Increased orientation uncertainty does not account for slower reading in peripheral vision

J. S. Mansfield, S. T.L. Chung, G. E. Legge

Research output: Contribution to journalArticlepeer-review

Abstract

Purpose. Why is reading slower in peripheral vision? Previous studies have shown that neither print size nor eye-movement demands are the limiting factor. However, it is well known that several forms of spatial hyperacuity decline rapidly in peripheral vision. These deficits can he modeled as an increase in intrinsic noise. In this study we asked whether the peripheral reading-speed deficit is due to a higher level of intrinsic noise in the coding of orientation and position. Method. Four subjects read sentences presented using the RSVP method. A staircase procedure was used to determine the presentation time (sec/word) for 80% correct reading. Reading thresholds were obtained with different levels of orientation noise (added independenlly to each letter) and different levels of positional noise (added to the vertical position of each letter). Text was presented either foveally, or at 10° in the inferior visual field. Eye movements were monilored. Print size was scaled lo support the maximum reading speed at each eccentricity (i.e., 2x critical print size). Results. The equivalent noise for reading was estimated by fitting the data with curves of the form: I - k y(c: + ;:) where / is threshold reading time, e is the s.d. of the noise added to the stimulus, and / is the s.d. of the equivalent intrinsic noise. Contrary to our expectations, the equivalent orientation noise in peripheral vision (i-22.3° ±2.99 s.e.m.) was less than in central vision (/-37.60 ±2.26). The resulls with positional noise are not yet conclusive: 2 subjects showed a subslanlial reduction in equivalent noise in the periphery while the other two showed a substantial increase. C'onclusioiL These findings indicate thai the reduction in reading speed in peripheral vision cannot be accounted for by higher intrinsic orientation noise. Indeed, compared to central vision, letter recognition in the periphery appears to rely on a mechanism that has stronger orientation dependence.

Original languageEnglish (US)
Pages (from-to)S646
JournalInvestigative Ophthalmology and Visual Science
Volume38
Issue number4
StatePublished - Dec 1 1997

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