Fonts, height and reading speed
Reading performance was also measured with text that was defined by differing
amounts of color and luminance contrast, in order to determine the influence of
color information on reading. Results indicated that when luminance contrast was
well above threshold, varying the chromatic (color) contrast had little effect on
reading performance. However, when luminance contrast was very low, near � threshold,
chromatic contrast sustained reading rates of nearly 300 words per minute, almost
as high as those found with high luminance contrasts. On the other hand, for some
low vision observers, text defined by color contrast interfered with reading performance.
Further investigations are planned to determine why the reading of some low vision
observers is adversely affected by color contrast that is not accompanied by sufficient
luminance contrast.
The National Institute on Aging, with Mars Perceptrix Inc., were working to develop
an adjustable font software for users with low vision. The software allows the adjustment
of many font parameters in real-time, so that the user can see the impact of parameter
adjustments on legibility as it happens. The prototype software works, but evaluation
using participants with low vision suggested that font legibility could not be significantly
improved above and beyond that provided by highly evolved and readily available
fonts such as TrueType Arial and TrueType Times New Roman (Arditi, in press).
By comparing the letter confusions observed under wide and narrow inter-letter
spacing, they were able to determine that a large portion of the deterioration of
legibility under narrow spacing conditions could be attributed to unique letter
confusions which did not occur when inter-letter spacing was wider. The cause of
these unique letter confusions was lateral interference (inhibition) from neighboring
letters.
The human observers not only made mistakes in identifying closely packed small
letters, but they also misjudged the number of letters in the string. Using interlaced
four-letter and five-letter strings, Drs. Arditi and Liu demonstrated that human
observers tended to mistake more five-letter strings for four-letter strings when
the inter-letter spacing was narrowed. Typically, the observers would either omit
one of the three letters in the middle of the five-letter string, or combine two
neighboring letters into a new letter. The researchers used a computer simulation
to demonstrate that an optical blur of the eye might have played an important role
in this new aspect of the "crowding effect".
Visual acuity is measured as a function of the separation between the Landolt
C and the flanking bars. The inhibitory effect of the flanking bars is demonstrated
as reductions of visual acuity at certain separations. Drs. Liu and Arditi studied
the effects of contrast polarity by measuring contour interaction between a black
C with four white bars, and a white C with four black bars. They found that features
of different contrast polarities were still engaged in inhibitory interaction, although
the interaction appeared to be weaker than that observed with features of the same
contrast polarity. Therefore, a simple linear receptive field model was not applicable
to suprathreshold contour interaction.
Flanking bars that were parallel exerted the strongest inhibition at the narrowest
separation between the Landolt C and the bars. At separations narrower than two
gap widths, the inhibition caused by a pair of parallel bars was stronger than that
observed when all four bars were present. The orthogonal bars only exerted moderate
inhibition at wider separations. It appeared that when four flanking bars were present,
the orthogonal bars alleviated the inhibitory effect of the parallel bars at narrower
separations and enhanced it at wider separations.
Such a deficit could affect reading performance by interfering with the discriminability
of letters having the same spatial frequency content but different spatial phase
spectra (i.e., mirror image letters like "b" vs. "d�). However, they found that
when letters were size-scaled to compensate for differences in contrast sensitivity,
the relationship between detection and identification performance was the same in
both the central and peripheral retinas. These results thus argue against the hypothesis
that the poorer reading performance outside the fovea is, somehow, due to reduced
letter discriminability that might occur secondarily to a loss of peripheral-retina
phase sensitivity.
http://www.lighthouse.org/research_legibility.htm
What is speed reading.
Speed reading techniques
|