The crowding factor method applied to parafoveal vision

Multi-res: An interface for improving reading without central vision

Loss of sharp foveal vision, as is inherent to Macular Degeneration (MD), severely impacts reading. One strategy for preserving patients' reading ability involves a one-by-one serial visual presentation (SVP) of words, whereby words are viewed extrafoveally. However, the method is limited as patients often retain the natural tendency to foveate words, thus bringing those words in the scotomal region. Additionally, SVP offers no compensation for the fact that orthographic input is degraded outside the fovea. Addressing these issues, here we tested a novel interface wherein texts are presented word-by-word, but with multiple repetitions (Multi-Res) of each word being displayed simultaneously around the fovea. We hypothesized that the Multi-Res setup would lead readers to make fewer detrimental eye movements, and to recognize words faster as a consequence of multiplied orthographic input. We used eye-tracking to simulate a gaze-contingent foveal scotoma in normally-sighted participants, who read words either in classic SVP or in Multi-Res mode. In line with our hypotheses, reading was drastically better in the Multi-Res condition, with faster recognition, fewer saccades and increased oculomotor stability. We surmise that the Multi-Res method has good potential for improving reading in central vision loss, over and above classic SVP techniques.

Reduced fixation stability induced by peripheral viewing does not contribute to crowding

Attending to peripheral visual targets while maintaining central fixation, a process that involves covert attention, reduces fixation stability. Here, we tested the hypothesis that changes in fixation stability induced by peripheral viewing contribute to crowding in peripheral vision by increasing positional uncertainty. We first assessed whether fixation was less stable during peripheral versus central (foveal) viewing for both crowded and uncrowded stimuli. We then tested whether fixation stability during peripheral viewing was associated with the extent of crowding. Fourteen participants performed a tumbling E orientation discrimination task at three different eccentricities (0°, 5°, 10°). The target was presented with or without flankers. Fixational eye movements were measured using an infrared video-based eyetracker. A central fixation cross was provided for the two peripheral viewing conditions, and optotype size was scaled for each eccentricity. Discrimination of appropriately scaled uncrowded stimuli was unaffected by eccentricity, whereas discrimination of crowded stimuli deteriorated dramatically with eccentricity, despite scaling. Both crowded and uncrowded peripheral stimuli were associated with reduced fixation stability, increased microsaccadic amplitude, and a greater proportion of horizontal microsaccades relative to centrally presented stimuli. However, these effects were not associated with the magnitude of crowding. This suggests that reduced fixation stability due to peripheral viewing does not contribute to crowding in peripheral vision.