Roxana Ismail-Beigi¹, Marvin Chun¹, Yaoda Xu¹; ¹Yale University

English letter recognition is easier with uppercase than lowercase letters, and easier with sans-serif than serif fonts. To understand the neural bases of these effects, in Experiment 1, we showed human participants individual letters in either uppercase or lowercase sans-serif (Arial) or serif (Times New Roman) font while they performed an orthogonal image jitter detection task. The average letter size between the two fonts was equated, while within each font, letter size difference between uppercase and lowercase was unaltered to preserve how these letters are normally perceived. We examined fMRI responses in retinotopic areas V1 to V4, object-selective areas in the occipitotemporal cortex, and the visual word form area (VWFA). Response amplitude was higher to uppercase than lowercase letters in V1 and V2, and higher to serif than to sans-serif letters in object-selective areas. Meanwhile, response patterns were more distinctive for sans-serif than serif letters in object-selective areas, and more distinctive for uppercase than lowercase letters across several areas. To replicate these results while controlling for typeface, in Experiment 2, we used the serif and the sans-serif fonts in the Lucida family. We additionally equated the average size of the uppercase and lowercase letters within each font style. With size equated, response amplitude measures no longer showed an effect of letter case in V1 and V2, but higher responses to serif fonts persisted in object-selective areas. Response patterns were again more distinctive for sans-serif letters in object-selective areas, and more distinctive for uppercase letters in several areas. Across both experiments, case and font style effects were largely absent in VWFA. Overall, these results showed that while letter size may contribute to the letter case effect by modulating response amplitudes, representational distinctiveness likely plays a greater role in mediating the relative ease of recognizing uppercase letters and sans-serif fonts.

Acknowledgements: Supported by NIH Grant R01EY030854 to YX.