense and can act as filters,
shifting the wavelength that excites the photopigments (Granda and O’Shea, 1972;
Granda and Dvorak, 1977; Peterson, 1992). Specific colored oil droplets appear to
be paired with a specific photopigment: the clear oil droplet appears to be associated
with the 440 nm photopigment (no shift in absorbed spectral sensitivity), the yellow
oil droplet with the 502 nm photopigment (shifting the absorbed spectral sensitivity
to 520 nm), and the orange oil droplet with the 562 nm photopigment (shifting the
absorbed spectral sensitivity to 600 nm) (Granda and O’Shea, 1972; Peterson, 1992).
FIGURE 3.2 Visual pigment measurements, using microspectrophotometric techniques, of
rod and cone photoreceptors for both C. mydas (solid lines) and P. scripta (dotted lines).
(Data redrawn from Liebman, P.A. and Granda, A.M., Microspectrophotometric measurements of visual pigments in two species of turtle, Vision Res. , 11, 105, 1971.)
1123 book.book Page 83 Monday, November 11, 2002 11:11 AM
83
An ERG is a recording of rapid action potentials between the cornea and retina
when the eye is stimulated, and is a robust measurement of early retinal stages in
the visual pathway (preganglion cell responses) (Davson, 1972; Riggs and Wooten,
1972; Ali and Klyne, 1985). Granda and O’Shea (1972) found the spectral sensitivity
for C. mydas to peak at 520 nm, with secondary peaks at 450–460 and 600 nm. The
spectral sensitivities recorded using these methods were longer (except for the
shortest wavelength) than those found through light microspectrophotometric measurements (440, 502, and 562 nm; Leibman and Granda, 1971), and the discrepancy
of wavelength measurements is attributed to the interaction of the visual pigments
and the cone oil droplets (Granda and O’Shea, 1972). For cone photoreceptors, light
must first pass through oil droplets before it reaches and excites the photopigments.
In C. mydas , the cone oil droplets are saturated oil globules that can be clear, yellow,
or orange. The orange and yellow droplets are optically dense and can act as filters,
shifting the wavelength that excites the photopigments (Granda and O’Shea, 1972;
Granda and Dvorak, 1977; Peterson, 1992). Specific colored oil droplets appear to
be paired with a specific photopigment: the clear oil droplet appears to be associated
with the 440 nm photopigment (no shift in absorbed spectral sensitivity), the yellow
oil droplet with the 502 nm photopigment (shifting the absorbed spectral sensitivity
to 520 nm), and the orange oil droplet with the 562 nm photopigment (shifting the
absorbed spectral sensitivity to 600 nm) (Granda and O’Shea, 1972; Peterson, 1992).
FIGURE 3.2 Visual pigment measurements, using microspectrophotometric techniques, of
rod and cone photoreceptors for both C. mydas (solid lines) and P. scripta (dotted lines).
(Data redrawn from Liebman, P.A. and Granda, A.M., Microspectrophotometric measurements of visual pigments in two species of turtle, Vision Res. , 11, 105, 1971.)
1123 book.book Page 83 Monday, November 11, 2002 11:11 AM