Signal frequency and shock probability as determinants of prolonged vigilance performance in rhesus monkeys.

Researchers watched rhesus monkeys do a vigilance task. The monkeys had to spot a light that came on rarely. If they missed it, they got a shock. The team changed how often the light flashed and how likely the shock was.

They tested fast lights (40 to 310 per hour), slow lights (7 or 4 per hour), and lowered shock odds. Each monkey worked alone in a cage with a lever.

Monkeys stayed sharp when lights came 40-plus times an hour. Once the rate dropped to 7 or 4 an hour, hits fell off a cliff. Lower shock chance had the same bad effect. Attention crashed quickly, not slowly.

Rider et al. (1984) let rats pick between short or long shock warnings. The rats chose short warnings, showing timing matters across species. That study extends this one by giving the animal control, yet both find brief signals beat long gaps.

Brown et al. (2025) saw rats miss rare cues in a plain discrimination task. No shock was used, but low prevalence still hurt accuracy. Their result backs the monkey data: when targets are scarce, detection drops.

Allen et al. (2016) gave pigeons extra time to spot picture changes. Longer displays helped, the opposite of what low signal rate did here. The two studies together say timing helps, but sparse input hurts.

If you run vigilance or safety drills, keep the cues coming fast enough. Waiting minutes between targets trains learners to tune out. Instead, give many quick trials early, then thin slowly. Check that the penalty for misses stays meaningful; soft consequences let attention slide.