Effects of Temporal Modulation on Crowding, Visual Span, and Reading.

PURPOSE Crowding, the increased difficulty in recognizing a target due to the proximity of adjacent objects, is identified as the main sensory constraint for the size of the visual span (the number of letters recognized without moving the eyes) and reading speed in peripheral vision. The goal of the present study is to assess the impact of temporal modulation on crowding, visual span, and reading in the periphery. METHODS Six normally sighted young adults participated in the study. Four temporal modulation patterns were examined: (1) moving scotoma (sequentially masking the component letters in a letter string or word), (2) moving window (sequentially presenting the component letters), (3) flashing (repeatedly masking and presenting all letters simultaneously), and (4) static (the control condition; no temporal changes during the presentation). For each condition, we obtained the spatial extent of crowding, the size of the visual span, and reading speeds measured by the rapid serial visual presentation method. RESULTS Compared with the static condition, the spatial extent of crowding was reduced in the moving window condition. Both the moving window and moving scotoma conditions led to a faster reading speed for print sizes smaller than critical print size (the smallest print size that allows maximum reading speed). However, none of the temporal modulations increased the size of the visual span and reading speed for print sizes larger than critical print size. CONCLUSIONS The results suggest that the temporal modulation patterns are of limited benefit for peripheral reading despite the substantial improvement for slow reading when print size is close to acuity threshold.