Contribution of internal noise and calculation efficiency to face discrimination deficits in older adults.

Classification images (CIs) measured in a face discrimination task differ significantly between older and younger observers. These age differences are consistent with the hypothesis that older adults sample diagnostic face information less efficiently, or have higher levels of internal noise, compared to younger adults. The current experiments assessed the relative contributions of efficiency and internal noise to age differences in face discrimination using the external noise masking and double-pass response consistency paradigms. Experiment 1 measured discrimination thresholds for faces embedded in several levels of static white noise, and the resulting threshold-vs.-noise curves were used to estimate calculation efficiency and equivalent input noise: older observers had lower efficiency and higher equivalent input noise than younger observers. Experiment 2 presented observers with two identical sequences of faces embedded in static white noise to measure the association between response accuracy and response consistency and estimate the internal:external (i/e) noise ratio for each observer. We found that i/e noise ratios did not differ significantly between groups. These results suggest that age differences in face discrimination are due to differences in calculation efficiency and additive internal noise, but not to age differences in multiplicative internal noise.