Adding noise can reduce response biases in addition to improving perceptual performance

"Stochastic resonance" (SR) is a phenomenon whereby adding an "optimal" amount of noise can improve perceptual capabilities. Although this performance enhancement is important, in many tasks we also want to reduce biases, such as the tendency to respond "absent" to an infrequent stimulus. To address this, we designed a perceptual task where we presented six possible letters ("C,""B,""H," "O,""E," and "U") at threshold levels. We induced a response bias by manipulating the frequency of the consonants and vowels at 80% (frequent stimuli) versus 20% (rare stimuli) and induced SR using Gaussian visual luminance noise. We observed SR-based improvements in performance (accuracy and d') across 22 observers at low to intermediate noise levels. Additionally, response biases (i.e., criterion) decreased due to an increase in correctly identified rare stimuli. Our results suggest that low-to-moderate noise can improve performance and reduce response biases, with potential implications for real-world tasks (such as cancer screening) where target (i.e., tumor) occurrence is rare.