Two simultaneous 5-quanta flashes under scotopic conditions at two locations are perceived as how many ganglion cells contributing to perception?

• A. 1 ganglion cell sums up the information
• B. 2 ganglion cells sum up
• C. 3 ganglion cells sum up
• D. 4 ganglion cells sum up

Answer: (A)

In scotopic (low-light) vision, many rods feed into a small number of ganglion cells, giving each ganglion cell a relatively large receptive field. Signals from all the rods within that field are pooled and carried by that single ganglion cell to the brain. So when two simultaneous 5-quanta flashes occur at locations that lie within the same ganglion cell’s receptive field, their combined input is represented by the activity of that one ganglion cell. That’s why perception in this scenario comes from a single ganglion cell. If the flashes were outside the same receptive field, you’d involve more than one ganglion cell.