T3D Re: vernier acuity

[Jim Crowell <crowell@xxxxxxxxxxxxxxx>]

At 8:04 AM -0800 3/30/98, john bercovitz wrote:
>I was thinking about vernier acuity which is the ability
>to align lines to each other such as on vernier calipers.
>Since vernier acuity and stereo acuity probably use much
>the same machinery, and since stereo acuity is used to
>check the relative positions of vertical edges, I was
>wondering if a test has been done to see if vernier acuity
>is just as accurate vertically as horizontally.  In other
>words, can you align
>
>this
>        __ __
>
>
>just as well as you can align this
>
>          |
>          |
>
>Anyone know?

John,

This paper compares oblique vs. non-oblique; I haven't read it, it might
say something about vertical vs. horizontal...

-Jim C.


TI ORIENTATION ANISOTROPY IN VERNIER ACUITY
AU Saarinen-J
AU Levi-DM
CS Univ Houston,Coll Optometry/Houston//TX/77204
JN VISION RESEARCH
VO 35
NO 17
PG 2449-2461
PY 1995
AB An oblique effect is evident in vernier acuity for abutting lines.  In
   Experiment 1 we show that the oblique effect in vernier acuity exists over a
   range of contrast levels, and is evident even when the horizontal and
   oblique lines are equally detectable or discriminable.  Since this oblique
   effect cannot be explained by the lower visibility of oblique vernier lines
   or of the ''dipole'' cue, it is unlikely to be a consequence of lower
   neuronal sensitivity, In Experiment 2 we measured the orientation and
   spatial frequency tuning characteristics of vernier acuity for horizontal
   and oblique (45 deg) stimuli using a simultaneous masking paradigm, Our
   results showed no significant differences between either the orientation or
   spatial frequency tuning for horizontal and oblique stimuli; thus the
   oblique effect is unlikely to result from differences in the tuning of
   neurons sensitive to the oblique meridians, Finally, in Experiment 3, we
   tested the notion that the oblique effect for vernier judgments might
   reflect limitations imposed beyond the initial filtering operation by
   measuring vernier acuity for horizontal and oblique lines with either the
   observer or the frame tilted at an angle of 45 deg. The oblique effect for
   vernier followed retinal (rather than gravitational) coordinates, and was
   unaffected by the orientation of the frame, suggesting a relatively low
   level cause, By exclusion, we suggest that the dependence of vernier acuity
   on orientation may result from increased positional uncertainty at oblique
   orientations, perhaps as a consequence of lower cortical neuronal density
   and/or increased topographic noise.
RE 57
DT Article
LO BIOL
UD 19951231
KW OBLIQUE EFFECT
KW MASKING
KW VERNIER ACUITY
KW ORIENTATION ANISOTROPY
KW STIMULUS ORIENTATION
KW SPATIAL MECHANISMS
KW VISUAL-CORTEX
KW HUMAN-VISION
KW HYPERACUITY
KW UNCERTAINTY
KW VISIBILITY
KW DISCRIMINATION
KW ECCENTRICITY
KW LOCALIZATION

----------------------
Jim Crowell
Caltech Division of Biology
Mail Code 216-76
1200 E. California Blvd.
Pasadena, CA 91125
Tel: (626) 395-8337
Fax: (626) 795-2397
jim@xxxxxxxxxxxxxxx
http://vis.caltech.edu/~jim/Home.html




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End of TECH-3D Digest 281
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