Letter Recognition at Low Contrast Levels: Effects of Letter Size

Abstract

Contrast variation was used to measure recognition thresholds for lowercase letters, with the aim of obtaining a better understanding of the role that early stages of visual processing play in letter recognition. Frequency-of-recognition curves were measured for alphabets of different letter size. Since variation of the adaptational state of the eye changes the characteristics of primary visual processing in a quantifiable way, recognition thresholds were measured both at a high (150 cd m-2) and at a low (0.9 cd m-2) adaptation level. Thresholds decreased as letter size increased, in a way comparable with data on visual acuity. At the lower adaptation level, recognition thresholds became higher, which is also in accordance with visual acuity data. Furthermore, the slopes of the frequency-of-recognition curves for alphabets as a function of log contrast decreased with decreasing letter size. It is argued that this is mainly caused by an increasing dispersion of internal representations of individual letters on the internal psychological scale as letter size decreases.

What Children See Affects How They Read

“…Our finding that there was a trend for all children to make more errors as print size was reduced is consistent with the findings of Erdmann et al (1968) and Blommaert et al (1987), who showed that reducing print size makes words more difficult to read. But of greatest importance was the finding that only the children who failed the DT read differently as print size was reduced; they made more non-word errors.…”

Quantitative and functional influence of surround luminance on the letter contrast sensitivity function

“…This influence is small for the larger letter sizes (3 and 10 c deg −1 ) but is clearly more important for 20 c deg −1 and particularly for 30 c deg −1 letter sizes. This result was previously observed by Blommaert and Timmers (1987) and by Khanani et al. (2004) but they could not provide any information concerning the functional influence of surround luminance for each letter size (spatial frequency), because these two studies were performed with only two surround lighting conditions: non‐illuminated and illuminated surround.…”

“…Some previous experiments showed that an illuminated surround yielded contrast sensitivities higher than those obtained with a dark or an almost dark surround. Blommaert and Timmers (1987) performed an experiment with letters from 18 to 42 c deg −1 fundamental spatial frequency, but with only two observers, and found that an adapting field of 150 cd m −2 generated higher CS values than an adapting field of 0.9 cd m −2 . Cox et al.…”

Typography in children’s reading schemes may be suboptimal: Evidence from measures of reading rate

“…Reducing perceptual difficulty in decoding text should therefore help improve general reading ability. Erdman and Neal (1968) and Blommaert and Timmers (1987) both demonstrated that adults found it more difficult to recognise words and letters when the print size was reduced. Cornelissen, Bradley, Fowler and Stein (1991) report an increase in visuo-perceptual problems, in proportion to a decrease in spatial dimensions of text.…”