Documented: Desvousges, Kahneman and colleagues' 1990s studies on Exxon-era environmental valuation found willingness to pay nearly flat across 2,000, 20,000, and 200,000 affected birds. Fetherstonhaugh and colleagues (1997) named the pattern scope neglect and showed interventions rated by lives saved drew similar support whether the count was 10,000 or far higher, while a single identified child outdrew statistical thousands.
The explanation the field converged on: affect runs on prototypes, one imageable victim, and quantity enters only through deliberate calculation, a system most people do not engage for charity. The response measures the vividness of the mental image, not the size of the problem, which is why campaigns learned to lead with one face and bury the count.
The tension this creates, documented in the effective altruism literature: if intuition ignores scope, then scope-sensitive ethics must be done by arithmetic against intuition, which is exactly what effective altruism proposes and exactly what readers find cold. The bird study is the small print on every large moral number.
When the number of lives stops changing the response, what is the response actually about?