Spatial Frequency Sensitivity Differences between Adults of Good and Poor Reading Ability Geoffrey R. Patching and Timothy R. Jordan 4–14 PURPOSE. To determine whether normal adults of good and sitivity to spatial frequencies. In particular, study results poor reading ability exhibit different patterns of sensitivity to indicate that dyslexic individuals have reduced sensitivity to spatial frequency, as previously found between dyslexic and certain spatial frequencies, and this reduction tends to be nondyslexic control subjects. greatest in the low- to midfrequency range (i.e., between 2 and 4–8,10,11,13–15 METHODS. The visual acuity, spatial frequency sensitivity, and 8 cyc/deg). However, despite a wealth of re- reading ability of 96 normal, nondyslexic adults was assessed. search involving dyslexic individuals there is a dearth of studies Participants were ranked according to reading ability. The top examining spatial frequency sensitivity differences between 50% were classified as good readers and the bottom 50% as “normal,” nondyslexic adults of good or poor reading ability. poor readers. Surveys of reading ability reveal a considerable range of reading abilities in the normal adult population.16,17 For in- RESULTS. Despite no differences in visual acuity, good and poor stance, the International Adult Literacy Survey (IALS; 1994– readers showed different patterns of spatial frequency sensitiv- 1998, National Literacy Secretariat, Canada)17 indicates that up ity. In particular, compared with good readers, poor readers to 52% of the normal adult population, although able to read, showed reduced sensitivity to spatial frequencies between 2 have sufficiently low levels of reading ability to make it difficult and 6 cyc/deg, and no differences in sensitivity were found at for them to face novel demands, such as acquiring new work lower or higher spatial frequencies. skills. Accordingly, the purpose of the present study was to CONCLUSIONS. The findings indicate that spatial frequency sen- assess the reading ability of normal adults and determine sitivity differences found previously between dyslexic and non- whether good and poor readers exhibit different patterns of dyslexic controls can extend to the normal (nondyslexic) adult sensitivity to spatial frequencies. population. (Invest Ophthalmol Vis Sci. 2005;46:2219–2224) The present study drew on a sample of normal, nondyslexic DOI:10.1167/iovs.03-1247 adults recruited from the university population. Reading ability was assessed by measuring effective reading speed. Effective phthalmic clinicians have long used letter charts as the reading speed is a measure widely used to assess the reading Ostandard measure of vision necessary for fluent reading. ability of normal (nondyslexic) adults.18–28 It is defined as the However, letter charts measure a person’s ability to resolve time taken to read short passages or sentences in words per fine detail and, even when visual acuity is normal, other visual minute (wpm) multiplied by either the number of words read factors may also play an important role in reading. Spatial correctly26 or the number of questions answered correctly in a frequency sensitivity is one such factor of increasing interest. brief comprehension test.19 As a combined measure of reading Spatial frequency sensitivity provides an indication of a speed and comprehension, effective reading speed encapsu- person’s ability to perceive visual information across the full lates not only participants’ ability to comprehend what they visual spectrum, from fine to broad scale, and is measured with have read but also the efficiency with which they are able to repetitive patterns of black-and-white bars. The luminance pat- achieve understanding, and this combined measure of speed tern across these bars describes a sine wave, and the patterns and comprehension was selected as the index of reading ability are referred to as sine-wave gratings. Spatial frequency is ex- in our study. pressed as the number of cycles (one black plus one white bar) Contrast sensitivity was measured with a spatial two-alter- per degree of visual angle. The amount of contrast required native, forced-choice (2AFC) task in which participants were (i.e., contrast threshold) for detection of sine-wave gratings is required to indicate on which side of a display screen a sinu- known to vary systematically as a function of their spatial soidal grating was presented. The QUEST staircase procedure frequency. The reciprocal of the threshold contrast (i.e., 1/con- was used to estimate each participant’s contrast threshold.29 trast threshold) is the contrast sensitivity, and the contrast This procedure has been effective in several investigations26,30 sensitivity function (CSF) describes the variation of the sensi- and enabled assessment of participants’ sensitivity to a range of tivity over a range of spatial frequencies.1–3 spatial frequencies from 0.5 to 12 cyc/deg. Comparison of A substantial body of evidence indicates that dyslexic and sensitivity to spatial frequencies