Overestimation of stereo thresholds by the TNO stereotest is not due to global stereopsis. by Vancleef K, Read JCA, Herbert W, Goodship N, Woodhouse M, Serrano-Pedraza I, VancleefReadHerbertGoodshipWoodhouseSerranoPedraza2017_2.pdf (18 KiB) - Purpose
It has been repeatedly shown that the TNO stereotest overestimates stereo threshold compared to other clinical stereotests. In the current study, we test whether this overestimation can be attributed to a distinction between ‘global’ (or ‘cyclopean’) and ‘local’ (feature or contour-based) stereopsis.
Methods
We compared stereo thresholds of a global (TNO) and a local clinical stereotest (Randot Circles). In addition, a global and a local psychophysical stereotest were added to the design. One hundred and forty-nine children between 4 and 16 years old were included in the study.
Results
Stereo threshold estimates with TNO were a factor of two higher than with any of the other stereotests. No significant differences were found between the other tests. Bland-Altman analyses also indicated low agreement between TNO and the other stereotests, especially for higher stereo threshold estimates. Simulations indicated that the TNO test protocol and test disparities can account for part of this effect.
Discussion
The results indicate that the global – local distinction is an unlikely explanation for the overestimated thresholds of TNO. Test protocol and disparities are one contributing factor. Potential additional factors include the nature of the task (TNO requires depth discrimination rather than detection) and the use of anaglyph red/green 3D glasses rather than polarizing filters, which may reduce binocular fusion.
Blog Archives
Avoiding monocular artifacts in clinical stereotests presented on column-interleaved digital stereoscopic displays
Avoiding monocular artifacts in clinical stereotests presented on column-interleaved digital stereoscopic displays by Serrano-Pedraza I, Vancleef K, Read JCA, SerranoPedrazaVancleefRead.pdf (1.5 MiB) - New forms of stereoscopic 3-D technology offer vision
scientists new opportunities for research, but also
come with distinct problems. Here we consider
autostereo displays where the two eyes’ images are
spatially interleaved in alternating columns of pixels
and no glasses or special optics are required. Columninterleaved
displays produce an excellent stereoscopic
effect, but subtle changes in the angle of view can
increase cross talk or even interchange the left and
right eyes’ images. This creates several challenges to
the presentation of cyclopean stereograms (containing
structure which is only detectable by binocular vision).
We discuss the potential artifacts, including one that is
unique to column-interleaved displays, whereby scene
elements such as dots in a random-dot stereogram
appear wider or narrower depending on the sign of
their disparity. We derive an algorithm for creating
stimuli which are free from this artifact.We show that
this and other artifacts can be avoided by (a) using a
task which is robust to disparity-sign inversion—for
example, a disparity-detection rather than
discrimination task—(b) using our proposed algorithm
to ensure that parallax is applied symmetrically on the
column-interleaved display, and (c) using a dynamic
stimulus to avoid monocular artifacts from motion
parallax. In order to test our recommendations, we
performed two experiments using a stereoacuity task
implemented with a parallax-barrier tablet. Our
results confirm that these recommendations eliminate
the artifacts. We believe that these recommendations
will be useful to vision scientists interested in running
stereo psychophysics experiments using parallaxbarrier
and other column-interleaved digital displays
scientists new opportunities for research, but also
come with distinct problems. Here we consider
autostereo displays where the two eyes’ images are
spatially interleaved in alternating columns of pixels
and no glasses or special optics are required. Columninterleaved
displays produce an excellent stereoscopic
effect, but subtle changes in the angle of view can
increase cross talk or even interchange the left and
right eyes’ images. This creates several challenges to
the presentation of cyclopean stereograms (containing
structure which is only detectable by binocular vision).
We discuss the potential artifacts, including one that is
unique to column-interleaved displays, whereby scene
elements such as dots in a random-dot stereogram
appear wider or narrower depending on the sign of
their disparity. We derive an algorithm for creating
stimuli which are free from this artifact.We show that
this and other artifacts can be avoided by (a) using a
task which is robust to disparity-sign inversion—for
example, a disparity-detection rather than
discrimination task—(b) using our proposed algorithm
to ensure that parallax is applied symmetrically on the
column-interleaved display, and (c) using a dynamic
stimulus to avoid monocular artifacts from motion
parallax. In order to test our recommendations, we
performed two experiments using a stereoacuity task
implemented with a parallax-barrier tablet. Our
results confirm that these recommendations eliminate
the artifacts. We believe that these recommendations
will be useful to vision scientists interested in running
stereo psychophysics experiments using parallaxbarrier
and other column-interleaved digital displays