Abstract

Several discriminability measures were examined for their ability to predict reading search times for three levels of text contrast and a range of backgrounds (plain, a periodic texture, and four spatial-frequency-filtered textures created from the periodic texture). Search times indicate that these background variations only affect readability when the text contrast is low, and that spatial frequency content of the background affects readability. These results were not well predicted by the single variables of text contrast (Spearman rank correlation=-0.64) and background RMS contrast (0.08), but a global masking index and a spatial-frequency-selective masking index led to better predictions (-0.84 and -0.81, respectively).

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References

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  1. G. Legge, G. Rubin, and A. Luebker, "Psychophysics of reading V. The role of contrast in normal vision," Vision Res. 27, 1165-1177 (1987).
    [CrossRef] [PubMed]
  2. K. Knoblauch, A. Arditi, and J. Szlyk, "Effects of chromatic and luminance contrast on reading," J. Opt. Soc. Am. A. 7, 1976-1984 (1990).
  3. G. Legge, and G. Rubin, "Psychophysics of reading IV. Wavelength effects in normal and low vision," J. Opt. Soc. Am. A. 3, 40-51 (1986).
    [CrossRef] [PubMed]
  4. S. Pastoor, "Legibility and subjective preference for color combinations in text," Human Factors, 32, 157-171 (1990).
    [PubMed]
  5. G. Legge, D. Pelli, G. Rubin, and M. Schleske, "Psychophysics of reading I. Normal vision," Vision Res. 25, 239-252 (1985).
    [CrossRef] [PubMed]
  6. J. Farrell and A. Fitzhugh, "Discriminability metric based on human contrast sensitivity," J. Opt. Soc. Am. A. 7, 1976-1984 (1990).
    [CrossRef] [PubMed]
  7. J. A. Solomon and D. G. Pelli, "The visual filter mediating letter identification," Nature 369, 395-397 (1994).
    [CrossRef] [PubMed]
  8. D. H. Parish and G. Sperling, "Object spatial frequencies, retinal spatial frequencies, noise, and the efficiency of letter discrimination," Vision Res. 31, 1399-1415 (1991).
    [CrossRef] [PubMed]
  9. D. Regan and X. H. Hong, "Recognition and detection of texture-defined letters," Vision Res. 34, 2403-2407 (1994).
    [CrossRef] [PubMed]
  10. P. Kember and D. Varley, "The legibility and readability of a visual display unit at threshold," Ergonomics 30, 925-931 (1987).
    [CrossRef] [PubMed]
  11. B. Parker and L. V. Scharff, Influences of contrast sensitivity on text readability in the context of a GUI, (1997) http://hubel.sfasu.edu/research/agecontrast.html.
  12. A. Hill and L. V. Scharff, "Readability of screen displays with various foreground/background color combinations, font styles, and font types," Proceedings of the Eleventh National Conference on Undergraduate Research, II, 742-746 (1997).
  13. M. Youngman and L. V. Scharff, "Text width and border space influences on readability of GUIs," Proceedings of the Eleventh National Conference on Undergraduate Research, III, 786-789 (1998).
  14. A. L. Hill and L. F. V. Scharff, "Readability of computer displays as a function of colour, saturation, and background texture" in Engineering Psychology and Cognitive Ergonomics Volume Four, D. Harris, ed. (Ashgate, Aldershot, England, 1999).
  15. L. F. V. Scharff, A. J. Ahumada, Jr., and Alyson L. Hill, "Discriminability Measures for Predicting Readability," Human Vision and Electronic Imaging IV, SPIE Proc. 3644, 270-277 (1999).
  16. Scharff, L. V. Example stimuli using different text contrast levels and spatial-frequency-filtered backgrounds. (2000), http://hubel.sfasu.edu/research/stim/exfiltstim.html
  17. A. J. Ahumada, Jr., A. M. Rohaly, and A. B. Watson, "Models of human image discrimination predict object detection in natural backgrounds," in B. Rogowitz and J. Allebach, eds., Human Vision, Visual Processing, and Digital Display IV, SPIE Proc. 2411, 355-362 (1995).
  18. A. M. Rohaly, A. J. Ahumada, Jr., and A. B. Watson, "Object detection in natural backgrounds predicted by discrimination performance and models," Vision Res. 37, 3225-3235 (1997).
    [CrossRef]
  19. B. L. Beard and A. J. Ahumada, Jr., "Image discrimination models predict detection in fixed but not random noise," J. Opt. Soc. Amer. A 14, 2471-2476 (1997).
    [CrossRef]
  20. A. B. Watson and J. A. Solomon, "Model of visual contrast gain control and pattern masking." J. Opt. Soc. A. A. 14, 2379-2391 (1997). * Links to some of the above-referenced research may be found on webpages maintained by Lauren Scharff (http://hubel.sfasu.edu/research/reslvs.html) and Al Ahumada (http://vision.arc.nasa.gov/~al/ahumada.html).
    [CrossRef]

Other (20)

G. Legge, G. Rubin, and A. Luebker, "Psychophysics of reading V. The role of contrast in normal vision," Vision Res. 27, 1165-1177 (1987).
[CrossRef] [PubMed]

K. Knoblauch, A. Arditi, and J. Szlyk, "Effects of chromatic and luminance contrast on reading," J. Opt. Soc. Am. A. 7, 1976-1984 (1990).

