Retina Journey: Photoreceptor Accuracy Happy Hours
Photoreceptors! The first stop on our journey through the retina.
Photoreceptors are actually located at the back of the retina, which means that light has to travel through the entire retina before reaching them. Glial Müller cells in the retina act as a kind of optical fiber, guiding the light to its destination.
Once light reaches the photoreceptors, it is processed through the outer segments of the cells, which are made up of a series of discs containing light-sensitive opsin proteins.
There are two types of photoreceptors – rods and cones! They both process light, but are each only activated under different light conditions.
Rods
Rods are activated in low-light conditions, make up the majority of photoreceptor cells in the retina. There are approximately 120 million rod cells in the human retina, vs only about 6-7 million cone cells.
Rods use their high volume to send many weak light signals together in tandem downstream towards the bipolar, and eventually ganglion cells. This means they can collectively send a strong signal indicating the presences of light, but the signal is less precise than that of a cone.
Rods do not detect color, which is why our low-light vision is in black and white! Instead they detect only shadows and brightness levels.
Cones
Although there are many fewer cones in the retina, they are extremely important to human sight, and are responsible for all color vision!
Cones come in three types –
- S cones (blue sensitive)
- M cones (green sensitive)
- L cones (red sensitive)
When colors of various wavelengths enter the eye, they will trigger a response from one or more of these cone types. The combination of the signal activation and the strength of the activation determines which color we see.
For example, a green object will activate the M cone strongly, and the S and L cones weakly, signaling “green” to the brain. A red object activates a strong signal from the L cone, a weaker signal from the M cone, and no signal from the S cone.
Cones provide high-contrast, color accurate images to vision, but require a minimum threshold of light to activate. There is also a special location in the retina called the fovea, which contains a high concentration of cones, and no rods. This densely packed area of the retina allows for a sharp, focused central vision during daylight conditions.
Not all animals have all three cones however. Our e2198 dataset comes from a mouse, an animal which has dichromatic vision with just two types of cone cells. They see a much more limited color palette that lacks a sensitivity to red light. Red-green colorblind humans can relate!
It’s nearly time for our Accuracy Happy Hours, so you’ll need your photoreceptors in good working order! Whether you’re tracing under bright florescent lights or in a dimly lit room, let your rods and cones lead the way!
Session 1 – 8:00 AM to 10:00 AM on 6/19
Session 2 – 2:00 PM to 4:00 PM on 6/20
Session 3 – 10:00 PM to midnight on 6/20
HQ will bestow typical Happy Hour bonuses for your work during each of those time frames, but there’s more than that to earn! Check your in-game notifications to see the full accuracy bonus breakdown.
Mentors: You are still allowed to mentor people during these time windows. Please just use your best judgment as to whether someone is asking you for basic newbie help vs. trying to have you boost their accuracy on cube after cube.
Scythes: Please avoid scything during these time windows. Even though accuracy for this will be retroactively calculated, we would prefer to go with accuracy based on players’ raw tracing. By the time this challenge is scored, don’t worry, admins will have corrected consensus as needed.
Image Credits: Daniela Gamba, Celia David, Wei Li