T Kakizawa
Institute of Disability Sciences, University of Tsukuba, Tsukuba-city, Ibaraki, 305-8572, Japan
Purpose: Low-vision readers often complain of slow reading speed during reading, still using a closed-circuit television (CCTV). This study was designed to observe reading performance of simulated CCTV reading of low-vision readers and to clarify causes of slow reading speed from a viewpoint of oculomotor skills of low-vision readers.
Method: Five patients with low-vision were participated. Texts consisted of Japanese characters, which were similar to or larger than the critical letter size, were presented, one line at a time, on the computer display and scrolled horizontally across it. Five types of scrolling rate were provided; 50%, 75%, 100%, 125%, and 150% of the critical scrolling rate of each participant. Eye movements of the participants were measured during reading the texts in each letter size and scrolling rate. Before testing, smooth-pursuit responses toward a light-emitting diode (LED) moved horizontally in a sinusoidal waveform were evaluated by measuring gain (peak eye velocity / peak target velocity) and phase (temporal synchrony between the target and the eye) of each participant.
Results: As Bower et al. (1994) and Kakizawa et al. (1999) mentioned, an optokinetic nystagmus type of eye movement was observed among the participants during reading scrolling texts. Both frequencies and amplitudes of nystagmus increased with the scrolling rate. Beyond critical scrolling rates, the participants could not continue to read the texts and nystagmus disappeared. The critical scrolling rate might depend on the letter size, that is, the larger the letter size, the slower the critical scrolling rate. In addition, relationship among the values of the critical scrolling rate and of gain and phase of smooth-pursuit responses was observed in the participants.
Conclusion: It might be concluded that reading performance during using CCTV might based briefly on the oculomotor skills of the low-vision readers.
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