Response bias indices and working memory errors. (A) Mean left-versus-right side bias index (Y-axis) for young (black) and aged (gray) rats as a function of the first 13 test days (X-axis). (B) Mean object bias index (Y-axis) for young and aged rats for each of the first 13 test days (X-axis). (C) Mean response index across all test days (Y-axis) for the left-versus-right side and object biases. Prior to reaching criterion performance, all rats were significantly more likely to respond with a side bias than an object bias, F(1,28) = 67.49, p< .001; repeated-measures, but these response index values did not differ significantly with age, F(1, 28) = 2.55, p= .12. (D) Mean number of working memory errors (Y-axis) made by young (black) and aged (gray) rats before reaching criterion performance. The number of working memory errors did not differ significantly between age groups (T(30)= 0.92, p= .37). Error bars show +/−1 standard error of the mean.