The influence of similarity, sensitivity and bias on letter identification

Previous studies have demonstrated that bias, sensitivity and similarity between letters are causes of errors in letter identification. However, these factors and their relative contribution in letter identification have not been investigated extensively. Our previous model (noisy template model) was devised to calculate the effect of bias and sensitivity on letter identification. In the current study, we used the method of constant stimuli to assess letter identification and the pattern of errors for Sloan letters with a range of sizes at an eccentricity of 7 deg from fixation (temporal visual field). Similar to our previous work, we devised and tested a variety of models to estimate the joint role of bias and sensitivity but extended our model to also incorporate the similarity between letters. The Modelling results revealed that bias is the major factor in determining the pattern of total, correct and incorrect responses in letter identification. Furthermore, the joint effect of similarity and bias was found to be higher than the joint effect of either bias and sensitivity or similarity and sensitivity in shaping the pattern of overall responses in letter identification. Incorporating the similarity factor into the noisy template model improved our understanding of the simultaneous contribution of bias, sensitivity and similarity between letters in letter identification.