between good and poor read- nondyslexic control subjects exhibit different patterns of sen- ers promised to reveal whether normal adults of good or poor reading ability differ in their sensitivity to certain spatial fre- quencies. From the Department of Psychology, Stockholm University, Stock- holm, Sweden; and the School of Psychology, University of Leicester, University Road, Leicester, United Kingdom. Supported by Wellcome Trust Grant 059727 (TRJ). METHOD Submitted for publication November 15, 2003; revised July 4, 2004; accepted August 5, 2004. Participants Disclosure: G.R. Patching, None; T.R. Jordan, None Ninety-six undergraduate students (38 men and 58 women) between The publication costs of this article were defrayed in part by page charge payment. This article must therefore be marked “advertise- the ages of 18 and 35 took part in the experiment. All participants were ment” in accordance with 18 U.S.C. §1734 solely to indicate this fact. native speakers of English, and none reported any history of epilepsy Corresponding author: Geoffrey R. Patching, Department of Psy- or dyslexia or demonstrated any reading problems when tested. Each chology, Stockholm University, S-106 91 Stockholm, Sweden; participant took part in one 75-minute session, in which each partici- [email protected]. pant was tested for visual acuity, contrast sensitivity, and reading Investigative Ophthalmology & Visual Science, June 2005, Vol. 46, No. 6 Copyright © Association for Research in Vision and Ophthalmology 2219 Downloaded from iovs.arvojournals.org on 09/29/2021 2220 Patching and Jordan IOVS, June 2005, Vol. 46, No. 6 ability. Informed consent was obtained from each participant before Reading Speed the experiment, in accordance with the Declaration of Helsinki. Stimuli. Seven passages were selected from Notes From a Small Island by Bill Bryson,36 which provided an engaging text. On average, Visual Acuity each passage contained 527 words. After each passage, five multiple- choice questions were presented. The questions referred to different 31 Visual acuity was tested with the Bailey-Lovie eye chart. Participants detailed aspects of the preceding paragraph and were designed to were required to continue reading letters down the chart from a ensure that participants read each paragraph in full.37,38 distance of 3 m until they failed to identify any letters on one line. Visual Conditions. Viewing was binocular. Each passage was Performance was scored by the method recommended by Kitchin and presented on the same ␥-corrected video monitor as that used to test 32 Bailey. The total number of letters read incorrectly was recorded, and contrast sensitivity. The text was presented in black on a light gray an “error” score of 0.02 assigned to each. These scores were added to background, and a complete passage of text filled an area approxi- the last line on which any letters were read. To continue participating mately 18° (horizontal) ϫ 27° (vertical) and had proportions similar to in the study, participants were required to have a minimum binocular those of an A4 page of text (which is familiar in the British reading acuity of 10/10 (3/3), indicative of normal visual acuity. environment). Background illumination of the monitor screen was 46 cd/m2, and the luminance of text was 0.15 cd/m2. Contrast Sensitivity Design. Each participant was presented with all seven passages. One passage (the first shown) was always used as practice, and the Stimuli. Contrast sensitivity was tested with gray-scale vertical remaining six as test passages, shown in a random order. sine-wave gratings of 0.5, 1, 2, 4, 6, 8, 10, and 12 cyc/deg. These spatial Procedure. Participants were told that the experiment would frequencies were chosen to conform to previous psychophysical examine the time taken to read different passages of text, and that they 1–3 studies of spatial frequency sensitivity and to cover the range of should read through each passage once, from start to finish, as rapidly spatial frequencies used in previous studies involving dyslexic indi- as if they were reading a page of a book. As soon as a button was 4–13,15 viduals. A Gaussian patch modulated each sine wave grating, to pressed, a passage was presented (shown in its entirety on the screen) create eight Gabor stimuli, each with a different spatial frequency. and the timer started. Participants pressed the button again when they Visual Conditions. Viewing was binocular. The Gabor stimuli had read the final word of each passage, and this stopped the timer. were presented on a ␥-corrected video monitor with a resolution of The passage was immediately replaced with five multiple-choice ques- 980 ϫ 1024 pixels. Viewed from a distance of 57 cm, the viewable area tions and participants were required to select one of three answers of the monitor measured 23° horizontally and 29° vertically. Back- from each of the five questions before continuing. ground illumination of the monitor screen and space-averaged lumi- nance of each Gabor was kept constant at 35 cd/m2.