Rhodopsin just like a photomultiplier detector has a certain noise level. The rate of noise counts decreases with temperature - so you would expect the performance of a person at this task to improve as you cooled their body.

This was actually done for toads. The experimenter would train a toad to lash its tongue at faint flashes of light and the performance of the toad at discriminating light from no light was measured as the toad's body temperature was cooled. As the toad was chilled the quality of its guesses improved. Interestingly it's error rate as a function of temperature matched the change in signal to noise ratio for the currents in the retinal cells. Bizzare! The toad's brain controlled it's tongue at the threshold of being able to statistically distinguish signal from noise.