Phase and Coherent Structure in Texture
((F. Phillips1, J. T. Todd2))
1Skidmore College, Eye, Brain, and Vision Laboratories, Saratoga Springs, NY;2The Ohio
State University, Vision Laboratory, Columbus, OH;
Purpose. What can the perception of scale and coherence of texture features tell us
about the nature of our visual representation of shape? A trivial gedankenexperiment
shows that the scale of features in 2- & 3-D textures has a direct effect on the ability
of an observer to make ‘same/different’ judgments. Fields of uniformly distributed,
high spatial frequency features are more difficult to match than their lower frequency
cousins. However, in cases where the distribution of point features is not uniform, ‘meta-
features’ may cohere in the form of clusters or linear structures that alter the scale at
which matching is possible. What is the nature of this scale/structure relationship?
Methods. In a series of experiments, fields of uniformly distributed noise were pre-
sented in a same/different matching task. Spatial frequency of the noise varied in concert
with different structuring and de-structuring operations. These included introduction of
linear and area structures through filtering and the modification of phase information.
Results. Spatial frequency thresholds for the noise-only discrimination tasks were on
the range of 1.5-2.5 degrees of visual angle. Linear structuring of the noise yielded per-
formance consistent with the scale of the introduced structuring. Disturbing the phase
in the structured noise again degraded performance consistent with the unstructured
conditions.
Conclusions. Our results show that structuring the point features of uniform noise
creates emergent features that are more readily used as ‘landmarks’ for a matching
task. At least part of the structuring takes place in the texture’s phase-space because
disturbing phase degrades performance back to unstructured levels.