SLAG(+) performance requires ambient light. 19 B6 mice were pre-identified as SLAG(+), and this scoring was confirmed upon repeating the test under normal conditions that include ambient light (Light SLAG). Upon removing ambient light, no mouse produced SLAG(+) behavior, as observed by an experimenter using infrared night vision goggles (Dark SLAG). Finally, ambient light was returned, and of 10 mice re-tested, all reproduced SLAG(+) behavior (Light SLAG re-test). One-tailed Chi-square analysis showed statistical differences between Light SLAG and Dark SLAG groups: *** p < 0.0001.