G. Legge, and G. Rubin, "Psychophysics of reading IV. Wavelength effects in normal and low vision," J. Opt. Soc. Am. A. 3, 40-51 (1986).
[CrossRef] [PubMed]

S. Pastoor, "Legibility and subjective preference for color combinations in text," Human Factors, 32, 157-171 (1990).
[PubMed]

G. Legge, D. Pelli, G. Rubin, and M. Schleske, "Psychophysics of reading I. Normal vision," Vision Res. 25, 239-252 (1985).
[CrossRef] [PubMed]

J. Farrell and A. Fitzhugh, "Discriminability metric based on human contrast sensitivity," J. Opt. Soc. Am. A. 7, 1976-1984 (1990).
[CrossRef] [PubMed]

J. A. Solomon and D. G. Pelli, "The visual filter mediating letter identification," Nature 369, 395-397 (1994).
[CrossRef] [PubMed]

D. H. Parish and G. Sperling, "Object spatial frequencies, retinal spatial frequencies, noise, and the efficiency of letter discrimination," Vision Res. 31, 1399-1415 (1991).
[CrossRef] [PubMed]

D. Regan and X. H. Hong, "Recognition and detection of texture-defined letters," Vision Res. 34, 2403-2407 (1994).
[CrossRef] [PubMed]

P. Kember and D. Varley, "The legibility and readability of a visual display unit at threshold," Ergonomics 30, 925-931 (1987).
[CrossRef] [PubMed]

B. Parker and L. V. Scharff, Influences of contrast sensitivity on text readability in the context of a GUI, (1997) http://hubel.sfasu.edu/research/agecontrast.html.

A. Hill and L. V. Scharff, "Readability of screen displays with various foreground/background color combinations, font styles, and font types," Proceedings of the Eleventh National Conference on Undergraduate Research, II, 742-746 (1997).

M. Youngman and L. V. Scharff, "Text width and border space influences on readability of GUIs," Proceedings of the Eleventh National Conference on Undergraduate Research, III, 786-789 (1998).

A. L. Hill and L. F. V. Scharff, "Readability of computer displays as a function of colour, saturation, and background texture" in Engineering Psychology and Cognitive Ergonomics Volume Four, D. Harris, ed. (Ashgate, Aldershot, England, 1999).

L. F. V. Scharff, A. J. Ahumada, Jr., and Alyson L. Hill, "Discriminability Measures for Predicting Readability," Human Vision and Electronic Imaging IV, SPIE Proc. 3644, 270-277 (1999).

Scharff, L. V. Example stimuli using different text contrast levels and spatial-frequency-filtered backgrounds. (2000), http://hubel.sfasu.edu/research/stim/exfiltstim.html

A. J. Ahumada, Jr., A. M. Rohaly, and A. B. Watson, "Models of human image discrimination predict object detection in natural backgrounds," in B. Rogowitz and J. Allebach, eds., Human Vision, Visual Processing, and Digital Display IV, SPIE Proc. 2411, 355-362 (1995).

A. M. Rohaly, A. J. Ahumada, Jr., and A. B. Watson, "Object detection in natural backgrounds predicted by discrimination performance and models," Vision Res. 37, 3225-3235 (1997).
[CrossRef]

B. L. Beard and A. J. Ahumada, Jr., "Image discrimination models predict detection in fixed but not random noise," J. Opt. Soc. Amer. A 14, 2471-2476 (1997).
[CrossRef]

A. B. Watson and J. A. Solomon, "Model of visual contrast gain control and pattern masking." J. Opt. Soc. A. A. 14, 2379-2391 (1997). * Links to some of the above-referenced research may be found on webpages maintained by Lauren Scharff (http://hubel.sfasu.edu/research/reslvs.html) and Al Ahumada (http://vision.arc.nasa.gov/~al/ahumada.html).
[CrossRef]

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Figures (4)

Fig. 1.
Fig. 1.

Six texture samples used to create the backgrounds for the experiment. The lower right pattern shows the original, unfiltered texture. Starting from the top left are the band-pass filtered versions named: Band 1 (0.1875-0.375 cpl), Band 2 (0.375-0.75 cpl), Band 3 (0.75–1.5 cpl), Band 4 (1.5–3 cpl), and a plain texture of the same mean luminance.

Fig. 2.
Fig. 2.

Search times (sec) for all conditions that were readable. The effect of spatial frequency filtering was greatest when the text contrast was low. The text was not readable for the low text contrast using the unfiltered background (all frequencies) and the Band 3 filtered background. Vertical bars represent standard errors of the means.

Figure 3.
Figure 3.

(a,b). Mean search times for each background plotted against text contrast (left) and background RMS contrast (right) and the two rank correlation coefficients (non-parametric). Numbers/letters to the side of each symbol indicate the frequency band (1–4), A (all frequencies), or P (plain texture).

Fig. 4.
Fig. 4.

(a,b). Mean search times for each background plotted against the global masking model equivalent contrast (left) and the frequency-selective model d’ index (right), and the two rank correlation coefficients (non-parametric). Numbers/letters to the side of each symbol are as indicated in Figure 3.

Tables (1)

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Table 1. Parameter values.

Equations (5)

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C T = ( L B L T ) L B ,
C RMS = L RMS L B ,
L RMS = ( ( Σ ( L i L B ) 2 ) n ) 0.5 ,
d = s n T 0.5 C T ( 1 + ( C RMS C 2 ) 2 ) 0.5 ,
C M = C T ( 1 + ( C RMS C 2 ) 2 ) 0.5 .

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